LM3556

SNVS796D – AUGUST 2011 – REVISED OCTOBER 2015

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Device Functional Modes (continued)

Data can be written to the mode bits (bits[1:0]) in Enable Register (0x0A) only after the flash has ramped down to

the desired value, and VOUT has decayed.

Table 1 shows the I2C commands and the state of the mode bits, if the STROBE pin is used to enable the Flash

Mode.

Table 1. I2C Commands and the State of the Mode Bits

ENABLE AND CONFIGURATION

STATUS OF MODE BITS IN THE ENABLE REGISTER AFTER

MODE CHANGE REQUIRED

REGISTER SETTING (0x0A=Enable

A FLASH

Register, 0x07=Configuration Register)

Using edge-triggered STROBE to Flash

0x0A = 0x23; 0x07 = 0x78 (default setting)

Mode bits are cleared after a single flash. To reflash, 0x23 has to

be written to 0x0A.

Using level-triggered STROBE to Flash

0x0A = 0x23; 0x07 = 0xF8

Mode bits are cleared after a single flash. To reflash, 0x23 has to

be written to 0x0A.

Part is required to go from external TORCH

0x0A = 0x33; 0x07 = 0x78 (default setting)

Mode bits are cleared after a single flash. To reflash, 0x33 has to

Mode to external STROBE mode using

be written to 0x0A.

edge-triggered STROBE

Part is required to go from external TORCH

0x0A = 0x33; 0x0 7= 0xF8

Mode bits are cleared only if the part has an internal flash time-

Mode to external STROBE mode using

out event happening before the STROBE level goes low. To re-

Level Triggered STROBE

flash, 0x33 has to be written to 0x0A. If the STROBE level goes

low before an internal flash time-out event, then mode bits are not

cleared.

7.4.4 Torch Mode

In Torch Mode, the current source (LED) is programmed via the Current Control Register (0x09). Torch Mode is

activated by the Enable Register (0x0A) or by the hardware TORCH input. Once the Torch Mode is enabled the

current source ramps up to the programmed torch current level. The ramp-up and ramp-down times are

independently adjustable via the Torch Ramp Time Register (0x06). Torch Mode is not affected by flash timeout.

7.4.5 Indicator Mode

This mode has two options: the Internal Indicator Mode and the External Indicator mode. Both these modes are

activated by the Configuration Register (0x07) in addition to the Enable Register (0x0A).

In the Internal Indicator Mode, the current source (LED) can be programmed to 8 different intensity levels, with

current values being 1/8th the values in Current Control Register (0x09) bits [6:4]. The ramp-up, ramp-down, the

pulse time, number of blanks and periods of the desired output current can be independently controlled via the

Indicator Ramp Time Indicator (0x03), Indicator Blinking Register (0x04) and the Indicator Period Count Register

(0x05).

In the External Indicator Mode, the current source (LED) is controlled via the TORCH pin. An external PWM

signal can be input to the part via the TORCH pin to choose any one of the 8 available intensity settings (bits

[6:4] of the Current Control Register (0x09)) for the current source (LED).

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