cat660 Catalyst Semiconductor, cat660 Datasheet - Page 7

• Manufacturer Part Number: cat660
• Description: 100ma Cmos Charge Pump Inverter/doubler
• Manufacturer: Catalyst Semiconductor

OSCILLATOR FREQUENCY CONTROL
The switching frequency can be raised, lowered or driven from an external source. Figure 5 shows a functional diagram
of the oscillator circuit.
The CAT660 oscillator has four control modes:
If BOOST/FC and OSC are left floating (Open), the
nominal oscillator frequency is 10kHz. 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 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
Figure 4. CAT660 Block Diagram
BOOST/FC Pin Connection
Open
BOOST/FC= V+
Open or BOOST/FC= V+
Open
BOOST/FC
OSC
(1)
(7)
8x
OSC
LV
(6)
OSC Pin Connection
Open
Open
External Capacitor
External Clock
V +
(8)
2
CLOSED WHEN
V + > 3.0V
7
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 6. The output
current from Pin 7 is small, typically 1 A to 8 A, so a
CMOS can drive the OSC pin. For 5V applications, a TTL
logic gate can be used if an external 100k
resistor is used as shown in figure 6.
SW1
CAP +
CAP -
GND
+
(2)
(4)
(3)
C1
Nominal Oscillator Frequency
10kHz
80kHz
—
Frequency of external clock
(N) = Pin Number
SW2
VOUT
(5)
+
C2
Doc. No. MD-5000, Rev. W
pull-up