SX8723
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Input Multiplexers
The ZoomingADC has eight analog inputs AC0 to AC7 and four reference inputs AC_R0 to AC_R3. Let us first
define the differential input voltage VIN and reference voltage VREF,ADC respectively as:
and:
VIN = VINP − VINN
(V)
Equation 3
VREF , ADC = VREFP − VREFN
(V)
Equation 4
As shown in Table 2, the inputs can be configured in two ways: either as 4 differential channels (VIN1 = AC1 -
AC0,..., VIN3 = AC5 – AC4), or AC0 can be used as a common reference, providing 5 signal paths all referred to
AC0. The control word for the analog input selection is AMUX[4:0]. Notice that the bit AMUX[3] controls the sign
of the input voltage.
AMUX[4:0]
(RegACCfg5[5:1])
VINP
AMUX[4:0]
VINN
(RegACCfg5[5:1])
VINP
VINN
00x00
00x01
00x10
10000
10001
10010
10011
10100
10101
AC1 (VREF)
AC3
AC5
AC0 (VSS)
AC1 (VREF)
AC2
AC3
AC4
AC5
AC0 (VSS)
AC2
AC4
AC0 (VSS)
01x00
01x01
01x10
11000
11001
11010
11011
11100
11101
AC0 (VSS)
AC2
AC4
AC0 (VSS)
AC1 (VREF)
AC3
AC5
AC0 (VSS)
AC1 (VREF)
AC2
AC3
AC4
AC5
Table 2 - Analog Input Selection
Similarly, the reference voltage is chosen among two differential channels (VREF,ADC = AC_R1 - AC_R0 or
VREF,ADC = AC_R3 - AC_R2) as shown in Table 3. The selection bit is VMUX. The reference inputs VREFP and
VREFN (common-mode) can be up to the power supply range.
VMUX
(RegACCfg5[0])
0
1
VREFP
AC_R1 (VBATT)
AC_R3 (VREF)
VREFN
AC_R0 (VSS)
AC_R2 (VSS)
Table 3 - Analog Reference Input Selection
V1.5 © 2007 Semtech Corp.
19
www.semtech.com