CAT3200_14 Datasheet, PDF (6/12 Pages) ON Semiconductor – Low Noise Regulated Charge Pump DC-DC Converter

CAT3200, CAT3200−5
Block Diagram
CNEG CPOS
CNEG CPOS
IN
SHDN
1.25 V
SGND
2 MHz
Voltage
Doubler
2V_IN
EN
+
−
PGND
5 V / 100 mA
OUT
FB
Figure 15. CAT3200 Adjustable Output
IN
SHDN
1.25 V
GND
2 MHz
Voltage
Doubler
2V_IN
EN
+
−
100 k ^{300 k}
5V
OUT
100 mA
Figure 16. CAT3200−5 5 V Fixed 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 1 mF to 4.7 mF low
ESR (Equivalent Series Resistance) ceramic capacitor
For filtering, a low ESR ceramic bypass capacitor (1 mF)
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 (1 mF) 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 2 MHz. Adequate
filtering on the pin can typically be achieved through the use
a low ESR ceramic bypass capacitor (1 mF to 4.7 mF) 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
resistor network (400 kW). The feedback network will result
in a reverse current of 10 mA to 20 mA 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.
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