M40Z300MH1F(2007) Ver la hoja de datos (PDF) - STMicroelectronics

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M40Z300MH1F
(Rev.:2007)

5V or 3V NVRAM supervisor for up to 8 LPSRAMs

STMicroelectronics 

Operation

M40Z300, M40Z300W

2.1

Two to four decode

The M40Z300/W includes a 2 input (A, B) decoder which allows the control of up to 4

independent SRAMs. The Truth Table for these inputs is shown in Table 2.

Table 2.

Truth table

Inputs

Outputs

E

B

A

E1CON

E2CON

E3CON

E4CON

H

X

X

H

H

H

H

L

L

L

L

H

H

H

L

L

H

H

L

H

H

L

H

L

H

H

L

H

L

H

H

H

H

H

L

Figure 6. Address-decode time

A, B

tAS

Note:

E

tEDL

tEDH

E1CON - E4CON

AI02551

During system design, compliance with the SRAM timing parameters must comprehend the

propagation delay between E1CON - E4CON.

2.2

Data retention lifetime calculation

Most low power SRAMs on the market today can be used with the M40Z300/W NVRAM

SUPERVISOR. There are, however some criteria which should be used in making the final

choice of which SRAM to use. The SRAM must be designed in a way where the chip enable

input disables all other inputs to the SRAM. This allows inputs to the M40Z300/W and

SRAMs to be “Don't Care” once VCC falls below VPFD(min). The SRAM should also

guarantee data retention down to VCC = 2.0V. The chip enable access time must be

sufficient to meet the system needs with the chip enable propagation delays included. If the

SRAM includes a second chip enable pin (E2), this pin should be tied to VOUT.

If data retention lifetime is a critical parameter for the system, it is important to review the

data retention current specifications for the particular SRAMs being evaluated. Most SRAMs

specify a data retention current at 3.0V. Manufacturers generally specify a typical condition

for room temperature along with a worst case condition (generally at elevated

temperatures). The system level requirements will determine the choice of which value to

use.

The data retention current value of the SRAMs can then be added to the IBAT value of the

M40Z300/W to determine the total current requirements for data retention. The available

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