MAX32600 User’s Guide
Analog Front End
8.4 DAC
The DAC outputs are high impedance. Each DAC has a built-in load that is correct on the positive output at full power and is correct on the negative output at all
power levels. It is possible to add an external load in some configurations, but this is not advised.
In order to facilitate proper variable power function, switches are included in the DAC resistor network. This creates an additional gain error and some small
temperature dependency. As a result, the positive output avoids interference and is left pristine.
Power Control Table
Output Current
uA
vs Reference Voltage
Load
Power Mode(pm)
Output to Use
Factor
1.024V
1.5V
2.048V
2.5V
(Ohms)
0x01 (PM0)
Negative
1/16X
10.5
15.4
21
25.6
97680
0x03 (PM1)
Negative
5/16X
62.9
92.1
125.8
153.6
16280
0x05 (PM2)
Negative
11/16X
115.3
168.9
230.6
281.5
8880
0x07 (PM3)
Positive
1X
167.7
245.7
335.5
409.5
6105
0x00
Negative
1/95X
6.6
546,510
8.4.4.2
Correcting for Distortion at High Output Frequency
The DAC is vulnerable to second order harmonic behavior while operating at higher frequencies. As operating frequency increases, the time between bounce events
decreases until the reference voltage does not have time to recover before the next bounce. When this point is reached, the error current accumulates until the
direction of the DAC current changes.
Internal compensation in the DAC block is able to correct for this distortion while the code is rising; however, above 1MHz, the compensation function becomes less
and less effective. Another limitation of the internal compensation on the DAC is its inability to go negative; thus, it cannot properly correct for distortion caused by
falling edges. The proper procedure to compensate for this is to predistort the input waveform to the DAC as described below.
sin
(
x
) +
k
×
sin
(
2
x
+
t
)
Where:
•
k
is a function of frequency and code, varying from 0 to 0.12
• Suggested setting for
k
is:
k
= (
0
.
005
×
f
)
if code
<
2048, 0 otherwise; where
f
is frequency of DAC in MHz.
Rev.1.3 April 2015
Maxim Integrated
Page 461
Содержание MAX32600
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