Z-World Fox LP3500, Руководство пользователя

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User’s Manual 31
Single-ended measurements are made by connecting the analog signal between an analog
input channel (AIN0–AIN7) and AGND. Differential measurements are made by connect-
ing
a pair of differential analog signals to an adjacent pair of analog input channels
(AIN0–AIN1, …, AIN6–AIN7). The A/D converter is only capable of converting positve
voltages, and so will convert the
difference between an adjacent pair of input channels,
and must be scaled for a voltage range appropriate for the voltage differences.
Table 7 lists the jumper configurations for header J3 used to set the 4–20 mA and the volt-
age measurement options.
CAUTION: If you have enabled the 4–20 mA current option on any of the AIN0–AIN3
channels, be careful with any voltage sources that you might connect to these inputs.
The voltage must be less than 2.5 V to keep the current across the 100
Ω
resistor below
the maximum allowed current.
The A/D converter inputs are factory-calibrated, and the calibration constants are stored in
flash memory. You may calibrate the A/D converter inputs at a later time using the software
functions described in Section 4.5.5, “A/D Converter Inputs.”
NOTE: If you are using a fixed voltage range, you should recalibrate your LP3500 at that
range.
AIN7 can be used to monitor Vcc using the
VccMonitorInit
function. While Vcc can
be monitored in all the power modes, Vcc monitoring is particularly useful when the
LP3500 is being operated from an external battery to monitor the voltage being supplied
by the battery.
The
VccMonitorInit
function requires the operation of the A/D converter, which con-
sumes about 500 µA.
The Vcc monitoring circuit itself consumes about 15 µA while it is
engaged.
Turn off
VccMonitorInit
(and the A/D converter if it is not going to be used)
when the test is done to extend your battery life.
Table 7. Header J3 Configuration for Analog I/O Options
Analog Input Channel
Voltage Option
(Factory Default)
4–20 mA Option
AIN0 Jumper “parked” on pin 2 Pins 1–2 connected
AIN1 Jumper “parked” on pin 4 Pins 3–4 connected
AIN2 Jumper “parked” on pin 6 Pins 5–6 connected
AIN3 Jumper “parked” on pin 8 Pins 7–8 connected