MIC3832/3833

Micrel

4-136

April 1998

Pin Description

Pin Number

Pin Name

Pin Function

1

GND

Ground: Use as single-point ground tie point.

2

PWM

PWM Output: Variable duty-cycle totem pole output.

3

Q

Switch (Output): Totem pole output. Noninverting 50% duty cycle output

(180

° out-of-phase with Q with no dead time).

4V

DD

Supply Voltage (Input): Clamped to 22V by internal zener diode.

5

5V REF

5V Bandgap Reference (Output)

6

EA –

Inverting Error Amplifier Input

7

EA +

Noninverting Error Amplifier Input

8

EA OUT

Error Amplifier Output: Connect to the appropriate feedback network to

adjust the open loop gain or frequency response.

9

NC

No Connection: Do not use—leave open.

10

SHDN

Overcurrent Shutdown (Input): >1 V disables outputs, >1.25V initiates soft-

start restart. For cycle-by-cycle current limiting, even in voltage-mode control

applications, connect to current sensor. If current sense is not used, connect

to GND.

11

MDC/SS

Maximum Duty Cycle/Soft Start (Input): Apply a dc voltage to adjust maxi-

mum duty cycle (see chart). Adjust soft start by adding capacitance to

increase turn-on time during initial start up or restart after overcurrent

shutdown.

12

CMR

Current Mode Ramp: Feed point for a sample of inductor current when using

current mode control. For voltage-mode control, connect directly to the C

T

pin.

13

SYNC

Synchronization (Input): AC coupled input from an external master clock

(reference) signal. If not used, leave unconnected. A high (>1.5V) resets the

C

14

R

T

Oscillator Timing Resistor: Connect 4k

Ω minimum resistor to GND.

15

C

T

Oscillator Timing Capacitor: Connect capacitor to GND. See “Typical

Characteristics: Discharge Time” graph for capacitor value.

Maximum oscillator frequency

1

2

discharge time

=

×

()

16

Q

Switch (Output): Totem pole output. Inverting 50% duty cycle output (180

°

out-of-phase with Q with no deadtime).