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4.6 VIN Monitor

The VIN MONITOR button controls the on/off state of the VIN MONITOR function. When this button is

pushed, bit 0 in the VIN Monitor Register is set to ‘1’, and the VIN Monitor feature in the LM3554 is

enabled. When the button is not pushed, bit 0 in the VIN Monitor Register is programmed with a ‘0’, and

the VIN Monitor feature is disabled.

The VIN Monitor Slider selects the 4 different VIN Monitor Thresholds shown in Table 6 and programs the

VIN Threshold Bits (bits [2:1] of VIN Monitor Register). The box to the right of the slider shows the

Hexadecimal equivalent of the VIN Threshold bits.

Table 6. VIN Monitor Thresholds

UVLO Slider Setting Under Voltage Lockout Threshold

0 3.1V (Default)

1 3.2V

2 3.3V

3 3.4V

4.7 Configuration Buttons

The following buttons correspond to bits in the Configuration Register 1 (0xD0):

4.7.1 EXT TORCH

When pushed, the EXT TORCH Button writes a ‘1’ to bit 7 (Hardware Torch Mode Enable) of

Configuration Register 1. This makes the TX1/TORCH input a hardware Torch enable. When not pushed,

the bit is written with a ‘1’, and the TX1/TORCH input is a transmit interrupt flash inhibit.

4.7.2 TX2 POL

When pushed, the TX2 POL button writes a ‘1’ to bit 6 (TX2 Polarity bit) of Configuration Register 1. This

makes the ENVM/TX2 input (when in TX2 mode) an active high flash inhibit. When not pushed, the bit is

written with a ‘0’, and the ENVM/TX2 (when in TX2 mode) an active low flash inhibit.

4.7.3 TX2

When pushed, the TX2 button writes a ‘1’ to bit 5 (ENVM/TX2 bit) of Configuration Register 1. This makes

the ENVM/TX2 input a transmit interrupt flash inhibit with adjustable polarity. When not pushed, the bit is

written with a ‘0’, and the ENVM/TX2 input is a hardware Voltage mode enable.

4.7.4 HYST

When pushed the HYST button writes a ‘1’ to bit 4 (HYST bit) of Configuration Register 1 and selects 100

mV hysteresis for the thermistor comparator. When not pushed, the bit is written with a ‘0’, and 200 mV of

hysteresis is selected.

4.7.5 NTC

When pushed, the NTC button writes a ‘1’ to bit 3 (LEDI/NTC bit) of Configuration Register 1 and makes

the LEDI/NTC pin an input to the thermistor comparator. In this mode, when the voltage at LEDI/NTC falls

below 1.05V (typical), the flash event is terminated. When not pushed, the bit is written with a zero, and

the LEDI/NTC pin is an indicator current source output.

4.7.6 Dis STR

When the Dis STR button is pushed, a ‘1’ is written to Bit 2 of Configuration Register 1. This disables the

STROBE input. When not pushed, the STROBE input is an active high Flash mode enable.

SNVA646B–January 2009–Revised July 2013 AN-1742 LM3554 Evaluation Board

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