CAT3200HU2

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7

Pin Functions

VIN 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. VIN 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 pins 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.

VOUT 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

of a low ESR ceramic bypass capacitor (1

mF to 4.7 mF) in

close proximity to the VOUT 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 k

W). 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 ms.

SGND is the ground reference for all voltages on the

CAT3200HU2.

FB is the feedback input pin. An output divider should be

connected from VOUT to FB to program the output voltage

when used in adjustable output mode. When used in 5 V

fixed output mode, connect the FB pin directly to GND.

PGND is the power ground.

Device Operation

The CAT3200HU2 uses 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 (FB pin = GND) 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 VOUT. 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

CAT3200HU2 draws only leakage current from the VIN

supply. VOUT is disconnected from VIN. The SHDN pin is

a CMOS input with a threshold voltage of approximately

0.8 V. The CAT3200HU2 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. It

must always be driven with a valid logic level.

Short−Circuit and Thermal Protection

The CAT3200HU2 has 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 CAT3200HU2 will cycle in

and out of thermal shutdown indefinitely without latch−up

or damage until a short−circuit on VOUT is removed.

Programming the CAT3200HU2 Output Voltage (FB Pin)

The CAT3200HU2 version has an internal resistive

divider to program the output voltage. The programmable

CAT3200HU2 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 20 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

W up to 1 MW.

Figure 20. Programming the Adjustable Output

OUT

FB

PGND

SGND

1.27 V

R1

R2

8

7

4

5

CPOS CNEG

IN

SHDN

3

2

6

1

1 ) R1

R2