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KTZ8866

January 2022 - Revision 04b

Page 17 of 37

Company Confidential

Functional Description

Overview

KTZ8866 is the ideal power solution for LED backlighting and LCD bias power of small and medium size panels.

It integrates a step-up converter for LED backlighting, a step-up converter with LDO and inverting charge pump

for LCD bias power, resulting in a simpler and smaller solution with fewer external components. High switching

frequency allows the use of smaller inductors and capacitors. Its operating input ranges from 2.7V to 5.5V,

accommodating 1-cell lithium ion batteries or 5V supply.

The

LED driver’s six regulated current sinks can regulate up to 30mA in backlight mode with its maximum boost

output voltage up to 40V. 11bit linear or exponential ILED resolution can be obtained over I2C or PWM diming.

For additional flexibility, PWM dimming offers wide range frequency and duty cycle to support Content Adaptive

Brightness Control (CABC).

The LCD bias power includes a step-up converter, LDO and an inverting charge pump to generate dual outputs,

OUTP and OUTN, whose voltages can be programmed via an I2C interface. By integrating synchronous

rectification MOSFETs for the step-up converter and charge pump, the KTZ8866 maximizes conversion

efficiency up to 85%.

Various protection features are built into KTZ8866, including inductor current limit protection, output short circuit

protection, output over-voltage protection, LED fault (open or short) protection and thermal shutdown protection.

KTZ8866 is equipped with I2C interface for various controls and status monitor.

Hardware Enable & Standby Mode

KTZ8866 has a logic input HWEN pin to enable/disable the device. When HWEN is set low, the device goes into

shutdown mode, all I2C registers are reset to default, and the I2C interface is disabled. Under this condition, the

device does not respond to any I2C command. Even when

SCL/SDA’s pull up voltage is much less than VIN

voltage, it will not cause any extra leakage current.

When HWEN is set high, the device goes into standby mode, the I2C interface is enabled, and the device can

respond to I2C command. Under this condition, if

SCL/SDA’s pull up voltage is much less than VIN voltage, it

can cause a small leakage current from VIN

. For example, if VIN = 4.2V and SCL/SDA’s pull up voltage is 1.8V,

there will be around 6.8µA additional leakage current from VIN in this standby mode.

Based on HWEN’s connection, there are two kinds of power-up sequences as below

• If HWEN is tied to VIN, once VIN goes above around 2.0V, HWEN should stay high for at least

TI2C_RESET = 150

s time before any I2C command can be accepted.

• If HWEN is driven by a GPIO, once HWEN goes from low to high, HWEN should stay high for at least

TI2C_RESET = 150

s time before receiving any I2C command.

Either HWEN input or I2C command can be used to turn off the part, but there are some differences.

• If setting HWEN input low to turn off the part, the ILED will be turned off immediately without any ramp down

control. After that, the I2C interface is disabled.

• If using an I2C command to turn off backlight while keeping HWEN high, the ILED will have ramp down

control. After the LED current ramp down is finished, the I2C interface is still alive waiting for new command.

Backlight Boost

A step-up converter is used to generate high voltage for driving LED strings. An adaptive control method

automatically adjusts output voltage by monitoring the headroom voltage of current sinks. In this way, KTZ8866

can offer much better efficiency. The switching frequency of KTZ8866 Backlight Boost is typical 1.0MHz.

Backlight Current Sink Setting

Each current sink can be enabled or disabled by register 0x08 bits [5:0]. They can be enabled by writing the

backlight enable bit to HIGH in register 0x08 bit [6] after correctly setting of LED configuration and brightness. If

a current sink is not used, connect its output to GND. During the startup, KTZ8866 will automatically detect and

disable the corresponding channel.