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VTech proprietary and confidential
VTech Communications LTD.
R&D Department
The document is VTech’s proprietary information, Please do not disclose to third party without VTech’s consent
Ref. No.: 20191009 Version: 01 Date: 09 Oct, 2019 Page 26 of 33
Figure 9-1 shows the mode-to-mode transition voltages.
9.1 External mode
The external mode is for charging higher capacity batteries using an external pass device. The current is controlled by sinking
a varying current into the CHG_EXT pin, and the current is determined by measuring the voltage drop across a resistor,
Rsense, connected in series with the external pass device. The voltage drop is determined by looking at the difference
between the VBAT_SENSE and VBAT pins. The charger regulates the current drawn from CHG_EXT pin to maintain
nominal voltage drop of 200 mV across Rsense. The value of the external series resistor determines the charger current. This
current can be trimmed with a PS Key.
Figure 9-2 shows R1 (220 mΩ) and C1 (4.7 μF) form a RC snubber that is required to maintain stability
across all battery ESRs. The battery ESR must be < 1.0 Ω.
Figure 9-2 Battery charger external mode typical configuration