ISL26132 Datasheet, PDF (12/23 Pages) Intersil Corporation – Low-Noise 24-bit Delta Sigma ADC

ISL26132, ISL26134
Functional Description
Analog Inputs
The analog signal inputs to the ISL26132 connect to a 2-Channel
differential multiplexer and the ISL26134 connect to a 4-Channel
differential multiplexer (Mux). The multiplexer connects a pair of
inputs to the positive and negative inputs (AINx+, AINx-), selected
by the Channel Select Pins A0 and A1 (ISL26134 only). Input
channel selection is shown in Table 7. On the ISL26132, the
TEMP pin is used to select the Temperature Sensor function.
TABLE 7. INPUT CHANNEL SELECTION
CHANNEL SELECT PINS
ANALOG INPUT PINS SELECTED
A1
A0
AIN+
AIN-
0
0
AIN1+
AIN1-
0
1
AIN2+
AIN2-
1
0
AIN3+
AIN3-
1
1
AIN4+
AIN4-
Whenever the MUX channel is changed (i.e. if any one of the
following inputs - A0/A1, Gain1/0, SPEED is changed), the
digital logic will automatically restart the digital filter and will
cause SDO/RDY to go low only when the output is fully settled.
But if the input itself is suddenly changed, then the user needs to
ignore first four RDY pulses (going low) to get an accurate
measurement of the input signal.
1.25V
3.75
2.50
AIN+
1.25
3.75
INPUT VOLTAGE RANGE = ±0.5VREF/GAIN
VREF = 5V, GAIN = 1X
2.50
AIN-
The input span of the ADC is ±0.5 VREF/GAIN. For a 5V VREF and
a gain of 1x, the input span will be 5V_P-P fully differential as
shown in Figure 23. Note that input voltages that exceed the
supply rails by more than 100mV will turn on the ESD protection
diodes and degrade measurement accuracy.
If the differential input exceeds well above the +VE or the -VE FS
(by ~1.5x times) the output code will clip to the corresponding FS
value. Under such conditions, the output data rate will become
1/4th of the original value as the Digital State Machine will
RESET the Delta-Sigma Modulator and the Decimation Filter.
Temperature Sensor (ISL26132 only)
When the TEMP pin of the ISL26132 is set High, the input
multiplexer is connected to a pair of diodes, which are scaled in
both size and current. The voltage difference measured between
them corresponds to the temperature of the die according to
Equation 1:
V= 102.2mV + (379μV^∗T(°C))^∗Gain
(EQ. 1)
Note: Valid only for GAIN = 1x or 2x
Where T is the temperature of the die, and Gain = the PGA Gain
Setting.
At a temperature of +25°C, the measured voltage will be
approximately 111.7mV. Note that this measurement indicates
only the temperature of the die itself. Applying the result to
correct for the temperature drift of a device external to the
package requires that thermal coupling between the sensor and
the die be taken into account.
Low-Noise Programmable Gain Amplifier
(PGA)
The chopper-stabilized programmable gain amplifier features a
variety of gain settings to achieve maximum dynamic range and
measurement accuracy from popular sensor types with excellent
low noise performance, input offset error, and low drift, and with
minimal external parts count. The GAIN0 and GAIN1 pins allow the
user to select gain settings of 1x, 2x, 64x, or 128x. A block diagram
is shown in Figure 24. The differential input stage provides a gain of
64, which is bypassed when the lower gain settings are selected.
The lower gain settings (1 and 2) will accept inputs with common
mode voltages up to 100mV outside the rails, allowing the device to
accept ground-referred signals. At gain settings of 64 or 128 the
common mode voltage at the inputs is limited to 1.5V inside the
supply rails while maintaining specified measurement accuracy.
1.25
2.50V
FIGURE 23. DIFFERENTIAL INPUT FOR VREF = 5V, GAIN = 1X
12
FN6954.1
September 9, 2011