Remedies

AN1009

2

Remedies

ST is continually making design and process modifications to improve the performance of

its products. Immunity to negative undershoot will be improved over time, but only where it

does not have a negative impact on other performance measures, such as operating

speed.

The application designer is, therefore, advised to take steps to avoid negative undershoot

pulse from being introduced. The first step is to improve the cleanliness of each of the

signals. Table 1: "List of the pins on devices that are affected by the problem"lists the pins

of ST’s NVRAMS that are affected (those that consist of an N+ diffusion in a P-well on an

N-type substrate).

Table 1: List of the pins on devices that are affected by the problem

Device

Substrate type

Pins connected to N+ diffusion

M40Z111

N-

13, 16

M40Z300

N-

4, 10, 13, 16, 20, 22, 23

M48Z02, M48Z12

N-

All

M48Z08, M48Z18

P-

None (not applicable)

M48Z58, M48Z58Y

N-

1, 11-13, 15-19, 26, 28

M48Z35, M48Z35Y

N-

All

M48T02, M48T12

N-

All

M48T08, M48T18

P-

(none) not applicable

M48T58, M48T58Y, M48T59, M48T559

N-

1, 11-13, 15-19, 26, 28

M48T35, M48T35Y, M48T35AV

N-

All

M48T37V, M48T37Y

N-

1, 4-10, 13, 15-20, 22-26, 30, 31, 33-39

All pins that are connected to N+ diffusion are susceptible to negative undershoot, but

increases the pin’s sensitivity to negative undershoots, to the extent that pulses of greater

than -0.3 V may affect the substrate voltage.

diode, to short out any attempt by them to go negative. Its effectiveness depends on its

speed of operation set against the speed and energy content of the negative-going pulse

0.32 V, and a current rating of 100 mA, will generally reduce the occurrence of the problem

to negligible proportions. However, the higher the current sink capability of the negative

pulse, the more likely an RF Schottky diode is required.

The Schottky diode should be placed as close to the device pin as possible.

spikes coming from the power supply during initial power up. The third step, then, is to

clean up the power supply, particularly its behavior at power-on and power-off, where the

memory device is expected to continue to power itself from its internal battery. Particular

care should be taken when working with programmable power supplies. Forcing a

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