TL494
SLVS074I – JANUARY 1983 – REVISED JULY 2022
TL494 Pulse-Width-Modulation Control Circuits
1 Features
•
•
•
•
•
•
•
Complete PWM Power-Control Circuitry
Uncommitted Outputs for 200-mA Sink or
Source Current
Output Control Selects Single-Ended or
Push-Pull Operation
Internal Circuitry Prohibits Double Pulse at
Either Output
Variable Dead Time Provides Control Over
Total Range
Internal Regulator Provides a Stable 5-V
Reference Supply With 5% Tolerance
Circuit Architecture Allows Easy Synchronization
2 Applications
•
•
•
•
•
•
•
•
•
•
Desktop PCs
Microwave Ovens
Power Supplies: AC/DC, Isolated, With or Without
PFC
Server PSUs
Solar Micro-Inverters
Washing Machines: Low-End and High-End
E-Bikes
Power: Telecom/Server AC/DC Supplies:
Dual Controller: Analog
Smoke Detectors
Solar Power Inverters
3 Description
The TL494 device incorporates all the functions
required in the construction of a pulse-widthmodulation (PWM) control circuit on a single chip.
Designed primarily for power-supply control, this
device offers the flexibility to tailor the power-supply
control circuitry to a specific application.
The TL494 device contains two error amplifiers,
an on-chip adjustable oscillator, a dead-time control
(DTC) comparator, a pulse-steering control flip-flop,
a 5-V, 5%-precision regulator, and output-control
circuits.
The error amplifiers exhibit a common-mode voltage
range from –0.3 V to VCC – 2 V. The dead-time
control comparator has a fixed offset that provides
approximately 5% dead time. The on-chip oscillator
can be bypassed by terminating RT to the reference
output and providing a sawtooth input to CT, or it can
drive the common circuits in synchronous multiple-rail
power supplies.
The uncommitted output transistors provide either
common-emitter or emitter-follower output capability.
The TL494 device provides for push-pull or singleended output operation, which can be selected
through the output-control function. The architecture
of this device prohibits the possibility of either output
being pulsed twice during push-pull operation.
The TL494 device is characterized for operation from
0°C to 70°C. The TL494I device is characterized for
operation from –40°C to 85°C.
Device Information(1)
PART NUMBER
TL494
(1)
PACKAGE (PIN)
BODY SIZE
SOIC (16)
9.90 mm × 3.91 mm
PDIP (16)
19.30 mm × 6.35 mm
SOP (16)
10.30 mm × 5.30 mm
TSSOP (16)
5.00 mm × 4.40 mm
For all available packages, see the orderable addendum at
the end of the data sheet.
4 Simplified Block Diagram
TL494
1
16
+
+
2
15
3
14
VREF
4
13
12
5
Osc
6
11
Control
10
7
8
9
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
TL494
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SLVS074I – JANUARY 1983 – REVISED JULY 2022
Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Simplified Block Diagram............................................... 1
5 Revision History.............................................................. 2
6 Pin Configuration and Functions...................................3
7 Specifications.................................................................. 4
7.1 Absolute Maximum Ratings........................................ 4
7.2 ESD Ratings............................................................... 4
7.3 Recommended Operating Conditions.........................4
7.4 Thermal Information....................................................4
7.5 Electrical Characteristics, Reference Section............. 5
7.6 Electrical Characteristics, Oscillator Section...............5
7.7 Electrical Characteristics, Error-Amplifier Section...... 5
7.8 Electrical Characteristics, Output Section...................6
7.9 Electrical Characteristics, Dead-Time Control
Section.......................................................................... 6
7.10 Electrical Characteristics, PWM Comparator
Section.......................................................................... 6
7.11 Electrical Characteristics, Total Device..................... 6
7.12 Switching Characteristics..........................................6
7.13 Typical Characteristics.............................................. 7
8 Parameter Measurement Information............................ 8
9 Detailed Description......................................................10
9.1 Overview................................................................... 10
9.2 Functional Block Diagram......................................... 10
9.3 Feature Description...................................................10
9.4 Device Functional Modes..........................................12
10 Application and Implementation................................ 13
10.1 Application Information........................................... 13
10.2 Typical Application.................................................. 13
11 Power Supply Recommendations..............................20
12 Layout...........................................................................20
12.1 Layout Guidelines................................................... 20
12.2 Layout Example...................................................... 21
13 Device and Documentation Support..........................21
13.1 Trademarks............................................................. 21
13.2 Electrostatic Discharge Caution..............................21
13.3 Glossary..................................................................21
14 Mechanical, Packaging, and Orderable
Information.................................................................... 21
5 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision H (March 2017) to Revision I (July 2022)
Page
• Updated the numbering format for tables, figures, and cross-references throughout the document..................1
Changes from Revision G (January 2015) to Revision H (March 2017)
Page
• Updated package illustration.............................................................................................................................. 1
• Corrected resistor polarity references in the Current-Limiting Amplifier section...............................................15
• Updated Figure 12. .......................................................................................................................................... 15
Changes from Revision F (January 2014) to Revision G (January 2015)
Page
• Added Applications, Device Information table, Pin Functions table, ESD Ratings table, Thermal Information
table, , Feature Description section, Device Functional Modes, Application and Implementation section,
Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section.............................................................................. 1
Changes from Revision E (February 2005) to Revision F (January 2014)
Page
• Updated document to new TI data sheet format - no specification changes...................................................... 1
• Removed Ordering Information table..................................................................................................................1
• Added ESD warning........................................................................................................................................... 1
2
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6 Pin Configuration and Functions
D, DB, N, NS, OR PW PACKAGE
(TOP VIEW)
1IN+
1IN−
FEEDBACK
DTC
CT
RT
GND
C1
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
2IN+
2IN−
REF
OUTPUT CTRL
VCC
C2
E2
E1
Table 6-1. Pin Functions
PIN
NAME
1IN+
NO.
