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Add basic comparison between STUSB and TPS

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Folkert Kevelam 2024-11-25 22:28:40 +01:00
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@ -39,7 +39,44 @@ standard uses it.
- STUSB4500
- STUSB4500L
- Some Texas Instruments chips
- TPS25730
- TPS25751
#### Comparison
All of the PD chips can basically run in auto-run mode--also called
dead battey mode. Since Ethy does not have any battery, the PD devices
have to be able to auto-configure or atleast allow for the standard 5V
output of the USB. The STUSB4500 are specc'ed for USB type-C rev 1.2
(for STUSB4500) and type-c rev 1.4 (for STUSB4500L). Both seem to function
with the PD rev 2.0 standard. However, according to the STUSB4500 documentation
it is interoperable with USB PD rev 3.0
Both the TPS devices are built for USB PD rev 3.1.
The biggest difference, to me, seems to be the control of an external
power path. The STUSB devices can only function with an external power path
while the TPS devies also have an internal power path. The biggest difference
however, is the type of switch that can be used for each chip.
The STUSB4500 and STUSB4500L have active drain outputs, meaning that the
switches should be based on P-channel MOSFETS, as uses in their reference
design. The TPS devies have an internal charge pump which means they can
use N-channel MOSFETS. N-channel MOSFETS generally have a smaller footprint
and smaller R_ds(on) than the P-channel counterparts. This can be seen in
the reference designs of PD IC's. The TPS chips use the CSD87501L dual common
drain n-channel from Texas Instruments. This dual channel MOSFET has a
source-to-source R_ds(on) of 6.6 milliOhm at a Gate Source Voltage of 10 V.
For the maximum load of 12V @ 5A, the power loss would be around 165mW.
Comparing to the P-channel MOSFETS in the STUSB chips, the reference design
uses the STL6P3LLH6 MOSFET from STM. This MOSFET has a maximum R_ds(on) of
around 30milliOhm. at 5A this would result in 0.75 W of loss. Considering
that both designs need two MOSFETS, the loss in the MOSFETS for the STUSB chips
would be around 1.5W.
This difference in power loss can also be seen in the package size, since
the CSD87501L is half the size of a single STL6P3LLH6 MOSFET.
#### Possible DC/DC chips for controllers