參數(shù)資料
型號: MCP3421DM-WS
廠商: Microchip Technology
文件頁數(shù): 22/42頁
文件大小: 0K
描述: BOARD DEMO MCP3421 WEIGHT SCALE
標(biāo)準(zhǔn)包裝: 1
主要目的: 參考設(shè)計,稱量臺
嵌入式: 是,MCU,8 位
已用 IC / 零件: MCP3421,MCP6V07,PIC18F4550
主要屬性: 2Kg測壓元件,靈敏度為1 mV/V
已供物品: 板,線纜,CD,電源
2009 Microchip Technology Inc.
DS22003E-page 29
MCP3421
6.2
Application Examples
6.2.1
VOLTAGE MEASUREMENT
The MCP3421 device can be used in a broad range of
sensor and data acquisition applications.
Figure 6-5 shows a circuit example measuring the
battery voltage. When the input voltage is greater than
the internal reference voltage (VREF = 2.048V), it needs
a voltage divider circuit to prevent the output code from
being saturated. In the example, R1 and R2 form a volt-
age divider. The R1 and R2 are set to yield VIN to be
less
than
the
internal
reference
voltage
(VREF = 2.048V).
If the input voltage range is much less than the internal
reference voltage, the voltage divider at the input pin is
not needed, and the user may use the internal PGA
with a gain of up to 8.
When the voltage divider or internal PGA is used for the
input signal, these factor must be taken into account
when the user converts the output codes to the actual
input voltage.
Find the Microchip Application Note AN1156 for the
input voltage and current measurement using the
MCP342X device family. The MCU firmware is well
documented in the reference.
FIGURE 6-5:
Battery Voltage
Measurement.
6.2.2
CURRENT MEASUREMENT
shows
a
circuit
example
of
current
measurement. For the current measurement, the
device measures the voltage across the current sensor,
and converts it to current by dividing the measured
voltage by a known resistance value of the current
sensor. The voltage drops across the sensor is waste.
Therefore, the current measurement often prefers to
use a current sensor with smaller resistance value,
which, in turn, requires high resolution ADC device.
The high precision MCP342x devices from Microchip
Technology
Inc.
are
suitable
for
the
current
measurement with low resistive current sensors. These
devices can measure the input voltage as low as 2 V
range (or current in ~ A range) with 18 bit resolution
and PGA = 8 settings. The MSB (= sign bit) of the
output code indicates the direction of the current.
FIGURE 6-6:
Battery Current
Measurement.
Output Code
LSB
R
1
R
2
+
R
2
-------------------
×
1
PGA
-----------
×
=
R1
Battery
R1 and R2 = Voltage Divider
V
IN
R
2
R
1
R
2
+
-------------------
V
BAT
×
=
(V)
To Load
VIN+
VIN-
VDD
Input Voltage Calculation from Output Code:
R2
Measured Analog Input Voltage
VBAT
MCP3421
Battery
(V)
To Load
VIN-
VDD
VIN+
Current Sensor
Discharging Current
Charging
Current
Current Calculation from Output Code:
Current
Output Code
LSB
×
RSensor
()
----------------------------------------------------
1
PGA
------------
A
()
×
=
MCP3421
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