MIC3808_11 datasheet(3/11 Pages) MIC

3 / 11 page

April 2005

MIC3808/3809

Micrel

Pin Description

Pin Number

Pin Name

Pin Function

GND

Ground

OUTB

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

OUTA

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 switch from VDD to GND.

Each output stage also provides a very low impedance to overshoot and

undershoot. This means that in many cases, external Schottky clamp diodes

are not required.

VDD

The power input connection for this device. Although quiescent VDD current

is very low, total supply current will be higher, depending on OUTA and

OUTB current, and the programmed oscillator frequency. Total VDD current

is the sum of quiescent VDD current and the average OUT current. Knowing

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

current can be calculated from IOUT = Qg × F, where F is 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.

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