General Description
The RT8511B is an LED driver IC that can support up to 10 WLED in series. It is composed of a current mode boost converter integrated with a 43V/2.2A power switch running at a fixed 500kHz frequency and covering a wide VIN range from 2.7V to 24V.
The white LED current is set with an external resistor, and the feedback voltage is regulated to 200mV (typ.). During operation, the LED current can be controlled by the PWM input signal in which the duty cycle determines the feedback reference voltage.
For brightness dimming, the RT8511B is able to maintain steady control of the LED current. Therefore, no audible noises are generated on the output capacitor. The RT8511B also has programmable overvoltage pin to prevent the output from exceeding absolute maximum ratings during open LED conditions. The RT8511B is available in WDFN-8L 2x2 package.
Performance Sepcification Summary
Summary of the RT8511BGQW Evaluation Board performance specificiaiton is provided in Table 1. The ambient temperature is 25°C.
Table 1. RT8511B Evaluation Board Performance Specification Summary
|
Specification
|
Test Conditions
|
Min
|
Typ
|
Max
|
Unit
|
|
Input Voltage Range
|
|
2.7
|
--
|
24
|
V
|
|
Feedback Voltage
|
|
0.195
|
0.2
|
0.205
|
V
|
|
LX Current Limit
|
|
1.66
|
2.2
|
2.74
|
A
|
|
Overvoltage Protection Threshold
|
|
1.14
|
1.2
|
1.26
|
V
|
|
Switching Frequency
|
VIN = 2.7V to 24V
|
0.4
|
0.5
|
0.6
|
MHz
|
|
PWM Dimming Frequency
|
|
0.1
|
--
|
8
|
kHz
|
Power-up Procedure
Suggestion Required Equipments
- RT8511B Evaluation Board
- DC power supply capable of at least 20V 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, connect the power supply for EN and GND pins.
3) With power off, connect the Function Generator to PWM pin.
4) With power off, connect the LED Load Board to VOUT and FB 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 , 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
|
|
OVP
|
Overvoltage protection for boost converter. The detecting threshold is 1.2V.
|
|
FB
|
Feedback. Connect a resistor between this pin and GND to set the LED current.
|
|
DIMC
|
PWM filter. Filter the PWM signal to a DC voltage.
|
|
GND
|
Ground.
|
|
LX
|
Switch node for boost converter.
|
|
VIN
|
Power supply input.
|
|
PWM
|
Dimming control input.
|
|
EN
|
Chip enable (active high) for boost converter.
|
|
GND
|
The exposed pad must be soldered to a large PCB and connected to AGND for maximum power dissipation.
|
Bill of Materials
|
VIN = 12V, VOUT = LED Load Board , IOUT = 60mA
|
|
Reference
|
Count
|
Part Number
|
Value
|
Description
|
Package
|
Manufacturer
|
|
U1
|
1
|
RT8511BGQW
|
RT8511BGQW
|
LED Drver
|
WDFN-8L 2x2
|
RICHTEK
|
|
C2, C3
|
2
|
0603X105K250CT
|
1µF
|
Capacitor, Ceramic
25V/X5R
|
0603
|
WALSIN
|
|
C4, C5
|
2
|
0603B104K500CT
|
1µF
|
Capacitor, Ceramic
50V/X7R
|
1206
|
WALSN
|
|
C6
|
1
|
UMK316BJ225KD-T
|
2.2µF
|
Capacitor, Ceramic
50V/X5R
|
1206
|
TAIYO YUDEN
|
|
D1
|
1
|
SR26
|
60V/2A
|
D-SMA_DO-214AC
|
SMA/DO-214AC
|
PANJIT
|
|
L1
|
1
|
LSXNH8080YKL100MJG
|
10µH
|
L-8x8
|
|
TAIYO YUDEN
|
|
R1
|
1
|
WR06X1003FTL
|
100k
|
Resistor, Chip
0603
|
0603
|
WALSIN
|
|
R2, R5, R6
|
3
|
WR06X1003FTL
|
0
|
Resistor, Chip
0603
|
0603
|
WALSIN
|
|
R3
|
1
|
WR06W3304FTL
|
3.3M
|
Resistor, Chip
0603
|
0603
|
WALSIN
|
|
R4
|
1
|
WR06W3R30FTL
|
3.3
|
Resistor, Chip
0603
|
0603
|
WALSIN
|
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
|
Efficiency vs. Input Voltage
|
FB Reference Voltage vs. Input Voltage
|
|
|
|
|
FB Reference Voltage vs. Temperature
|
Frequency vs. Input Voltage
|
|
|
|
|
Current Limit vs. Input Voltage
|
LED Current vs. PWM Duty Cycle
|
|
|
|
Evaluation Board Layout
Figure 1. Top View
Figure 2. Bottom View