LM3559TLX National Semiconductor Corporation, LM3559TLX Datasheet - Page 19

• Manufacturer Part Number: LM3559TLX
• Description: Synchronous Boost Flash Driver With Dual 900 Ma High Side Current Sources 1.8a Total Flash Current
• Manufacturer: National Semiconductor Corporation

mode. With Configuration Register 2 bit [1] set to ‘1’ the NTC
interrupt will force the LED current into shutdown.
Whether in NTC force torch or NTC shutdown, in order to re-
enter flash mode or torch mode after an NTC event, two things
must occur. First, the NTC input must be above the 1V thresh-
old. Secondly, the Flags Register must be read.
To avoid noise from falsely triggering the NTC Comparator,
this mode incorporates a 250 µs deglitch timer. With NTC
mode active, V
remain below it, for 250 µs before the LEDs are forced into
Torch mode (or shutdown) and the NTC Flag is written.
ALTERNATE EXTERNAL TORCH (AET MODE)
Configuration Register 2 bit [2] programs the LM3559 for Al-
ternative External Torch mode. With this bit set to (0) (default)
TX1/TORCH is a flash current interrupt that forces Torch
VIN MONITOR
The LM3559 has an internal comparator at IN that monitors
the input voltage and can force the LED current into Torch
mode or into shutdown, if V
VIN Monitor Threshold. Bit 0 in the VIN Monitor Register en-
ables or disables this feature. Bits [2:1] of the VIN Monitor
Register program the 4 adjustable thresholds of 2.9V, 3.0V,
3.1V, and 3.2V. Bit 3 in Configuration Register 2 selects
whether an undervoltage event forces Torch mode or forces
the LEDs off. See
the VIN Monitor is active and V
VIN Monitor threshold, the active current sources (LED1 and/
LEDI/NTC
Table 13
must go below the trip point (V
IN
for additional information. When
falls below the programmable
IN
falls below the programmed
FIGURE 10. AET Mode Timing
TRIP
) and
19
mode only during a Flash event. For example, if TX1/TORCH
goes high while the LED current is in Flash mode, the LEDs
will be forced into Torch mode only for the duration of the
timeout counter. At the end of the timeout counter the LEDs
will turn off.
With Configuration Register 2 bit [2] set to (1) the LM3559 is
configured for AET mode and the operation of TX1/TORCH
becomes dependent on its occurrence relative to the
STROBE input. In this mode, if TX1/TORCH goes high first,
then STROBE goes high next, the LEDs are forced into Torch
mode with no timeout. In this mode, if TX1/TORCH goes high
after STROBE has gone high, then the TX1/TORCH pin op-
erates as a normal LED current interrupt and the LEDs will
turn off at the end of the timeout duration (see
a detailed operation of this mode).
or LED2) will either turn off or be forced into the Torch current
setting. To reset the LED current to its previous level, V
go above the VIN Monitor threshold and the Flags register
must be read back. See
Waveform.
To avoid noise from falsely triggering the VIN Monitor, this
mode incorporates a 250 µs deglitch timer. With the VIN Mon-
itor active, V
(V
forced into Torch mode (or shutdown) and the VIN Monitor
Flag is written.
IN_TH
) and remain below it for 250 µs before the LEDs are
IN
must go below the VIN Monitor Threshold
Figure 11
for the VIN Monitor Timing
Figure 10
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IN
must
for