SC622_09 datasheet(13/21 Pages) SEMTECH

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SC622

General Description

This design is optimized for handheld applications

supplied from a single Li-Ion cell and includes the

following key features:

A high efficiency fractional charge pump that

supplies power to the flash LED

An LED flash output that provides up to 400mA

of momentary current or up to 250mA of

continuous spotlight current

Two adjustable LDOs with outputs ranging from

2.5V to 3.3V for LDO1 and 1.5V to 1.8V for LDO2,

adjustable in 100mV increments

A SemWire single wire interface that provides

control of all device functions

High Current Fractional Charge Pump

The flash output is supported by a high efficiency, high

current fractional charge pump output at the VOUT pin.

The charge pump multiplies the input voltage by 1, 1.5, or

2 times. The charge pump switches at a fixed frequency of

250kHz in 1.5x and 2x modes and is disabled in 1x mode

to save power and improve efficiency.

The mode selection circuit automatically selects the

1x, 1.5x or 2x mode based on circuit conditions. Circuit

conditions such as low input voltage, high output current,

or high LED voltage place a higher demand on the charge

pump output. A higher numerical mode may be needed

momentarily to maintain regulation at the VOUT pin

during intervals of high demand, such as the high current

of an LED flash or the droop at the VIN pin during a supply

voltage transient. The charge pump responds to these

momentary high demands, setting the charge pump to

the optimum mode (1x, 1.5x or 2x), as needed to deliver

the output voltage and load current while optimizing

efficiency.

Hysteresis is provided to prevent mode

toggling.

The charge pump requires two bucket capacitors for

low ripple operation. One capacitor must be connected

between the C1+ and C1- pins and the other must be

connected between the C2+ and C2- pins as shown in

the typical application circuit diagram. These capacitors

should be equal in value, with a minimum capacitance of

•

2.2μF to support the charge pump current requirements.

The device also requires a 2.2μF capacitor on the VIN

pin and a 4.7μF capacitor on the VOUT pin to minimize

noise and support the output drive requirements.

Capacitors with X7R or X5R ceramic dielectric are

strongly recommended for their low ESR and superior

temperature and voltage characteristics. Y5V capacitors

should not be used as their temperature coefficients

make them unsuitable for this application.

LED Flash and Spotlight Current Sink

A single output current sink is provided to drive both flash

and spotlight functions. In flash mode, this current sink

provides up to 400mA for a flash LED or array of parallel

LEDs. Flash current settings are in 50mA increments from

50mA to 400mA. The FLEN pin directly triggers the FLASH

function when pulled high, or it can be wired to VIN to

enable software control via the serial interface.

In spotlight mode, the output can be set for up to 250mA

of continuous current. Settings are available in 50mA

increments from 50mA to 250mA. Continuous operation

above 250mA is not recommended due to high power

dissipation.

Flash and Spotlight Safety Timer

A safety timer disables the flash and spotlight output

current sink if the sink remains active for an extended

period. The timer protects the SC622 and the LED from

high power dissipation that can cause overheating. The

timer’s default state is on, but the timer may be disabled

via the serial interface to allow continuous output current

in spotlight mode. The safety timer affects only the FL pin

and will turn off the sink after a period of 1 second. The

timer may be reset by either forcing the FLEN pin low

or by resetting the Flash/Spotlight control bits via the

interface.

Programmable LDO Outputs

Two low dropout (LDO) regulators are provided for

camera module I/O and core power. Each LDO has at least

100mA of available load current with ±3.5% accuracy. The

minimum current limit is 200mA, so outputs greater than

100mA are possible at somewhat reduced accuracy.

Applications Information

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