High-Voltage PWM

Power-Supply Controller

6

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0

2

3

4

5

6

7

8

9

10

0

5

10

15

20

1

0

50

150

100

300

250

200

350

12

13

14

15

16

MAXIMUM FREQUENCY vs. INPUT VOLTAGE

AND FET TOTAL GATE-SWITCHING CHARGE

V+ (V)

25nC

30nC

10nC

15nC

20nC

Pin Description

Typical Operating Characteristics (continued)

NAME

FUNCTION

1

V+

Preregulator Input. Connect to the power line for use with 25V to 110V line voltages. Bypass V+ to ground

with a 0.1µF capacitor, close to the IC. Connects internally to the drain of a depletion FET preregulator.

2

INDIV

Undervoltage Sensing and Feed-Forward Input. Connect to the center point of an external resistive divider

connected between the main power line and AGND. Undervoltage lockout takes over and shuts down

PIN

3

ES

Preregulator Output. When V+ ranges above 36V, bypass ES to AGND with a 0.1µF capacitor close to

the IC. When V+ is always below 36V, connect ES to V+.

4

FREQ

Oscillator Frequency Adjust and Synchronization Input. In internal free-running mode, the voltage on this

pin is internally regulated to 1.25V. Connect a resistor between this pin and AGND to set the PWM fre-

8

COMP

Compensation Connection. Output of the error amplifier, available for compensation.

7

CON

Control Input of the PWM Comparator

6

REF

Reference Voltage Output (3.0V). Bypass to AGND with a 0.1µF capacitor.

5

SS

Soft-Start Capacitor Connection. Ramp time to full current limit is approximately 0.5ms/nF. Limits duty

10

MAXTON

Maximum On-Time Programming. A resistor from MAXTON to AGND sets the PWM gain and limits the

maximum duty cycle. The voltage on MAXTON tracks the voltage on the INDIV pin. Maximum on-time is

proportional to the value of the programming resistor. The maximum duty cycle is limited to 75%, regard-

less of the programming resistor.

9

FB