CAT660EVA-GT3 Datasheet, PDF (8/13 Pages) ON Semiconductor – 100 mA CMOS Charge Pump Inverter/Doubler

CAT660
Capacitor Selection
Low ESR capacitors are necessary to minimize voltage
losses, especially at high load currents. The exact values of
C1 and C2 are not critical but low ESR capacitors are
necessary.
The ESR of capacitor C1, the pump capacitor, can have a
pronounced effect on the output. C1 currents are
approximately twice the output current and losses occur on
both the charge and discharge cycle. The ESR effects are
thus multiplied by four. A 0.5 Ω ESR for C1 will have the
same effect as a 2 Ω increase in CAT660 output impedance.
Output voltage ripple is determined by the value of C2 and
the load current. C2 is charged and discharged at a current
roughly equal to the load current. The internal switching
frequency is one−half the oscillator frequency.
VRIPPLE + IOUTń(FOSC C2) ) IOUT ESRC2
For example, with a 10 kHz oscillator frequency (5 kHz
switching frequency), a 150 mF C2 capacitor with an ESR of
0.2 Ω and a 100 mA load peak−to−peak ripple voltage is
87 mV.
Table 5. VRIPPLE vs. FOSC
VRIPPLE (mV)
IOUT (mA)
87
100
28
100
FOSC (kHz)
10
80
C2 (mF)
150
150
C2 ESR (W)
0.2
0.2
V⁺
BOOST/FC
(1)
7.0 I
I
OSC
(7)
~18 pF
7.0 I
I
LV
(6)
REQUIRED FOR TTL LOGIC
NC
+
C1
CAT660
1
BOOST/FC
V+ ⁸
2 _CAP+
7
OSC
3 _GND
6
LV
4
5
CAP−
OUT
100 k
−V⁺
C2
+
V⁺
OSC
INPUT
Figure 16. Oscillator
Figure 17. External Clocking
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