I do with the Tps61021A voltage boost, battery power input voltage 3.0V, output voltage 3.9V, to the GPRS module power supply,with the 2A peak current in burst mode of the GSM , Burst time 577us, normal time 4.6ms, Tps61021 voltage output in the Burst timing for 3.7V, Burst at the end of the voltage for 4.1V, Please look at how to solve