LM3554TMXSLASHNOPB datasheet(15/47 Pages) TI1

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LM3554

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SNVS549C – JUNE 2009 – REVISED FEBRUARY 2016

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Feature Description (continued)

7.3.9 ENVM/TX2/GPIO2

The ENVM/TX2/GPIO2/INT pin has four functions. In ENVM mode (Configuration Register 1 bit [5] = 0), the

ENVM/TX2/GPIO2/INT pin is an active high logic input that forces the LM3554 into voltage-output mode. In TX2

mode (Configuration Register 1 bit [5] = 1), the ENVM/TX2/GPIO2/INT pin is a Power Amplifier Synchronization

input that forces the LM3554 from Flash mode into Torch mode. In GPIO2 mode (GPIO Register Bit [3] = 1) the

ENVM/TX2/GPIO2/INT pin is configured as a general purpose logic input/output and controlled via bits[3:5] of the

GPIO Register. In INT mode the ENVM/TX2/GPIO2/INT pin is a hardware interrupt output which pulls low when

the LM3554 is in NTC mode, and the voltage at LEDI/NTC falls below VTRIP.

In TX2 mode, when Configuration Register 1 bit [6] = 0 the ENVM/TX2/GPIO2 pin is an active low transmit

interrupt input. Under this condition, when the LM3554 is engaged in a flash event, and ENVM/TX2/GPIO2 is

pulled low, both LED1 and LED2 are forced into either torch mode or LED shutdown depending on the logic state

of Configuration Register 2 bit [0]. In TX2 mode with Configuration Register 1 bit [6] = 1, the ENVM/TX2/GPIO2

pin is an active high transmit interrupt. Under this condition when the LM3554 is engaged in a Flash event, and

the TX2 pin is driven high, both LED1 and LED2 are forced into torch mode or LED shutdown, depending on the

logic state of Configuration Register 2 bit [0]. After a TX2 event, if the ENVM/TX2/GPIO2 pin is disengaged, and

the TX2 Shutdown bit is set to force Torch mode, the LED current ramps back to the previous Flash current

level. If the TX2 shutdown bit is programmed to force LED shutdown upon a TX2 event the Flags Register must

be read to resume normal LED operation. Table 5, Figure 33, and Figure 34 detail the Functionality of the

ENVM/TX2 input.

7.3.9.1 ENVM/TX2/GPIO2/INT as an Interrupt Output

In GPIO2 mode the ENVM/TX2/GPIO2 pin can be made to reflect the inverse of the LED Thermal Fault flag

(bit[5] in the Flags Register). To configure the LM3554 for this feature:

set GPIO Register Bit [6] = 1 (NTC External Flag)

set GPIO Register Bit [3] = 1 (GPIO2 mode)

set GPIO Register Bit [4] = 1 (GPIO2 is an output)

set Configuration Register 1 Bit [3] = 1 (NTC mode)

When the voltage at the LEDI/NTC pin falls below VTRIP (1.05 V typical), the LED Thermal Fault Flag (bit [5] in

the Flags Register) is set, and the ENVM/TX2/GPIO2/INT pin is forced low. In this mode the interrupt can only be

reset to the open-drain state by reading back the Flags register.

7.3.10 Indicator LED/Thermistor (LEDI/NTC)

The LEDI/NTC pin serves a dual function: either as an LED indicator driver or as a threshold detector for a

negative temperature coefficient (NTC) thermistor.

7.3.10.1 LED Indicator Mode (LEDI)

LEDI/NTC is configured as an LED indicator driver by setting Configuration Register 1 bit [3] = (0) and Torch

Brightness Register bits [1:0] = (0, 1), or Flash Brightness Register bits [1:0] = (0, 1). In Indicator mode there are

4 different current levels available (2.3 mA, 4.6 mA, 6.9 mA, 8.2 mA). Bits [7:6] of the Torch Brightness Register

set the 4 different indicator current levels. The LEDI current source has a 1-V typical headroom voltage.

7.3.10.2 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 becomes the negative input of an internal

comparator with the positive input internally connected to a reference (VTRIP = 1.05 V typical). Additionally,

Configuration Register 2 bit [1] determines the action the device takes if the voltage at LEDI/NTC falls below

VTRIP (while the device is in NTC mode). With the Configuration Register 2 bit [1] = 0, the LM3554 is forced into

torch mode when the voltage at LEDI/NTC falls below VTRIP. With the Configuration Register 2 bit [1] = 1 the

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