RT1985 - 23V/8A Ideal Diode Protection Switch | Richtek
MPN: RT1985 ✓ Active| Qty | Unit Price | Extended |
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| 1 | $0 | $0.00 |
| 10 | $0 | $0.00 |
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| 500 | $0 | $0.00 |
| 1,000 | $0 | $0.00 |
RT1985 Overview
An ideal diode protection switch is a high-side power path protection device that replaces a discrete Schottky diode with an actively controlled MOSFET. In the broader power management hierarchy (ideal diode controller -> high-side protection switch -> power management IC), it forwards current with a very low forward voltage drop while actively blocking reverse current when the input falls below the output. This makes it fundamental in diode-OR power source sharing, where two supplies must feed one load without back-feeding each other.
Key features include the integrated back-to-back 20mΩ MOSFETs, which deliver both forward conduction and true reverse current blocking in a single IC, eliminating the external MOSFET and sense elements of conventional ideal diode controllers. The low forward voltage at multi-amp loads dramatically reduces conduction loss and heat compared with a Schottky diode. Programmable soft-start controls inrush current during hot-plug events, while overvoltage, over-temperature, and short-circuit protection guard the downstream load. An enable input allows the device to disconnect the load entirely.
Architecturally, the RT1985 senses forward voltage across its internal MOSFETs and regulates the gate drive to emulate a diode in the forward direction, then opens the back-to-back FETs on detecting reverse current or fault conditions such as overvoltage or short circuit. The 28V absolute maximum rating provides transient headroom above the 23V operating ceiling, valuable on USB-C and other consumer DC inputs exposed to surges.
The 3.4V to 23V operating range and 8A continuous rating make the RT1985 well suited for multi-port USB-C sink current applications, notebook and tablet power-path management, diode-OR sharing of adapters and batteries, and hot-swap protection of 5V-to-20V DC rails. According to Richtek, operation is specified over a -40°C to +125°C junction temperature range.
When designing with this part, budget the conduction loss as I² x R (for example, 8A through 20mΩ dissipates roughly 1.3W) and provide adequate PCB copper on the VDFN-12TL thermal pads. Verify that the programmable soft-start setting limits inrush within the source adapter's capability.
This page synthesizes distributor listings, manufacturer datasheet content, drop-in alternative analysis, and practical design notes not found in the datasheet alone.
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Request AlternativesRT1985 Maximum Ratings & Electrical Characteristics
| Product Type | Ideal Diode Protection Switch (High-Side) |
| Input Operating Range | 3.4 V to 23 V |
| Absolute Maximum Input Rating | 28 V |
| Continuous Current Rating | 8 A |
| Peak Current Rating | 20 A |
| Integrated MOSFET On-Resistance | 20 mOhm (back-to-back pair) |
| Reverse Current Blocking | Yes (ideal diode function) |
| Enable Input | Yes (load disconnection) |
| Protection Features | Overvoltage, Over-temperature, Short-circuit, Programmable soft-start |
| Power Source Sharing | Diode-OR capable |
| Package | VDFN-12TL 3x3 |
| Mounting Type | Surface Mount |
| Operating Junction Temperature | -40C to +125C |
| Application Focus | Multi-port USB-C sink current applications |
RT1985 vdfn-12tl 3x3 Pin Configuration Guide
Pin configuration for RT1985 (vdfn-12tl 3x3 package). This power device features gate, drain, and source terminals. For non-polarized packages, refer to the manufacturer datasheet for exact pin 1 orientation and footprint details. Common applications include power supply design, motor driving, and load switching.
No detailed pinout data available for RT1985.
Refer to the datasheet for full pin configuration.
Typical Applications
RT1985 is suitable for 6 applications: Multi-Port USB-C Sink Power Path, Diode-OR Adapter and Battery Sharing, Hot-Swap DC Rail Protection, Notebook and Tablet Power Path Management, Reverse Polarity and Reverse Current Blocking, Industrial 24V-Adjacent Rail Protection.
Multi-Port USB-C Sink Power Path
The RT1985's headline application, explicitly called out by Richtek: multi-port USB-C sink current management. In a notebook, dock, or monitor with several USB-C ports, any port's VBUS may become the active 5V-20V power source, and the sink controller must gate each port path. The RT1985's 3.4V-23V input range covers the full USB-C PD voltage ladder, its 8A continuous rating supports high-power sink profiles, and its 20mΩ integrated MOSFETs keep conduction loss low - about 1.28W at 8A versus roughly 4W for an equivalent Schottky. The ideal diode function prevents back-feeding between ports, while the enable input lets the PD controller isolate a port during contract negotiation and fault events.
