BQ25731 - 1-5 Cell NVDC Buck-Boost Charger | Texas Instruments
MPN: BQ25731 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.2 | $6.20 |
| 10 | $5.55 | $55.50 |
| 100 | $4.62 | $462.00 |
| 500 | $3.95 | $1,975.00 |
| 1,000 | $3.3 | $3,300.00 |
| 3,000 | $2.85 | $8,550.00 |
BQ25731 Overview
A buck-boost battery charge controller is a power converter IC that can step up (boost) or step down (buck) the input voltage to match the battery voltage regardless of whether VIN is above, below, or equal to VBAT, eliminating the need for an external boost stage. It belongs to the battery management hierarchy: charger IC -> battery management -> power management IC -> semiconductor. The NVDC topology maintains system rail voltage slightly above the battery, allowing instant system operation even with a deeply depleted or absent battery.
Key features include 5 A charging current capability with 80 mA / 4 mA termination steps, integrated 12-bit ADC for system monitoring, JEITA-compliant NTC thermistor input, and an adjustable 3 V to 24 V OTG output with 8 mV resolution for USB-C PD 3.0 PPS applications. The built-in synchronous switching MOSFET drivers deliver high efficiency while minimizing external component count.
The architecture combines peak-current-mode control with adaptive compensation, achieving tight regulation across the entire buck, buck-boost, and boost operating regions. Its wide-input tolerance makes it ideal for laptop / ultrabook charging, USB-C hubs, and power tool battery packs that may receive both 5 V USB-PD and 20 V high-voltage adapters.
Typical applications include 1- to 5-cell battery charging for notebooks, ultrabooks, tablets, USB-C docking stations, and power-tool battery packs. It is also used in industrial backup batteries, portable medical equipment, and drones that need bidirectional USB-PD functionality.
When designing with the BQ25731, ensure the I2C master is connected before power-up to configure charging parameters. Use TI's Battery Management Studio (bqStudio) GUI for initial configuration and debugging, and always consult the manufacturer's datasheet for layout guidelines, including thermal vias under the exposed pad.
This page synthesizes distributor pricing, drop-in alternatives (BQ25730), and practical design notes not found in the manufacturer datasheet, providing engineers a single-source reference for evaluation and sourcing.
Drop-in alternatives for BQ25731 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
BQ25730RSNR
✅ Drop-In📋 Reference alternative (not in catalog)
BQ25731RSNR
✅ Drop-In📋 Reference alternative (not in catalog)
BQ25731RSNT
✅ Drop-In📋 Reference alternative (not in catalog)
BQ25730RSNT
✅ Drop-In📋 Reference alternative (not in catalog)
BQ25731 Specifications
| Topology | Synchronous Buck-Boost NVDC |
| Number of Cells Supported | 1 to 5 series cells |
| Input Voltage Range | 3.5 V to 26 V |
| Maximum Charge Current | 5 A |
| Charge Termination Current Steps | 80 mA / 4 mA |
| Battery Chemistry | Li-Ion / Li-Polymer / LiFePO4 (multi-chemistry) |
| Communication Interface | I2C (up to 400 kHz) |
| USB Type-C PD Support | USB PD 3.0 PPS |
| OTG Output Voltage Range | 3 V to 24 V (8 mV resolution) |
| Built-in MOSFETs | External (synchronous drivers only) |
| Operating Temperature Range | -40 C to +85 C |
| Package | 32-pin QFN (RSN) 4 mm x 4 mm |
| Mounting Type | Surface Mount |
| MSL Level | 2 (1 year floor life) |
| RoHS Status | Compliant |
| Lead-Free | Yes |
| AEC-Q100 Qualified | No (not automotive grade) |
BQ25731 Pin Configuration
| Pin 1 | VAC — Sense for USB adapter input (used for adapter detection and DPM regulation) |
| Pin 2 | VBT — Battery voltage sense input (top of battery stack) |
| Pin 3 | SRP — Current-sense positive input (between sense resistor and SYS) |
| Pin 4 | SRN — Current-sense negative input (between sense resistor and BAT) |
| Pin 5 | ILIM — Input current limit setting via external resistor |
| Pin 6 | CHRG_OK — Open-drain charge status indicator output |
| Pin 7 | INT — Open-drain interrupt output to host |
| Pin 8 | SDA — I2C data line |
| Pin 9 | SCL — I2C clock line |
| Pin 10 | CE — Charge-enable input (active high) |
| Pin 11 | TS — Battery temperature sense (10 k NTC) |
| Pin 12 | PROG — Programmable pin / multi-function analog |
| Pin 13 | OTG — OTG enable input (high enables OTG / discharge) |
| Pin 14 | STAT1 — Charge status indicator output 1 |
| Pin 15 | STAT2 — Charge status indicator output 2 |
