SM6702 datasheet(5/10 Pages) NPC

5 / 10 page

SM6702 series

NIPPON PRECISION CIRCUITS—5

FUNCTIONAL DESCRIPTION

Step-up Principle

The SM6702 series use a transistor to switch the input supply in a non-isolated chopper switching regulator

conﬁguration. The ﬁgure below shows the basic step-up switching regulator circuit.

If the transistor is ON for an interval tON and then instantly turned OFF, the energy stored in the coil L during

the interval tON generates a voltage VL across the coil. This voltage is superimposed on the input voltage such

that the peak voltage reaches VIN + VL which forces the diode D to conduct and release the stored energy into

the output.

During normal operation, the above switching occurs repeatedly at a frequency controlled by an oscillator

(which can change depending on the input and output load conditions), generating a square wave output which

is then smoothed by the output capacitor C. Thus the output voltage (VOUT > VIN) has been stepped up.

PFM Control

In SM6702 series, the LX transistor ON interval is ﬁxed, and the OFF interval varies in response to the input

voltage and load changes. Thus the resulting switching cycle frequency varies, called pulse frequency modula-

tion.

VIN

VOUT

GND

SM6702 Datasheet(PDF) 5 Page - Nippon Precision Circuits Inc