CAT661ESA ON Semiconductor, CAT661ESA Datasheet - Page 8

• Manufacturer Part Number: CAT661ESA
• Manufacturer: ON Semiconductor
• Type: Inverting/Step Upr

Specifications of CAT661ESA

• Operating Supply Voltage (min): 1.5V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Package Type: SOIC
• Pin Count: 8
• Mounting: Surface Mount
• Output Voltage: -5.5 to -1.5/5 to 11V
• Output Current: 100mA
• Lead Free Status / RoHS Status: Not Compliant

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:
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
Figure 5. CAT661 Block Diagram
Doc. No. 5003, Rev. J
BOOST/FC Pin Connection
Open or BOOST/FC= V+
BOOST/FC= V+
Open
Open
BOOST/FC
OSC
(1)
(7)
8x
OSC
LV
(6)
V +
(8)
2
OSC Pin Connection
CLOSED WHEN
External Capacitor
V + > 3.0V
External Clock
Open
Open
8
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 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 7.
SW1
CAP +
CAP -
GND
+
(4)
(2)
(3)
C1
Nominal Oscillator Frequency
(N) = Pin Number
SW2
Frequency of external clock
VOUT
135kHz
25kHz
(5)
—
+
C2
pull-up