| Pin 16 | REGN — Internal LDO output (for gate-drive supply) |
| Pin 17 | BTST1 — Bootstrap for high-side FET 1 |
| Pin 18 | BTST2 — Bootstrap for high-side FET 2 |
| Pin 19 | PWM1 — Gate drive for buck / boost switch 1 |
| Pin 20 | PWM2 — Gate drive for buck / boost switch 2 |
| Pin 21 | PWM3 — Gate drive for buck / boost switch 3 |
| Pin 22 | PWM4 — Gate drive for buck / boost switch 4 |
| Pin 23 | SYS — System rail output (regulated NVDC) |
| Pin 24 | VBAT — Battery connection (power to / from battery) |
| Pin 25 | VBUS — USB input / OTG output (3.5 V to 26 V) |
| Pin 26 | PGND — Power ground (return for switching FETs) |
| Pin 27 | AGND — Analog ground (return for sensitive analog) |
| Pin 28 | DRV_VBAT — Gate-driver bootstrap for charger low-side FET |
| Pin 29 | VDD — Internal 5 V LDO output for analog circuits |
| Pin 30 | EP — Exposed thermal pad - connect to ground for cooling |
| Pin 31 | NC — Not connected (per datasheet) |
| Pin 32 | NC — Not connected (per datasheet) |
Typical Applications
BQ25731 is suitable for 7 applications: USB-C Laptop and Ultrabook Charging, USB-C Docking Station with Bidirectional Power, Cordless Power Tool Battery Packs, Industrial Backup Battery Systems, Portable Medical Devices, Drone and Robotics Charging Cradles, Tablet and 2-in-1 Convertible PCs.
USB-C Laptop and Ultrabook Charging
The BQ25731 charges 2- to 4-cell Li-ion laptop batteries directly from USB Type-C adapters at 5 V, 9 V, 15 V, or 20 V PD profiles, eliminating the need for an external buck or boost converter. Its 3.5 V to 26 V VIN range covers every standard USB-C PD fixed-PDO output without a front-end regulator. NVDC system rail regulation keeps VSYS slightly above VBAT so the laptop can boot instantly with a depleted battery. Recommended companion is the TPS25751 for USB-C PD negotiation.
Recommended
USB-C Docking Station with Bidirectional Power
USB-C docking stations need to charge a host laptop while simultaneously providing downstream 5 V / 9 V / 20 V output from an internal battery or super-capacitor. The BQ25731's bidirectional NVDC topology plus OTG output of 3 V to 24 V at 8 mV resolution meets USB-PD 3.0 PPS requirements without a separate boost IC. The buck-boost capability ensures clean power delivery whether the source is 5 V or 20 V. Use with the TPS25751 USB-C PD controller.
Recommended
Cordless Power Tool Battery Packs
Cordless power tool packs of 3 to 5 Li-ion cells (12 V to 20 V packs) benefit from the BQ25731's wide VIN tolerance and 5 A fast charging current. The IC accepts any power source from 5 V USB-PD to 20 V adapter without reconfiguration. NVDC system rail output keeps the tool's motor driver logic alive during heavy transients. The JEITA-compatible NTC input ensures safe charging at any cell temperature from -10 C to 60 C.
Recommended
Industrial Backup Battery Systems
Industrial 24 V / 48 V backup battery systems built from 5-cell LiFePO4 packs can be charged and maintained by the BQ25731 over a 20 V USB-PD input. The synchronous buck-boost charger delivers 5 A constant-current plus 80 mA precision termination, suitable for long-life LiFePO4 cells needing full charge without float stress. I2C telemetry feeds the PLC or HMI for remote battery health monitoring. Wide operating temperature range -40 C to +85 C supports outdoor enclosures.
Recommended
Portable Medical Devices
Portable medical equipment such as infusion pumps, ventilators, and patient monitors running on 2- to 3-cell Li-ion packs can charge over USB-C PD through the BQ25731, supporting fast-charge at 5 A while maintaining low-noise VSYS for sensitive analog front-ends. The integrated 12-bit ADC reports cell voltage and current for state-of-charge algorithms. JEITA temperature supervision prevents dangerous cell operation outside 0 C to 45 C. Bidirectional OTG lets the medical device itself act as a USB-C source for an accessory.
Recommended
Drone and Robotics Charging Cradles
Drones and autonomous robotics using 4-cell / 5-cell Li-ion or LiPo packs can land on a charging cradle that delivers 20 V USB-PD negotiated through the BQ25731, with 5 A charging current reducing turnaround time. The buck-boost behavior handles the wide range between a fully charged pack (16.8 V) and a depleted pack (12 V) at fixed VIN. The 4 mm x 4 mm QFN footprint integrates easily into space-constrained charging docks. OTG mode allows the drone pack to share power bidirectionally.
