Question about PCA9555 spec

[scottlbaker]

Hi,

The band-select relay circuit uses an NXP PCA9555 (LCSC part number C128392).
According to the spec sheet (p.20) it can supply an Ioh current of 10mA with a Voh of 4V.
The relays require 21mA of current to switch. How does this reconcile?

73,
Scott

[scottlbaker]

I did some searches and found the PCA9555E which has better Ioh and Iol specs than
the standard PCA9555 part. I was not able to find the PCA9555E in stock but
the PCA9535E is compatible for this application and the DigiKey part number
PCA9535ECDTR2GOSCT-ND and it is (currently) in stock.

73,
Scott KJ7NLA

[mm0gyx]

Hi,

The band-select relay circuit uses an NXP PCA9555 (LCSC part number C128392).
According to the spec sheet (p.20) it can supply an Ioh current of 10mA with a Voh of 4V.
The relays require 21mA of current to switch. How does this reconcile?

73,
Scott

Page 18 indicates absolute maximum I/O current, it looks perfectly safe for 21 mA, doesn’t it? Also, it’s a short pulse.

I’ve used my (tr)uSDX for about a month now without any trouble from relay circuit.

73,

Ian

[OH2CBD]

So do both of you confirm that PCA9535E is compatible for this build? I already finished my first unit with proper TCA5555 but I'm building a second one and I only have this substituting parts available.

[OH2CBD]

In case somebody ever visits this topic I can confirm that NXP PCA9535PW works for U7 on the RF board. Mouser P/N 771-PCA9535PW-T

I have also onsemi PCA9535ECDTR2G on hand and I will check if it works on later builds.