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New FETs with lower Rds_on

A project log for USB-C Power Delivery Sink (BCR)

A USB-C PD Sink up to 20V 5A based on the Cypress CYPD3177 USB PD Controller

MagicWolfiMagicWolfi 08/17/2020 at 02:180 Comments

 Time passes...

I finished the design of Rev4 (and Rev3 in between). Most important improvement is a 2nd switch to select the current and new switching FETs . The new FETs have a Rds_on of only 9.5 mOhm (at Vsg = 4.5V), which cuts the dissipation almost in half and keeps the board cooler, even with 5 A current draw.

This FET is the AON7407.

And I did a measurement with 24 boards, which showed to real Rds_on to be 7.1mOhm onaverage, because the Vsg is ~15V at the 20V setting. Also the calculated junction temperature is quite low and much more manageable now.

Results (fixed width font anybody?):

Vfet*2    Vload    I load    P load    P fet    Tjunc    Rds on
73.3        19.55    4.89    95.55    0.358    47.4    0.0075
72.5        19.58    4.90    95.84    0.355    47.2    0.0074
70.2        19.6      4.90    96.04    0.344    46.5    0.0072
69.3       19.6      4.90    96.04    0.340    46.2    0.0071
71.2         19.55    4.89    95.55    0.348    46.7    0.0073
68.6        19.65    4.91     96.53    0.337    46.1     0.0070
71.2         19.59    4.90    95.94    0.349    46.8    0.0073
68.1         19.68    4.92    96.83    0.335    45.9    0.0069
69.7        19.67    4.92     96.73    0.343    46.4     0.0071
68.5        19.67    4.92    96.73    0.337    46.1      0.0070
68.4       19.7      4.93     97.02    0.337    46.1      0.0069
68.7        19.7       4.93    97.02    0.338    46.1      0.0070
72.8        19.69    4.92    96.92    0.358    47.4    0.0074
69.5       19.71     4.93     97.12     0.342    46.4    0.0071
70.6       19.71     4.93     97.12     0.348    46.7     0.0072
68.3       19.72    4.93     97.22    0.337    46.0    0.0069
68.4       19.71     4.93     97.12     0.337    46.1      0.0069
70.7        19.71     4.93     97.12      0.348    46.8    0.0072
71.1          19.7      4.93     97.02     0.350    46.9    0.0072
68.4       19.7      4.93     97.02     0.337     46.1     0.0069
70.2       19.68    4.92     96.83    0.345    46.6    0.0071
73.5       19.68    4.92     96.83    0.362    47.6     0.0075
68.4       19.7      4.93     97.02     0.337    46.1      0.0069
70.6       19.7      4.93     97.02     0.348    46.7     0.0072
                                                         Average:      0.0071

PS: I just could not bring myself to copy every single cell into the table here.

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