SC630

10

General Description

The SC630 is a 3.3V output charge pump regulator

designed to support up to 400mA (T

85°C, 3.15V

5.5V) of continuous current. It is used for powering Micro

HDDs (Hard Disk Drives) and other 3.3V devices in porta-

ble handheld equipment including Compact Flash and

CF+ products.

The SC630 has three operating modes — 1x, 1.5x, and 2x.

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

output resistance of only 300m

as a low noise series linear regulator. The 1.5x and 2x

modes are a low noise constant frequency, constant 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 frequency,

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 SC630 package is thermally efficient when the circuit

board layout connects the thermal pad through multiple

vias to the ground plane. The thermal resistance is depen-

dent 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-tempera-

ture limit while operating the SC630 within the specified

electrical conditions. A poor layout may allow the junc-

tion 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 load current and battery voltage range of the applica-

tion should be compared with the efficiency plots on

page 6 to determine if 2x mode is required by the appli-

cation. The data provided in the following derating curve

for 2x mode is based on the peak power dissipation that

could occur while in 2x mode. 1x and 1.5x modes do not

require derating.

100

150

200

250

300

350

400

450

35

45

55

65

75

85

95

105

Ambient Temperature (°C)

Derating for applications

requiring only 1x and 1.5x

modes

Derating for applications

requiring 2x mode

Maximum Continuous Output

Protection Circuitry

The SC630 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.

Short-Circuit Current Protection

Short-circuit current protection is provided to limit the

current that can be sourced when the output is shorted

to ground. When a short circuit forces V

OUT

to drop below

2V, the SCCP detects the condition and limits the output

current to 250mA (typical).

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Applications Information