Cirrus Logic CS5513 - Manual (Page 11)

CS5510/11/12/13
DS337F4 11
CS5512/13. The CS5510/11 follow the same
curve, but are limited to 16 bits of resolution. Note
that the reference voltage should not be estab-
lished prior to having the supply voltages on the V+
and V- pins.
2.2.1 Voltage Reference Input Model
Figure 5 illustrates the input model for the VREF
pin. It includes a coarse/fine charge buffer which
reduces the dynamic current demand of the exter-
nal reference. Typical CVF (sampling) current is
about 6 nA (See Figure 5).
The nominal input span of the converter is defined
to be a bipolar span equal to ±(VREF - V-)*(0.80
±0.08).
2.3 Power Supply Arrangements
The CS5510/11/12/13 are designed to operate
from single or dual supplies. Figure 6 illustrates the
CS5510/11/12/13 connected with a single +5 V
supply to measure differential inputs relative to a
common mode of 2.5 V. Figure 7 illustrates the
CS5510/11/12/13 connected with ±2.5 V analog
supplies to measure ground-referenced, bipolar
signals. It is not necessary that the dual supples on
the ADCs be balanced, however, they must sum to
five volts. Figure 8 illustrates the ADCs configured
with V+ = +3.3 V and V- = -1.7 V, accommodating
a +3.3 V digital supply.
2.3.1 Digital Logic Levels
The many power supply configurations available in
the CS5510/11/12/13 allow for a wide range of dig-
ital logic levels. The logic-high input and output lev-
els are determined by the V+ pin. The logic-low
output on SDO is referenced to and driven by the
current logic-low voltage on CS. Since the
CS5510/11/12/13 do not include a dedicated
13
14
15
16
17
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
VREF (V)
Effective Bits
Figure 4. CS5512/13 Measured Noise-Free Bits vs.
VREF.
VREF
C = 7 p F
2
φ
1
φ
V
≤ 2 5 mV
o s
i = f V C
o s n
f = 32.768 kHz
Coarse
Fine
Figure 5. Input model for VREF pin.