Functional Descriptions - Epson Power Supply IC S1F70000 Technical Manual

FUNCTIONAL DESCRIPTIONS

CR Oscillator
S1F76620 has a built-in CR oscillator as the internal os-
cillator, and an external oscillation resistor R
nected between the pins OSC1 and OSC2 before opera-
tion.
OSC1
OSC2
Note 1
Since the oscillation frequency varies with wiring ca-
pacitance, make the cables between the terminals OSC1
and OSC2 and R as short as possible.
OSC
When setting the external resistor R
able for f that brings about the maximum efficiency
OSC
from characteristics graph (9) and (10). The relations
between R and f in characteristics graph (1) are
OSC OSC
expressed approximately with the following formula as
far as the
straight portion (500k < R
R = A • (1/f
OSC
(A : Constant, When GND is 0V and V
10
approximately 2.0 10 (I/F).)
So, the R value can be obtained from this formula.
OSC
(Recommended oscillation frequency : 10kHz to 30kHz
(R : 2M to 680k ))
OSC
When the external clock operates, make the pin OSC2
open as shown below and input the 50% duty of the ex-
ternal clock from the pin OSC1.
OSC1
OSC2 Open
S1F70000 Series
Technical Manual
is con-
OSC
(Note 1)
R
OSC
, find R suit-
OSC OSC
< 2M ) is concerned:
OSC
)
OSC
is 5V, A is
DD
External clock
EPSON
Voltage Conversion Circuit
The voltage conversion circuit uses clocks generated in
the CR oscillator to double the input supply voltage
V .
DD
In case of 2 times step-up, 2 times voltage (2V
the input voltage is obtained from the V
pump up capacitor is connected between CAP1+ and
CAP2– and a smoothing capacitor is connected be-
tween V and V outside.
DD O
When GND is 0 and V
DD
input/output and voltage are as shown below:
CAP1=2V =10V
DD
V =5V
DD
G =0V
ND
S1F76620 Series
) of
DD
pin when a
O
is 5, the relations between
1–13