SN74LV595A: questions

Allan Fan

Part Number: SN74LV595A
Other Parts Discussed in Thread: SN74LVC595A, TLV809E, SN74LV594A

Hi Expert,

Customer used SN74LVC595A for led driving and they want to light led right away when power up(before clocks timing triggered). Checked DS the initial output Qx status seems cannot be sure, correct?

What would you suggest to fulfill customer's need? Any concerns if implement like this?

Thanks,.

Allan

over 3 years ago

+1 Clemens Ladisch over 3 years ago

Guru 281470 points

A pull-down resistor will not help.

Use a device like the SN74LV594A that can reset the output registers with the /RCLR input. (Use a reset IC like the TLV809E, or a simple R+C circuit.)

What is the forward voltage and the desired current of the LED? 33 Ω is quite small, and similar to the LV output impedance.