LM3492, LM3492Q

SNVS656C – SEPTEMBER 2010 – REVISED MAY 2013

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Figure 16. Switching Frequency

The two-channel current regulator of the LM3492 is fast response so that it can allow very high contrast ratio

(1000:1 at 3 kHz LED dimming frequency, minimum pulse width of the dimming signal is 300 ns). The two

channels are dimmable individually. Channel 1 of the current regulator can be disabled by a digital command

send through the COMM pin. In this case, the DIM1 pin can serve only as a clock signal for the data flow of the

COMM pin. The power dissipated by the current regulator is adaptively minimized by Dynamic Headroom Control

in order to maximize efficiency.

The LM3492 can be applied in numerous applications like automotive LCD backlight panels. It can operate

efficiently for inputs as high as 65V. Diagnostic functions including power good indication, over-temperature

indication, IOUT over- and under-voltage indications facilitate the interface of the LM3492 application circuit with

external micro-processors (MCUs). The LM3492 will not latch off and continue to operate in the presence of the

indications. Other useful features include thermal shutdown, VCC under-voltage lock-out, and precision enable.

The LM3492 is available in the thermally enhanced HTSSOP package.

LDO Regulator

should be connected between the VCC and GND pins. The current limit of the LDO is typically 30 mA. It can be

used to pull-up the open-drain COMM pin with an external resistor, and inject current to the ILIM pin to adjust the

lock-out (UVLO) threshold of 3.78V, the LM3492 is enabled and the CDHC pin sources a current to charge up an

Enable and Disable

CDHC pin is internally grounded. The EN pin is internally pulled up. After enable, the EN pin is pulled up by a 40

µA current source. If the EN pin is connected to low such that the LM3492 is shutdown, the pull-up current is

reduced to 2 µA. These take the advantages that the LM3492 can effectively avoid false disabling by noise

during operation, and minimize power consumption during shutdown. The enable threshold is precise such that it

can be used to implement an UVLO function for the input voltage as shown in Figure 17. The input voltage can

the following equation:

(1)

caused by the increase of the input voltage.

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