TYPE
DESCRIPTION
1
I
Noninverting input to error amplifier 1
1IN-
2
I
Inverting input to error amplifier 1
2IN+
16
I
Noninverting input to error amplifier 2
2IN-
15
I
Inverting input to error amplifier 2
C1
8
O
Collector terminal of BJT output 1
C2
11
O
Collector terminal of BJT output 2
CT
5
—
Capacitor terminal used to set oscillator frequency
DTC
4
I
Dead-time control comparator input
E1
9
O
Emitter terminal of BJT output 1
E2
10
O
Emitter terminal of BJT output 2
FEEDBACK
3
I
Input pin for feedback
GND
7
—
OUTPUT
CTRL
13
I
Selects single-ended/parallel output or push-pull operation
REF
14
O
5-V reference regulator output
RT
6
—
Resistor terminal used to set oscillator frequency
VCC
12
—
Positive Supply
Ground
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7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)
MIN
VCC
Supply voltage(2)
VI
Amplifier input voltage
VO
Collector output voltage
IO
Tstg
(1)
(2)
MAX
UNIT
41
V
VCC + 0.3
V
41
V
Collector output current
250
mA
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds
260
°C
150
°C
Storage temperature range
–65
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating
Conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltages are with respect to the network ground terminal.
7.2 ESD Ratings
MAX
V(ESD)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins
500
Charged device model (CDM), per JEDEC specification JESD22C101, all pins
200
UNIT
V
7.3 Recommended Operating Conditions
MIN
VCC
Supply voltage
VI
Amplifier input voltage
VO
Collector output voltage
MAX
7
40
V
–0.3
VCC – 2
V
Collector output current (each transistor)
Current into feedback terminal
fOSC
Oscillator frequency
CT
Timing capacitor
RT
Timing resistor
TA
Operating free-air temperature
TL494C
TL494I
UNIT
40
V
200
mA
0.3
mA
1
300
kHz
0.47
10000
nF
1.8
500
kΩ
0
70
–40
85
°C
7.4 Thermal Information
over operating free-air temperature range (unless otherwise noted)
PARAMETER
Rθ JA
(1)
(2)
4
Package thermal
impedance(1) (2)
TL494
UNIT
D
DB
N
NS
PW
73
82
67
64
108
°C/W
Maximum power dissipation is a function of TJ(max), θJA, and TA. The maximum allowable power dissipation at any allowable ambient
temperature is PD = (TJ(max) – TA) / θJA. Operating at the absolute maximum TJ of 150°C can affect reliability.
The package thermal impedance is calculated in accordance with JESD 51-7.
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7.5 Electrical Characteristics, Reference Section
over recommended operating free-air temperature range, VCC = 15 V, f = 10 kHz (unless otherwise noted)
TEST CONDITIONS(1)
PARAMETER
TL494C, TL494I
MIN TYP(2)
MAX
4.75
5
5.25
UNIT
Output voltage (REF)
IO = 1 mA
Input regulation
VCC = 7 V to 40 V
2
25
mV
Output regulation
IO = 1 mA to 10 mA
1
15
mV
Output voltage change with temperature
ΔTA = MIN to MAX
2
10
mV/V
Short-circuit output current(3)
REF = 0 V
(1)
(2)
(3)
25
V
mA
For conditions shown as MIN or MAX, use the appropriate value specified under recommended operating conditions.
All typical values, except for parameter changes with temperature, are at TA = 25°C.
Duration of short circuit should not exceed one second.
7.6 Electrical Characteristics, Oscillator Section
CT = 0.01 μF, RT = 12 kΩ (see Figure 8-1)
TEST CONDITIONS(1)
PARAMETER
TL494C, TL494I
MIN TYP(2)
Frequency
Standard deviation of frequency(3)
All values of VCC, CT, RT, and TA constant
Frequency change with voltage
VCC = 7 V to 40 V, TA = 25°C
Frequency change with temperature(4)
ΔTA = MIN to MAX
(1)
(2)
(3)
MAX
UNIT
10
kHz
100
Hz/kHz
1
Hz/kHz
10
Hz/kHz
For conditions shown as MIN or MAX, use the appropriate value specified under recommended operating conditions.
