MIC2169B(2009) 데이터 시트보기 (PDF) - Micrel
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MIC2169B Datasheet PDF : 24 Pages
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Micrel, Inc.
1000pF capacitor is recommended between the switch
node and GND.
Internal VDD Supply
The MIC2169B controller internally generates VDD for
self biasing and to provide power to the gate drives. This
VDD supply is generated through a low-dropout regulator
and generates 5V from VIN supply greater than 5V. For
supply voltage less than 5V, the VDD linear regulator is
approximately 200mV in dropout. Therefore, it is
recommended to short the VDD supply to the input supply
through a 10Ω resistor for input supplies between 3.0V
to 5V.
MOSFET Gate Drive
The MIC2169B high-side drive circuit is designed to
switch an N-Channel MOSFET. The Functional Block
Diagram on page 8 shows a bootstrap circuit, consisting
of D1 and CBST, supplies energy to the high-side drive
circuit. Capacitor CBST is charged while the low-side
MOSFET is on and the voltage on the VSW pin is
MIC2169B
approximately 0V. When the high-side MOSFET driver is
turned on, energy from CBST is used to turn the MOSFET
on. As the MOSFET turns on, the voltage on the VSW
pin increases to approximately VIN. Diode D1 is reversed
biased and CBST floats high while continuing to keep the
high-side MOSFET on. When the low-side switch is
turned back on, CBST is recharged through D1. The drive
voltage is derived from the internal 5V VDD bias supply.
The nominal low-side gate drive voltage is 5V and the
nominal high-side gate drive voltage is approximately
4.5V due the voltage drop across D1. An approximate
50ns delay between the high-side and low-side driver
transitions is used to prevent current from
simultaneously flowing unimpeded through both
MOSFETs (shoot-through).
Adaptive gate drive is implemented on the high-side (off)
to low-side (on) driver transition to reduce losses in the
flywheel diode and to prevent shoot-through. This is
operated by detecting the VSW pin; once this pin is
detected to reach 1.5V, the high-side MOSFET can be
assumed to be off and the low side driver is enabled.
June 2009
10
M9999- 060309-A
(408) 944-0800
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