Specifications

Élan™SC310 Microcontroller Data Sheet 73
PRELIMINARY
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.
T
A
= 70°C, V
OL
TTL
= 0.4 V, V
OH
TTL
= 2.4 V
I/O Drive Type VCCIO (V) IOL
TTL
(mA) IOH
TTL
(mA)
1
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