CS5126 Cirrus Logic, CS5126 Datasheet - Page 14

• Manufacturer Part Number: CS5126
• Description: 16-Bit Stereo A/D Converter for Digital Audio
• Manufacturer: Cirrus Logic

The CS5126 can operate with a wide range of
reference voltages, but signal-to-noise perform-
ance is maximized by using as wide a signal
range as possible. The recommended reference
voltage is 4.5 volts. The CS5126 can actually
accept reference voltages up to the positive ana-
log supply. However, as the reference voltage
approaches VA+ the external drive requirements
may increase at VREF.
An internal reference buffer is used to protect
the external reference from current transients
during conversion. This internal buffer enlists
the aid of an external 0.1 F ceramic capacitor
which mu st be tied between it s outp ut,
REFBUF, and the negative analog supply, VA-.
Analog Input Connection
Each time the CS5126 finishes a conversion cy-
cle it switches the internal capacitor array to the
appropriate analog input pin, AINL or AINR.
This creates a minor dynamic load at the sam-
pling frequency. All throughput specifications
apply for maximum analog source impedances
of 200
comparator requires source impedances of less
than 400
met by practically all bipolar op amps. For more
information, see our Application Note: "Input
Buffers for the CS501X/CSZ511X Series of A/D
Converters"
Analog Input Range/Coding Format
The CS5126 features a bipolar input range with
the reference voltage applied to VREF defining
both positive and negative full-scale. The coding
format is set by the state of the CODE input. If
high, coding is 2’s complement; if low, the
CS5126’s output is in offset-binary format.
14
at AINL and AINR. In addition, the
around 2MHz for stability, which is
Grounding and Power Supply Decoupling
T h e C S 5 1 2 6 u s e s t h e a n a l o g g r o u n d
connection, AGND, only as a reference voltage.
No dc power or signal currents flow through the
AGND connection, thus minimizing the potential
for interchannel crosstalk. Also, AGND is com-
pletely independent of DGND. However, any
noise riding on the AGND input relative to the
system’s analog ground will induce conversion
errors. Therefore, both analog inputs and the ref-
erence voltage should be referred to the AGND
pin, which should be used as the entire system’s
analog ground. The digital and analog supplies
are isolated within the CS5126 and are pinned
out separately to minimize coupling between the
analog and digital sections of the chip. All four
supplies should be decoupled to their respective
grounds using 0.1 F ceramic capacitors. If sig-
nificant low frequency noise is present on the
supplies, 1 F tantalum capacitors are recom-
mended in parallel with the 0.1 F capacitors.
The positive digital power supply of the CS5126
must never exceed the positive analog supply by
more than a diode drop or the CS5126 could
experience permanent damage. If the two sup-
plies are derived from separate sources, care
must be taken that the analog supply comes up
first at power-up. The system connection dia-
grams in figures 2 and 9 show a decoupling
scheme which allows the CS5126 to be powered
from a single set of
digital supply is derived from the analog supply
through a 10
ply dropping below the digital supply. If this
scheme is utilized, care must be taken to insure
that any digital load currents (which flow
through the 10
magnitude of digital supplies to drop below the
analog supplies by more than 0.5 volts. Digital
resistor to avoid the analog sup-
resistors) do not cause the
5V rails. The positive
CS5126
DS32F1