MCP3421DM-BFG Microchip Technology, MCP3421DM-BFG Datasheet - Page 17

• Manufacturer Part Number: MCP3421DM-BFG
• Description: BOARD DEMO FOR MCP3421
• Manufacturer: Microchip Technology

Specifications of MCP3421DM-BFG

• Main Purpose: Power Management, Battery Gauge
• Utilized Ic / Part: MCP3421
• Processor To Be Evaluated: MCP3421
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

© 2007 Microchip Technology Inc.
* Discharging Fuel (mAh) = Discharging Current (mAs)/3600
ADC Input Voltage Calibration:
The potentiometer (R1) is used to calibrate the ADC input voltage. If the displayed bat-
tery voltage on the LCD is suspicious, the customer can calibrate the ADC input voltage
using the following method:
1. Connect a digital voltmeter between the TP9 (Battery) and Ground (TP4).
2. Read the volts value on the LCD while adjusting the potentiometer. Adjust the
FIGURE 2-1:
Note:
Fuel Used (mAh) =
potentiometer until the reading on the LCD is the same as the reading on the
Digital Volt Meter (DVM). This completes the ADC input calibration.
The MCP3421 (U5) is used to measure the battery voltage. The internal
reference voltage of the MCP3421 is 2.048V. The MCP3421 (U5) will give
a saturated output if the input is greater than its reference voltage (2.048V).
To avoid the saturation, the MCP3421 Battery Fuel Gauge Demo Board
uses a voltage divider formed by R3, R4 and R1. The potentiometer (R1) is
used to calibrate the voltage divider, and provide 50% of the voltage applied
at TP9 to the input pin of the MCP3421 (U5).
The microcontroller (U2) firmware takes into account this voltage divider
value automaticaly. The firmware multiplies a factor of 2 on the U5 result
and displays the result on the LCD.
( for Discharging Current)
Display Battery Volts and
Get ADC value from U1
Get ADC value from U5
Battery Volts < 50% ?
( for Battery Voltage)
Discharging Current
Display Fuel Used
MCP3421 Battery Fuel Gauge Computation Algorithm.
i
∑
START
=
N
0
Discharging Fuel (mAh)
No
Draft
(ADC Input = Voltage after voltage divider)
Battery Volt = 2 * Acquired Volts
Yes
Beep
DS51683A-page 13