LM3556_15 Datasheet, PDF (16/39 Pages) Texas Instruments – Synchronous Boost LED Flash Driver With High-Side Current Source

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 V_OUT 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
MODE CHANGE REQUIRED
Using edge-triggered STROBE to Flash
Using level-triggered STROBE to Flash
Part is required to go from external TORCH
Mode to external STROBE mode using
edge-triggered STROBE
Part is required to go from external TORCH
Mode to external STROBE mode using
Level Triggered STROBE
ENABLE AND CONFIGURATION
REGISTER SETTING (0x0A=Enable
Register, 0x07=Configuration Register)
0x0A = 0x23; 0x07 = 0x78 (default setting)
0x0A = 0x23; 0x07 = 0xF8
0x0A = 0x33; 0x07 = 0x78 (default setting)
0x0A = 0x33; 0x0 7= 0xF8
STATUS OF MODE BITS IN THE ENABLE REGISTER AFTER
A FLASH
Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Mode bits are cleared after a single flash. To reflash, 0x23 has to
be written to 0x0A.
Mode bits are cleared after a single flash. To reflash, 0x33 has to
be written to 0x0A.
Mode bits are cleared only if the part has an internal flash time-
out event happening before the STROBE level goes low. To re-
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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