Texas Instruments TPS92691, User Manual, Page: 12 / 25

AGND
PWM
VCC
IADJ
COMP
V
CS
+
Rail to Rail
CS Amplifier
(Gain = 14)
TPS92691-Q1
+
V
IS
R2 R3
R4*
R23*
C26 C25
TP5
IADJ
2.4V
I
L E D
=
V
I A D J
1 4
1
R
C S
Performance Data and Typical Characteristic Curves
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6.5 Analog Adjust Settings
LED current can be varied from 100 mA to 1.7 A by varying the voltage at analog adjust, IADJ pin from
140 mV to 2.4 V, respectively. The EVM is configured with the IADJ voltage, V
IADJ
, set to 420 mV using
resistor divider network, R23 and R4 between VCC and GND. The resulting LED current is 300 mA for a
current sense resistor, R
CS
= R5, of 100 m Ω . Calculation is based on:
The desired LED current can be achieved by setting the corresponding voltage, V
IADJ
and reconfiguring the
resistor divider network, R23 and R4. The internal reference clamp of 2.4 V can be activated by
depopulating resistor R4 and connecting IADJ to VCC through pull-up resistor R23.
External control via IADJ test point, TP5 can be enabled by depopulating resistor R23 and R4. The IADJ
voltage and hence the LED current can be modulated over the entire operating range by connecting a DC
power supply or a function generator across TP5 to GND. To ensure proper operation and limit
temperature rise, the maximum output power should be limited to 25 W for any given LED stack voltage
and LED current combination.
* Depopulate resistors prior to connecting external signal to IADJ test point, TP5
Figure 16. Circuit Configurations to Set Analog Adjust Reference Voltage
12 TPS92691 SEPIC LED Driver Evaluation Board SLVUAL8 – December 2015
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