Functional Descriptions - Epson Power Supply IC S1F70000 Technical Manual

100
90
80
70
Ta = 25 C
60 V = –2.0V
I
50
40
30
20
10
0
0 1 2 3 4
I
O
(13) Multiplication efficiency/input current
vs. Output current

FUNCTIONAL DESCRIPTIONS

CR Oscillator
S1F76600 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
S1F70000 Series
Technical Manual
40
36
Peff
32
28
24
20
I
I
16
12
8
4
0
5 6 7 8 9 10
[mA]
is con-
OSC
(Note 1)
R
OSC
, find R suit-
OSC OSC
EPSON
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
Voltage Multiplier
The voltage multiplier uses the clock signal from the
oscillator to double the input voltage. This requires two
external capacitors—a charge-pump capacitor, C1, be-
tween CAP1+ and CAP1–, and a smoothing capacitor,
C2, between V and V .
I O
V = 0 V
DD
5 V
V = –5 V
I
1
2
1M
3
4
Doubled potential levels
V
CC
V = 0 V
DD
(+5V)
GND V = –5 V
I
(–5V) V = (2V
O
S1F76600 Series
< 2M ) is concerned:
OSC
)
OSC
is 5V, A is
DD
External clock
8
+
C2
10 F
7
V = –10V (2V )
O1 I
6
C1
+
10 F
5
) = –10 V
I
1–7