CAT3200_07 Datasheet, PDF (6/12 Pages) Catalyst Semiconductor – Low Noise Regulated Charge Pump DC-DC Converter

CAT3200/3200-5
BLOCK DIAGRAM
CNEG CPOS
2MHz
2VIN
IN
Voltage
Doubler
SHDN
1.25V
+ ^EN
—
5V/100mA
OUT
SGND
FB
PGND
CAT3200 Adjustable Output
PIN FUNCTIONS
IN is the power supply. During normal operation the
device draws a supply current which is almost constant.
A very brief interval of non-conduction will occur at the
switching frequency. The duration of the non-conduction
interval is set by the internal non-overlapping
“break-before-make” timing. IN should be bypassed
with a 1µF to 4.7µF low ESR (Equivalent Series
Resistance) ceramic capacitor.
For filtering, a low ESR ceramic bypass capacitor (1µF)
in close proximity to the IN pin prevents noise from being
injected back into the power supply.
SHDN is the logic control input (Active LOW) that places
the device into shutdown mode. The internal logic is
CMOS and the pin does not use an internal pull-down
resistor. The SHDN pin should not be allowed to float.
CPOS, CNEG are the positive and negative connections
respectively for the charge pump flying capacitor. A low
ESR ceramic capacitor (1µF) should be connected
between these pins. During initial power-up it may be
possible for the capacitor to experience a voltage reversal
and for this reason, avoid using a polarized (tantalum or
aluminum) flying capacitor.
OUT is the regulated output voltage to power the load.
During normal operation, the device will deliver a train of
current pulses to the pin at a frequency of 2MHz.
Adequate filtering on the pin can typically be achieved
through the use a low ESR ceramic bypass capacitor
(1µF to 4.7µF) in close proximity to the OUT pin. The
ESR of the output capacitor will directly influence the
output ripple voltage.
When the shutdown mode is entered, the output is
immediately isolated from the input supply, however, the
output will remain connected to the internal feedback
CNEG CPOS
IN
SHDN
1.25V
GND
2MHz
Voltage
Doubler
2VIN
+ ^EN
—
100k
300k
5V
OUT
100mA
CAT3200-5 5V Fixed Output
resistor network (400kΩ). The feedback network will
result in a reverse current of 10µA to 20µA to flow back
through the device to ground.
Whenever the device is taken out of shutdown mode, the
output voltage will experience a slew rate controlled
power-up. Full operating voltage is typically achieved in
less than 0.5 msec.
GND is the ground reference for all voltages on CAT3200-
5 devices.
FB (CAT3200 Only) is the feedback input pin. An output
divider should be connected from OUT to FB to program
the output voltage.
PGND (CAT3200 Only). Is the same as GND for the
CAT3200-5 except for the internal reference connection
to SGND.
SGND (CAT3200 Only) Ground pin for the internal
reference. The CNEG connection is switched to this pin
during the normal charge pump operation.
Doc. No. MD-5002, Rev. L
6
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice