Texas Instruments TPS61042EVM-226, User Manual, Page: 14 / 22

Setup
2-4
2.2.3 PWM Dimming Using CTRL
The third method for dimming the LEDs is to inject a PWM voltage into the
CTRL pin of the TPS61042. The LED current is proportional to the CRTL pin
duty cycle. Refer to the TPS61042 data sheet for more information on this
dimming method. For this dimming method, R2 and R3 are not needed. R2
may be shorted and R3 may be removed if desired. R1 is calculated by the
following equation where V
ref
is the reference voltage of the TPS61042
(0.25 V) and I
out_max
is the maximum desired output current. The reference
designators correspond to the EVM schematic shown in Chapter 4.
R
1
+
V
ref
Io_max
For an output current of 20 mA, R1 = 12.5
Ω
.
2.3 Setup
After the EVM has been modified for the appropriate dimming method,
connect an input supply between J1 and J2. The EVM operates with an input
voltage between 1.8 V and 6.0 V. The user must ensure that the input voltage
never exceeds the part’s absolute maximum input voltage rating of 7.0 V. To
enable the supply, move the jumper on J4 so that the CTRL pin is connected
to the ON pin. The EVM comes preloaded with four white light LEDs; therefore,
no external load is required for the EVM to operate properly.