All typical values, except for parameter changes with temperature, are at TA = 25°C.
Standard deviation is a measure of the statistical distribution about the mean as derived from the formula:
N
2
å (xn - X )
s=
(4)
n =1
N -1
Temperature coefficient of timing capacitor and timing resistor are not taken into account.
7.7 Electrical Characteristics, Error-Amplifier Section
See Figure 8-2
PARAMETER
TEST CONDITIONS
TL494C, TL494I
MIN TYP(1)
MAX
UNIT
Input offset voltage
VO (FEEDBACK) = 2.5 V
2
10
mV
Input offset current
VO (FEEDBACK) = 2.5 V
25
250
nA
Input bias current
VO (FEEDBACK) = 2.5 V
0.2
1
μA
Common-mode input voltage range
VCC = 7 V to 40 V
Open-loop voltage amplification
ΔVO = 3 V, VO = 0.5 V to 3.5 V, RL = 2 kΩ
Unity-gain bandwidth
VO = 0.5 V to 3.5 V, RL = 2 kΩ
Common-mode rejection ratio
ΔVO = 40 V, TA = 25°C
65
80
dB
Output sink current (FEEDBACK)
VID = –15 mV to –5 V, V (FEEDBACK) = 0.7 V
0.3
0.7
mA
Output source current (FEEDBACK)
VID = 15 mV to 5 V, V (FEEDBACK) = 3.5 V
–2
(1)
–0.3 to VCC – 2
70
V
95
dB
800
kHz
mA
All typical values, except for parameter changes with temperature, are at TA = 25°C.
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7.8 Electrical Characteristics, Output Section
PARAMETER
TEST CONDITIONS
Collector off-state current
VCE = 40 V, VCC = 40 V
Emitter off-state current
VCC = VC = 40 V, VE = 0
Collector-emitter saturation voltage
TYP(1)
2
MAX
UNIT
100
μA
–100
μA
Common emitter
VE = 0, IC = 200 mA
1.1
1.3
Emitter follower
VO(C1 or C2) = 15 V, IE = –200 mA
1.5
2.5
Output control input current
(1)
MIN
VI = Vref
3.5
V
mA
All typical values, except for temperature coefficient, are at TA = 25°C.
7.9 Electrical Characteristics, Dead-Time Control Section
See Figure 8-1
PARAMETER
TEST CONDITIONS
Input bias current (DEAD-TIME CTRL)
VI = 0 to 5.25 V
Maximum duty cycle, each output
VI (DEAD-TIME CTRL) = 0, CT = 0.01 μF,
RT = 12 kΩ
Input threshold voltage (DEAD-TIME CTRL)
(1)
MIN TYP(1)
MAX
UNIT
–2
–10
μA
45%
Zero duty cycle
Maximum duty cycle
—
3
3.3
MIN TYP(1)
MAX
4
4.5
0
V
All typical values, except for temperature coefficient, are at TA = 25°C.
7.10 Electrical Characteristics, PWM Comparator Section
See Figure 8-1
PARAMETER
TEST CONDITIONS
Input threshold voltage (FEEDBACK)
Zero duty cyle
Input sink current (FEEDBACK)
V (FEEDBACK) = 0.7 V
(1)
0.3
0.7
UNIT
V
mA
All typical values, except for temperature coefficient, are at TA = 25°C.
7.11 Electrical Characteristics, Total Device
PARAMETER
MIN TYP(1)
MAX
VCC = 15 V
6
10
VCC = 40 V
9
15
TEST CONDITIONS
Standby supply current
RT = Vref,
All other inputs and outputs open
Average supply current
VI (DEAD-TIME CTRL) = 2 V, See Figure 8-1
(1)
7.5
UNIT
mA
mA
All typical values, except for temperature coefficient, are at TA = 25°C.
7.12 Switching Characteristics
TA = 25°C
PARAMETER
Rise time
Fall time
Rise time
Fall time
(1)
6
TEST CONDITIONS
Common-emitter configuration, See Figure 8-3
Emitter-follower configuration, See Figure 8-4
MIN TYP(1)
MAX
UNIT
100
200
ns
25
100
ns
100
200
ns
40
100
ns
All typical values, except for temperature coefficient, are at TA = 25°C.
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100
100 k
VCC = 15 V
TA = 25°C
40 k
−2%
10 k
0.001 µF
−1%
0.01 µF
0%
4k
A − Amplifier Voltage Amplification − dB
f − Oscillator Frequency and Frequency Variation − Hz
7.13 Typical Characteristics
0.1 µF
1k
400
(1)
Df = 1%
100
VCC = 15 V
ΔVO = 3 V
TA = 25°C
90
80
70
60
50
40
30
20
10
CT = 1 µF
0
40
1
10
100
1k
10 k
100 k
1M
f − Frequency − Hz
10
1k
xxx xxx
4k
10 k
40 k
100 k
400 k
1M
RT − Timing Resistance − Ω
Figure 7-2. Amplifier Voltage Amplification vs
Frequency
Frequency variation (Δf) is the change in oscillator frequency
that occurs over the full temperature range.
