OE pull up resistance value for SN54LV573A

I happened to notice this note on the TI SN54LV573A datasheet (pg 2)...

formatting link

"To ensure the high-impedance state during power up or power down, OE should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver."

Could somebody with some digital logic experience explain the resistance value derivation. I am planning to use 5V supply for the device so the sink current is spec'd at 16mA. Also...why is there a minimum resistance value requirement for the OE ?

Reply to
gravpoet
Loading thread data ...

The sink current in question is that of the driver, not the '573.

To understand the minimum resistance requirement, consider what happens if you're driving the '573 with a part that can sink 2mA, and you use a 1 ohm resistor. That's kind of an extreme example -- but I should hope that it gets my point across.

You say 54LV573 -- I'm not familiar with that line. Is it bipolar, CMOS? The 'LV' would imply that it's not going to be happy at 5V, unless it works over some range of voltages.

At any rate, you want to choose a pull-up resistor that pulls the OE line up fast enough so that any glitches on the output of the part are unimportant, that the chip driving the '573 can overcome to pull the OE line low, and that doesn't cause excessive current consumption in your design.

"Fast enough" and "excessive" are both unspecific -- so you need to start by turning the one into a number in seconds, and the other into a number in amps.

--
Tim Wescott 
Wescott Design Services 
 Click to see the full signature
Reply to
Tim Wescott

The idea is to not burn up the device driving this part. That gives the minimum value. The maximum value is determined by the leakage of this node or the switching speed needed, if this is driven by an open-drain driver. Answer = 47K. ;-)

Reply to
krw

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.