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TIDA-00653: Schematic of Bi-Directional Firmware for TIDA-00653

Part Number: TIDA-00653


Can you explain the role of these capacitors in this schematic (tidrl18.pdf  P4)?


(1)Are the two large capacitors C47 and C48 designed to protect the battery?

(2)What is the role of four 1nF capacitors in series and four 1uF capacitors in series?

  • Hello Scarecrow

    1/ Yes - C47 and C48 are both intended to protect the batteries from high frequency currents.

    C47 is part of a filter network whose function is to  to provide a low impedance source for the high frequency pulse currents which are present in the input to the power stage (eg. through Q5) so that these currents do not have to be sourced from the battery. Batteries, in general don't like high frequency pulsating currents - either while charging or discharging. The filter network also serves to attenuate the ripple currents coming from the power stage while the power flow is in the other direction.

    C48 is part of the filter between the 12V battery and the power stage - its function is the same as C47.

    2/ The four capacitors in series are actually two sets of two capacitors in series. C43 & C46 connect from Bat_12V to Chassis (E) and C55 & C58 connect from PGND to Chassis (E). The 1nF capacitors, (C39 etc) have the same arrangement. Their function is to provide common mode filtering of noise currents by bypassing them into the Chassis.

    BTW: Two capacitors in series are sometimes used where a single part would suffice in order to provide protection against one of the capacitors failing short circuit.