BQ27425-G2_15 Datasheet, PDF (30/39 Pages) Texas Instruments – Fuel Gauge With Integrated Sense Resistor

bq27425-G2
SLUSB23B – OCTOBER 2012 – REVISED JUNE 2015
www.ti.com
9.2.1 Design Requirements
As shipped from the TI factory, many bq27425-G2 parameters in NVM are left in the unprogrammed state (zero)
while some parameters directly associated with the CHEMID are preprogrammed. This partially programmed
configuration facilitates customization for each end application. Upon device reset, the contents of NVM are
copied to associated volatile RAM-based Data Memory blocks. For proper operation, all parameters in RAM-
based Data Memory require initialization — either by updating Data Memory parameters in a lab or evaluation
situation or by programming the NVM for customer production.
Table 9 shows the design parameter values that are present in the device.
9.2.2 Detailed Design Procedure
9.2.2.1 BAT/REGIN Voltage Sense Input
A ceramic capacitor at the input to the BAT/REGIN pin is used to bypass AC voltage ripple to ground, greatly
reducing its influence on battery voltage measurements. It proves most effective in applications with load profiles
that exhibit high-frequency current pulses (that is, cell phones) but is recommended for use in all applications to
reduce noise on this sensitive high-impedance measurement node.
9.2.2.2 Integrated LDO Capacitor
The fuel gauge has an integrated LDO with an output on the VCC pin of approximately 2.5 V. A capacitor of
value at least 1 μF should be connected between the VCC pin and VSS. The capacitor should be placed close to
the gauge IC and have short traces to both the VCC pin and VSS.
9.2.3 Application Curves
2.65
VREGIN = 2.7 V
VREGIN = 4.5 V
2.6
2.55
2.5
2.45
2.4
2.35
Temperature (GC)
D001
Figure 12. Regulator Output Voltage vs Temperature
34
33.5
33
32.5
32
31.5
31
30.5
30
-40 -20
0
20
40
60
80 100
Temperature (GC)
D003
Figure 14. Low-Frequency Oscillator Frequency vs
Temperature
8.8
8.7
8.6
8.5
8.4
8.3
8.2
8.1
8
-40 -20
0
20
40
60
80 100
Temperature (GC)
D002
Figure 13. High-Frequency Oscillator Frequency vs
Temperature
5
4
3
2
1
0
-1
-2
-3
-4
-5
-30 -20 -10 0 10 20 30 40 50 60
Temperature (GC)
D004
Figure 15. Reported Internal Temperature Measurement vs
Temperature
30
Submit Documentation Feedback
Product Folder Links: bq27425-G2
Copyright © 2012–2015, Texas Instruments Incorporated