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UC1526

UC2526

UC3526

Regulating Pulse Width Modulator

FEATURES

8 To 35V Operation

DESCRIPTION

•

The UC1526 is a high performance monolithic pulse width modulator

circuit designed for fixed-frequency switching regulators and other

power control applications. Included in an 18-pin dual-in-line pack-

age are a temperature compensated voltage reference, sawtooth os-

cillator, error amplifier, pulse width modulator, pulse metering and

setting logic, and two low impedance power drivers. Also included

are protective features such as soft-start and under-voltage lockout,

digital current limiting, double pulse inhibit, a data latch for single

pulse metering, adjustable deadtime, and provision for symmetry cor-

rection inputs. For ease of interface, all digital control ports are TTL

and B-series CMOS compatible. Active LOW logic design allows

wired-OR connections for maximum flexibility. This versatile device

can be used to implement single-ended or push-pull switching regu-

lators of either polarity, both transformerless and transformer cou-

pled. The UC1526 is characterized for operation over the full military

temperature range of -55°C to +125°C. The UC2526 is characterized

for operation from -25°C to +85°C, and the UC3526 is characterized

for operation from 0° to +70°C.

5V Reference Trimmed To ±1%

1Hz To 400kHz Oscillator Range

Dual 100mA Source/Sink Outputs

Digital Current Limiting

Double Pulse Suppression

Programmable Deadtime

Under-Voltage Lockout

Single Pulse Metering

Programmable Soft-Start

Wide Current Limit Common Mode Range

TTL/CMOS Compatible Logic Ports

Symmetry Correction Capability

Guaranteed 6 Unit Synchronization

BLOCK DIAGRAM

6/93

UC1526

UC2526

UC3526

ABSOLUTE MAXIMUM RATINGS (Note 1, 2)

RECOMMENDED OPERATING CONDITIONS (Note 3)

Input Voltage (+VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +40V Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +8V to +35V

Collector Supply Voltage (+VC) . . . . . . . . . . . . . . . . . . . . . +40V Collector Supply Voltage . . . . . . . . . . . . . . . . . . . +4.5V to +35V

Logic Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +5.5V Sink/Source Load Current (each output) . . . . . . . . . 0 to 100mA

Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +VIN Reference Load Current . . . . . . . . . . . . . . . . . . . . . . 0 to 20mA

Source/Sink Load Current (each output) . . . . . . . . . . . . . 200mA Oscillator Frequency Range . . . . . . . . . . . . . . . . 1Hz to 400kHz

Reference Load Current. . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA Oscillator Timing Resistor . . . . . . . . . . . . . . . . . . . 2kΩ to 150kΩ

Logic Sink Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15mA Oscillator Timing Capacitor . . . . . . . . . . . . . . . . . . . 1nF to 20µF

Power Dissipation at TA = +25°C (Note 2) . . . . . . . . . . 1000mW Available Deadtime Range at 40kHz. . . . . . . . . . . . . 3% to 50%

Power Dissipation at TC = +25°C (Note 2). . . . . . . . . . 3000mW Operating Ambient Temperature Range

Operating Junction Temperature . . . . . . . . . . . . . . . . . . +150°C

Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C

Lead Temperature (soldering, 10 seconds) . . . . . . . . . . +300°C

Note 1: Values beyond which damage may occur.

Note 2: Consult packaging section of databook for thermal

limitations and considerations of package.

UC1526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . -55°C to +125°C

UC2526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -25°C to +85°C

UC3526 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0°C to +70°C

Note 3: Range over which the device is functional and

parameter limits are guaranteed.

CONNECTION DIAGRAMS

PACKAGE PIN FUNCTION

DIL-18, SOIC-18 (TOP VIEW)

J or N Package, DW Package

PLCC-20, LCC-20

(TOP VIEW)

Q and L Packages

FUNCTION

N/C

1

2

3

4

+Error

-Error

Comp.

CSS

______

5

Reset

6

- Current Sense

7

+ Current Sense

_________

8

Shutdown

RTIMING

CT

RD

Sync

Output A

VC

N/C

Ground

Output B

+VIN

9

10

11

12

13

14

15

16

17

18

19

20

VREF

ELECTRICAL CHARACTERISTICS: +VIN = 15V, and over operating ambient temperature, unless otherwise

specified, TA = TJ.

