Advanced_Regulating_Pulse_Width

UC1524

UC2524

UC3524

REFERENCE

REGULATOR

REF

+5V TO ALL

INTERNAL

CIRCUITRY

OSC

(RAMP)

OSC OUT

+5V

–SENSE

+SENSE

C L

COMPENSATION

10k

GROUND

(SUBSTRATE)

+5V

E A

INV INPUT

NI INPUT

COMPARATOR

SHUTDOWN

BLOCK DIAGRAM

DESCRIPTION

The UC1524, UC2524 and UC3524 incorporate on a single monolithic chip

all the functions required for the construction of regulating power supplies, in-

verters or switching regulators. They can also be used as the control element

for high-power-output applications. The UC1524 family was designed for

switching regulators of either polarity, transformer-coupled dc-to-dc convert-

ers, transformerless voltage doublers and polarity converter applications em-

ploying fixed-frequency, pulse-width modulation techniques. The dual

alternating outputs allow either single-ended or push-pull applications. Each

device includes an on-chip reference, error amplifier, programmable oscilla-

tor, pulse-steering flip-flop, two uncommitted output transistors, a high-gain

comparator, and current-limiting and shut-down circuitry. The UC1524 is

characterized for operation over the full military temperature range of -55°C

to +125°C. The UC2524 and UC3524 are designed for operation from -25°C

to +85°C and 0° to +70°C, respectively.

Advanced Regulating Pulse Width Modulators

FEATURES

• Complete PWM Power Control

Circuitry

• Uncommitted Outputs for

Single-ended or Push-pull

Applications

• Low Standby Current…8mA Typical

• Interchangeable with SG1524,

SG2524 and SG3524, Respectively

SLUS180A - NOVEMBER 1999

UC1524

UC2524

UC3524

REF

REG

OSC

S/D

INV INPUT

NON INV

INPUT

OSC OUT

CLSENSE(+)

CLSENSE (–-)

GND

REF

S/D

COMP

CONNECTION DIAGRAM

ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage, V

(Notes 2 and 3) . . . . . . . . . . . . . . . . . 40V

Collector Output Current. . . . . . . . . . . . . . . . . . . . . . . . . 100mA

Reference Output Current . . . . . . . . . . . . . . . . . . . . . . . . 50mA

Current Through C

Terminal . . . . . . . . . . . . . . . . . . . . . . –5mA

Power Dissipation at T

= +25°C (Note 4). . . . . . . . . . 1000mW

Power Dissipation at T

= +25°C (Note 4). . . . . . . . . . 2000mW

Operating Junction Temperature Range . . . . –55°C to +150°C

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

Note 1: Over operating free-air temperature range unless oth-

erwise noted.

Note 2: All voltage values are with respect to the ground termi-

nal, pin 8.

Note 3: The reference regulator may be bypassed for opera-

tion from a fixed 5V supply by connecting the V

and

reference output pins both to the supply voltage. In this

configuration the maximum supply voltage is 6V.

Note 4: Consult packaging section of databook for thermal lim-

itations and considerations of package.

RECOMMENDED OPERATING CONDITIONS

Supply Voltage, V

. . . . . . . . . . . . . . . . . . . . . . . . . . 8V to 40V

Reference Output Current . . . . . . . . . . . . . . . . . . . . . 0 to 20mA

Current through C

Terminal . . . . . . . . . . . . . –0.03mA to –2mA

Timing Resistor, R

. . . . . . . . . . . . . . . . . . . . . 1.8k

Ω to 100kΩ

Timing Capacitor, C

. . . . . . . . . . . . . . . . . . . 0.001

µF to 0.1µF

Operating Ambient Temperature Range

UC1524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . –55°C to +125°C

UC2524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –25°C to +85°C

UC3524 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications apply for T

= –55°C to +125°C

for the UC1524, –25°C to +85°C for the UC2524, and 0°C to +70°C for the UC3524, V

= 20V, and f = 20kHz,

= T

PARAMETER

TEST CONDITIONS

UC1524/UC2524

UC3524

UNITS

MIN

MAX

MIN

MAX

Reference Section

Output Voltage

4.8

5.0

5.2

4.6

5.0

5.4

Line Regulation

= 8 to 40V

Load Regulation

= 0 to 20mA

Ripple Rejection

f = 120Hz, T

= 25°C

Short Circuit Current Limit

REF

= 0, T

= 25°C

100

Temperature Stability

Over Operating Temperature Range

0.3

Long Term Stability

= 125°C, t = 1000 Hrs.

