LM3492, LM3492Q

SNVS656C – SEPTEMBER 2010 – REVISED MAY 2013

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DESCRIPTION CONTINUED

The fast slew rate current regulator allows high frequency and narrow pulse width dimming signals to achieve a

very high contrast ratio of 1000:1 at a dimming frequency of more than 3 kHz. The LED current is programmable

from 50 mA to 200 mA by a single resistor.

To maximize the efficiency, Dynamic Headroom Control (DHC) automatically adjusts the output voltage to a

minimum. DHC also facilitates a single BOM for different number of LED in a string, which is required for

backlight panels of different size, thereby reducing overall development time and cost. The LM3492 comes with a

versatile COMM pin which serves as a bi-directional I/O pin interfacing with an external MCU for the following

functions: power-good, over-temperature, IOUT over- and under-voltage indications, switching frequency tuning,

and channel 1 disabling. Other supervisory functions of the LM3492 include precise enable, VCC under-voltage

lock-out, current regulator over-power protection, and thermal shutdown protection. The LM3492 is available in

the thermally enhanced 20-pin HTSSOP package.

CONNECTION DIAGRAM

Figure 1. 20-Pin HTSSOP (Top View)

See PWP0020A Package

PIN DESCRIPTIONS

Pin

Name

Description

Application Information

1

EN

Enable

Internally pull-up. Connect to a voltage higher than 1.63V to provide

precision enable for the device.

2

VIN

Input Supply Voltage

Supply pin to the device. Input range is 4.5V to 65V.

3, 4

SW

Switch Node

Internally connected to the drain of the integrated MOSFET.

5

VOUT

Output Voltage Sense

Sense the output voltage for nearly constant switching frequency control.

6

RT

Frequency Control

An external resistor from the VOUT pin to this pin sets the switching

frequency.

7

FB

Output Voltage Feedback

The output voltage is connected to this pin through a feedback resistor

divider for output voltage regulation. The voltage of this pin is from 1.05V to

2.5V.

8

GND

Analog Ground

Signal Ground

9

IOUT2

Current Regulator Input of Channel 2

Input of the current regulator of channel 2. The regulated current is

programmable (refer to the IREF pin).

10

IOUT1

Current Regulator Input of Channel 1

Input of the current regulator of channel 1. The regulated current is

programmable (refer to the IREF pin).

11

CDHC

Dynamic Headroom Control

An external capacitor connected to this pin sets the DHC sensitivity. At

startup, a 120 µA internal current source charges an external capacitor to

provide a soft-start function.

12

IREF

Current Setting of the Current Regulator An external resistor connected from this pin to ground programs the

regulated current of the current regulator of channels 1 and 2.

13

COMM

Bi-directional Logic Communication

This pin is open drain for various indications (power-good, over-

temperature, IOUT over- and under-voltage) and command sending

(switching frequency tuning and channel 1 disabling).

2

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