SC630A

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General Description

The SC630A is a 3.3V output charge pump regulator

designed to support up to 300mA (T

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 SC630A has three operating modes — x, .5x, and

2x. The x mode is a linear series regulation mode with a

tions as a low noise series linear regulator. The .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. The hysteresis between charge pump

modes is shown in the efficiency plots of the Typical

Characteristics section. For optimum transient perfor-

mance, the input should be decoupled to prevent steps

greater than the hysteresis voltage. Note that hysteresis is

load dependent, and increases with the load current to

prevent chatter between the charge pump modes.

Thermal Resistance

The SC630A package is thermally efficient when the

circuit board layout connects the thermal pad through

multiple vias to the ground plane. The thermal resistance

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 SC630A 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 load current and battery voltage range of the appli-

cation 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. x and .5x modes do not

require derating.

100

150

200

250

300

350

35

45

55

65

75

85

95

105

Ambient Temperature (°C)

Derating for applications

requiring 2x mode

Maximum Continuous Output

Protection Circuitry

The SC630A 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

output to A 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

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

current to 600mA (typical).

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Applications Information