LM3559TLE/NOPB National Semiconductor, LM3559TLE/NOPB Datasheet - Page 20

• Manufacturer Part Number: LM3559TLE/NOPB
• Description: LM3559
• Manufacturer: National Semiconductor
• Series: -r

Specifications of LM3559TLE/NOPB

• Constant Current: Yes
• Constant Voltage: -
• Topology: High Side, PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 1.8MHz ~ 2.2MHz
• Voltage - Supply: 2.5 V ~ 5.5 V
• Voltage - Output: -
• Mounting Type: Surface Mount
• Package / Case: 16-UFBGA
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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VIN FLASH MONITOR (FLASH CURRENT RISING)
A second comparator at IN is available to monitor the input
voltage during the flash current turn-on. Bit [3] of the VIN
Monitor Register enables/disables this feature. With this bit
set to ‘1’ the VIN Flash Monitor is active. Bits [5:4] of the VIN
Monitor Register program the 4 selectable thresholds of
(2.9V, 3.0V, 3.1V, and 3.2V). The feature operates as follows:
during flash current turn-on the active current sources (LED1
and/or LED2) will transition through each of the lower flash
and torch current levels until the target flash current is
reached. With the VIN Flash Monitor active, if during the flash
current turn-on, the input voltage falls below the VIN Flash
Monitor threshold, the flash current is set to the level that the
current ramp had risen to at the time of the undervoltage
event. The Input Voltage Flash Monitor only operates during
the ramping up of the flash LED current.
The VIN Flash Monitor ignores the first 2 flash codes during
the flash pulse turn on. As a result, if the VIN Flash Monitor is
enabled and VIN were to fall below the VIN Flash Threshold
as the LED current ramps up through either of the first two
levels, then the flash pulse would not be halted until code #3
(168.75 mA per current source).
To avoid noise from falsely triggering the VIN Flash Monitor,
this mode incorporates an 8 µs deglitch timer as well as an
internal analog filter at the input of the VIN Flash Monitors
Comparator. With the VIN Flash Monitor active, V
FIGURE 11. VIN Monitor Waveform
IN
must go
20
below the VIN Flash Monitor Threshold (V
main below it for 8 µs before the flash current ramp is halted
and the VIN Flash Monitor Flag is written.
LAST FLASH REGISTER
Once the VIN Flash Monitor is tripped, the flash code that
corresponded to the LED current at which the flash current
ramp was halted is written to the Last Flash Register. The Last
Flash Register is a read-only register; the lower 4 bits are
available to latch the code for LED1 and the upper 4 bits to
latch the code for LED2.
For example, suppose that the LM3559 is set up for a single
LED with a target flash current of 1125 mA. The VIN Flash
Monitor is enabled with the VIN Flash Monitor threshold set
to 3.0V (VIN Monitor Register bits [5:4] = 0, 1). When the
STROBE input is brought high, the LED current begins ramp-
ing up through the torch and flash codes at 32 µs/code. As
the input current increases, the input voltage at the LM3559’s
IN pin begins to fall due to the source impedance of the bat-
tery. By the time the LED current has reached 900 mA (code
0x77 or 450 mA per current source), VIN falls below 3.0V. The
VIN Flash Monitor will then stop the flash current ramp and
the LM3559 will continue to proceed with the flash pulse, but
at 900 mA instead of 1125 mA.
quence.
Figure 12
30102809
IN_FLASH
details this se-
) and re-