Figure 7-1. Oscillator Frequency and Frequency
Variation vs Timing Resistance
80
60
Gain − (dB)
VO − Output Voltage − (V)
4
3
2
40
20
1
0
0
0
10
VI − Input Voltage − (mV)
20
0
10k
100k
f − Frequency − (Hz)
1M
Figure 7-4. Error Amplifier Bode Plot
Figure 7-3. Error Amplifier Transfer Characteristics
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8 Parameter Measurement Information
VCC = 15 V
150 W
2W
12
VCC
4
Test
Inputs
3
12 kW
C1
DTC
6
5
FEEDBACK
E1
RT
C2
CT
0.01 mF
1
1IN+
1IN−
2
16
15
13
2IN+
E2
8
150 W
2W
Output 1
9
11
Output 2
10
Error
Amplifiers
2IN−
OUTPUT
CTRL
REF
14
GND
50 kW
7
TEST CIRCUIT
VCC
Voltage
at C1
0V
VCC
Voltage
at C2
0V
Voltage
at CT
Threshold Voltage
DTC
0V
Threshold Voltage
FEEDBACK
0.7 V
Duty Cycle
0%
0%
MAX
VOLTAGE WAVEFORMS
Figure 8-1. Operational Test Circuit and Waveforms
8
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Amplifier Under Test
+
VI
FEEDBACK
−
+
Vref
−
Other Amplifier
Figure 8-2. Amplifier Characteristics
15 V
68 W
2W
Each Output
Circuit
tf
Output
tr
90%
90%
CL = 15 pF
(See Note A)
10%
10%
TEST CIRCUIT
OUTPUT VOLTAGE WAVEFORM
NOTE A: CL includes probe and jig capacitance.
Figure 8-3. Common-Emitter Configuration
15 V
Each Output
Circuit
Output
90%
90%
68 W
2W
CL = 15 pF
(See Note A)
10%
10%
tf
tr
TEST CIRCUIT
OUTPUT VOLTAGE WAVEFORM
NOTE A: CL includes probe and jig capacitance.
Figure 8-4. Emitter-Follower Configuration
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9 Detailed Description
9.1 Overview
The design of the TL494 not only incorporates the primary building blocks required to control a switching power
supply, but also addresses many basic problems and reduces the amount of additional circuitry required in
the total design. The TL494 is a fixed-frequency pulse-width-modulation (PWM) control circuit. Modulation of
output pulses is accomplished by comparing the sawtooth waveform created by the internal oscillator on the
timing capacitor (CT) to either of two control signals. The output stage is enabled during the time when the
sawtooth voltage is greater than the voltage control signals. As the control signal increases, the time during
which the sawtooth input is greater decreases; therefore, the output pulse duration decreases. A pulse-steering
flip-flop alternately directs the modulated pulse to each of the two output transistors. For more information on the
operation of the TL494, see the application notes located on ti.com.
9.2 Functional Block Diagram
OUTPUT CTRL
(see Function Table)
13
RT 6
CT 5
Oscillator
Q1
1D
DTC
4
Dead-Time Control
Comparator
≈0.1 V
≈0.7 V
1IN+
1IN−
2
9
Q2 11
PWM
Comparator
10
+
16
2IN− 15
−
12
C2
E2
VCC
+
Reference
Regulator
−
14
7
FEEDBACK
E1
Pulse-Steering
Flip-Flop
Error Amplifier 2
2IN+
C1
C1
Error Amplifier 1
1
8
3
REF
GND
0.7 mA
9.3 Feature Description
9.3.1 5-V Reference Regulator
The TL494 internal 5-V reference regulator output is the REF pin. In addition to providing a stable reference,
it acts as a preregulator and establishes a stable supply from which the output-control logic, pulse-steering
flip-flop, oscillator, dead-time control comparator, and PWM comparator are powered. The regulator employs a
band-gap circuit as its primary reference to maintain thermal stability of less than 100-mV variation over the
operating free-air temperature range of 0°C to 70°C. Short-circuit protection is provided to protect the internal
reference and preregulator; 10 mA of load current is available for additional bias circuits. The reference is
internally programmed to an initial accuracy of ±5% and maintains a stability of less than 25-mV variation over
an input voltage range of 7 V to 40 V. For input voltages less than 7 V, the regulator saturates within 1 V of the
input and tracks it.
9.3.2 Oscillator
The oscillator provides a positive sawtooth waveform to the dead-time and PWM comparators for comparison to
the various control signals.
