CAT660EVA-GT3 Datasheet, PDF (7/13 Pages) ON Semiconductor – 100 mA CMOS Charge Pump Inverter/Doubler

CAT660
Oscillator Frequency Control
The switching frequency can be raised, lowered or driven
from an external source. Figure 16 shows a functional
diagram of the oscillator circuit.
The CAT660 oscillator has four control modes:
Table 4.
BOOST/FC
Pin Connection
Open
BOOST/FC = V+
Open or
BOOST/FC = V+
Open
OSC Pin
Connection
Open
Open
External Capacitor
External Clock
Nominal
Oscillator
Frequency
10 kHz
80 kHz
−
Frequency of
external clock
If BOOST/FC and OSC are left floating (Open), the
nominal oscillator frequency is 10 kHz. The pump
frequency is one−half the oscillator frequency.
BOOST/FC
8x
(1)
OSC
(7)
OSC
V⁺
(8)
f
B2
f
By connecting the BOOST/FC pin to V+, the charge and
discharge currents are increased, and the frequency is
increased by approximately 8 times. Increasing the
frequency will decrease the output impedance and ripple
currents. This can be an advantage at high load currents.
Increasing the frequency raises quiescent current but allows
smaller capacitance values for C1 and C2.
If pin 7, OSC, is loaded with an external capacitor the
frequency is lowered. By using the BOOST/FC pin and an
external capacitor at OSC, the operating frequency can be
set.
Note that the frequency appearing at CAP+ or CAP− is
one−half that of the oscillator.
Driving the CAT660 from an external frequency source
can be easily achieved by driving Pin 7 and leaving the
BOOST pin open, as shown in Figure 16. The output current
from Pin 7 is small, typically 1 mA to 8 mA, so a CMOS can
drive the OSC pin. For 5 V applications, a TTL logic gate can
be used if an external 100 kΩ pull−up resistor is used as
shown in Figure 17.
SW1
CAP⁺
(2)
SW2
+
C1
CAP^−
(4)
VOUT
(5)
LV
GND
(6)
CLOSED WHEN
(3)
V⁺ > 3.0 V
Figure 15. CAT660 Block Diagram
C2
+
(N) = Pin Number
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