PARAMETER

TEST CONDITIONS

UC1526 / UC2526

UC3526

TYP MAX

UNITS

MIN

TYP

MAX

MIN

Reference Section (Note 4)

Output Voltage

TJ = + 25°C

4.95

5.00

10

5.05

20

4.90

5.00

10

5.10

30

V

Line Regulation

+VIN = 8 to 35V

IL = 0 to 20mA

mV

V

Load Regulation

10

30

10

50

Temperature Stability

Over Operating TJ

15

50

15

50

Total Output

Voltage Range

Over Recommended

Operating Conditions

4.90

25

5.00

5.10

4.85

25

5.00

5.15

Short Circuit Current

VREF = 0V

50

100

0.4

50

100

0.4

mA

Under -Voltage Lockout

_______

RESET Output Voltage

VREF = 3.8V

VREF = 4.8V

0.2

4.8

0.2

4.8

V

2.4

Note 4: IL = 0mA.

2

UC1526

UC2526

UC3526

+VIN = 15V, and over operating ambient temperature, unless otherwise

specified, TA = TJ.

ELECTRICAL CHARACTERISTICS:

PARAMETER

TEST CONDITIONS

UC1526 / UC2526

UC3526

TYP MAX

UNITS

MIN

TYP

MAX

MIN

Oscillator Section (Note 5)

Initial Accuracy

TJ = + 25°C

+VIN = 8 to 35V

±3

0.5

7

±8

1

±3

0.5

3

±8

1

%

Voltage Stability

Temperature Stability

Minimum Frequency

Maximum Frequency

Sawtooth Peak Voltage

Sawtooth Valley Voltage

Error Amplifier Section (Note 6)

Input Offset Voltage

Input Bias Current

Over Operating TJ

RT = 150kΩ, CT = 20µF

RT = 2kΩ, CT = 1.0nF

+VIN = 35V

10

1

5

%

1

Hz

kHz

V

400

0.5

400

0.5

3.0

1.0

3.5

3.0

1.0

3.5

+VIN = 8V

V

RS ≤ 2kΩ

2

5

2

10

mV

nA

dB

V

-350 -1000

-350 -2000

Input Offset Current

DC Open Loop Gain

HIGH Output Voltage

35

72

100

35

72

200

RL ≥ 10MΩ

64

60

VPIN1-VPIN2 ≥ 150mV, ISOURCE =

100µA

3.6

4.2

3.6

4.2

LOW Output Voltage

Common Mode Rejection

Supply Voltage Rejection

PWM Comparator (Note 5)

Minimum Duty Cycle

VPIN2-VPIN1 ≥ 150mV, ISINK = 100µA

Rs ≤ 12kΩ

0.2

94

80

0.4

0.2

94

80

0.4

V

70

66

70

66

dB

+VIN = 12 to 18V

VCOMPENSATION = +0.4V

VCOMPENSATION = +3.6V

0

%

Maximum Duty Cycle

45

49

45

49

Digital Ports (SYNC, SHUTDOWN, and RESET)

HIGH Output Voltage

LOW Output Voltage

HIGH Input Current

LOW Input Current

ISOURCE =40µA

ISINK = 3.6mA

VIH = +2.4V

2.4

4.0

0.2

2.4

4.0

0.2

V

0.4

-125

-225

-200

-360

-125

-225

-200

-360

µA

VIL = +0.4V

Current LImit Comparator (Note 7)

Sense Voltage

RS ≤ 50Ω

90

50

100

-3

110

-10

80

50

100

-3

120

-10

mV

Input Bias Current

µA

Soft-Start Section

Error Clamp Voltage

Cs Charging Current

RESET = +0.4V

RESET =+2.4V

0.1

0.4

0.1

0.4

V

100

150

100

150

µA

Output Drivers (Each Output) (Note 8)

HIGH Output Voltage

ISOURCE = 20mA

12.5

12

13.5

13

12.5

12

13.5

13

V

ISOURCE = 100mA

ISINK = 20mA

ISINK = 100mA

VC = 40V

LOW Output Voltage

0.2

1.2

50

0.3

2.0

150

0.6

0.2

1.2

50

0.3

2.0

150

0.6

0.2

V

Collector Leakage

Rise Time

µA

µs

CL = 1000pF

0.3

0.1

0.3

0.1

Fall Time

Power Consumption (Note 9)

Standby Current

____________

SHUTDOWN = +0.4V

18

30

18

30

mA

Note 4: IL = 0mA.

Note 5: FOSC = 40kHz (RT = 4.12kΩ ± 1%, CT = 0.1µF ± 1%,

RD = 0Ω)

Note 6: VCM = 0 to +5.2V

Note 8: VC = +15V

Note 9: +VIN = +35V, RT = 4.12kΩ

3

UC1526

UC2526

UC3526

APPLICATIONS INFORMATION

Voltage Reference

The reference regulator of the UC1526 is based on a tem-

perature compensated zener diode. The circuitry is fully

active at supply voltages above +8V, and provides up to

20mA of load current to external circuitry at +5.0V. In sys-

tems where additional current is required, an external

PNP transistor can be used to boost the available current.

