ADP1655

Rev. 0 | Page 19 of 24

SAFETY FEATURES

For critical system conditions, such as output overvoltage,

flash timeout, LED output short circuit, and overtemperature

conditions, the ADP1655 has built-in safety mechanisms. If

one of the fault conditions occurs, the device shuts down and

a corresponding flag is set in the fault information register

processor can read the fault information register through the

and, consequently, the fault flag is cleared. The device is

disabled until the fault information register is cleared.

available. To clear a fault, set EN1, EN2, and TORCH low.

OVERVOLTAGE FAULT

The ADP1655 contains a comparator at the VOUT pin that

monitors the voltage between VOUT and SGND. If the voltage

Bit 7 in the fault information register is read back as high. The

ADP1655 is disabled until the fault is cleared, ensuring protec-

tion against an open circuit.

OUTPUT CAPACITOR FAULT

If no output capacitor is present at the VOUT pin when the

ADP1655 is enabled for a flash, torch, or assist light event,

the part shuts down and Bit 7 in the fault information register

is read back as high. The ADP1655 is disabled until the fault is

cleared. The output capacitor detection scheme does not cause

the VOUT pin to rise above the overvoltage threshold even though

the overvoltage flag (Bit 7) in the fault information register

(Register 5) is set. The overvoltage and output capacitor fault

flags share a single register bit to reduce the required number

of registers.

TIMEOUT FAULT

If the 2-bit logic interface is used, the maximum duration for

flash being enabled (EN1/EN2 = 1) is preset to 850 ms. If EN1

and EN2 remain high for longer than 850 ms, ADP1655 is

disabled until the fault is cleared (EN1, EN2, and TORCH low).

strobe is set to level sensitive mode (Register 0x04, Bit 5), and

if strobe remains high for longer than 850 ms, the timeout fault

bit, Register 0x05, Bit 4), is read back as high. The ADP1655 is

disabled until the fault is cleared.

OVERTEMPERATURE FAULT

If the junction temperature of the ADP1655 rises above 150°C,

Bit 5 of the fault information register is read back as high. The

ADP1655 is disabled until the fault is cleared.

SHORT-CIRCUIT FAULT

The LED_OUT pin features short-circuit protection that

disables the ADP1655 if it detects a short circuit to ground at

the LED_OUT pin. The ADP1655 monitors the LED voltage

when the LED driver is enabled. If the LED_OUT pin remains

below the short-circuit detection threshold during startup, a

short circuit is detected. Bit 6 of the fault information register

is read back as high. The ADP1655 is disabled until the fault is

cleared.

CURRENT LIMIT

The internal switch limits battery current by ensuring that the

peak inductor current does not exceed the programmed limit

(current limit is set by Bit 6 and Bit 7 in the output mode register,

Register 0x04). If the peak inductor current exceeds the limit,

the part shuts down and Bit 1 of the fault information register

is read back as high. The ADP1655 is disabled until the fault is

cleared.

AMOUNT OF LED DETECTION

The ADP1655 is able to detect the amount of LED connected in

series between the LED_OUT pin and the PGND potential. In

register. The part uses an 80 mA LED driver current setting to

detect the LED forward voltage (Vf) with a voltage comparator

at the start of a flash, torch, or assist light event. If the detected

forward voltage is higher than 4.3 V (typical), Bit 3 of the fault

information register is read back as high.

INPUT UNDERVOLTAGE

The ADP1655 includes an input undervoltage lockout circuit. If

the battery voltage drops below the 2.4 V (typical) input UVLO

threshold, the ADP1655 shuts down. In this case, information

in all registers is lost, and when power is reapplied, a power-on

reset circuit resets the registers to their default conditions.