10
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The frequency of the oscillator is programmed by selecting timing components RT and CT. The oscillator charges
the external timing capacitor, CT, with a constant current, the value of which is determined by the external
timing resistor, RT. This produces a linear-ramp voltage waveform. When the voltage across CT reaches 3 V, the
oscillator circuit discharges it, and the charging cycle is reinitiated. The charging current is determined by the
formula:
ICHARGE =
3V
RT
(1)
The period of the sawtooth waveform is:
T=
3 V ´ CT
ICHARGE
(2)
The frequency of the oscillator becomes:
fOSC =
1
R T ´ CT
(3)
However, the oscillator frequency is equal to the output frequency only for single-ended applications. For
push-pull applications, the output frequency is one-half the oscillator frequency.
Single-ended applications:
f=
1
R T ´ CT
(4)
Push-pull applications:
f=
1
2RT ´ CT
(5)
9.3.3 Dead-time Control
The dead-time control input provides control of the minimum dead time (off time). The output of the comparator
inhibits switching transistors Q1 and Q2 when the voltage at the input is greater than the ramp voltage of the
oscillator. An internal offset of 110 mV ensures a minimum dead time of ∼3% with the dead-time control input
grounded. Applying a voltage to the dead-time control input can impose additional dead time. This provides a
linear control of the dead time from its minimum of 3% to 100% as the input voltage is varied from 0 V to 3.3 V,
respectively. With full-range control, the output can be controlled from external sources without disrupting the
error amplifiers. The dead-time control input is a relatively high-impedance input (II < 10 μA) and should be
used where additional control of the output duty cycle is required. However, for proper control, the input must be
terminated. An open circuit is an undefined condition.
9.3.4 Comparator
The comparator is biased from the 5-V reference regulator. This provides isolation from the input supply for
improved stability. The input of the comparator does not exhibit hysteresis, so protection against false triggering
near the threshold must be provided. The comparator has a response time of 400 ns from either of the
control-signal inputs to the output transistors, with only 100 mV of overdrive. This ensures positive control of the
output within one-half cycle for operation within the recommended 300-kHz range.
9.3.5 Pulse-Width Modulation (PWM)
The comparator also provides modulation control of the output pulse width. For this, the ramp voltage across
timing capacitor CT is compared to the control signal present at the output of the error amplifiers. The timing
capacitor input incorporates a series diode that is omitted from the control signal input. This requires the control
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signal (error amplifier output) to be ∼0.7 V greater than the voltage across CT to inhibit the output logic, and
ensures maximum duty cycle operation without requiring the control voltage to sink to a true ground potential.
The output pulse width varies from 97% of the period to 0 as the voltage present at the error amplifier output
varies from 0.5 V to 3.5 V, respectively.
9.3.6 Error Amplifiers
Both high-gain error amplifiers receive their bias from the VI supply rail. This permits a common-mode input
voltage range from –0.3 V to 2 V less than VI. Both amplifiers behave characteristically of a single-ended
single-supply amplifier, in that each output is active high only. This allows each amplifier to pull up independently
for a decreasing output pulse-width demand. With both outputs ORed together at the inverting input node of the
PWM comparator, the amplifier demanding the minimum pulse out dominates. The amplifier outputs are biased
low by a current sink to provide maximum pulse width out when both amplifiers are biased off.
9.3.7 Output-Control Input
The output-control input determines whether the output transistors operate in parallel or push-pull. This input
is the supply source for the pulse-steering flip-flop. The output-control input is asynchronous and has direct
control over the output, independent of the oscillator or pulse-steering flip-flop. The input condition is intended
to be a fixed condition that is defined by the application. For parallel operation, the output-control input must
be grounded. This disables the pulse-steering flip-flop and inhibits its outputs. In this mode, the pulses seen at
the output of the dead-time control/PWM comparator are transmitted by both output transistors in parallel. For
push-pull operation, the output-control input must be connected to the internal 5-V reference regulator. Under
this condition, each of the output transistors is enabled, alternately, by the pulse-steering flip-flop.
9.3.8 Output Transistors
Two output transistors are available on the TL494. Both transistors are configured as open collector/open
emitter, and each is capable of sinking or sourcing up to 200 mA. The transistors have a saturation voltage of
less than 1.3 V in the common-emitter configuration and less than 2.5 V in the emitter-follower configuration.
The outputs are protected against excessive power dissipation to prevent damage, but do not employ sufficient
current limiting to allow them to be operated as current-source outputs.
9.4 Device Functional Modes
When the OUTPUT CTRL pin is tied to ground, the TL494 is operating in single-ended or parallel mode. When
the OUTPUT CTRL pin is tied to VREF, the TL494 is operating in normal push-pull operation.
12
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10 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification,
and TI does not warrant its accuracy or completeness. TI’s customers are responsible for
determining suitability of components for their purposes, as well as validating and testing their design
implementation to confirm system functionality.
10.1 Application Information
The following design example uses the TL494 to create a 5-V/10-A power supply. This application was taken
from application note SLVA001.
