BQ4050 Datasheet, PDF (38/53 Pages) Texas Instruments – CEDV Gas Gauge and Protection Solution

bq4050
SLUSC67A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
8.2.2.3.3 PACK and FET Control
The PACK and V_CC inputs provide power to the bq4050 from the charger. The PACK input also provides a
method to measure and detect the presence of a charger. The PACK input uses a 100-Ω resistor; whereas, the
V_CC input uses a diode to guard against input transients and prevents mis-operation of the date driver during
short-circuit events.
Figure 33. bq4050 PACK and FET Control
The N-CH charge and discharge FETs are controlled with 5.1-kΩ series gate resistors, which provide a switching
time constant of a few microseconds. The 10-MΩ resistors ensure that the FETs are off in the event of an open
connection to the FET drivers. Q4 is provided to protect the discharge FET (Q3) in the event of a reverse-
connected charger. Without Q4, Q3 can be driven into its linear region and suffer severe damage if the PACK+
input becomes slightly negative.
Q4 turns on in that case to protect Q3 by shorting its gate to source. To use the simple ground gate circuit, the
FET must have a low gate turn-on threshold. If it is desired to use a more standard device, such as the 2N7002
as the reference schematic, the gate should be biased up to 3.3 V with a high-value resistor. The bq4050 device
has the capability to provide a current-limited charging path typically used for low battery voltage or low
temperature charging. The bq4050 device uses an external P-channel, pre-charge FET controlled by PCHG.
8.2.2.3.4 Temperature Output
For the bq4050 device, TS1, TS2, TS3, and TS4 provide thermistor drive-under program control. Each pin can
be enabled with an integrated 18-kΩ (typical) linearization pullup resistor to support the use of a 10-kΩ at 25°C
(103) NTC external thermistor such as a Mitsubishi BN35-3H103. The reference design includes four 10-kΩ
thermistors: RT1, RT2, RT3, and RT4. The bq4050 device supports up to four external thermistors. Connect
unused thermistor pins to V_SS.
38
Submit Documentation Feedback
Product Folder Links: bq4050
Copyright © 2016, Texas Instruments Incorporated