36V High Efficiency Converter with I²C Controlled 6-CH LED Driver Evaluation Board

General Description

The Evaluation Board demonstrates the RT4527A to be designed for high efficiency driver for white LEDs. It is suitable for single/two cell battery input to drive LED light bars which contains six strings in parallel and up to 10 WLEDs per string.

The RT4527A contains I²C interface for controlling the dimming mode, operating frequency and the LED current. The internal 250mΩ, 36V power switch with current-mode control provides overcurrent protection. The switching frequency of the RT4527A is also adjustable from 100kHz to 1.6MHz, which allows flexibility between efficiency and component size.

The RT4527A is available in the WQFN-20L 3.5x3.5 package.

Performance Sepcification Summary

Summary of the RT4527AGQW Evaluation Board performance specificiaiton is provided in Table 1. The ambient temperature is 25°C.

Table 1. RT4527A Evaluation Board Performance Specification Summary

Power-up Procedure

Suggestion Required Equipments

• RT4527A Evaluation Board
• DC power supply capable of at least 30V and 5A
• LED Load Board
• Function Generator
• Oscilloscope

Quick Start Procedures

The Evaluation Board is fully assembled and tested. Follow the steps below to verify board operation. Do not turn on supplies until all connections are made. When measuring the output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the output voltage ripple by touching the probe tip and ground ring directly across the last output capacitor.

Proper measurement equipment setup and follow the procedure below.

1) With power off, connect the power supply for VIN and GND pins.

2) With power off, use jumper to pull high for EN pin.

3) With power off, connect the Function Generator to PWM pin.

4) With power off, connect the LED Load Board to VOUT and LEDx pins.

5) Turn on the power supply at the input. Make sure that the input voltage does not exceeds 24V on the Evaluation Board.

6) Turn on the Function Generator at the PWM pin.

7) Check LED Load Board brightness.

8) Once the proper output voltage is established, adjust the PWM duty within the operating ranges and observe the output LED brightness, I_CHx, efficiency and other performance.

Detailed Description of Hardware

Headers Description and Placement

Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and then make sure all the components are undamaged and correctly installed. If there is any missing or damaged component, which may occur during transportation, please contact our distributors or e-mail us at evb_service@richtek.com.

Test Points

The EVB is provided with the test points and pin names listed in the table below.

Test Point/ Pin Name	Function
SDA	Data signal pin of I2C interface.
SCL	Clock signal pin of I2C interface.
VDC	Output of internal regulator.
COMP	Boost external compensator pin.
A0	Device address select (7bits), A0 = 0 (Low) à (0x6Ch), A0 = 1 (High) à (0x6Eh).
CH6	Current sink for LED6.
CH5	Current sink for LED5.
CH4	Current sink for LED4.
CH3	Current sink for LED3.
CH2	Current sink for LED2.
CH1	Current sink for LED1.
VOUT	Output of boost converter.
PGND	Power ground.
LX	Switch node of boost converter.
VIN	Power supply input.
EN	Enable control input (active high).
PWM	PWM dimming control input.
AGND	Analog ground. The exposed pad must be soldered to a large PCB and connect to AGND for maximum power dissipation.

Bill of Materials

Typical Applications

EVB Schematic Diagram

1. The capacitance values of the input and output capacitors will influence the input and output voltage ripple.

2. MLCC capacitors have degrading capacitance at DC bias voltage, and especially smaller size MLCC capacitors will have much lower capacitance.

Measure Result

Quiescent Current vs. Input Voltage	Switching Frequency vs. Temperature
Switching Frequency vs. Input Voltage	Channel Output Current vs. CHx
LED Current vs. PWM Duty_ PWM Mode	LED Current vs. PWM Duty_ DC Mode

LED Current vs. PWM Duty_ MIX Mode	LED Current vs. PWM Duty_ MIX-26K Mode
Power On from EN	Power Off from EN

Evaluation Board Layout

Figure 1 to Figure 4 are RT4527A Evaluation Board layout. This board size is 70mmx50mm and is constructed on four-layer PCB, outer layers with 2 oz. Cu and inner layers with 1 oz. Cu.

Figure 1. Top View (1^st layer)

Figure 2. PCB Layout—Inner Side (2^nd Layer)

Figure 3. PCB Layout—Inner Side (3^rd Layer)

Figure 4. Bottom View (4^th Layer)