CAT3200_14 Datasheet, PDF (7/12 Pages) ON Semiconductor – Low Noise Regulated Charge Pump DC-DC Converter

CAT3200, CAT3200−5
Device Operation
The CAT3200/CAT3200−5 use a switched capacitor
charge pump to boost the voltage at IN to a regulated output
voltage. Regulation is achieved by sensing the output
voltage through an internal resistor divider (CAT3200−5)
and modulating the charge pump output current based on the
error signal. A 2−phase non−overlapping clock activates the
charge pump switches. The flying capacitor is charged from
the IN voltage on the first phase of the clock. On the second
phase of the clock it is stacked in series with the input voltage
and connected to OUT. The charging and discharging the
flying capacitor continues at a free running frequency of
typically 2 MHz.
In shutdown mode all circuitry is turned off and the
CAT3200/CAT3200−5 draw only leakage current from the
V_IN supply. OUT is disconnected from IN. The SHDN pin
is a CMOS input with a threshold voltage of approximately
0.8 V. The CAT3200/CAT3200−5 is in shutdown when a
logic LOW is applied to the SHDN pin. The SHDN pin is a
high impedance CMOS input. SHDN does not have an
internal pull−down resistor and should not be allowed to
float and. It must always be driven with a valid logic level.
Short−Circuit and Thermal Protection
The CAT3200 and CAT3200−5 have built−in
short−circuit current limiting and over temperature
protection. During overload conditions, output current is
limited to approximately 225 mA. At higher temperatures,
or if the input voltage is high enough to cause excessive chip
self heating, the thermal shutdown circuit shuts down the
charge pump as the junction temperature exceeds
approximately 160°C. Once the junction temperature drops
back to approximately 140°C, the charge pump is enabled.
The CAT3200 and CAT3200−5 will cycle in and out of
thermal shutdown indefinitely without latch−up or damage
until a short−circuit on OUT is removed.
Programming the CAT3200 Output Voltage (FB Pin)
The CAT3200−5 version has an internal resistive divider
to program the output voltage. The programmable CAT3200
may be set to an arbitrary voltage via an external resistive
divider. Since it employs a voltage doubling charge pump,
it is not possible to achieve output voltages greater than
twice the available input voltage. Figure 17 shows the
required voltage divider connection. The voltage divider
ratio is given by the formula:
R1
R2
+
V_OUT
1.27 V
*
1
Typical values for total voltage divider resistance can
range from several kWs up to 1 MW.
1
CPOS
2
IN
3
CNEG
8
OUT
6
SHDN
7
FB
4
PGND
5
SGND
V_OUT
ǒ Ǔ _R1
1.27 V
1
)
R1
R2
C_OUT
R2
Figure 17. Programming the Adjustable CAT3200
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