RT9478M - 24V 4-Switch NVDC Buck-Boost Charger | Richtek
MPN: RT9478M ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.2 | $3.20 |
| 10 | $2.88 | $28.80 |
| 100 | $2.55 | $255.00 |
| 500 | $2.21 | $1,105.00 |
| 1,000 | $1.92 | $1,920.00 |
RT9478M Overview
A buck-boost charge controller is a switching power-supply topology that can step the input voltage either up or down to match the battery voltage, enabling seamless charging from sources whose voltage may lie above, below, or equal to the battery stack voltage. NVDC (Narrow Voltage DC) specifically refers to power-path architecture in which the system rail is held slightly above the battery voltage via a buck converter, allowing the system to operate directly from the adapter when present and seamlessly transition to battery power when unplugged. The RT9478M belongs to the Battery Management -> Multi-Cell Switching Charger family, a hypernym hierarchy of charger IC -> power management IC -> semiconductor.
Key differentiating features include nine operating modes - Low Power, Performance, Active VBUS, Charging, Supplement, OTG, VAP, HiZ, and Learn - giving the system designer fine-grained control over system power states. Integrated protections include over-voltage, under-voltage, over-current, thermal shutdown, and battery temperature sensing through an external thermistor interface. The OTG (On-The-Go) mode allows the battery pack to source 5V back to a USB-C port for powering external devices, supporting modern USB-PD DRP (Dual Role Port) applications.
Architecturally, the RT9478M uses a 4-switch H-bridge buck-boost topology with peak-current-mode control and adaptive dead-time insertion, achieving high efficiency across the entire input voltage range. The internal state machine coordinates the bidirectional power flow between adapter, system rail, and battery, while the integrated ADC monitors voltage, current, and temperature for both telemetry and protection. Compared to discrete solutions, the RT9478M dramatically reduces BOM count by integrating drivers, switches coordination logic, and the protection/monitoring ADC.
Typical applications include USB-C PD charging for 2-4S notebook computers, power banks, portable medical equipment, industrial tablets, and drone battery stations. The wide input range makes it compatible with USB-PD 5V/9V/15V/20V profiles without requiring a separate front-end regulator. The bidirectional OTG capability also enables the same pack to power USB-PD powered accessories.
When designing with the RT9478M, careful attention must be paid to inductor selection and input/output capacitor sizing to maintain stability across the buck and boost operating regions. The thermal pad must be soldered to a sufficiently large copper pour on the PCB, as the device dissipates significant power during boost-mode operation at high VIN. Designers should consult the Richtek reference design for recommended external component values.
This page synthesizes the official datasheet, parametric cross-reference data, and practical design guidance for the RT9478M, providing context beyond what the manufacturer datasheet alone offers for engineers evaluating this part for a multi-cell USB-C PD application.
Drop-in alternatives for RT9478M — 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:
RT9478D
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
RT9470
✅ Drop-In📋 Reference alternative (not in catalog)
RT9478M Maximum Ratings & Electrical Characteristics
| Topology | 4-switch bidirectional buck-boost NVDC charge controller |
| Battery Cell Count | 2S to 4S (2 to 4 cells in series) |
| Input Voltage Range | 3.8 V to 24 V |
| Maximum Input Voltage (Transient) | 26 V |
| Charging Current | Up to 5 A (programmable) |
| Switching Topology | 4-switch H-bridge buck-boost |
| Control Method | Peak current mode with adaptive dead-time |
| OTG Output | 5 V reverse mode (USB On-The-Go) |
| Integrated Gate Driver | 5 V NMOSFET gate driver |
| ADC | 8-bit integrated ADC for telemetry |
| Operating Modes | 9 (Low Power, Performance, Active VBUS, Charging, Supplement, OTG, VAP, HiZ, Learn) |
| Supported Input Sources | USB-C PD, AC-DC adapter, mobile battery |
| Package | QFN (Richtek standard, see datasheet) |
| Mounting Type | Surface Mount |
RT9478M qfn (richtek standard, see datasheet) Pin Configuration Guide
Pin configuration for RT9478M (qfn (richtek standard, see datasheet) package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for RT9478M.
Refer to the datasheet for full pin configuration.
Typical Applications
RT9478M is suitable for 6 applications: USB-C PD Notebook Charger (2S-4S), Portable Power Bank with USB-C PD DRP, Industrial Tablet and Ruggedized Device Charger, Drone Battery Charging Hub, Portable Medical Equipment Charger, Power Tool Battery Charger (18V-20V Max Platforms).
USB-C PD Notebook Charger (2S-4S)
The RT9478M is purpose-built for USB-C PD charging of 2S-4S notebook battery packs. Its 3.8V to 24V input range directly accepts USB-PD 5V/9V/15V/20V profiles without a separate front-end PD trigger IC, while the 4-switch buck-boost topology seamlessly steps the adapter voltage either up or down to match the battery voltage - critical because a fully-charged 4S pack at 16.8V exceeds the 15V PD profile. The integrated 5V NMOSFET gate driver and 9 operating modes simplify notebook power-path design.
