ELANSC310 datasheet(73/119 Pages) AMD

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Élan™SC310 Microcontroller Data Sheet

PREL IMINARY

DERATING CURVES

This section describes how to use the derating curves

on the following pages in order to determine potential

specified timing variations based on system capacitive

loading. The pin characteristics tables in this document

(see page 21) have a column called “Spec. Load.” This

column describes the specification load presented to

the specific pin when testing was performed to gener-

ate the timing specification documented in the “AC

Characteristics” section of this data sheet.

For example, to find out the effect of capacitive loading

on a DRAM specification such as MWE hold from CAS

Low, first find the specification load for MWE from the

pin characteristics table. The value here is 70 pF. Note

the output drive type is D. Also, assume that the system

DRAM interface is 3.3 V and our system load on the

ÉlanSC310 microcontroller’s MWE pin is 90 pF.

Referring to Figure 13, 3.3 V I/O Drive Type D Rise

Time, a time value of approximately 9.8 ns corresponds

to a capacitive load of 70 pF.

Also referring to Figure 13, a time value of approxi-

mately 12.3 ns corresponds to a capacitive load of 90

pF. Subtracting 9.8 ns from the 12.3 ns, it can be seen

that the rise time on the MWE signal will increase by

2.5 ns. Therefore, the MWE hold from CAS Low (min)

parameter will increase from 15 ns to 17.5 ns (15 ns +

2.5 ns).

If the capacitive load on MWE was less than 70 pF, the

time given in the derating curve for the load would be

subtracted from the time given for the specification

load. This difference can then be subtracted from the

MWE hold from CAS Low (min) parameter (ISNS) to

determine the derated AC Timing parameter.

Table 42.

I/O Drive Type Description (Worst Case)

Notes:

1. Current out of pin is given as a negative value.

TA= 70°C, VOLTTL = 0.4 V, VOHTTL = 2.4 V

I/O Drive Type

VCCIO (V)

IOLTTL (mA)

IOHTTL (mA)

A3.0

4.5

2.6

3.7

–3.5

–13.9

B3.0

4.5

5.1

7.3

–5.2

–20.7

C3.0

4.5

7.7

10.8

–8.6

–34.2

D3.0

4.5

7.7

10.8

–10.3

–40.8

E3.0

4.5

10.2

14.1

–13.6

–53.9

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