SSL3250A_3

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 03 — 30 June 2009

14 of 26

NXP Semiconductors

SSL3250A

Photo flash dual LED driver

8.4.4 Short circuit protection

To prevent device and battery overloading, the converter is short circuit protected. In case

the LED pin is shorted to GND due to an application failure, the switching of the converter

is inhibited. Typical response times between detection of the LED pin shorted to GND and

inhibit switching of the converter is less than 1 ms. The short circuit protection is functional

at any time during Torch mode and also during the soft start phase of the flash period.

The short circuit protection may also be triggered when either the inductor or the diode is

not connected. Also, a shorted diode may trigger the output short protection, if two LEDs

are connected in series between VO and LED pins. Therefore little or no current will flow

When an overvoltage is encountered, the OS_PROT flag (bit 3) is set in the status

register.

pins, the Schottky diode may be irreversibly damaged when the LED pin is shorted. This is

inherent to the asynchronous boost converter topology.

8.4.5 Interrupt line

The interrupt pin INT is an active LOW open-drain output allowing for multiple devices to

be connected as a wired OR, using the same interrupt line to the external control logic. On

the interrupt line, only one pull-up resistor is needed in the complete system.

8.4.6 Undervoltage lockout

As a result of a low battery voltage, the input voltage can drop too low to guarantee normal

operation. When the input voltage has dropped below the undervoltage lockout level, the

device switches to an undervoltage lockout state stopping all operations of the device.

Start-up is only possible by crossing the start-up level again. Recovering from this error

results in the loss of all register settings. This protection does not generate an interrupt on

the INT line nor is it flagged in the status register 03h.

8.5 Soft start

To avoid battery overloading when entering the Torch mode or the Flash mode, the device

is equipped with a soft start circuit. This circuit limits the rate of rise of the LED current to

4.5 mA/

µs until the required LED current has been reached. When the device ends Flash

mode or Torch mode, the LED current decreases with a controlled slope of 9 mA/

µs.

Whenever a protection is activated, the LED current decreases without the controlled

slope and drops immediately to zero.

8.6 Peak current limit

To avoid saturation of the inductor, the device is equipped with a peak current limit

function. This circuit limits the peak inductor currents to 2.2 A. No protection is activated.

communicate between different ICs or modules. The two wires are an SDA wire and an

SCL wire. Both lines must be connected to a positive supply via a pull-up resistor when