A rugged low frequency audio-type transistor should be

used, and lead lengths between the PWM and transistor

should be as short as possible to minimize the risk of os-

cillations. Even so, some types of transistors may require

collector-base capacitance for stability. Up to 1 amp of

load current can be obtained with excellent regulation if

the device selected maintains high current gain.

Figure 2. Under-Voltage Lockout Schematic

Soft-Start Circuit

The soft-start circuit protects the power transistors and

rectifier diodes from high current surges during power

supply turn-on. When supply voltage is first applied to the

_______

UC1526, the under-voltage lockout circuit holds RESET

LOW with Q3. Q1 is turned on, which holds the soft-start

capacitor voltage at zero. The second collector of Q1

clamps the output of the error amplifier to ground, guaran-

teeing zero duty cycle at the driver outputs. When the

_______

supply voltage reaches normal operating range, RESET

will go HIGH. Q1 turns off, allowing the internal 100mA

current source to charge CS. Q2 clamps the error ampli-

fier output to 1VBE above the voltage on CS. As the soft-

Figure 1. Extending Reference Output Current

Under-Voltage Lockout

The under-voltage lockout circuit protects the UC1526 start voltage ramps up to +5V, the duty cycle of the PWM

and the power devices it controls from inadequate supply linearly increases to whatever value the voltage regula-

voltage, If +VIN is too low, the circuit disables the output tion loop requires for an error null.

_______

drivers and holds the RESET pin LOW. This prevents

spurious output pulses while the control circuitry is stabi-

lizing, and holds the soft-start timing capacitor in a dis-

charged state.

The circuit consists of a +1.2V bandgap reference and

comparator circuit which is active when the reference

voltage has risen to 3VBE or +1.8V at 25°C. When the ref-

erence voltage rises to approximately +4.4V, the circuit

_______

enables the output drivers and releases the RESET pin,

allowing a normal soft-start. The comparator has 200mV

of hysteresis to minimize oscillation at the trip point.

When +VIN to the PWM is removed and the reference

_______

drops to +4.2V, the under-voltage circuit pulls RESET

LOW again. The soft-start capacitor is immediately dis-

charged, and the PWM is ready for another soft-start cy-

cle.

Figure 3. Soft-Start Circuit Schematic

Digital Control Ports

The three digital control ports of the UC1526 are bi-direc-

tional. Each pin can drive TTL and 5V CMOS logic di-

rectly, up to a fan-out of 10 low-power Schottky gates.

Each pin can also be directly driven by open-collector

The UC1526 can operate from a +5V supply by connect-

ing the VREF pin to the +VIN pin and maintaining the sup-

ply between +4.8 and +5.2V.

4

UC1526

UC2526

UC3526

APPLICATIONS INFORMATION (cont.)

TTL, open-drain CMOS, and open-collector voltage com-

parators; fan-in is equivalent to 1 low-power Schottky

Multiple devices can be synchronized together by pro-

gramming one master unit for the desired frequency and

then sharing its sawtooth and clock waveforms with the

gate. Each port is normally HIGH; the pin is pulled LOW

______

to activate the particular function. Driving SYNC LOW in-

slave units. All CT terminals are connected to the CT pin

______

itiates a discharge cycle in the oscillator. Pulling

____________

of the master, and all SYNC terminals are likewise con-

______

SHUTDOWN LOW immediately inhibits all PWM output

_______

nected to the SYNC pin of the master. Slave RT termi-

nals are left open or connected to VREF. Slave RD

terminals may be either left open or grounded.

pulses. Holding RESET LOW discharges the soft-start

capacitor. The logic threshold is +1.1V at +25°C. Noise

immunity can be gained at the expense of fan-out with an

external 2k pull-up resistor to +5V.

Error Amplifier

The error amplifier is a transconductance design, with an

output impedance of 2MΩ . Since all voltage gain takes

place at the output pin, the open-loop gain/frequency

characteristics can be controlled with shunt reactance to

ground. When compensated for unity-gain stability with

100pF, the amplifier has an open-loop pole at 800Hz.

The input connections to the error amplifier are deter-

mined by the polarity of the switching supply output volt-

age. For positive supplies, the common-mode voltage is

+5.0V and the feedback connections in Figure 6A are

used. With negative supplies, the common-mode voltage

is ground and the feedback divider is connected between

the negative output and the +5.0V reference voltage, as

shown in Figure 6B.

Figure 4. Digital Control Port Schematic

Oscillator

The oscillator is programmed for frequency and dead time

with three components: RT, CT and RD. Two waveforms

are generated: a sawtooth waveform at pin 10 for pulse

width modulation, and a logic clock at pin 12. The follow-

ing procedure is recommended for choosing timing val-

ues:

Output Drivers

The totem-pole output drivers of the UC1526 are de-

signed to source and sink 100mA continuously and

200mA peak. Loads can be driven either from the output

pins 13 and 16, or from the +VC, as required.

