SN74ACT244: SN74ACT244 output is not stable when the device is in power up process

Wayne Wang20

Part Number: SN74ACT244

Hi team,

My customer is testing SN74ACT244. When the whole system is in power up status, we captured below waveform:

CH1: OE. OE is always 0V

CH2: output.

When VCC just rises up from 0V, output will follow VCC to rise up
When VCC gets to ~1.5V, output drops to 0V
When input signal begins to rise up, output begins to follow input signal to rise up.

CH3: input. input is from C2000 GPIO

CH4: VCC power supply

So the unregulated output signal will trigger some unwanted action. So can you help check how to avoid this issue during power up?

Best regards,

Wayne

0 Clemens Ladisch over 5 years ago

Guru 316440 points

While the supply voltage is outside the recommended operating conditions, the device is not guaranteed to work correctly.

Section 8.1 of the datasheet says:

To ensure the high-impedance state during power up or power down, OE should be tied to V_CC through a pullup resistor.

0 Chad Crosby over 5 years ago

Hi Wayne,

See Clemens' reply. It is recommended that the device's OE pin be pulled HIGH during powerup or powerdown.

Thanks!

Chad Crosby

Logic forum