LM3559 datasheet(16/50 Pages) TI1

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STROBE

LED

Current

Flash Timeout

VIN_MON_TH

Input

Voltage

ITORCH

IFLASH

Deglitch Time

(250 Ps)

LM3559

SNVS624B – JUNE 2011 – REVISED JUNE 2016

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Feature Description (continued)

8.3.5.4.1.3

Updating The Message Indicator

The best way to update the message indicator is to disable the message indicator output via the Enable Register

bit [7], write the new sequence to the Indicator Register and/or Indicator Blinking Register, and then re-enable the

message indicator. Updating the Indicator Registers on the fly can lead to long delays between pattern changes.

This is especially true if the PERIOD# or BLANK# setting is changed from a high setting to a lower setting.

8.3.6 Input Voltage (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 VIN falls below the programmable VIN monitor threshold. Bit 0 in the VIN Monitor

thresholds of 2.9 V, 3 V, 3.1 V, and 3.2 V. Bit 3 in Configuration Register 2 selects whether an undervoltage

event forces torch mode or forces the LEDs off. See Table 13 for additional information. When the VIN monitor is

active and VIN falls below the programmed VIN Monitor threshold, the active current sources (LED1 and/or

LED2) either turns off or is forced into the torch current setting. To reset the LED current to its previous level, VIN

must go above the VIN monitor threshold and the Flags Register must be read back. See Figure 30 for the VIN

monitor timing waveform.

To avoid noise from falsely triggering the VIN monitor, this mode incorporates a 250 µs deglitch timer. With the

VIN monitor active, VIN must go below the VIN monitor threshold (VIN_TH) and remain below it for 250 µs before

the LEDs are forced into torch mode (or shut down) and the VIN monitor flag is written.

Figure 30. VIN Monitor Waveform

8.3.7 VIN Flash Monitor (Flash Current Rising)

A second comparator at IN is available to monitor the input voltage during the flash current turnon. 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 (2.9 V, 3 V, 3.1 V, and 3.2 V). The feature

operates as follows: during flash current turnon the active current sources (LED1 and/or LED2) 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 the input voltage falls below the VIN flash monitor threshold during the flash current turnon,the flash

current is set to the level that the current ramp had risen to at the time of the undervoltage event. The VIN 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 turnon. 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).

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