April 2005

3

MIC3838/3839

MIC3838/3839

Micrel

Pin Description

Pin Number

Pin Name

Pin Function

7, 8

OUTB, OUTA

Alternating high current output stages. Both stages are capable of driving

the gate of a power MOSFET. Each stage is capable of 500mA peak source

current, and 1A peak sink current.

The output stages switch at half the oscillator frequency, in a push/pull

configuration. When the voltage on the RC pin is rising, one of the two

outputs is high, but during fall time, both outputs are off. This “dead time”

between the two outputs, along with a slower output rise time than fall time,

insures that the two outputs can not be on at the same time. This dead time

is typically 60ns to 200ns and depends upon the values of the timing

capacitor and resistor.

The high-current output drivers consist of MOSFET output devices, which

impedance to overshoot and undershoot. This means that in many cases,

external Schottky clamp diodes are not required.

9

VDD

the operating frequency and the MOSFET gate charge (Qg), average OUT

current can be calculated from IOUT = Qg • F, where Qg is the total gate

change of all MOSFETs (OUTA and OUTB) and F is oscillator switching

frequency. To prevent noise problems, bypass VDD to GND with a ceramic

capacitor as close to the chip as possible. A 1µF decoupling capacitor is

recommended.

10

VREF

Internal 3V supply. Will source 1mA maximum.