10.2 Typical Application
NTE331
32-V
Input
140 mH
VO
R12
30 W
Q2
R11
100 W
R1
1 kW
R2
4 kW
16 15
+
5-V
REF
NTE6013
NTE153
Q1
R8
5.1 k
R10
270 W
14
13
−
12 11
10
R9
5.1 k
9
VREF
TL494
Control
Load
+
1
Osc
−
2
3
RF
51 kW
4
CT
0.001 mF
5
6
7
8
RT
50 kW
R7
9.1 kW
R5
510 W
5-V
REF
5-V
REF
R3
5.1 kW
R4
5.1 kW
R6
1 kW
C2
2.5 mF
R13
0.1 W
Figure 10-1. Switching and Control Sections
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10.2.1 Design Requirements
•
•
•
•
•
•
VI = 32 V
VO = 5 V
IO = 10 A
fOSC = 20-kHz switching frequency
VR = 20-mV peak-to-peak (VRIPPLE)
ΔIL = 1.5-A inductor current change
10.2.2 Detailed Design Procedure
10.2.2.1 Input Power Source
The 32-V dc power source for this supply uses a 120-V input, 24-V output transformer rated at 75 VA. The 24-V
secondary winding feeds a full-wave bridge rectifier, followed by a current-limiting resistor (0.3 Ω) and two filter
capacitors (see Figure 10-2).
Bridge Rectifiers
3 A, 50 V
0.3 Ÿ
120 V
PinName
24 V
3A
+
20 mF
20 mF
PinName
Figure 10-2. Input Power Source
The output current and voltage are determined by Equation 6 and Equation 7:
VRECTIFIER = VSECONDARY ´ 2 = 24 V ´ 2 = 34 V
IRECTIFIER(AVG) »
(6)
VO
5V
´ IO »
´ 10 A = 1.6 A
VI
32 V
(7)
The 3-A/50-V full-wave bridge rectifier meets these calculated conditions. Figure 10-1 shows the switching and
control sections.
10.2.2.2 Control Circuits
10.2.2.2.1 Oscillator
Connecting an external capacitor and resistor to pins 5 and 6 controls the TL494 oscillator frequency. The
oscillator is set to operate at 20 kHz, using the component values calculated by Equation 8 and Equation 9:
fOSC =
1
R T ´ CT
(8)
Choose CT = 0.001 μF and calculate RT:
RT +
1
f OSC
CT
+
(20
10 3)
1
(0.001
10 *6)
+ 50 kW
(9)
10.2.2.2.2 Error Amplifier
The error amplifier compares a sample of the 5-V output to the reference and adjusts the PWM to maintain a
constant output current (see Figure 10-3).
14
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VO
14
13
VREF
R3
5.1 kW
R5
510 W
+
2
−
Error
Amplifier
R9
5.1 kW
3
R4
5.1 kW
TL494
1
R7
51 kW
R8
5.1 kW
TL494
Figure 10-3. Error-Amplifier Section
The TL494 internal 5-V reference is divided to 2.5 V by R3 and R4. The output-voltage error signal also is
divided to 2.5 V by R8 and R9. If the output must be regulated to exactly 5.0 V, a 10-kΩ potentiometer can be
used in place of R8 to provide an adjustment.
To increase the stability of the error-amplifier circuit, the output of the error amplifier is fed back to the inverting
input through RT, reducing the gain to 101.
10.2.2.2.3 Current-Limiting Amplifier
The power supply was designed for a 10-A load current and an IL swing of 1.5 A, therefore, the short-circuit
current should be:
ISC = IO +
IL
= 10.75 A
2
(10)
The current-limiting circuit is shown in Figure 10-4.
R2
4 NŸ
TL494
TL494
15
14
R1
1 NŸ
+
VO
VREF
Load
16
R13
0.1 Ÿ
Figure 10-4. Current-Limiting Circuit
Resistors R1 and R2 set the reference of approximately 1 V on the inverting input of the current-limiting amplifier.
Resistor R13, in series with the load, applies 1 V to the non-inverting terminal of the current-limiting amplifier
when the load current reaches 10 A. The output pulse width reduces accordingly. The value of R13 is calculated
in Equation 11.
R13 =
1V
= 0.1W
10 A
(11)
10.2.2.2.4 Soft Start and Dead Time
To reduce stress on the switching transistors at the start-up time, the start-up surge that occurs as the output
filter capacitor charges must be reduced. The availability of the dead-time control makes implementation of a
soft-start circuit relatively simple (see Figure 10-5).
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Oscillator Ramp
14
+5 V
Osc
C2
+
RT
5
4
0.1 V
R6
7
TL494
Pin 4 Voltage
Oscillator Ramp Voltage
ton
PWM Output
Figure 10-5. Soft-Start Circuit
The soft-start circuit allows the pulse width at the output to increase slowly (see Figure 10-5) by applying a
negative slope waveform to the dead-time control input (pin 4).
Initially, capacitor C2 forces the dead-time control input to follow the 5-V regulator, which disables the outputs
(100% dead time). As the capacitor charges through R6, the output pulse width slowly increases until the control
loop takes command. With a resistor ratio of 1:10 for R6 and R7, the voltage at pin 4 after start-up is 0.1 × 5 V, or
0.5 V.
The soft-start time generally is in the range of 25 to 100 clock cycles. If 50 clock cycles at a 20-kHz switching
rate is selected, the soft-start time is:
t=
1
1
=
= 50 msper clock cycle
f 20kHz
(12)
The value of the capacitor then is determined by:
C2 =
soft - start time 50 ms ´ 50 cycles
=
= 2.5 mF
R6
1 kW
(13)
This helps eliminate any false signals that might be created by the control circuit as power is applied.
