CS5525 Datasheet, PDF (8/29 Pages) Cirrus Logic – 16 BIT / 20 BIT MULTI RANGE ADC WITH 4 BIT LATCH

CS5525 CS5526
DETAILED DESCRIPTION
The CS5525 and CS5526 are 16-bit and 20-bit pin
compatible converters which include a chopper-
stabilized instrumentation amplifier input, and an
on-chip programmable gain amplifier. They are
both optimized for measuring low-level unipolar or
bipolar signals in process control and medical ap-
plications.
The CS5525/26 also include a fourth order delta-
sigma modulator, a calibration microcontroller,
eight digital filters, a 4-bit analog latch, and a serial
port. The digital filters provide any one of eight
different output update rates.
The CS5525/26 include a CPD (Charge Pump
Drive) output (shown in Figure 1). CPD provides a
negative bias voltage to the on-chip instrumenta-
tion amplifier when used with a combination of ex-
ternal diodes and capacitors. This enables the
CS5525/26 to measure negative voltages with re-
spect to ground, making the converters ideal for
thermocouple temperature measurements.
Theory of Operation
The CS5525/26 A/D converters are designed to op-
erate from a single +5 V analog supply and provide
several different input ranges. See the Analog
Characteristics section on page 3 for details.
Figure 1 illustrates the CS5525/26 connected to
generate their own negative bias supply using the
on-chip CPD (Charge Pump Drive). This enables
the CS5525/26 to measure ground referenced sig-
nals with magnitudes down to NBV (Negative Bias
Voltage, approximately -2.1 V in this example).
Figure 2 illustrates a charge pump circuit when the
converters are powered from a +3.0 V digital sup-
ply. Alternatively, the negative bias supply can be
generated from a negative supply voltage or a resis-
tive divider as illustrated in Figure 3.
+5V
A n alo g
S upply
2 .5 V
10 Ω
0.1 µF
2
VA+
20 _VREF+
13
VD+
10
XOUT
500kΩ
0.1 µF
20 pF
19
U p to ± 100 m V Inp ut
10 kΩ _BAV199
3
0.1 µF
4
1
10 kΩ
16
N ote: C old-junction
15
m easurem ent is perform ed
7
by a second A /D or via a
6
m ultiplexer.
Logic O utputs:
A 0 - A 3 S w itch fro m VA + to A G N D .
VREF-
C S5525 ^{XIN 9}
CS5526
AIN +
CS ¹⁸
AIN -
SCLK ¹¹
AGND
A3
A2
SDI ¹⁷
14
SDO
32.768 ~ 100kH z
O ptional
C lock
S o u rc e
S erial
D ata
In te rfa ce
A1
A0
NBV
CPD DGND
5
8
12 _{* O ptional, see C harge}
*5M Ω
P um p D rive section.
1N4148
10 µF
+
0.015 µF
1N4148
C harge-pum p n etw o rk
for V D + = 5 V o nly an d
XIN = 32.768 kH z.
Figure 1. CS5525/26 Configured to use on-chip charge pump to supply NBV.
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DS202F3