We were trying to power up M590E GSM GPRS module Diy kit and ATMEL ATMEGA328P-PU micro-controller with LM2596S-ADJ DC-DC Step Down Buck Converter Power Module. We rotated the pot in the power module and made output voltage to 4.5 volts that is going as input voltage to the above-mentioned GSM module and micro-controller. The output current of the power module is 3 Ampere whereas maximum current draw by GSM module is 2 Ampere and micro-controller withdraws 5 milliAmpere (Internal RC oscillator of 8 MHz). But what happened after connecting GSM module and micro-controller to power module is, that power module output becomes 7.2 volts. As per the datasheet of the above-mentioned power module, it's having a maximum load regulation of .5 %. The voltage will change by no more than 23 millivolts as per specification. But it's changing by approximately 2.7 volts.
Can you kindly explain the reason behind the unstable behavior of the power module?