LP8867-Q1

EvaluationModuleUser'sGuide

TheTexasInstrumentsLP8867Q1EVMevaluationmodulehelpsdesignerstoevaluatetheoperationand performanceof theLP8867-Q1andLP8869-Q1device. Thisdocument includesacompleteschematic diagram,printed-circuitboard(PCB) layout,andbillofmaterials(BOM)of theLP8867Q1EVM.

1 Introduction

The LP8867Q1EVM helps designers to evaluate the characteristics, operation, and use of the LP8867/9 Q1 device, a high-performance LED driver for automotive lighting. The LP8867/9-Q1 device is an easy-to use LED driver with integrated DC-DC converter. The device also has four/three 120-mA high-precision current sinks that can be controlled by a PWM input signal and integrates extensive fault detection features

1.1 Features

The EVM has the following features:

• Integrated boost or SEPIC for LED string power

• Four/Three high-precision current sinks

• Power-Line FET control for inrush current protection and standby energy saving

• Extensive fault detection features and fault output

• Automatic LED current reduction with external temperature sensor

1.2 Typical Applications

• Backlight for:

– Automotive infotainment

– Automotive instrument clusters

– Smart mirrors

– Heads-Up Displays (HUD)

– Central Information Displays (CID)

– Audio-Video Navigation (AVN）

2 LP8867Q1EVM Hardware Setup

This section describes the jumpers and connectors on the EVM as well as how to properly connect and setup the LP8867Q1EVM.

Figure 1 shows connectors and main components on the LP8867Q1EVM when used to evaluate the LP8867-Q1 device. When evaluating the LP8869-Q1 device, the only difference is to close the jumper J22.

Default resistor values and jumper positions are set to:

• Boost switching frequency- 400 kHz (set by external resistor R12)

• Maximum LED current per string- 120 mA (set by external resistor R14)

• J1, J4: Open to enable the power line FET and VIN_OCP protection

• J5: Open- a probing /noise injecting point for stability measurement

• J7, J8: Closed to enable the device

• J10: Close pins 2-3 to enable the spread spectrum feature

• J11: Close pins 2-3 to connect PWM to VDDIO/EN to set 100% brightness

• J13: Close pins 1-2 to enable the LED D3 for fault indication

• J14: Close pins 1-2 to disable the LED current dimming with external temperature sensor

• J15: Open to disable the LED current dimming with external temperature sensor

• J17: Open- used to connect external temperature sensor

• J18: Closed to use the NTC thermistor RT1 if LED current dimming with external temperature sensor is enabled

• J16, J19, J20, J22: Open to enable the four current sinks when configured to evaluate the LP8867-Q1 device

When configuring the LP8867Q1EVM to evaluate the LP8869-Q1 device, the only difference is that jumper J22 should be closed.

3 LP8867Q1EVM Test Setup

Figure 2 shows the test setup for the LP8867Q1EVM. Follow these steps for the EVM test:

• Set the voltage of the dc power supply to 12 V and set the current limit to 4 A.

• Connect four LED strings on the LED board to OUT1- OUT4 of connector J21. Connect Boost pin of the LED board to the Boost pin of connector J21. (Note: LED current default is 120 mA and maximum boost voltage default is 37 V. LED outputs that are not used must be grounded via corresponding jumpers J16, J19, J20 and J22.)

• Connect the positive and negative outputs of the power supply to connectors VBAT and GNDin on the EVM board.

• Turn on the power supply. The LEDs will be turned on immediately since the jumpers on the EVM are set for PWM input of 100% duty cycle.

For other connector and jumper positions, please refer to Figure 1 and Figure 6.

4 LP8867Q1EVM Board Layout

Figure 3 and Figure 4 illustrate the EVM board layout.

5 LP8867Q1EVMSchematic

Figure6showstheEVMschematic

6 LED Load Board

The LED board is intended to be used as the load for LED drivers and can be configured for up to 6 strings and up to 20 LEDs in the string (number of LEDs in use is defined by jumpers). Cree Xlamp ML-B LEDs with maximum current 175 mA and maximum forward voltage 3.5 V at 80 mA (3.3-V typical) are used on the board. For the LP8867-Q1, 4 strings must be connected to the EVM. For the LP8869-Q1, 3 strings are connected.

NOTE: The LED board is not included with the EVM-- contact your local TI sales representative if board is needed.