CAT3200_07 Datasheet, PDF (7/12 Pages) Catalyst Semiconductor – Low Noise Regulated Charge Pump DC-DC Converter

CAT3200/3200-5
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 2MHz.
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 0.8V. 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 225mA. 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 CAT3200and 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 1 shows the required voltage divider
connection. The voltage divider ratio is given by the
formula:
R1 ₌ VOUT _{− 1}
R2 1.27V
Typical values for total voltage divider resistance can
range from several kΩs up to 1MΩ.
1
3
CPOS CNEG
2 _IN
OUT ⁸
6 _SHDN
FB ⁷
PGND ⁴
SGND ⁵
VOUT
R1
( ) ^1.27V
1 + ^R1
R2
COUT
R2
Figure 1: Programming the Adjustable CAT3200
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
7
Doc No. MD-5002, Rev. L