pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 173

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
Embedded Controller Modules
4.11.3 Voltage Measurement
The ADC performs a linear conversion of the input voltage signal to a 10-bit, unsigned digital representation. The input signal
should be applied relative to the AGND pin and should range from 0V to V
The equations in the folowing table should be used to calculate the input voltage based on the reading from the Voltage
Channel Data result (VCHDAT field in VCHiDAT register).
An input signal of zero (ground) is converted to 000
Changing the input selection for a new measurement requires switching between inputs at different voltage levels. The input
interface circuits of the ADC, together with the externally added noise-rejection filters (if applicable), require a settling time
to reach the new voltage value with a 10-bit accuracy (less than 1/2 LSB error). Therefore, the ADC waits for a programma-
ble delay time between the selection of the input to be measured and the beginning of the A/D conversion. This Voltage
Channel Delay is expressed in ADC clock cycles in ADC Delay Control register (ADLYCTL). The number of ADC clock cy-
cles should be converted to time using the following formula:
To calculate the required delay value according to externally added components, see Section 4.11.7 on page 185.
4.11.4 Temperature Measurement
The ADC performs a linear conversion of the temperature, measured by a remote or a local diode, to an 8-bit, 2s complement
digital representation. The ADC generates a current that flows through the diode and measures the resulting voltage drop.
This differential voltage is converted to an 8-bit value, with the LSB equal to 1 C, according to Table 22.
AD0 to AD9
AD0 to AD9
AD10 to AD13
Input Channel
1. See Section 7.4.1 on page 378 for the dynamic range relevant for each input.
2. High Scale is undefined for these inputs.
3. These inputs are scaled down by 4 at the input and compensated back at the result read phase.
t
VD
= Number_of_ADC_clocks
1. Values higher than +125 C and lower than 40 C
are not within the specified operating temperature range.
Low
High
Low
Scale
2,3
Table 22. Temperature Format Conversion
Temperature
Vi = VCHDAT(9-0) * (1 / 1024) * V
Vi = VCHDAT(9-0) * (1 / 1024) * V
Vi = VCHDAT(9-0) * (1 / 1024) * V
+127
+125
+100
( C)
+40
+25
128
+1
(Continued)
0
25
40
1
1
1
16
; an input signal equal to (1023/1024)
Temperature Channel Data
0111 1111
0111 1101
0110 0100
0010 1000
0001 1001
0000 0001
0000 0000
1111 1111
1110 0111
1101 1000
1000 0000
Binary
173
*
(System_clock_cycle)
Calculation
FS
7D
FF
E7
D8
7F
64
28
19
01
00
80
Hex
(Full Scale).
FSL
FSH
FSV
16
16
16
16
16
16
16
16
16
16
16
1
*
V
FS
is converted to 3FF
*
SCLKDIV(5-0)
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16
.