Other Parts Discussed in Thread: SN74LV123A
Hi, team.
If the Cext of SN74LVC1G123 is large, is a protection diode necessary?
In the case of SN74LV123A, there are the following descriptions, but there is no description in SN74LVC1G123.
10.2.1.1 Power-Down Considerations
Large values of Cext can cause problems when powering down the 'LV123A devices because of the amount of
energy stored in the capacitor. When a system containing this device is powered down, the capacitor can
discharge from VCC through the protection diodes at pin 2 or pin 14. Current through the input protection diodes
must be limited to 30 mA; therefore, the turn-off time of the VCC power supply must not be faster than t = VCC ×
Cext/30 mA. For example, if VCC = 5 V and Cext = 15 pF, the VCC supply must turn off no faster than t = (5 V) ×
(15 pF)/30 mA = 2.5 ns. Usually, this is not a problem because power supplies are heavily filtered and cannot
discharge at this rate. When a more rapid decrease of VCC to zero occurs, the 'LV123A devices can sustain
damage. To avoid this possibility, use external clamping diodes.
Best Regards,
