Reference Design Note

DNS002 V2.0

Roland Kratz - December 2018

Page 4/8

Copyright © Würth Elektronik eiSos GmbH & Co. KG

4.5 Auxiliary Power

The linear regulator IC2 is used to supply the error amplifiers and the LEDs with 5V. In addition the potentiometers R29 and

R30 adjusts their set values from the 5V supply. The level shifters of the external error amplifiers which compensate the

input offset voltage are supplied as well from the 5V.

4.6 Optional Setting of Voltage and Current Using a Microcontroller

The output voltage and the output current limit can be dynamically set by PWM signals from a microcontroller. The

potentiometers must be disconnected and the PWM signals from the microcontroller must be connected to the appropriate

net where the wiper of the potentiometer was connected. The resistors R25 and R24 and the resistors R20 and R22

respectively scale down the PWM high state voltage to fit the end scale voltages of the actual values of the maximum output

voltage (1.37V) and the maximum output current (125mV).

4.7 Design Limitations

The maximum operating input voltage of 36V has been chosen to allow the use of 50V ceramic input capacitors and a linear

regulator in a very small package.