CAT661 Datasheet, PDF (9/16 Pages) Catalyst Semiconductor – High Frequency 100mA CMOS Charge Pump, Inverter/Doubler

CAT661
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 CAT661 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 25 kHz oscillator frequency
(12.5 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 45 mV.
Table 5. VRIPPLE vs. FOSC
VRIPPLE (mV)
IOUT (mA)
45
100
25
100
FOSC (kHz)
25
135
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
CAT661
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 22. Oscillator
Figure 23. External Clocking
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