Skip to main content
Knowledgebase
Home
Renesas Electronics Europe - Knowledgebase

What happen if overshoot exceeds Vcc+0.3V and no regulation with SRAM?

Latest Updated:03/16/2012

Question:

Why is there no regulation for overshoot with asynchronous SRAM? What happens when overshoot exceeding Vcc+0.3V is inputted?

Answer:

When voltage exceeding VIH = Vcc + 0.3V is inputted, the current from the input pin to the Vcc line may flow through the parasitic diode in an SRAM internal circuit.
The threshold voltage of this parasitic diode is about Vt = 0.3V to 0.4V, and if voltage greater than Vcc+Vt is applied to an input pin, diode forward direction current will flow towards the Vcc line. Although a single instance of overshoot input won’t instantly damage the SRAM, if voltage exceeding Vcc+Vt is applied repeatedly, there is the risk of negative effects on the reliability of the device, and on device product life. In addition, since current flows into the power supply side, it also becomes necessary to consider the influence on the user’s system.
Therefore, there is no regulation for overshoot, but usage below Vcc+0.3V is requested (and Vcc+0.2V is recommended).
Suitable Products
Asynchronous SRAM