Datasheet

Input/Output Connections
2-2
2.1 Input/Output Connections
The TPS61042EVM226 PWB has several connections, which are described
in Table 21.
Table 21.Input/Output Connections
Reference
Designator
Name Description
J1 Vin This is the positive connection to the input power supply. The leads to the input supply
should be twisted and kept as short as possible.
J2 GND This is the return connection for the input power supply
J3 ADJ Input for dimming adjust of LED current
J41 ON Connect J42 (CTRL) to J41 (ON) with a shorting jumper to enable the supply
J42 CTRL CTRL
J43 OFF Connect J42 (CTRL) to J43 (OFF) with a shorting jumper to disable the supply
2.2 EVM Operation
The EVM is configured as a constant current supply. Current regulation is
accomplished by regulating the voltage across a current sense resistor. The
EVM does not operate correctly unless a load is present. The EVM is shipped
with four white light LEDs as a load. If these are removed, they must be
replaced with another load that falls within the voltage and current limit specs
of the device. The TPS61042 has built-in overvoltage protection to keep the
EVM from being damaged under a no-load condition.
This EVM is designed to accommodate several LED-dimming techniques.
Because of this flexibility, circuitry may be present on the EVM that is not
needed for the particular dimming method that the user chooses. Depending
on the PWM dimming technique used, component values may need to be
changed to provide the desired LED current level. The first step to be
completed before the EVM is used is to determine the method of dimming.
Several dimming techniques are described below.
2.2.1 Analog Dimming With Analog Voltage
One method for dimming the LEDs is to inject a voltage through a resistor into
the FB pin of the TPS61042. The injected voltage artificially raises the voltage
seen at the FB pin, which lowers the LED current. If the resistor values are
chosen correctly, the analog control voltage varies the output current from
0mA to full LED current. This dimming method is accomplished by injecting an
analog voltage into the ADJ pin on J3. The equations below calculate the
required resistor values where:
- V
ref
is the TPS61042 reference voltage = 0.250 V
- V
adj_min
is the minimum adjust voltage
- V
adj_max
is the maximum adjust voltage