MIC3808 Datasheet, PDF (3/11 Pages) Micrel Semiconductor – Push-Pull PWM Controller

MIC3808/3809
Pin Description
Pin Number
5
6
7
8
Pin Name
GND
OUTB
OUTA
VDD
Micrel
Pin Function
Ground
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 switch from V_DD 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.
The power input connection for this device. Although quiescent V_DD current
is very low, total supply current will be higher, depending on OUTA and
OUTB current, and the programmed oscillator frequency. Total V_DD current
is the sum of quiescent V_DD current and the average OUT current. Knowing
the operating frequency and the MOSFET gate charge (Qg), average OUT
current can be calculated from I_OUT = Qg × F, where F is frequency. To
prevent noise problems, bypass V_DD to GND with a ceramic capacitor as
close to the chip as possible. A 1µF decoupling capacitor is recommended.
April 2005
3
MIC3808/3809