Recommended
Portable Power Bank with USB-C PD DRP
The RT9478M's bidirectional OTG mode makes it ideal for USB-C PD Dual Role Port (DRP) power bank applications. The charger can sink current from a USB-C PD adapter to charge the internal 2S-4S battery pack, then reverse the power path to source 5V back to a connected USB-C device. The wide VIN range and up to 5A programmable charge current enable fast charging of high-capacity packs, while the 8-bit integrated ADC monitors voltage, current, and temperature for accurate capacity reporting.
Recommended
Industrial Tablet and Ruggedized Device Charger
Industrial tablets, handheld scanners, and ruggedized field equipment commonly use 2S-4S battery packs charged from wide-input sources. The RT9478M's wide 3.8V to 24V input tolerates unregulated industrial DC rails, USB-C PD sources, and 12V automotive adapters in a single design. The thermal shutdown and over-current protection features are essential for harsh industrial environments, while the HiZ and Learn modes support low-power shipping states and battery impedance measurement for preventive maintenance diagnostics.
Recommended
Drone Battery Charging Hub
Commercial drone charging hubs typically charge multiple 4S-6S Li-ion packs from a single high-power DC source. The RT9478M's 4-switch buck-boost topology handles the dynamic voltage relationship between the DC bus and individual 4S battery packs as their state-of-charge changes during the charge cycle. The integrated gate driver reduces BOM count, while the VAP (Voltage Adaptive Power) mode allows dynamic adjustment of charge current based on adapter capability negotiation - important when multiple packs share a finite DC source.
Recommended
Portable Medical Equipment Charger
Portable medical devices such as infusion pumps, patient monitors, and handheld ultrasound probes use 2S-3S Li-ion battery packs for patient-ward mobility. The RT9478M's comprehensive protection features (OVP, UVP, OCP, thermal shutdown, thermistor monitoring) and integrated 8-bit ADC for accurate telemetry meet the reliability and traceability requirements of medical battery-powered designs. The Low Power Mode extends shelf life for emergency equipment, while bidirectional OTG enables powered accessory operation.
Recommended
Power Tool Battery Charger (18V-20V Max Platforms)
Cordless power tool platforms (18V-20V Max / 5S nominal Li-ion packs) increasingly adopt USB-C PD inputs for compatibility with universal laptop chargers and power banks. The RT9478M's 24V input range accommodates the common USB-PD 20V profile, while the buck-boost topology handles the 5S battery voltage range from 15V (depleted) to 21V (fully charged). The 5A programmable charge current and thermal management features support the fast-charge cycles demanded by professional users.
Recommended
Recommended Products Summary
Engineering reference data for RT9478M — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | RT9478D | RT9470 |
|---|---|---|---|
| Brand | Richtek | Richtek | Richtek |
| Package | QFN (Richtek standard) | QFN (same family) | QFN (same family) |
| Topology | 4-switch buck-boost NVDC | 4-switch buck-boost NVDC | 3A single-cell switching |
| Battery Cell Count | 2S-4S | 2S-4S | 1S |
| Input Voltage Range | 3.8V to 24V (26V transient) | 3.8V to 24V | Up to 6V (single cell) |
| Charge Current | Up to 5A | Up to 5A | Up to 3A |
Key Differentiators
- Wide VIN range (3.8V to 24V) eliminates front-end PD trigger IC (vs TI BQ25700 series)
- 9 integrated operating modes including bidirectional OTG (vs RT9470)
- 2S-4S battery support in single IC (vs RT9470 (1S only))
Design Notes
The RT9478M dissipates significant power during boost-mode operation, particularly when VIN is well below VOUT (e.g., charging a 4S depleted pack from a 5V USB source). The package thermal pad must be soldered to a continuous ground copper pour with multiple thermal vias to an internal ground plane. Estimated: at VIN=5V, VOUT=12V, IOUT=3A, the boost-mode power dissipation approaches 21W; without adequate heatsinking the junction temperature will exceed safe limits. Follow the Richtek reference layout guidelines for copper area recommendations.
Place the four power-path MOSFETs, the inductor, and the input/output ceramic capacitors as close to the IC as possible to minimize parasitic inductance in the high-current switching loops. Use a star-ground topology with the RT9478M's analog ground and power ground separated, joining at a single point near the exposed thermal pad. The I2C pull-up resistors and thermistor network components should be placed away from switching nodes to avoid noise coupling into telemetry signals.
Do not assume the buck-boost transitions are seamless without verifying output voltage behavior at the boundary. The RT9478M switches between buck and boost modes based on the VIN/VOUT ratio, and improper inductor selection can cause subharmonic oscillations or audible noise at the boundary frequency. Use the inductor value and saturation current rating specified in the Richtek reference design, and ensure input capacitance meets the buck-mode ripple current requirement of approximately 0.3 x IOUT.
Compliance Information
RoHS and lead-free per Richtek product page; halogen-free status not explicitly confirmed in available data.
