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TPS61162D

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SLVSC13A – JULY 2013 – REVISED MARCH 2016

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Copyright © 2013–2016, Texas Instruments Incorporated

8.3 Feature Description

8.3.1 Normal Operation

In order to provide high brightness backlighting for large-sized or high-resolution smart-phone panels, a greater

number of white LED diodes are used. Having all LED diodes in a string improves overall current matching;

however, the output voltage of a boost converter is limited when input voltage is low, and normally the efficiency

drops when the output voltage is very high. For these reasons, the TPS61162D is designed to configure the LED

diodes in two parallel strings.

8.3.2 Boost Converter

The boost converter of the TPS61162D integrates a 40-V, 1.5-A low-side switch MOSFET and has a fixed

switching frequency of 1.2 MHz. The control architecture is based on traditional current-mode PWM control. (For

operation see Functional Block Diagram.) Two current sinks regulate the dual-channel current, and the boost

output is automatically set by the voltage of the regulating IFBx pin. The output of the error amplifier and the

sensed current of the switch MOSFET are applied to a control comparator to generate the boost switching duty

cycle; slope compensation is added to the current signal to allow stable operation for duty cycles larger than

50%.

In order to ensure that both current sinks remain in regulation whenever there is a mismatch in string voltages

while the power dissipation of the current sink regulators is minimized, the minimum headroom voltage between

IFB1 and IFB2 becomes the regulation point for the boost converter. For example, if the LEDs connected to IFB1

require 20 V, and the LEDs connected to IFB2 require 20.5 V at the programmed current, then the voltage at

IFB2 is about 90 mV, and the voltage at IFB1 is about 0.59 V. In other words, the boost makes the cathode of

the highest voltage LED string the regulation point.

8.3.3 IFBx Pin Unused

If only one channel is needed, a user can easily disable the unused channel by connecting its IFBx pin to

ground. If both IFBx pins are connected to ground, the device does not start up.

8.3.4 Enable and Start-Up

In order to enable the device from shutdown mode, three conditions have to be met:

1. Power On Reset (POR), that is, VIN voltage is higher than UVLO threshold

2. Logic high on EN pin

3. PWM signal (logic high or PWM pulses) on PWM pin

When all these conditions are met, an internal LDO linear regulator is enabled to provide supply to internal

circuits, and the device can start up.

The TPS61162D supports two dimming interfaces: one-wire digital interface (EasyScale interface) and PWM

interface. The device begins an EasyScale detection window after start-up to detect which interface is selected. If

the EasyScale interface is needed, signals of a specific pattern must be input into the EN pin during the

EasyScale detection window; otherwise, PWM dimming interface is enabled (see details in One-Wire Digital

Interface (Easyscale Interface) ).

After the EasyScale detection window, the TPS61162D checks the status of IFBx pins. If one IFBx pin is

detected to connect to ground, the corresponding channel is disabled and removed from the control loop. The

soft start then begins, and the boost converter starts switching. If both IFBx pins are shorted to ground, the

TPS61162D does not start up.

Either pulling EN pin low for more than 2.5 ms, or pulling the PWM pin low for more than 20 ms, can disable the

device, and the TPS61162D enters into shutdown mode.

8.3.5 Soft Start

Soft start is implemented internally to prevent voltage overshoot and inrush current. After the IFBx pin status

detection, the COMP pin voltage starts ramp up, and the boost starts switching. During the beginning 5 ms

operation of the boost converter.