SSL3250A_3

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 03 — 30 June 2009

7 of 26

NXP Semiconductors

SSL3250A

Photo flash dual LED driver

2. Trigger the Flash mode either by the hardware STRB pin or by the FLASH_STRB bit

in the Flash strobe register 02h. When the external strobe pin is not used it should be

connected to GND to prevent false strobing of the main LED.

The external current setting resistor R_FL can still be used in Flash mode but is not

required. When the external current setting resistor R_FL is not used, the pin should

preferably be connected to VIN, this way a default resistor value of approximately 50 k

Ω is

assumed. The current setting resistors for the indicator LED, R_IND and for the

connected to VIN.

8.3 Operational modes

8.3.1 Shut-down mode

The device is in Shut-down mode when the activate pin (ACT) is LOW. In Shut-down

mode the internal circuitry of the device is turned off to guarantee a low shut-down

current. The N-channel MOSFET (NMOS) is set to high-impedance. To limit the LED

current to a minimum leakage, the current sink circuitry for both the main LED and the

indicator LED are switched to high-impedance. After making the pin ACT HIGH, the

device will start up and is ready to receive commands through the selected interface.

8.3.2 Standby mode

In Standby mode the internal circuitry of the device remains on, but the converter is not

switching. The NMOS is set to high-impedance. To limit the LED current to a minimum

leakage, the current sink circuitry for both the main LED and the indicator LED are

communication.

8.3.3 Torch mode

The Torch mode allows the main LED to be switched on, without timing limitations, at a

lower LED current setting. The Torch mode current in the main LED can be set between

ignored. If an external R_FL resistor is connected, this resistor will also scale down the set

using Equation 1. When not using the resistor R_FL, assume a value of 50 k

Ω in the

equation. Entering Torch mode is done by writing the required current setting in the

current control register. The LED will light to the set torch current. Switching off the Torch

mode can be done by writing 0h into the current control register, or by entering Flash

mode, see Section 8.3.4.

(1)

When using the Direct enable mode, the torch current is defined by an external resistor

connected to the R_TR pin. The LED current is defined using Equation 2. When not using

the current set resistor, the torch current will be set to a default level of 125 mA. The

I

LED

50 k

Ω

R

R_FL

---------------





35 mA

15 mA

Register

×

++

=