sx8725 Semtech Corporation, sx8725 Datasheet - Page 15

• Manufacturer Part Number: sx8725
• Description: Sx8725 Zoomingadc? For Pressure And Temperature Sensing
• Manufacturer: Semtech Corporation

ADVANCED COMMUNICATIONS & SENSING
ZoomingADC
Features
The ZoomingADC is a complete and versatile low-power analog front-end interface typically intended for sensing
applications.
In the following text the ZoomingADC will be referred as ZADC.
The key features of the ZADC are:
Overview
The total acquisition chain consists of an input multiplexer, 3 programmable gain amplifier stages and an over
sampled A/D converter. The reference voltage can be selected on two different channels. Two offset compensation
amplifiers allow for a wide offset compensation range. The programmable gain and offset allow the application to
zoom in on a small portion of the reference voltage defined input range.
ZADC Description
Acquisition Chain
Figure 8 shows the general block diagram of the acquisition chain (AC). A control block (not shown in Figure 8)
manages all communications with the I2C peripheral. The clocking is derived from the internal 4 MHz Oscillator.
Analog inputs can be selected through a 4 input multiplexer, while reference input is selected between two differential
channels. It should however be noted that only 3 acquisition channels (including the V
configured as single ended since the input amplifier is always operating in differential mode with both positive and
negative input selected through the multiplexer.
The core of the zooming section is made of three differential programmable amplifiers (PGA). After selection of an
input and reference signals
stages 1 to 3. Fine gain programming up to 1'000 V/V is possible. In addition, the last two stages provide
programmable offset. Each amplifier can be bypassed if needed.
V1.5 © 2007 Semtech Corp.
Reference
Analog
Inputs
Inputs
Programmable 6 to 16-bit dynamic range over-sampled ADC
Flexible gain programming between 0.5 and 1000
Flexible and large range offset compensation
2-channel differential or 3-channel single-ended input
2-channel differential reference inputs
Power saving modes
V
V
V
V
V
V
AC
AC
BATT
SS
REF
SS
SS
REF
2
3
Reference
Selection
Selection
AC
AC
Input
+
-
+
-
0
1
V
IN
V
f
s
REF,ADC
V
Figure 8 - ZADC General Functional Block Diagram
IN
GD1
and V
Gain 1
PGA1
REF,ADC
ZoomingADC™ for Pressure and Temperature Sensing
V
D1
combination, the input voltage is modulated and amplified through
GD2
Gain 2 Offset 2
PGA2
15
OFF2
ZOOM
+
-
V
D2
GD3
Gain 3 Offset 3
PGA3
OFF3
+
REF
-
) are available when
V
www.semtech.com
IN,ADC
SX8725
ADC
f
s
16