How to read datasheet

1. How To
How To
Read Datasheet
Electrical Specification
t h l ti t
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1

2. What Where Why
What Where Why
Electrical Specification
Read all Information?
DC value gives the
 Not necessary
Not necessary.
driveability, consumption
Two main classifications values
 DC AC value provides detail in
 AC timing requirement
What Type of Specifications?
 Guaranteed‐minimum Min & Max values are use for
design consideration, whereas
 Guaranteed‐maximum typical value are purely used as
 Typical an indication only
 Guaranteed‐but‐not‐tested
Under what Conditions? The data provided will be
based on certain condition If
condition.
 Operating Temperature operation is out of this range,
 Voltage the data will not be guarantee.
 Load Condition Thus a chart is normally
Other
Oth provided f f th
id d for further
 Recommended circuitry information
Design have to abide to the chip specification.
This is to ensure a reliable & quality product
The following slides extracted some examples. 2

3. Maximum Rating
M i R ti
This will always appear in the 1st page of the data sheet
Supply < 7V
IO signal < V (7V)
i l Vcc
System operation
temperature < 75 ºC
The chip will be damage if operating at this range
3

4. DC Characteristic
DC Ch t i ti Test Conditions
Make sure-
right comparison is make:
Eg.+
Eg + 1 % error at 25 ºC has no
meaning in design
consideration
Values for Vcc
ranging 4- 5.5V
VIH - minimum input voltage
p g Note: Different requirements when
q
into the chip, so that this is Conditions are different.
recognized as a “High” level.
Ie Input signal must be more The input shall not exceed this
than 0.8Vcc. Maximum value
VIL - maximum input voltage
p g
into the chip, so that this is
recognized as a “Low” level.
I.e. input signal must be less
than 0.2Vcc
4

5. DC Characteristic
DC Ch t i ti VOL - maximum output low
voltage out of the chip. I.e.
when the chip output a “Low”,
the i
th signal will not exceed
l ill t d
0.6V.
Different Port
Pins may have
different
drivability
d i bilit Note that the Max Value of
VOL is different at different load
condition (IOL)
This will determine what can
the port drive, such as LED.
Take note of extra comment
On Test conditions
5

6. DC Characteristic
DC Characteristic
This part show how much
current the chip itself will
consume at each particular
mode
Note the allowable current for
each & total pins.
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7. AC Characteristic
AC Ch t i ti Timing requirement for Serial Port
Take note of the units
This may in nsec, or relative to
some other reference
Find the symbol in the timing
diagram to understand what does
it really mean.
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8. Timing requirement for Bus Access
Read Cycle
Write Cycle
8

9. Timing Requirement for Bus Access
Timing Requirement for Bus Access
Write Cycle
The Chip Datasheet provide how fast
the data and control signal are being
g g
output.
Check point  external chip:-
Can the external device (RAM, Chip)
( , p)
be able to “latch” in this data?
Read Cycle
y
The Chip Datasheet provide the
specification on how can the external
data be “latched-in” to the chip.
Check point  This Chip:-
Can the external data remained on
the data bus “long” enough to meet
the minimum setup timer ( RDS) &
p (t
hold timer (tRDH)
Setup time Hold time
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10. Operating Conditions/ Range
O ti C diti / R
Data in the table is limited to the Test condition.
Thus X-Y axis Graph is also provided to show the relative
operating condition
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11. Circuitry
Very Important
Connection
requirement
Suggested use for high current
port
Test Condition
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12. Pin States
Pi St t
The states of each Pin at each
operating mode is important in
the system design.
Example:
If power up state is “High
Impedance”, It will be important
to have a pull up resistor to
pull-up
have a clear define state. This
will prevent data contention, or
even sudden activation of a
motor.
motor
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13. Pin ‐ Internal Configuration
Pi I t l C fi ti
Pull Up MOS for extra current
drive
Output Control
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