SSL3250A datasheet(5/26 Pages) NXP

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SSL3250A_3

Product data sheet

Rev. 03 — 30 June 2009

5 of 26

NXP Semiconductors

SSL3250A

Photo ﬂash dual LED driver

Functional description

8.1 Introduction

The SSL3250A is an asynchronous boost converter intended to drive either a single high

power ﬂash LED or two high power ﬂash LEDs in series. The main LED current is

controlled by the output voltage of the boost converter and the integrated linear current

sink. The SSL3250A has two interface modes and ﬁve operational modes. The control

interface is selected by the interface select pin IF_SEL. Depending on the interface mode

selected, the device can either be controlled by an I2C interface or by external enable

lines. Both interface modes control the ﬁve operational modes. These operational modes

are:

• Shut-down mode

• Standby mode

• Indicator mode

• Torch mode

• Flash mode

The ﬁrst mode is entered by putting a LOW level on the activate pin (ACT). This pin is

common for both interface modes. The operational modes Torch and Flash apply to the

same main LED current source, and the Indicator mode applies to a separate indicator

LED current source. Only when the I2C interface mode is enabled, the operational modes

Indicator, Flash and/or Torch can be used in parallel.

In normal operation, the regulated converter uses Pulse Width Modulation (PWM), so the

switching frequency is constant in all modes.

In applications where the required main LED voltage is lower than the applied input

voltage, the converter switches to linear mode. The excess voltage difference between the

required LED voltage and the input voltage is now compensated by increasing the voltage

over the current sink and therefore on the LED pin.

Apart from the main LED(s), a separate indicator LED can be driven from the SSL3250A.

This indicator LED is driven by a linear current sink circuit that operates independently

from the switch mode converter for the main LED(s).

8.2 Interface modes

The device is equipped I2C mode and Direct enable mode interfaces. Which interface

mode is used, is deﬁned by the level of the IF_SEL pin at the start-up of the device

(VACT → LOW to HIGH). The state of the IF_SEL pin should be kept static after powering

up the device. Table 4 shows the interface possibilities.

Table 4.

Interface modes

IF_SEL

Interface mode

Relevant controls

0I2C mode

SDA, SCL, STRB, ACT, R_FL, INT.

Direct enable mode

EN1, EN2, ACT, INT, R_TR, R_FL, R_IND, INT.

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