4116 RAMs: -5V must be applied first and removed last for long term reliability?

neither the NEC uPD416 or the TI TMS4116 datasheet make any reference to timing of the -5v, 5v or 12v power

have a look at the Williams Defender documentation - theory of operation
 
I've alwasy heard that too... so I went to datasheetarchive.com and looked up the MK4116 chip and pulled up Mostek's app guide.

It says this in the MK4027/4116 Application Guide:

The data sheets for the MK4027 and MK4116 state that no special power sequencing is required for proper device operation. This does not mean that the power sequencing should be ignored. In many systems the power supply lines exhibit overshoot on power up. This can cause Vdd at the memory to exceed data sheet limits for a short period of time. If Vbb is not applied when Vdd overshoots, breakdown can occur and destroy the memory. If a system does have this overshoot, sequencing the supplies so that Vbb is appliaed first will provide extra margin and help prevent device destruction.

It also states that "Vbb should not be allowed to go positive with respect to ANY other input. If it does, injection currents can occur and cause loss of functionality." In other words, be careful with your logic probes and scope probes. :)

So.... Yes, applying power in the proper order isn't necessary unless your power supply overshoots. If it does you could end up with fried chips.
 
Excellent explanation. In that 4116 era, since we could not control the power supplies used in some applications, we would often use a germanium diode in series from the power trace to the power pin on the ic to prevent reverse injection current flow until everything stabilized. It cost you a 0.2 VDC voltage drop across the diode, but it was worth protecting the components, especially expensive CMOS DACs or ADCs which were especially sensitive to power supply sequencing and had no internal protection like the newer ones available today.

Bill



I've alwasy heard that too... so I went to datasheetarchive.com and looked up the MK4116 chip and pulled up Mostek's app guide.

It says this in the MK4027/4116 Application Guide:



It also states that "Vbb should not be allowed to go positive with respect to ANY other input. If it does, injection currents can occur and cause loss of functionality." In other words, be careful with your logic probes and scope probes. :)

So.... Yes, applying power in the proper order isn't necessary unless your power supply overshoots. If it does you could end up with fried chips.
 
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