SM6702 Nippon Precision Circuits Inc, SM6702 Datasheet - Page 5

• Manufacturer Part Number: SM6702
• Description: PFM Step-up DC/DC Converter
• Manufacturer: Nippon Precision Circuits Inc

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 t
the interval t
that the peak voltage reaches V
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 (V
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.
ON
GND
generates a voltage V
V
IN
IN
+ V
L
L
L
ON
across the coil. This voltage is superimposed on the input voltage such
which forces the diode D to conduct and release the stored energy into
and then instantly turned OFF, the energy stored in the coil L during
Tr
SM6702 series
D
C
OUT
> V
NIPPON PRECISION CIRCUITS—5
IN
) has been stepped up.
V
OUT