SM8172A Datasheet, PDF (8/17 Pages) Nippon Precision Circuits Inc – 2-output Power Supply IC

SM8172A
12-2. DC/DC Converter
12-2-1. Basic Operation
The SM8172A DC/DC converter is a step-down converter that is controlled using a 2MHz switching frequency
current-mode PWM waveform, and which incorporates a MOSFET synchronous rectifier.
12-2-2. Soft Start Function
A soft start circuit is built-in to prevent output voltage overshoot and inrush current at startup. The soft start
time is the interval during which the output current is limited internally in the IC, and is different from the
DC/DC converter output voltage rise time. The time varies with the load current, output capacitance, and other
conditions.
12-2-3. Overcurrent Protection Function
The P-channel MOSFET is turned OFF when the inductor current exceeds the current limit (1.5A). Normal
operation is restored when the overcurrent condition is resolved.
1.5A
Inductor
current
Overcurrent detector
Pch MOS OFF
Overloaded status
VIN1
LX
Normal operation
when resolving overload
Output
control
12-3. Reset Function
When the supply voltage is within the rated range, the RESETN output is high-impedance (Hi-Z). When the
supply voltage falls below 3.7V (typ), the undervoltage detector circuit operates, setting the RESETN output
LOW. When the supply voltage subsequently rises above 3.9V (typ), the RESETN output goes high-impedance
again. However, when the supply voltage rises above 3.9V (typ), a built-in delay circuit sets the RESETN out-
put to high-impedance after a delay of 65ms (typ). When at standby status, the RESETN output is LOW. When
standby status is released, the RESETN output goes high-impedance after delay time if the supply voltage is
more than 3.9V (typ).
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