Since the bottom transistor of the totem-pole is allowed to

saturate, there is a momentary conduction path from the

+VC terminal to ground during switching. To limit the re-

sulting current spikes a small resistor in series with pin 14

is always recommended. The resistor value is deter-

mined by the driver supply voltage, and should be chosen

for 200mA peak currents.

1. With RD = 0 (pin 11 shorted to ground) select values

for RT and CT from Figure 7 to give the desired oscillator

period. Remember that the frequency at each driver out-

put is half the oscillator frequency, and the frequency at

the +VC terminal is the same as the oscillator frequency.

2. If more dead time is required, select a large value of

RD. At 40kHz dead time increases by 400ns/Ω .

3. Increasing the dead time will cause the oscillator fre-

quency to decrease slightly. Go back and decrease the

value of RT slightly to bring the frequency back to the

nominal design value.

The UC1526 can be synchronized to an external logic

clock by programming the oscillator to free-run at a fre-

quency 10% slower than the sync frequency. A periodic

______

LOW logic pulse approximately 0.5µs wide at the SYNC

pin will then lock the oscillator to the external frequency.

Figure 5. Oscillator Connections and Waveforms

5

UC1526

UC2526

UC3526

Figure 6. Error Amplifier Connections

Figure 8. Single-Ended Configuration

Figure 7. Push-Pull Configuration

Figure 9. Driving N-channel Power Mosfets

TYPICAL CHARACTERISTICS

Oscillator Period vs RT and CT

Oscillation Period

6

UC1526

UC2526

UC3526

TYPICAL CHARACTERISTICS

Output Driver Deadtime vs RD Value

Under Voltage Lockout Characteristic

Error Amplifier Open Loop Gain vs Frequency

Current Limit Transfer Function

Shutdown Delay

Output Driver Saturation Voltage

UNITRODE INTEGRATED CIRCUITS

7 CONTINENTAL BLVD. • MERRIMACK, NH 03054

TEL. (603) 424-2410 • FAX (603) 424-3460

7

PACKAGE OPTION ADDENDUM

www.ti.com

27-Sep-2005

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI

to Customer on an annual basis.

Addendum-Page 2

PACKAGE OPTION ADDENDUM

www.ti.com

18-Oct-2005

PACKAGING INFORMATION

Orderable Device

Status ⁽¹⁾

Package Package

Pins Package Eco Plan ⁽²⁾Lead/Ball Finish MSL Peak Temp ⁽³⁾

Qty

Type

LCCC

CDIP

LCCC

CDIP

PDIP

Drawing

85515012A

8551501VA

UC1526J

ACTIVE

FK

J

20

18

20

18

1

TBD

POST-PLATE Level-NC-NC-NC

A42 SNPB

Level-NC-NC-NC

J

UC1526J883B

UC1526L

J

FK

J

POST-PLATE Level-NC-NC-NC

UC1526L883B

UC2526J

A42 SNPB

Level-NC-NC-NC

UC2526N

N

20 Green (RoHS & CU NIPDAU Level-NC-NC-NC

no Sb/Br)

UC2526NG4

UC3526DW

ACTIVE

PDIP

SOIC

N

18

20 Green (RoHS & CU NIPDAU Level-NC-NC-NC

no Sb/Br)

DW

40 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR

no Sb/Br)

UC3526DWG4

UC3526DWTR

UC3526DWTRG4

40 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR

no Sb/Br)

2000 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR

no Sb/Br)

2000 Green (RoHS & CU NIPDAU Level-2-260C-1 YEAR

no Sb/Br)

UC3526J

UC3526N

ACTIVE

CDIP

PDIP

J

18

1

TBD

A42 SNPB

Level-NC-NC-NC

N

20 Green (RoHS & CU NIPDAU Level-NC-NC-NC

no Sb/Br)

UC3526NG4

ACTIVE

PDIP

N

18

20 Green (RoHS & CU NIPDAU Level-NC-NC-NC

no Sb/Br)

⁽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.

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)

Eco Plan

-

The planned eco-friendly classification: Pb-Free (RoHS) or Green (RoHS

&

no Sb/Br)

-

please check

http://www.ti.com/productcontent for the latest availability information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements

for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered

at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame

retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)

(3)

MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder

temperature.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is

provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the

accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take

reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on

incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited

information may not be available for release.

Addendum-Page 1

PACKAGE OPTION ADDENDUM

www.ti.com

18-Oct-2005

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI

to Customer on an annual basis.

Addendum-Page 2

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