SC633

0

General Description

The SC633 is a 5.3V output charge pump regulator

designed to support up to peak current of 400mA (T

55°C, 3.3V ≤ V

≤ 5.5V) of continuous current for powering 5.0V devices in

portable handheld equipment including Compact Flash

and CF+ products.

The SC633 has three operating modes — x, .5x, and 2x.

The x mode is a linear series regulation mode with a low

functions as a low-noise series linear regulator. The .5x

and 2x modes are a low noise, constant frequency, con-

stant duty cycle switch mode, using two bucket capacitors.

One bucket supports the full output current while the

other bucket charges from the input. The two buckets

exchange roles in the next phase, supplying continuous

output current in both phases and reducing the need for

a large output decoupling capacitor. The constant fre-

quency, constant duty cycle operation also produces

predictable constant frequency harmonics.

Thermal Resistance

The SC633 package is thermally efficient when the circuit

board layout connects the thermal pad through multiple

vias to the ground plane. The thermal resistance rating is

dependent upon the connection between the thermal

pad and the ground plane. A layout that is done correctly

should keep the junction temperature below the over-

temperature limit while operating the SC633 within the

specified electrical conditions. A poor layout may allow

the junction temperature to reach the over temperature

limit, so it is important to maintain adequate ground plane

around the device to maximize heat transfer to the PCB.

Temperature Derating

The maximum power dissipation of the package can be

calculated by the difference between the junction tem-

perature of 50 degree and the ambient temperature

divided by the thermal impedance 68 °C/W. The higher

the ambient temperature, the lower the maximum allow-

able power dissipation. At a given V

allowable power dissipation will correlates to the specific

output current related to the operation efficiency. The

following derating curve is obtained based on efficiency

at input voltage of 5V and 3.3V. For any input conditions,

due to the mode hysteresis, SC633 operation mode might

be determined from its previous operation voltage, it

could be in X, .5X, or 2X mode. The low efficiency

should always be used for worst case consideration. In

this case, at V

=5V, SC633 operates either in 2X or .5X mode. In the

derating curve below, the DC operating points beneath

each curve are in the safe operating temperature range

of the MLP package.

Maximum Continuous Output

Mode Transition

As input voltage varies, the SC633 will experience mode

transitions. The transition threshold changes with input

voltage and load conditions. The mode change hysteresis

at several load current conditions are shown in the oper-

ating curves on page 6. Mode transition will bring output

voltage dip or overshoots. The output voltage deviation

in mode transition can be improved by using larger

output capacitors if the output voltage going beyond the

regulation range.

Mode Transition Hysteresis

Hysteresis is provided to prevent chatter between charge

pump modes for input steps of up to 20mV. Decouple

the input to prevent steps greater than 20mV, for

Applications Information