Optimizing EVM Performance Based on LED String Voltage and Current
7
Optimizing EVM Performance Based on LED String Voltage and Current
The default EVM schematic is configured to operate over a wide range of LED currents (100 mA to 1.7 A)
and string configurations (1 to 20 LEDs). The driver operation, efficiency and transient response can be
improved by re-configuring the schematic for a given LED current and LED string forward voltage drop.
The LED current sense resistor, (R
CS
= R5 = R17) value can be calculated based on the maximum
allowable differential voltage of 172 mV which is achieved by pulling the IADJ pin to VCC through an
external resistor. The slope compensation voltage can be adjusted by changing the switch current sense
resistor, R
IS
= R15, based on the maximum expected LED stack voltage. The proportional integral
compensation network can be tuned to achieve high bandwidth and desired phase margin for a specified
range of input and output voltages. For more details and design procedure refer to the TPS92691-Q1
datasheet.
8
TPS92691EVM-001 Assembly Drawing and PCB layout
, and
show the design and assembly of the TPS92691EVM-001 printed
circuit board.
Figure 32. Assembly Drawing
17
SLVUAL8 – December 2015
TPS92691 SEPIC LED Driver Evaluation Board
Copyright © 2015, Texas Instruments Incorporated