16
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10.2.2.3 Inductor Calculations
The switching circuit used is shown in Figure 39.
L
S1
VI
D1
C1
R1
VO
Figure 10-6. Switching Circuit
The size of the inductor (L) required is:
d
= duty cycle = VO/VI = 5 V/32 V = 0.156
f
= 20 kHz (design objective)
ton
= time on (S1 closed) = (1/f) × d = 7.8 μs
toff
= time off (S1 open) = (1/f) – ton = 42.2 μs
L
≉ (VI – VO ) × ton/ΔIL
≉ [(32 V – 5 V) × 7.8 μs]/1.5 A
≉ 140.4 μH
10.2.2.4 Output Capacitance Calculations
Once the filter inductor has been calculated, the value of the output filter capacitor is calculated to meet the
output ripple requirements. An electrolytic capacitor can be modeled as a series connection of an inductance, a
resistance, and a capacitance. To provide good filtering, the ripple frequency must be far below the frequencies
at which the series inductance becomes important. So, the two components of interest are the capacitance and
the effective series resistance (ESR). The maximum ESR is calculated according to the relation between the
specified peak-to-peak ripple voltage and the peak-to-peak ripple current.
ESR(max) =
DVO(ripple)
DIL
=
V
» 0.067 W
1.5 A
(14)
The minimum capacitance of C3 necessary to maintain the VO ripple voltage at less than the 100-mV design
objective is calculated according to Equation 15:
C3 =
DIL
1.5 A
=
= 94 mF
8f DVO 8 ´ 20 ´ 103 ´ 0.1 V
(15)
A 220-mF, 60-V capacitor is selected because it has a maximum ESR of 0.074 Ω and a maximum ripple current
of 2.8 A.
10.2.2.5 Transistor Power-Switch Calculations
The transistor power switch was constructed with an NTE153 pnp drive transistor and an NTE331 npn output
transistor. These two power devices were connected in a pnp hybrid Darlington circuit configuration (see Figure
10-7).
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NTE331
32 V
R11
100 W
Q2
R12
30 W
DI
IO +
L
= 10.8 A
2
Q1
NTE153
R10
270 W
11
10
9
Control
TL494
8
Figure 10-7. Power-Switch Section
The hybrid Darlington circuit must be saturated at a maximum output current of IO + ΔIL/2 or 10.8 A. The
Darlington hFE at 10.8 A must be high enough not to exceed the 250-mA maximum output collector current of the
TL494. Based on published NTE153 and NTE331 specifications, the required power-switch minimum drive was
calculated by Equation 16 through Equation 18 to be 144 mA:
hFE (Q1) at IC of 3 A = 15
(16)
hFE (Q2) at IC of 10.0 A = 5
(17)
IL
2
³ 144mA
iB ³
hFE (Q2) ´ hFE (Q1)
(18)
IO +
The value of R10 was calculated by:
R10 £
VI - [VBE (Q1) + VCE (TL494)]
iB
=
32 - (1.5 + 0.7)
0.144
(19)
R10 £ 207 W
Based on these calculations, the nearest standard resistor value of 220 Ω was selected for R10. Resistors R11
and R12 permit the discharge of carriers in switching transistors when they are turned off.
The power supply described demonstrates the flexibility of the TL494 PWM control circuit. This power-supply
design demonstrates many of the power-supply control methods provided by the TL494, as well as the versatility
of the control circuit.
18
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10.2.3 Application Curves for Output Characteristics
VREF − Reference Voltage − (V)
6
5
4
3
2
1
0
0
1
2
3
4
5
6
7
VI − Input Voltage − (V)
Figure 10-8. Reference Voltage vs Input Voltage
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11 Power Supply Recommendations
The TL494 is designed to operate from an input voltage supply range between 7 V and 40 V. This input supply
should be well regulated. If the input supply is located more than a few inches from the device, additional bulk
capacitance may be required in addition to the ceramic bypass capacitors. A tantalum capacitor with a value of
47 μF is a typical choice, however this may vary depending upon the output power being delivered.
12 Layout
12.1 Layout Guidelines
Always try to use a low EMI inductor with a ferrite type closed core. Some examples would be toroid and
encased E core inductors. Open core can be used if they have low EMI characteristics and are located a bit
more away from the low power traces and components. Make the poles perpendicular to the PCB as well if using
an open core. Stick cores usually emit the most unwanted noise.
12.1.1 Feedback Traces
Try to run the feedback trace as far from the inductor and noisy power traces as possible. You would also like
the feedback trace to be as direct as possible and somewhat thick. These two sometimes involve a trade-off, but
keeping it away from inductor EMI and other noise sources is the more critical of the two. Run the feedback trace
on the side of the PCB opposite of the inductor with a ground plane separating the two.
