SN74LVC2T45: Power up sequence

narendar reddy

Part Number: SN74LVC2T45

Hi,

we are using SN74LVC2T45DCUT in one of our design, in datasheet it was mentioned VCCA comes first, later VCCB

but in our board we have power sequence, due to that VCCB coming 1st and later VCCB and inputs, so in this case this device can work as expect ?

this power sequence should be mandate ? coz we have freezes our design and cant do any modification!

kindly confirm whether this device will work as expect ?

ramp-up V1P8_V3P3 next v5a_val next input

Thanks,

Narendar

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 243910 points

The DIR input is powered by VCCA. So when VCCB powers up first, the state of the B pins is undefined. If they are inputs, everything is fine (all inputs are high impedance and overvoltage tolerant), but if they are outputs, they can randomly drive either high or low.

What is the desired state of the DIR input? What happens when the BOOT_LED2/3 signals are driven by the level shifter?

0 narendar reddy over 2 years ago in reply to Clemens Ladisch

Prodigy 210 points

Hi,

in my case DIR pin is high, so A side are the inputs B is output, here 5V(+V5A_VAL) LDO output is connected to V1P8_V3P3 LDO source

+1 Clemens Ladisch over 2 years ago in reply to narendar reddy

Guru 243910 points

So as far as I can see, the LEDs might show a wrong value for the short time the LDO takes to power up. I guess this is not a problem.

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SN74LVC2T45: Power up sequence