The MP8040 has two control pins (PWM and SHDN) which control whether the half-bridge is in HIGH/LOW/OFF mode. The table appears to be as follows:
SHDN=0 and PWM=0 : Bridge => LOW side switched
SHDN=0 and PWM=1 : Bridge => HIGH side switched
SHDN=1 and PWM=0 : Bridge => OFF
SHDN=1 and PWM=1 : Bridge => OFF
The “normal” operating mode appears to be feeding a PWM signal into the PWM line to have the half-bridge operate in HIGH/LOW mode.
Is it possible to drive a fixed value into the PWM, and a PWM signal into SHDN to have the half-bridge operate in HIGH/OFF or LOW/OFF mode?
If so, is there a limit to the frequency, or can it still operate at the 1.2MHz PWM rate?
Thanks,
Hi Malcolm,
Welcome to the MPS Technical Forum! I’ll take a look at this for you. In the meantime, please note that the datasheet shows an example circuit using a PWM controller to drive SHDN. I will confirm the operation of the device if PWM is kept high/low while SHDN switches and if the frequency is limited in this scenario.
Hi Malcolm,
Do you have the rough schematic for this application? Are you attempting to use the MP8040 as just an HS-driver or LS-driver? There may be a problem for the HS-driver case as the MP8040 has no internal charge pump. The BS capacitor (Pin 5) powers the high-side gate of the MP8040 and the SW pin needs to be low level periodically to guarantee that the BS cap can be charged on time. For the LS-driver case, what is the SHDN PWM frequency you would like to run at?
