pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 194

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

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Embedded Controller Modules
DAC Data Channel 0-3 Registers (DACDAT0-3)
These registers hold the data to be loaded into Channels 0-3 of the DAC. These registers are not affected by reset or disable
of the respective channel.
Location: Channel 0 - 00 FF42
Type: R/W
4.12.6 Usage Hints
Power Consumption
When a channel is enabled and no load is connected, the DAC current consumption depends on the value set in DACDAT
register. Minimal current is consumed when the data is 00
DAC Output Protection
To maintain the high performance of the analog circuits, the DAn (n=0 to 3) pins are not back-drive protected. Therefore, the
voltage applied to these pins must be within the AGND to AV
External circuits should not drive currents into these pins when the PC87591x is not powered up, because this may cause
the internal power-up reset circuit to fail.
Output Voltage Accuracy
Besides the intrinsic accuracy of the D/A channels, the output voltage accuracy directly depends on the accuracy of the
AV
AV
DACDATA7-0 in DACDATn registers (see Section 4.12.3 on page 190).
The external load on DA0-3 pins may also affect the final output voltage of the DAC. Since the output resistance of these
pins is typically 3 K
drivers.
For the worst case calculation, if the output resistance is 4 K
than 2 M
To work with loads of 3 K (1 mA at 3V) with an error lower than 1/2 LSB, the output resistance of the external driver should
be lower than:
Bit
Name
7-0
Bit
CC
CC
power supply, which serves as reference voltage. In order to improve the accuracy of the output voltage, the actual
value, measured by the ADC module (see Section 4.11 on page 170), should be used when computing the value of
DAC Data. 8-bit unsigned binary value used for the D/A operation.
Channel 1 - 00 FF44
Channel 2 - 00 FF46
Channel 3 - 00 FF48
see Figure 68). In this case, the error caused by the load is lower than 1/2 LSB.
7
use high-impedance loads; if high accuracy or high output currents are required, use external analog
16
16
16
16
R
6
OEXT
< 3 K
(Continued)
5
/ (2
*
16
256) = 5.8
Description
194
; maximum current is consumed when the data is 55
4
CC
DAC DATAi
(maximum limit), the external load (R
range; otherwise the device may be damaged.
3
2
1
L
) must not be lower
16
.
Revision 1.07
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