LM3554TME/NOPB National Semiconductor, LM3554TME/NOPB Datasheet - Page 20

• Manufacturer Part Number: LM3554TME/NOPB
• Description: IC LED DVR PHOTO FLASH 16-USMD
• Manufacturer: National Semiconductor
• Type: Photo Flash LED (I²C Interface)r

Specifications of LM3554TME/NOPB

• Constant Current: Yes
• Topology: High Side, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 2MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 16-MicroSMD
• Operating Temperature: -30°C ~ 85°C
• Current - Output / Channel: 600mA
• Internal Switch(s): Yes
• Efficiency: 90%
• Led Driver Application: LED Backlighting, Portable Electronics
• No. Of Outputs: 2
• Output Current: 1.2A
• Input Voltage: 2.7V To 5.5V
• Dimming Control Type: I2C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3554TMETR

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the Torch Brightness Register set the 4 different indicator
current levels. The LEDI current source has a 1V typical
headroom voltage.
Thermal Comparator Mode (NTC)
Writing a (1) to Configuration Register 1 bit [3] disables the
indicator current source and configures the LEDI/NTC pin as
a detector for an NTC thermistor. In this mode LEDI/NTC be-
comes the negative input of an internal comparator with the
positive input internally connected to a reference (V
1.05V typical). Additionally, Configuration Register 2 bit [1]
determines the action the device takes if the voltage at LEDI/
NTC falls below V
Configuration register 2 bit [1] = 0, the LM3554 will be forced
into Torch mode when the voltage at LEDI/NTC falls below
V
shut down the current sources when V
V
V
the same Flash pulse) can only be re-started by reading from
the Flags Register (0xD0) and ensuring the voltage at V
NTC
the Flags register is cleared, the LM3554 will go through a
250µs deglitch time before the flash current falls to either torch
mode or goes into shutdown.
ALTERNATIVE EXTERNAL TORCH (AET MODE)
Configuration Register 2 bit [2] programs the LM3554 for Al-
ternative External Torch mode. With this bit set to (0) (default)
TX1/TORCH is a transmit interrupt that forces Torch mode
only during a Flash event. For example, if TX1/TORCH goes
high during a Flash event then the LEDs will be forced into
TRIP
TRIP
LEDI/NTC
is above V
. With Configuration Register 2 bit [1] = 1 the device will
. When the LM3554 is forced from Flash into Torch (by
falling below V
TRIP
TRIP
. When VLEDI/NTC falls below VTRIP, and
(while the device is in NTC mode). With
TRIP
), normal LED operation (during
LEDI/NTC
falls below
TRIP
LEDI/
=
20
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 operation
of TX1/TORCH becomes dependent on its occurrence rela-
tive to STROBE. In this mode if TX1/TORCH goes high first,
then STROBE goes high, 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 TX interrupt, and the LEDs will turn off at
the end of the timeout duration. (See
GRAMS,
INPUT VOLTAGE MONITOR
The LM3554 has an internal comparator that monitors the
voltage at IN and can force the LED current into Torch mode
or into shutdown if V
Monitor Threshold. Bit 0 in the VIN Monitor register (0x80)
enables or disables this feature. When enabled, Bits 1and 2
program the 4 adjustable thresholds of 3.1V, 3.2V, 3.3V, and
3.4V. Bit 3 in Configuration Register 2 (0xF0) selects whether
an under-voltage event forces Torch mode or forces the LEDs
off. See
information.
There is a set 100mV hysteresis for the input voltage monitor.
When the input voltage monitor is active, and V
the programmed VIN Monitor Threshold, the LEDs will either
turn off or their current will get reduced to the programmed
Torch current setting. To reset the LED current to its previous
level, two things must occur. First, V
above the UVLO threshold and secondly, the Flags register
must be read back.
Figure 21/Table 7
Figure
10, and
IN
falls below the programmable VIN
Figure
and
Figure 23/Table 9
11.)
IN
must go at least 100mV
LM3554 TIMING DIA-
for additional
IN
falls below