DS1780 Dallas, DS1780 Datasheet - Page 9

• Manufacturer Part Number: DS1780
• Description: CPU Peripheral Monitor
• Manufacturer: Dallas

The worse such accident would be connecting -12V to +12V; a total of 24V difference, with the series
resistors this would draw a maximum of approximately 24 ma.
The internal scaling factor depends upon the particular input. The +12V
inputs are internally scaled such that the nominal value of the respective supply corresponds to 3/4 of full
range, or a decimal count of 192. The approximate resolution is thus equal to:
This is depicted below in Table 5.
VOLTAGE/DATA RELATIONSHIPS FOR POSITIVE ONLY VOLTAGE INPUTS
(+12V
The other two voltage inputs use a slightly different scaling technique, due to the nature of the PC voltage
they are monitoring. Because processor voltage (V
inputs are internally scaled such that the ADC result is 0h for a 0V input and the maximum value of FFh
is returned for a voltage of 3.60V. This corresponds to an LSb weighting of 14.1 mV.
The inputs can also be used to monitor a negative supply, such as -12V. However, a resistor ladder and
positive reference voltage (V
swings between OV and +3.6V. Assuming the DS1780 +V
input impedance and the V
LSb (R
ADC RESULT (BASE
LSb WEIGHTING
INPUT PIN
1
IN
, R
(mV)
, +5V
190
191
192
193
252
253
254
255
10)
0
1
2
3
4
•
•
•
•
•
•
2
)
255
3.6
IN
, +3.3V
é
ê
ë
R
1
PIN VOLTAGE (V)
R
1
R
REF
2
IN
ù
, and +2.5V
+12V
REF
11.875
11.938
12.063
15.813
15.875
15.938
is a perfect supply, then the resolution and range of -12V input are:
0.063
0.125
0.188
15.75
62.5
0.25
12.0
0
•
•
•
•
•
•
) must be used (see Figure 1) such that input voltage to the DS1780
IN
LSb (V
IN
PIN VOLTAGE (V)
) Table 5
NOM
9 of 28
CCP
+5V
0.026
0.052
0.078
0.104
4.948
4.974
5.026
6.563
6.589
6.615
6.641
)
26.0
5.0
0
•
•
•
•
•
•
) can vary to 3.6V, the +V
IN
4/3
256
V
NOM
CCP1
PIN VOLTAGE (V)
and +2.5V
+3.3V
IN
0.017
0.034
0.052
0.069
3.266
3.283
3.317
4.331
4.348
4.366
4.383
17.2
3.3
, +5V
0
•
•
•
•
•
•
IN
S
/+V
IN
CCP1
, +3.3V
CCP2
and +2.5V
PIN VOLTAGE (V)
pins have infinite
IN
, and +2.5V
+2.5V
0.013
0.026
0.039
0.052
2.474
2.487
2.513
3.281
3.294
3.307
13.0
3.32
2.5
0
•
•
•
•
•
•
S
/+V
IN
CCP1
IN