ADP315PC87570 National Semiconductor, ADP315PC87570 Datasheet - Page 127

• Manufacturer Part Number: ADP315PC87570
• Description: Keyboard and Power Management Controller
• Manufacturer: National Semiconductor

www.national.com
17.0 Digital to Analog Converter (DAC)
The DAC receives digital data and delivers analog signals
on four output pins. It includes four independent digital to
analog converters. Each of them has 8-bit resolution and a
full output range from AGND to AV
cal output impedance of 3 K
of about 1 s on a 50 pF load.
17.1 FEATURES
17.2 FUNCTIONAL DESCRIPTION
The DAC comprises four independent digital to analog con-
verters. The converters drive the four output pins DA0-3, as
shown in Figure 17-1.
After reset (on power-up or when a positive pulse is applied
on the HMR pin), all four channels are disabled and the volt-
age on the DA0-3 outputs is 0 V.
When a DAC channel is enabled, its output is defined by the
value written to its DACDAT Register. DACDAT0 through
DACDAT3 control DA0 through DA3, respectively. The
maximum output voltage is (255/256)
for a value of FFh. The minimum output, AGND, is obtained
for a value of 00h.
The reference voltage of the converters is the AV
power supply voltage. This allows full swing of the outputs
from zero to nearly AV
The Control Register is used to enable/disable each of the
four channels. The DAC can be disabled by software before
entering Idle mode.
17.2.1 DAC Reset
The DACCTRL Register is reset to its default value, in the
following two ways:
Cold Reset. Upon power-up, an internal power-up detect
circuit generates a reset cycle. See Section 2.3 on page 26.
Warm Reset. When the chip is powered up and a positive
pulse is applied on the HMR pin, a reset cycle is generated.
See HMR pin functionality in Table 2-2 on page 21.
17.2.2 Reference Voltage
The analog output voltages are converted relative to a ref-
erence voltage. See details in Figure 17-1 and Table 19-7
on page 135. The internally connected reference voltage of
the DAC is the analog power supply. To assure good signal
quality on the DAC outputs, a low noise analog power sup-
ply should be used.
•
•
•
•
•
•
•
8-bit resolution
4-channel D/A converter
Fast settling time, 1 s typical, on 50 pF capacitive load
Output swing from AGND to AV
Independent enable/disable for each channel
Zero power when disabled, low power when enabled
Outputs drive zero when disabled
CC
.
which allows a settling time
CC
CC
*
. The DAC has a typi-
AV
CC
and is obtained
Digital to Analog Converter (DAC)
CC
analog
127
17.2.3 Output Signal Range
The DAC performs a linear conversion of the input digital
value written into the DACDATA0-3 Registers to an un-
signed analog output signal. The output signal should be
taken relative to the analog ground pin (AGND), and can
range from a minimum of AGND to almost AV
Table 19-6 on page 134.
A 00h written to the DACDAT0-3 Registers results in an out-
put signal of zero (ground) for the respective output. An FFh
written to the DACDAT0-3 Registers results in an output
signal of (255/256)*AV
C
22
2
F
PC87570
Figure 17-1. DAC Functional Diagram
+
AV
0.1
C
CC
F
3
IDLE
AV
V
V
V
V
REF
REF
REF
REF
CC
DACDATA0
DACDATA1
DACDATA2
DACDATA3
CC
Register
AV
to other
modules
Control
DAC0
DAC1
DAC2
DAC3
DAC
3.3 V
5.0 V
for the respective output.
CC
or
Peripheral
Bus
Analog
Power
DAC
CC
AGND
DA0
DA1
DA2
DA3
. See