CAT3200, CAT3200−5

http://onsemi.com

7

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

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 +

1.27 V *

1

Typical values for total voltage divider resistance can

range from several k

Ws up to 1 MW.

Figure 17. Programming the Adjustable CAT3200

OUT

FB

1.27 V

R1

R2

8

7

4

5

CPOS

CNEG

IN

3

2

6

1

SHDN

PGND

SGND

1 ) R1

R2