Functional Descriptions - Epson Power Supply IC S1F70000 Technical Manual

FUNCTIONAL DESCRIPTIONS

CR Oscillator
S1F76640 has a built-in CR oscillator as the internal oscillator, and an external oscillation resistor R
connected between the pins OSC1 and OSC2 before operation. (Figure 5.1)
OSC1
OSC2
Figure 5-1 CR Oscillator
Note 1 : Since the oscillation frequency varies with wiring capacitance, make the cables between the terminals
OSC1 and OSC2 and R
When setting the external resistor R
ciency from Figures 6.5.12 and 6.5.13 and find R
R and f in Figure 6.5.1 are expressed approximately with the following formula as far as the straight portion
OSC OSC
(500k < R < 2M ) is concerned:
OSC
1
[ A : Constant, When GND is 0V and
R = A
OSC
f
OSC V is 5V, A is 2.0 10
DD
So, the R value can be obtained from this formula.
OSC
(Recommended oscillation frequency : 10kHz to 30kHz (R
When the external clock operates, make the pin OSC2 open as shown in Figure 5.2 and input the 50% duty of the
external clock from the pin OSC1.
Voltage Conversion Circuits (I) and (II)
The voltage conversion circuits (I) and (II) doubles and triples the input voltage V
generated in the CR oscillator.
In case of 2 times step-up, 2 times step-up output of the input voltage is obtained from the V
capacitor is connected between CAP1+ and CAP1–, CAP2+ and CAP3+ are short-circuited to V
capacitor is connected between V
In case of 3 times step-up, 3 V
CAP1+ and CAP1– and between CAP2+ and CAP2– respectively and a smoothing capacitor is connected between
the V and V pins outside.
DD O
In case of 4 times step-up, 4 V
CAP1+ and CAP1–, between CAP2+ and CAP2– and between CAP1+ and CAP3– respectively and a smoothing
capacitor is connected between the V
When GND is 0 and V
DD
Figures 5-3, 5-4 and 5-5.
S1F70000 Series
Technical Manual
(Note 1)
R
OSC
Figure 5-2 External Clock Operation
as short as possible.
OSC
, find the oscillation frequency f
OSC
suitable for the f
OSC
10
(1/F).)
and V outside.
DD O
is output from the V
DD
is output from the V
DD
and V pins outside.
DD O
is 5, the relations between the input voltage and the output voltage are as shown in
EPSON
OSC1
Open
OSC2
that brings about the maximum effi-
OSC
from Figure 6.5.1 The relations between
OSC
]
: 2M to 680k )
OSC
pin when a pump up capacitor is connected between
O
pin when a pump up capacitor is connected between
O
S1F76640 Series
OSC
External clock
respectively by using clock
DD
pin when a pump up
O
and a smoothing
O
2–43
is