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12.3 LDOs
The BQ76942 device contains an integrated 1.8-V LDO (REG18) that provides a regulated 1.8-V supply voltage
for the device's internal circuitry and digital logic. This regulator uses an external capacitor connected to the
REG18 pin, which should only be used for internal circuitry.
The device also integrates two separately programmable LDOs (REG1 and REG2) for external circuitry, such
as a host processor or external transceiver circuitry, which can be programmed to independent output voltages.
The REG1 and REG2 LDOs take their input from the REGIN pin, with this voltage either provided externally or
generated by an on-chip preregulator (referred to as REG0). The REG1 and REG2 LDOs can provide an output
current of up to 45 mA each.
12.3.1 Preregulator Control
The REG1 and REG2 LDOs take their input from the REGIN pin, which should be approximately 5.5 V. This
REGIN pin voltage can be supplied externally (such as by a separate DC/DC converter) or using the integrated
voltage preregulator (referring to as REG0), which drives the base of an external NPN BJT (using the BREG pin)
to provide the 5.5 V REGIN pin voltage. When the preregulator is being used, special care should be taken to
ensure the device retains sufficient voltage on its BAT pin per the
.
Note
• The system designer should ensure the external BJT can tolerate the peak power that may be
dissipated in it under maximum load expected on REG1 and REG2. If the maximum stack voltage
is 50 V, then the BJT experiences a collector-emitter voltage of approximately 45 V; thereby,
dissipating 4.05 W if REG1 and REG2 are both used to support a 45-mA load.
• There is a diode connection between the REGIN pin (anode) and the BAT pin (cathode), so the
voltage on REGIN should not exceed the voltage on BAT.
12.3.2 REG1 and REG2 LDO Controls
The REG1 and REG2 LDOs in the BQ76942 device are for customer use, and their output voltages can be
programmed independently to 1.8 V, 2.5 V, 3.0 V, 3.3 V, or 5.0 V. The REG1 and REG2 LDOs and the REG0
preregulator are disabled by default in the BQ76942 device. While in SHUTDOWN mode, the REG1 and REG2
pins have ≈10-MΩ resistances to VSS, to discharge any output capacitance. While in other power modes,
when REG1 and REG2 are powered down, they are pulled to VSS with an internal resistance of ≈2.5-kΩ. If
pullup resistors for serial communications are connected to the REG1 voltage output, the REG1 voltage can be
overdriven from an external voltage supply on the manufacturing line, to allow communications with the device.
The BQ76942 device can then be programmed to enable REG0 and REG1 with the desired configuration, and
this setting can be programmed into OTP memory. Thus, at each later power-up, the device will autonomously
load the OTP settings and enable the LDO as configured, without requiring communications first.
12.4 Standalone Versus Host Interface
The BQ76942 device can be configured to operate in a completely standalone mode, without any host processor
in the system, or together with a host processor. If in standalone mode, the device can monitor conditions,
control FETs and an in-line fuse based on threshold settings, and recover FETs when conditions allow, all
without requiring any interaction with an external processor. If a host processor is present, the device can still be
configured to operate fully autonomously, while the host processor can read measurements and exercise control
as desired. In addition, the device can be configured for manual host control, such that the device can monitor
and provide a flag when a protection alert or fault has occurred, but will rely on the host to disable FETs.
The host processor can interface with the BQ76942 device through a serial bus as well as selected pin controls.
Serial bus communication through I
2
C (supporting speeds up to 400 kHz), SPI or HDQ is available, with the
serial bus configured for I
2
C by default in the BQ76942, while the default communications mode may differ
SLUSE14B – DECEMBER 2020 – REVISED DECEMBER 2021
Copyright © 2021 Texas Instruments Incorporated
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