SSL3250A_3

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 03 — 30 June 2009

9 of 26

NXP Semiconductors

SSL3250A

Photo flash dual LED driver

8.3.4 Flash mode

The Flash mode allows the main LED to be used at high LED current setting. The Flash

maximum of 31 in the current control register. The external resistor R_FL can be used to

scale down the set current. This can be used in the application to enable TxMasking as

described in Section 8.3.6. The current in the main LED is defined using Equation 3.

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

Ω in the equation.

Entering Flash mode can be done either by using the STRB pin or the FLASH_STRB bit

in Flash Strobe register 02h. The duration of the flash can be determined by a timer,

STRB triggering or by a time-out. The flash timing is given by Equation 3 and in

Section 8.4.2.

(3)

When using the Direct enable mode, the flash current can be defined by an external

resistor connected to the R_FL pin. The current in the main LED is defined using

Equation 4. When not using the current set resistor, the flash current will be set to a

default level of 500 mA. The default current is equal to connecting an external current set

resistor of 50 k

Ω. Entering Flash mode in Direct enable mode can be done using the EN1

and EN2 pins. The LED will stay on in Flash mode for as long as the enable pins are set to

Flash mode, but is limited to 820 ms maximum by the time-out timer.

(4)

When no external current set resistor is used, the R_FL pin can be left unconnected but is

preferably connected to VIN. Never connect the R_FL pin to GND as this will cause

unnecessary reference currents to flow to GND.

illustrates the Flash mode current setting equation for the Direct enable mode.

Fig 7.

I

LED

50 k

Ω

R

R_FL

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

35 mA

15 mA

Register

×

+

()

×

=

I

LED

50 k

Ω

R

R_FL

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

500 mA

×

=

0

32

24

16

12

28

20

014aaa366

250

215

161

125

110

55

375

500

600

0

Register

Value (k

Ω)

200

100

No

Resistor