Part Number: TPS61178
Tool/software: WEBENCH® Design Tools
I’m going to use TPS61178 in my design. I selected this device because it supports output overvoltage and short protection. I designed it by Webench with the following parameters: Vin=2.75V to 4.2V Vout= 4.4V Iout=1.5A Temperature=40
I got the design with the recommended external P-channel FET of Vishay SI5499DC. The maximum Vgs of SI5499DC is 5V. But the Rgate calculated by the Webench is 162K. Equation from TPS61178 datasheet shows:
Vgate=Rgate * Idis_pfet Vgate=162K * 55uA Vgate=8.91V that is much higher than the Vgs absolute maximum of the FET SI5499DC. 1. Does the Webench calculated the Rgate correctly or I do not understand something? 2. SI5499DC has Vgs and Vds maximum of 5V and 8V respectively. That means by using this FET, the 23V Vout absolute maximum of TPS61178 will not be met by this design (when somebody connects voltage of 23V to the output). Am I right?
Attached image of the schematics:
Best Regards, Ramin
We are looking into it. We will get back to this soon.
Thanks & Regards,Praveen
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In reply to Praveen Badiger:
Do you have any answers for me?
In reply to Ramin Rahamim:
Currently, the calculation of Rgate resistor on WEBENCH is not dependent on the Vgs value. We will update the component selection and fix this issue. The second query about the VDS max rating of FET for short circuit protection, We are still looking into it. We will keep you updated on this.
We are working on this. We will keep you updated.
Thanks & Regards,
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