SC653 datasheet(14/22 Pages) SEMTECH

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SC653

To control LDOs exclusively by software, ENL1 and ENL2

may be permanently terminated to the battery voltage.

ENL1 must be high for the SPIF interface to control LDO1.

When low, ENL1 disables LDO1. ENL2 is used exactly the

same way to enable and disable LDO2.

A 1μF, low ESR capacitor should be used as a bypass

capacitor on each LDO output to reduce noise and ensure

stability. In addition, it is recommended that a nominal

minimum 22nF capacitor be connected between the BYP

pin and the GND1 pin to minimize noise and achieve

optimum power supply rejection. A larger capacitor can

be used for this function, but at the expense of increasing

turn-on time. Capacitors with X7R or X5R ceramic dielec-

tric are strongly recommended for their low ESR and

superior temperature and voltage characteristics. Y5V

capacitors should not be used as their temperature coef-

ficients make them unsuitable for this application.

Shutdown Mode

The device is disabled when the SPIF pin is held low for

the shutdown time specified in the electrical characteris-

tics section. All registers are reset to default condition at

shutdown. Typical current consumption in this mode is

0.1μA.

Sleep Mode

When all LEDs are disabled, sleep mode is activated. This

is a reduced current mode that helps minimize overall

current consumption by disabling the clock and the

charge pump while continuing to monitor the serial

interface for commands. The two LDOs can be enabled

when the device is in sleep mode.

Protection Features

The SC653 provides several protection features to safe-

guard the device from catastrophic failures. These fea-

tures include:

Output Open Circuit Protection

Over-Temperature Protection

Charge Pump Output Current Limit

LDO Current Limit

LED Float Detection

•

Applications Information (continued)

Output Open Circuit Protection

Over-Voltage Protection (OVP) is provided at the OUT pin

to prevent the charge pump from producing an exces-

sively high output voltage. In the event of an open circuit

at OUT, the charge pump runs in open loop and the

voltage rises up to the OVP limit. OVP operation is hyster-

etic, meaning the charge pump will momentarily turn off

until V

OUT

is sufficiently reduced. The maximum OVP

threshold is 6.0V, allowing the use of a ceramic output

capacitor rated at 6.3V.

Over-Temperature Protection

The Over-Temperature (OT) protection circuit prevents the

device from overheating and experiencing a catastrophic

failure. When the junction temperature exceeds 165°C, the

device goes into thermal shutdown with all outputs dis-

abled until the junction temperature is reduced. All regis-

ter information is retained during thermal shutdown.

Hysteresis of 30°C is provided to ensure that the device

cools sufficiently before re-enabling.

Charge Pump Output Current Limit

The device limits the charge pump current at the OUT pin.

When OUT is shorted to ground, the output current will

typically equal 250mA. The output current is also limited

to 250mA when over-loaded resistively.

LDO Current Limit

The device limits the output currents of LDO1 and LDO2

to help prevent the device from overheating and to

protect the loads. The minimum limit is 200mA, so load

current greater than the rated current and up to 200mA

can be used with degraded accuracy and larger dropout

without tripping the current limit.

LED Float Detection

Float detect is a fault detection feature of the LED current

sink outputs. If an output is programmed to be enabled

and an open circuit fault occurs at any current sink output,

that output will be disabled to prevent a sustained output

OVP condition from occurring due to the resulting open

loop. Float detect ensures device protection but does not

ensure optimum performance. Unused LED outputs must

be disabled to prevent an open circuit fault from

occurring.

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