MIC3838 Datasheet, PDF (3/11 Pages) Micrel Semiconductor – Flexible Push-Pull PWM Controller

MIC3838/3839
Pin Description
Pin Number
7, 8
9
10
Pin Name
OUTB, OUTA
VDD
VREF
Micrel
Pin Function
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. Total V_DD current is the sum of
quiescent V_DD current and the average gate drive (OUT) current. Knowing
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.
Internal 3V supply. Will source 1mA maximum.
August 2003
3
MIC3838/3839