Oscillator Section

Maximum Frequency

= .001mfd, R

= 2k

Ω

300

kHz

Initial Accuracy

and C

Constant

Voltage Stability

= 8 to 40V, T

= 25°C

Temperature Stability

Over Operating Temperature Range

Output Amplitude

Pin 3, T

= 25°C

3.5

Output Pulse Width

= .01mfd, T

= 25°C

0.5

µs

Error Amplifier Section

Input Offset Voltage

= 2.5V

0.5

Input Bias Current

= 2.5V

µA

Open Loop Voltage Gain

Common Mode Voltage

= 25°C

1.8

3.4

1.8

3.4

UC1524

UC2524

UC3524

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications apply for T

= –55°C to +125°C

for the UC1524, –25°C to +85°C for the UC2524, and 0°C to +70°C for the UC3524, V

= 20V, and f = 20kHz,

= T

PARAMETER

TEST CONDITIONS

UC1524/UC2524

UC3524

UNITS

MIN

MAX

MIN

MAX

Error Amplifier Section (cont.)

Common Mode Rejection Ratio T

= 25°C

Small Signal Bandwidth

= 0dB, T

= 25°C

MHz

Output Voltage

= 25°C

0.5

3.8

0.5

3.8

Comparator Section

Duty-Cycle

% Each Output On

Input Threshold

Zero Duty-Cycle

Maximum Duty-Cycle

3.5

Input Bias Current

µA

Current Limiting Section

Sense Voltage

Pin 9 = 2V with Error Amplifier

Set for Maximum Out, T

= 25°C

190

200

210

180

200

220

Sense Voltage T.C.

0.2

mV/°C

Common Mode Voltage

–1

Output Section (Each Output)

Collector-Emitter Voltage

Collector Leakage Current

= 40V

0.1

µA

Saturation Voltage

= 50mA

Emitter Output Voltage

= 20V

Rise Time

= 2k

Ω, T

= 25°C

0.2

µs

Fall Time

= 2k

Ω, T

= 25°C

0.1

µs

Total Standby Current (Note)

= 40V

Note: Excluding oscillator charging current, error and current limit dividers, and with outputs open.

The UC1524 is a fixed-frequency pulse-width-modulation

voltage regulator control circuit. The regulator operates at

a frequency that is programmed by one timing resistor

), and one timing capacitor (C

), R

establishes a

constant charging current for C

. This results in a linear

voltage ramp at C

, which is fed to the comparator pro-

viding linear control of the output pulse width by the error

amplifier. The UC1524 contains an on-board 5V regulator

that serves as a reference as well as powering the

UC1524’s internal control circuitry and is also useful in

supplying external support functions. This reference volt-

age is lowered externally by a resistor divider to provide a

reference within the common-mode range of the error

amplifier or an external reference may be used. The

power supply output is sensed by a second resistor di-

vider network to generate a feedback signal to the error

amplifier. The amplifier output voltage is then compared

to the linear voltage ramp at C

. The resulting modulated

pulse out of the high-gain comparator is then steered to

the appropriate output pass transistor (Q

or Q

) by the

pulse-steering flip-flop, which is synchronously toggled by

the oscillator output. The oscillator output pulse also

serves as a blanking pulse to assure both outputs are

never on simultaneously during the transition times. The

width of the blanking pulse is controlled by the valve of

. The outputs may be applied in a push-pull configura-

tion in which their frequency is half that of the base oscil-

lator, or paralleled for single-ended applications in which

the frequency is equal to that of the oscillator. The output

of the error amplifier shares a common input to the com-

parator with the current limiting and shutdown circuitry

and can be overridden by signals from either of these in-

puts. This common point is also available externally and

may be employed to control the gain of, or to compen-

sate, the error amplifier or to provide additional control to

the regulator.

PRINCIPLES OF OPERATION

UC1524

UC2524

UC3524

Oscillator

The oscillator controls the frequency of the UC1524 and is

programmed by R

and C

according to the approximate

formula:

R C

′

1.18

where

is in k

Ω

where

is in mF

where

f is in kHz

Practical values of C

fall between 0.001mF and 0.1mF.

Practical values of R

fall between 1.8k

Ω and 100kΩ.

This results in a frequency range typically from 120Hz to

500kHz.

Blanking

The output pulse of the oscillator is used as a blanking

pulse at the output. This pulse width is controlled by the

value of C

. If small values of C

are required for fre-

quency control, the oscillator output pulse width may still

be increased by applying a shunt capacitance of up to

100pF from pin 3 to ground. If still greater dead-time is

required, it should be accomplished by limiting the maxi-

mum duty cycle by clamping the output of the error ampli-

fier. This can easily be done with the circuit in Figure 1:

Synchronous Operation

When an external clock is desired, a clock pulse of ap-

proximately 3V can be applied directly to the oscillator

output terminal. The impedance to ground at this point is

approximately 2k

Ω. In this configuration R

must be

selected for a clock period slightly greater than that of the

external clock.

If two or more UC1524 regulators are to operated synchro-

nously, all oscillator output terminals should be tied to-

gether, all C

terminals connected to single timing

capacitor, and the timing resistor connected to a single R

terminal. The other R

terminals can be left open or shorted

to V

REF

. Minimum lead lengths should be used between

the C

terminals.

APPLICATION INFORMATION

REF

COMP

GND

1N916

Figure 1. Error amplifier clamp.

Figure 2. Single-ended LC switching regulator circuit.