Cirrus Logic CS5529 - Manual (Page 4)

CS5525/6/9 FAQ
4 DS202TB1
18) What benefit does an evaluation board offer?
The CDB5525/26 evaluation board saves time
and money over prototyping. The preassem-
bled board comes equipped with an 80C51 mi-
crocontroller and a 9-pin cable to link the
evaluation board to a PC-compatible computer.
The evaluation system also includes software
which provides easy access to the internal reg-
isters of the converter and displays the convert-
er’s time domain, frequency domain and noise
histogram performance.
19) How do the analog power supply configura-
tions differ between the CS5525/26 and the
CS5529?
The CS5525/26 converters can be powered
from a single +5 V analog supply and either a
+5 V or +3.3 V digital supply. They have a
charge pump which uses two external diodes
and two external capacitors to generate a nega-
tive supply (a negative bias voltage) allowing
digitization of ground-referenced signals. The
negative bias voltage can be supplied from a
separate negative supply, if desired. The
CS5529 A/D converter is designed to operate
from a single +5 V or a dual ±2.5 V analog sup-
ply and either a +5 V or +3.3 V digital supply.
Since the CS5529 can be powered from a neg-
ative analog supply, level shifting circuitry can
be eliminated when measuring ground-refer-
enced signals.
20) How do the voltage references differ between
the CS5525/26 and the CS5529?
The CS5529 supports differential reference
voltages up to the analog supply allowing the
analog supply to serve as the reference voltage.
The reference’s inputs are buffered through a
coarse/fine charge buffer. Since the inputs are
buffered, the dynamic current is typically 8 nA
and is independent of the reference voltage.
The CS5525/26 do not have buffers yet support
a differential reference voltage up to 3.0 V.
Since their reference inputs aren’t buffered the
dynamic input current is typically 1.2 µA/V.
21) How do the CS5525/26 and the CS5529 analog
input ranges differ?
The CS5529 has a nominal input range of
±2.5 V (with VREF=2.5 V). The analog inputs
for this range have a coarse/fine charge buffer
which reduces the dynamic current to typically
16 nA. The CS5525/26 have an instrumenta-
tion amplifier and a programmable gain ampli-
fier which provides nominal input ranges of 25
mV, 55 mV, and 100 mV. The instrumentation
amplifier is a chopper stabilized amplifier and
serves as a buffer reducing the dynamic input
current to typically 100 pA. In the 1 V, 2.5 V,
and 5 V ranges of the CS5525/26, the instru-
mentation amplifier is bypassed and no buffer
exists to reduce the input current. In these rang-
es the input current is typically 1.2 µA/V.
22) How do the output word rates differ between
the CS5525/26 and the CS5529?
All three converters have eight output word
rates. The CS5529 samples at ½ the rate of the
CS5525/26. Therefore, the CS5529’s output
word rate are ½ the CS5525/26.