Hello Team,
Could you please advise us if following design is acceptable for TCA6424A ?
Customer is planning to add 10k pull down resistor to each P-port output as the connected device requires low level at system power up.
(VCCI=1.8V, VCCP=3.0V, /RESET pin is pulled up to VCCI through 10k Ohm.)
[Q1]
Is this 10k pull down at P-port output acceptable ?
[Q2]
Can TCA6424A drive enough VOH (MIN 2.6V) with 1k pull down at P-port output pin ?
Best Regards,
Kawai
Hello Kawai-san,
[Q1] This is acceptable.
[Q2]The TCA6424A can drive a high to VOH above 2.6V with 1k resistor (did you mean 10k here, or were you actually meaning 1k?).
When looking at the specs:
We see that for a given Vccp and a given Ioh (load) we get a min Voh. Say for example you are operating at Vccp=3V, and we are forcing a Ioh = 10mA. Internally there is a FET that is turned on that is connected from Vccp to the output. That FET's max resistance is (Vccp-Voh)/Ioh, in this example we have (3V-2.5V)/10mA = 50 Ohms. Is the load is not a constant current source and is a resistance, then just treat it as a voltage devider to determine what the voltage will be on the output pin. NOTE: The lower the Vccp the higher the resistance, which makes sense because the Vgs is being reduced and the Ron of a FET gets lower with lower Vgs.
Please let me know if this is clear and if not I can draw a diagram.
-Francis Houde
