SC632

10

General Description

The SC632 is a 5.0V output charge pump regulator

designed to support up to 400mA (T

A

≤ 55°C, 3.15V ≤ V

IN

≤

4.2V) and 275mA (T

A

≤ 85°C, 3.15V ≤ V

IN

≤ 5.5V) of continu-

ous current for powering 5.0V devices in portable

handheld equipment including Compact Flash and CF+

products.

The SC632 has three operating modes — 1x, 1.5x, and 2x.

The 1x mode is a linear series regulation mode with a low

open-loop output resistance of only 250m

functions as a low-noise series linear regulator. The 1.5x

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.

Mode Transition Hysteresis

Hysteresis is provided to prevent chatter between charge

pump modes for input steps of up to 120mV. Decouple

the input to prevent steps greater than 120mV, for

optimum transient performance, when the input voltage

reaches the mode transition thresholds.

Thermal Resistance

The SC632 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 SC632 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 V

IN

supply range and ambient temperature range of

the application should be compared with the following

derating curve to determine the maximum safe continu-

ous load current. The DC operating points beneath each

curve are in the safe operating temperature range of the

MLP package.

150

200

250

300

350

400

450

35

45

55

65

75

85

95

105

Ambient Temp (°C)

Maximum Continuous Output

Protection Circuitry

The SC632 also provides protection circuitry that pre-

vents the device from operating in an unspecified state.

These functions include:

Over-Current Protection (OCP)

Short-Circuit Current Protection (SCCP)

Over-Temperature Protection (OTP)

Over-Current Protection

Over-current protection is provided to limit the output

current. When V

OUT

is greater than 2V, OCP limits the

output to 1A typical. The threshold at 2V allows the

device to recover from excessive voltage droop during an

over current.

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Applications Information