12.1.2 Input/Output Capacitors
When using a low value ceramic input filter capacitor, it should be located as close to the VCC pin of the IC as
possible. This will eliminate as much trace inductance effects as possible and give the internal IC rail a cleaner
voltage supply. Some designs require the use of a feed-forward capacitor connected from the output to the
feedback pin as well, usually for stability reasons. In this case it should also be positioned as close to the IC as
possible. Using surface mount capacitors also reduces lead length and lessens the chance of noise coupling into
the effective antenna created by through-hole components.
12.1.3 Compensation Components
External compensation components for stability should also be placed close to the IC. Surface mount
components are recommended here as well for the same reasons discussed for the filter capacitors. These
should not be located very close to the inductor either.
12.1.4 Traces and Ground Planes
•
•
•
•
•
•
•
20
Make all of the power (high current) traces as short, direct, and thick as possible. It is good practice on a
standard PCB board to make the traces an absolute minimum of 15 mils (0.381 mm) per Ampere.
The inductor, output capacitors, and output diode should be as close to each other possible. This helps
reduce the EMI radiated by the power traces due to the high switching currents through them. This will also
reduce lead inductance and resistance as well, which in turn reduces noise spikes, ringing, and resistive
losses that produce voltage errors.
The grounds of the IC, input capacitors, output capacitors, and output diode (if applicable) should be
connected close together directly to a ground plane. It would also be a good idea to have a ground plane on
both sides of the PCB. This will reduce noise as well by reducing ground loop errors as well as by absorbing
more of the EMI radiated by the inductor.
For multi-layer boards with more than two layers, a ground plane can be used to separate the power plane
(where the power traces and components are) and the signal plane (where the feedback and compensation
and components are) for improved performance.
On multi-layer boards the use of vias will be required to connect traces and different planes.
It is good practice to use one standard via per 200 mA of current if the trace will need to conduct a significant
amount of current from one plane to the other.
Arrange the components so that the switching current loops curl in the same direction. Due to the way
switching regulators operate, there are two power states. One state when the switch is on and one when the
switch is off. During each state there will be a current loop made by the power components that are currently
conducting. Place the power components so that during each of the two states the current loop is conducting
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in the same direction. This prevents magnetic field reversal caused by the traces between the two half-cycles
and reduces radiated EMI.
12.2 Layout Example
LEGEND
Power or GND Plane
VIA to Power Plane
VIA to GND Plane
2IN+
16
1IN
2IN±
15
3
FEEDBACK
REF
14
4
DTC
OUTPUT
CTRL
13
5
CT
VCC
12
6
RT
C2
11
7
GND
E2
10
8
C1
E1
9
2
±
VCC
Output
1IN+
TL494
1
GND
Figure 12-1. Operational Amplifier Board Layout for Noninverting Configuration
13 Device and Documentation Support
13.1 Trademarks
All trademarks are the property of their respective owners.
13.2 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
13.3 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
14 Mechanical, Packaging, and Orderable Information
The following pages include mechanical packaging and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser based versions of this data sheet, refer to the left hand navigation.
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21
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
TL494CD
ACTIVE
SOIC
D
16
40
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494C
Samples
TL494CDG4
ACTIVE
SOIC
D
16
40
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494C
Samples
TL494CDR
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU | SN
Level-1-260C-UNLIM
0 to 70
TL494C
Samples
TL494CDRE4
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494C
Samples
TL494CDRG4
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494C
Samples
TL494CN
ACTIVE
PDIP
N
16
25
RoHS & Green
NIPDAU
N / A for Pkg Type
0 to 70
TL494CN
Samples
TL494CNE4
ACTIVE
PDIP
N
16
25
RoHS & Green
NIPDAU
N / A for Pkg Type
0 to 70
TL494CN
Samples
TL494CNSR
ACTIVE
SO
NS
16
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494
Samples
TL494CNSRG4
ACTIVE
SO
NS
16
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
TL494
Samples
TL494CPW
ACTIVE
TSSOP
PW
16
90
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
T494
Samples
TL494CPWR
ACTIVE
TSSOP
PW
16
2000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
0 to 70
T494
Samples
TL494ID
ACTIVE
SOIC
D
16
40
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
TL494I
Samples
TL494IDG4
ACTIVE
SOIC
D
16
40
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
TL494I
Samples
TL494IDR
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU | SN
Level-1-260C-UNLIM
-40 to 85
TL494I
Samples
TL494IDRE4
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
TL494I
Samples
TL494IDRG4
ACTIVE
SOIC
D
16
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
TL494I
Samples
TL494IN
ACTIVE
PDIP
N
16
25
RoHS & Green
NIPDAU
N / A for Pkg Type
-40 to 85
TL494IN
Samples
TL494INE4
ACTIVE
PDIP
N
16
25
RoHS & Green
NIPDAU
N / A for Pkg Type
-40 to 85
TL494IN
Samples
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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