MIC3838/3839

Micrel

MIC3838/3839

8

April 2005

Functional Description

The MIC3838/9 is a high-speed power supply controller with

and turn-off than the MIC3839. The outputs of the controller

operate in a push-pull fashion with a guaranteed dead time

between them. A block diagram of the MIC3838/9 controller

is shown in Figure 1.

Functional Diagram

T

Q

/Q

Q

S

R

Q

S

R

Q

S

R

Oscillator

Peak Current

Comparator

Overcurrent

Comparator

PWM

Comparator

PWM

Latch

Slope = 1V/ms

Soft Start

2.2V

2.0V

0.5V

R

0.8V

14V

OUTA

OUTB

GND

0.5V

1.2R

0.75V

Error

Amplifier

RC

FB

COMP

RAMP

ILIM

Voltage

Reference

3.65V

Figure 1. MIC3838 Block Diagram

MIC3838

330pF

330pF

50k

150k

13k

4.5k

0.5V

0.75V

Peak Current

Comparator

Over Current

Comparator

PWM

Comparator

Oscillator

Figure 2. Volt Second Clamp and Voltage Feed Forward Circuit

The oscillator and output gate drive signals are disabled

output drivers eliminates glitching or random pulsing during

parator also turns off the internal soft-start discharge FET,

slowly bringing up the COMP pin voltage.

current draw of the IC. IDD currents greater than 20mA may

cause excessive power dissipation in the MIC3838/9.