BQ24140_14 Datasheet, PDF (16/39 Pages) Texas Instruments – Integrated Dual-Input Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

bq24140
SLUSAO5 – OCTOBER 2011
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0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55
Boost Output current (A)
Figure 15. VBUS OTG Efficiency
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DETAILED FUNCTIONAL DESCRIPTION
The bq24140 is a highly integrated dual input switch-mode battery charger with USB-OTG support. Due to the
switch-mode architecture, it provides the capability of charging the battery faster than traditional linear chargers
in the event that the power source is current limited, such as USB ports. In addition to the reduced charge time,
higher efficiencies reduce the power losses through the charger and allows for better thermal management of the
end product.
The bq24140 integrates a dual input 3MHz synchronous switching charger that targets space limited portable
applications powered by a single cell Li based battery pack. In addition to charge the battery, the bq24140
provides support for simultaneously boosting the battery voltage back to the USB input for USB-OTG support.
The bq24140 has two operation modes: default mode and host-control mode. In default mode, the charger will
start a charge cycle with the default parameters and wait for an I2C write to the IC before entering host-mode. In
host-control mode, the charger will switch to a 32s watchdog timer and the charge paramters will follow the
information set on the registers.
The bq24140 provides three ways of configuring the charger, charge mode, boost mode and high impedance
mode. These 3 configuration allows for multiple possible settings of the charge systems, including charging the
battery and providing power to an accessory. The high impedance mode reduces the quiescent current from the
device, effectively reducing the power consumption when the portable device is in standby mode. Integrated
control loops ensure smooth transitions between the different operating modes.
PWM Buck Charger
The IC provides an integrated, fixed 3 MHz frequency voltage-mode controller to regulate charge current or
voltage. This type of controller is used to improve line transient response, thereby, simplifying the compensation
network used for both continuous and discontinuous current conduction operation. The voltage and current loops
are internally compensated using a Type-III compensation scheme that provides enough phase margin for stable
operation, allowing the use of small ceramic capacitors with very low ESR. The device operates between 0% to
99.5% duty cycles.
The IC has back to back common-drain N-channel FETs at the high side and one N-channel FET at low side for
both VIN and VBUS inputs. The input N-FETs (Q1, Q4) prevents battery discharge when VIN and/or VBUS is
lower than VBAT. The second high-side N-FET (Q2, Q5) are the switching FETs. A charge pump circuit is used
to provide gate drive for Q1 and Q4, while a bootstrap circuit with an external bootstrap capacitor is used to
supply the gate drive voltage for Q2 and Q5.
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