LM3561 Datasheet, PDF (15/36 Pages) Texas Instruments – LM3561 Synchronous Boost Converter with 600mA High Side LED Driver and I 2 C-Compatible Interface

by stepping through all Torch and Flash levels (32µs/step)
until the programmed current is reached.
FLASH TERMINATION
Bit [2] of the Enable Register determines how the Flash pulse
terminates. With this bit = '1' the Flash current pulse will only
terminate by reaching the end of the Flash timeout period (see
Figure 6). With STR = '0', Flash mode can be terminated by
pulling STROBE low, programming bits [1:0] of the Enable
Register with (0,0), or by allowing the Flash timeout period to
elapse (see Figure 5). If STR = '0' and STROBE is toggled
before the end of the Flash timeout period, the timeout period
resets on the rising edge of STROBE. See LM3561 Timing
Diagrams regarding the Flash pulse termination for the dif-
ferent STR bit settings.
After the Flash pulse terminates, either by a flash timeout,
pulling STROBE low, or disabling it via the I²C-compatible in-
terface, the current source (LED) turns completely off. This
happens even when Torch is enabled via the I²C-compatible
interface and the Flash pulse is turned on by toggling
STROBE. After a Flash event ends (bits [1:0] of the Enable
Register are automatically re-written with (0, 0).
FLASH TIMEOUT
The Flash timeout period sets the maximum duration of the
flash current pulse. Bits [4:0] of the Flash Duration Register
programs the 32 different Flash timeout levels in steps of
32ms, giving a Flash timeout range of 32ms to 1024ms (see
Table 8).
TORCH MODE
In Torch mode the current source (LED) provides 8 different
current levels (see Table 6). The Torch currents are adjusted
by writing to bits [2:0] of the Torch Brightness Register. Torch
mode is activated by setting Enable Register bits [1:0] to (1,
0). Once the Torch mode is enabled the current sources will
ramp up to the programmed Torch current level by stepping
through all of the Torch currents at (32µs/step) until the pro-
grammed Torch current level is reached.
FLASH PULSE INTERRUPT (TX1), HARDWARE TORCH
INPUT (TORCH) AND GENERAL PURPOSE I/O (GPIO1)
The TX1/TORCH/GPIO1 input has a triple function; either as
a flash pulse interrupt (TX1), a hardware torch mode enable
(TORCH), or as a general purpose I/O (GPIO1).
Flash Interrupt (TX1)
With Configuration Register 1 Bit [7] = '0' (default), TX1/
TORCH/GPIO1 is a flash pulse interrupt input. This is de-
signed to force the flash pulse into a lower current state in
order to reduce the current pulled from the battery during high
battery current situations. For example, when the LM3561 is
engaged in a Flash event and TX1 is pulled high (active high
polarity) the current source (LED) is forced into Torch mode
at the programmed Torch current setting. If TX1 is then pulled
low before the Flash pulse terminates, the LED current will
ramp back to the previous Flash current level. At the end of
the Flash timeout, whether TX1 is high or low, the LED current
will turn off.
TX1 Polarity
In TX1 mode, TX1 can be programmed as an active low TX1
input where pulling TX1 to GND will cause a TX1 event. TX1
polarity inversion is done via Configuration Register 1 bit [5].
Hardware Torch Mode
With Configuration Register 1 Bit [7] = '1', TX1/TORCH/
GPIO1 is configured as a hardware Torch mode enable. In
this mode (TORCH mode), a high at TORCH turns on the LED
current at the programmed Torch current setting. The
STROBE input and I²C Enabled flash take precedence over
TORCH mode. In hardware torch mode, both the LED current
source will turn off after a flash event and Configuration Reg-
ister 1 Bit [7] will be reset to '0'. In this situation, to re-enter
torch mode via hardware torch, the hardware torch enable bit
(Configuration Register 1 Bit [7] must be reset to '1'). , , and
detail the functionality of the TX1/TORCH input.
GPIO1 Mode
With GPIO Register bit[0] = '1', the TX1/TORCH/GPIO1 pin is
configured as a general purpose I/O. In GPIO1 mode this pin
can be either a logic input or a logic output depending on the
bit settings in bits [2:1] of the GPIO Register (see Table 4).
FLASH PULSE INTERRUPT (TX2), GENERAL PURPOSE
I/O (GPIO2), AND INTERRUPT OUTPUT (INT)
The TX2/GPIO2/INT pin has a triple function: either a flash
interrupt input (TX2), a general purpose I/O (GPIO2), or as an
interrupt output (INT).
Flash Interrupt (TX2 Mode)
In TX2 mode (default), TX2 is a flash pulse interrupt input.
This is designed to force the flash pulse into a lower current
state in order to reduce the current pulled from the battery
during high battery current situations. For example, when the
LM3561 is engaged in a Flash event, and TX2 is pulled high
(active high polarity, the current source (LED) is forced into
torch mode at the programmed Torch current setting. If TX2
is then pulled low before the flash pulse terminates, the LED
current will step back to the previous flash current level. At the
end of the flash timeout, whether the TX2 pin is high or low,
the LED current will turn off. In addition to forcing torch mode
with a TX2 event, the TX2 input can be set to force shutdown.
Configuration Register 2 bit[0] sets this mode (see Table
11). In TX2 shutdown mode, a TX2 event will shut down the
flash pulse. Once shut down, the flash pulse must be re-en-
abled via STROBE or the flash enable bits in the Enable
Register.
TX2 Forcing Shutdown
TX2 also has the capability to force shutdown (see Figure 7).
When bit [0] of Configuration Register 2 is set to a '1', TX2 will
force shutdown when active. For example, if TX2 is config-
ured for TX2 mode with active high polarity, and bit [0] of
Configuration Register 2 is set to '1' then when TX2 is driven
high, (LED) will be forced into shutdown. Once the current
source is forced into shutdown by activating TX2, the current
source can only be re-enabled in flash mode if TX2 is pulled
low, and the Flags register is read back. If only the Flags reg-
ister is read back and TX2 is kept high, the device will be re-
enabled into torch mode and not shutdown. This occurs
because the TX2 shutdown feature is an edge-triggered
event. With active high polarity the TX2 shutdown requires a
rising edge at TX2 in order to force the current source back
into shutdown. Once shut down, it takes a read back of the
flags Register and another rising edge at TX2 to force shut
down again.
TX2 Polarity
In TX2 mode (default), TX2 is a flash pulse interrupt input.
This is designed to force the flash pulse into a lower current
state in order to reduce the current pulled from the battery
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