CAT661 Datasheet, PDF (8/16 Pages) Catalyst Semiconductor – High Frequency 100mA CMOS Charge Pump, Inverter/Doubler

CAT661
OSCILLATOR FREQUENCY CONTROL
The switching frequency can be raised, lowered or driven from an external source. Figure 6 shows a functional diagram
of the oscillator circuit.
The CAT661 oscillator has four control modes:
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
25kHz
135kHz
—
Frequency of external clock
If BOOST/FC and OSC are left floating (Open), the
nominal oscillator frequency is 25kHz. The pump
frequency is one-half the oscillator frequency.
By connecting the BOOST/FC pin to V+, the charge and
discharge currents are increased, and the frequency is
increased by approximately 6 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 CAT661 from an external frequency source
can be easily achieved by driving Pin 7 and leaving the
BOOST pin open, as shown in figure 6. The output
current from Pin 7 is small, typically 1µA to 8µA, so a
CMOS can drive the OSC pin. For 5V applications, a TTL
logic gate can be used if an external 100kΩ pull-up
resistor is used as shown in figure 7.
Figure 5. CAT661 Block Diagram
BOOST/FC
8x
(1)
OSC
(7)
OSC
LV
(6)
V+
(8)
Ο
2
Ο
SW1
CAP+
(2)
+
C1
SW2
CAP-
(4)
VOUT
(5)
CLOSED WHEN
V+ > 3.0V
C2
+
GND
(3)
(N) = Pin Number
Doc. No. 5003, Rev. J
8