High-Side Nfet Drivers - Texas Instruments 3 Series Manual

BQ76952
SLUSE13A – JANUARY 2020 – REVISED MAY 2021
• Data ROM Permanent Fail
• Instruction ROM Permanent Fail
• Internal LFO Permanent Fail
• Internal Voltage Reference Permanent Fail
• Internal VSS Measurement Permanent Fail
• Internal Stuck Hardware Mux Permanent Fail
• Commanded Permanent Fail
• Top of Stack Versus Cell Sum Permanent Fail

11.4 High-Side NFET Drivers

The BQ76952 device includes an integrated charge pump and high-side NFET drivers for driving CHG and DSG
protection FETs. The charge pump uses an external capacitor connected between the BAT and CP1 pins that is
charged to an overdrive voltage when the charge pump is enabled. Due to the time required for the charge pump
to bring the overdrive voltage on the external CP1 pin to full voltage, it is recommended to leave the charge
pump powered whenever it may be needed quickly to drive the CHG or DSG FETs.
The DSG FET driver includes a special option (denoted source follower mode) to drive the DSG FET with the
BAT pin voltage during SLEEP mode. This capability is included to provide low power in SLEEP mode, when
there is no significant charge or discharge current flowing. It is recommended to keep the charge pump enabled
even when the source follower mode is enabled, so whenever a discharge current is detected, the device can
quickly transition to driving the DSG FET using the charge pump voltage. The source follower mode is enabled
using a configuration setting and is not intended to be used when significant charging or discharging current is
flowing, since the FET will exhibit a large drain-source voltage and may undergo excessive heating.
The overdrive level of the charge pump voltage can be set to 5.5 V or 11 V, based on the configuration setting.
In general, the 5.5-V setting results in lower power dissipation when a FET is being driven, while the higher 11-V
overdrive reduces the on-resistance of the FET. If a FET exhibits significant gate leakage current when driven at
the higher overdrive level, this can result in a higher device current for the charge pump to support this. In this
case, using the lower overdrive level can reduce the leakage current and thus the device current.
The BQ76952 device supports a system with FETs in a series or parallel configuration, where the parallel
configuration includes a separate path for the charger connection versus the discharge (load) connection.
The control logic for the device operates slightly differently in these two cases, which is set based on the
configuration setting.
The FET drivers in the BQ76952 device can be controlled in several different manner, depending on customer
requirements:
Fully autonomous
Partially autonomous
Manual control
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The BQ76952 device can detect protection faults and autonomously disable the FETs, monitor for
a recovery condition, and autonomously reenable the FETs, without requiring any host processor
involvement.
The BQ76952 device can detect protection faults and autonomously disable the FETs. When the
host receives an interrupt and recognizes the fault, the host can send commands across the digital
communications interface to keep the FETs off until the host decides to release them.
Alternatively, the host can assert the CFETOFF or DFETOFF pins to keep the FETs off. As long
as these pins are asserted, the FETs are blocked from being reenabled. When these pins are
deasserted, the BQ76952 will reenable the FETs if nothing is blocking them being reenabled (such
as fault conditions still present, or the CFETOFF or DFETOFF pins are asserted).
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