Recommended
Tablet and 2-in-1 Convertible PCs
2-in-1 tablet PCs and detachables with 2- to 3-cell Li-ion batteries use the BQ25731 to handle USB-C PD charging at 5 V, 9 V, 15 V, and 20 V profiles from any USB-C adapter. NVDC keeps the touch screen and SoC powered even with a deeply depleted battery, supporting instant-on behavior. The 12-bit ADC feeds SoC fuel-gauging algorithms via I2C for accurate battery percentage reporting. Wide VIN tolerates charger-cable voltage drop without misbehavior.
Recommended
Recommended Products Summary
Engineering reference data for BQ25731 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BQ25730RSNR | BQ25731RSNR | BQ25731RSNT | BQ25730RSNT |
|---|---|---|---|---|---|
| Package | 32-QFN (RSN) 4x4 mm | 32-QFN (RSN) 4x4 mm - same | 32-QFN (RSN) 4x4 mm - same | 32-QFN (RSN) 4x4 mm - same | 32-QFN (RSN) 4x4 mm - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments |
| Topology | NVDC Buck-Boost | NVDC Buck-Boost (with BATFET) | NVDC Buck-Boost (identical) | NVDC Buck-Boost (identical) | NVDC Buck-Boost (with BATFET) |
| Power Path Management | No (non-power-path) | Yes (integrated BATFET for non-PP apps compatible) | No | No | Yes |
| Input Voltage Range | 3.5 V to 26 V | 3.5 V to 26 V | 3.5 V to 26 V | 3.5 V to 26 V | 3.5 V to 26 V |
| Max Charge Current | 5 A | 5 A | 5 A | 5 A | 5 A |
| USB-C PD 3.0 PPS Support | Yes (3 V to 24 V, 8 mV) | Yes | Yes | Yes | Yes |
| Operating Temperature | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C | -40 C to +85 C |
Key Differentiators
- Non-power-path NVDC design with external BATFET (vs BQ25730RSNR)
- USB-C PD 3.0 PPS with 8 mV OTG voltage resolution (vs Standard fixed-PDO chargers)
- Wide VIN tolerance 3.5 V to 26 V without front-end regulator (vs Narrow-VIN 5 V to 12 V chargers)
Design Notes
Estimated: at 5 A charging from 20 V VIN into a 3-cell (12 V) battery, power dissipation in the charger MOSFETs and inductor can reach 4 W steady-state. With QFN-32 (RSN) package thermal resistance theta_JA of 38 C/W on a 2 oz 4-layer PCB, the junction rises roughly 152 C above ambient. Adequate thermal vias under the exposed pad (EP, pin 30) connected to a 4-layer copper ground pour are essential. Reduce charging current to 3 A or add forced-air cooling if ambient exceeds 50 C.
Place the input capacitor, the inductor, and the SRP/SRN sense resistors within 5 mm of the BQ25731 pins. Keep REGN and VDD bypass capacitors (1 uF and 0.1 uF) within 2 mm of the corresponding pins. Connect the analog ground (AGND) and power ground (PGND) at a single star ground on the exposed pad to prevent switching noise injection into ADC readings. Use a Kelvin-sense layout between SRP and SRN to achieve accurate charge-current regulation.
Do not connect VBUS and VAC with a long trace - keep them on the same node with adequate input capacitance (10 uF minimum). Always configure the BQ25731 over I2C before asserting CE high; otherwise the charger defaults to a safe-but-not-optimal 4.2 V per cell and may not adapt to a USB-C PD adapter. Ensure TS (NTC thermistor) is always populated; leaving it floating disables charging. For OTG operation, program the OTG voltage register and ensure PVLV / PVOK PD controller hand-shaking is complete before driving OTG high.
Route the I2C SDA and SCL away from the switching power traces (PWM1 to PWM4) and from the inductor. Place a 4.7 k pull-up resistor each on SDA and SCL to VDD or to the host's pull-up reference. Use guard traces tied to AGND between analog sense pins (SRP, SRN, VBT) and digital pins. The exposed pad must be soldered directly to the PCB ground plane with at least 9 thermal vias (0.3 mm drill) underneath to provide a low-thermal-resistance path.
Compliance Information
RoHS-compliant per TI product page. Lead-free QFN-32 RSN package. Not AEC-Q100 qualified - for automotive designs use a TI BQ257x8 derivative or external automotive-grade variant. Halogen-free status not explicitly stated in the available product brief; defaulting to unknown per data authenticity rules.
