SC631

10

General Description

The SC631 is a 4.4V output charge pump regulator

designed to support up to 325mA (T

A

≤ 55°C, 2.92V ≤ V

IN

≤

5.5V) and 250mA (T

A

≤ 85°C, 2.90V ≤ V

IN

≤ 5.5V) of continu-

ous current. SC631 applications include power for LEDs

and audio amplifiers in portable handheld equipment.

SC631 may be used in conjunction with regulated current

sink devices such as the SC620 Octal LED Driver or with

ballast resistors.

The SC631 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 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. For optimum

transient performance, it is recommended for the supply

decoupling capacitance be large enough to prevent steps

greater than 120mV. Normally C

IN

= 22uF is sufficient to

minimize supply transients during the charge pump mode

transitions.

Thermal Resistance

The SC631 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 SC631 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

Ambient Temp (°C)

Maximum Continuous Output

Protection Circuitry

The SC631 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)

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Applications Information