Recommended
Diode-OR Adapter and Battery Sharing
Portable systems frequently combine an AC adapter and a battery pack feeding a common system rail. Two Schottky diodes traditionally performed this ORing, wasting several watts and heat. The RT1985 provides diode-OR power source sharing with its ideal diode function: it conducts forward with only the I²R drop of its 20mΩ MOSFETs and blocks reverse current whenever its input falls below the output, preventing the battery from back-feeding the adapter or the higher rail from charging the lower one unintentionally. The 3.4V-23V range accommodates 5V-to-20V adapters and multi-cell battery stacks, and the enable input allows firmware to select the source or fully disconnect it during fault isolation.
Recommended
Hot-Swap DC Rail Protection
Classified by distributors as a hot-swap voltage controller, the RT1985 protects downstream circuitry when a live DC rail is plugged in. Its programmable soft-start ramps the output voltage at a controlled rate, limiting inrush current into downstream bulk capacitors and preventing input sag and connector arcing on hot-plug events. Integrated overvoltage protection disconnects the load if the input exceeds safe limits, short-circuit protection reacts to load faults, and over-temperature protection folds back or shuts down the internal MOSFETs. The 28V absolute maximum rating adds surge headroom on unregulated adapter inputs, making the part a compact single-IC solution for 5V-20V hot-swap rails up to 8A continuous.
Recommended
Notebook and Tablet Power Path Management
Thin client devices route power among charger, battery, and system rails through narrow, thermally constrained spaces. The RT1985's VDFN-12TL 3x3 footprint integrates the power MOSFETs, eliminating the discrete FET and sense resistor of a controller-based ideal diode design and saving board area. Its low forward drop cuts heat compared with diode-based power paths, easing thermal design in fanless enclosures, and the enable input supports the power sequencing that modern embedded controllers execute during adapter attach, battery insertion, and sleep-state transitions. The 8A rating covers mainstream system rails, while 20A peak capability absorbs transient load steps from SoC power bursts.
Recommended
Reverse Polarity and Reverse Current Blocking
In systems with field-replaceable power sources - barrel-jack adapters, battery sleds, PoE-derived rails - reverse connection or brownout can force current backward into a supply. The RT1985's ideal diode function blocks reverse current by opening its back-to-back MOSFETs when it senses the output exceeding the input, protecting upstream adapters and preventing rail contention. Because the blocking element is a MOSFET rather than a diode, there is no forward recovery behavior and virtually no leakage path in the blocked state relative to a Schottky solution. The 3.4V minimum input means protection stays engaged even on depleted 5V-class rails, and the short-circuit protection limits fault energy if the output rail is dragged low.
Recommended
Industrial 24V-Adjacent Rail Protection
Industrial auxiliaries such as 19V-20V point-of-load inputs, monitor and display rails, and adapter-fed subassemblies sit inside the RT1985's 23V operating ceiling. The part's overvoltage protection guards against adapter miswiring or regulator failure, over-temperature protection suits enclosed fanless hardware, and the short-circuit protection limits damage from board-level faults. The 8A continuous rating covers display backlight drivers, compute modules, and motor-control logic supplies, while the 20A peak rating absorbs capacitive and motor-start transients. Its VDFN-12TL 3x3 package and -40°C to +125°C junction rating align with industrial temperature requirements for factory-floor equipment.
Recommended
Recommended Products Summary
Engineering reference data for RT1985 — comparison, design guidance, and compliance information.
Selection Guide
Key Differentiators
- Fully integrated back-to-back MOSFETs (vs External-MOSFET ideal diode controllers (e.g., generic controller + discrete FET solutions))
- USB-C PD voltage coverage with surge headroom (vs Lower-voltage load switches rated 5.5V or 18V)
- Multi-protection integration with soft-start (vs Simple ideal diode ORing controllers (reverse blocking only))
Design Notes
Estimated: at 8A continuous through the integrated 20mΩ back-to-back MOSFET path, conduction dissipation is I²R = 1.28W. The VDFN-12TL 3x3 package relies on its thermal slug and leadframe pads for heat extraction, so the PCB is the heatsink. Provide solid copper pours on both input and output power pads, use multiple thermal vias stitching to inner planes directly under the exposed pad, and verify junction temperature stays below +125°C at worst-case ambient using the theta-JA figures from the Richtek RT1985 datasheet for your specific board stackup.
Respect the 28V absolute maximum input rating - it provides transient headroom, not continuous operating range; sustained operation must stay within the 3.4V-23V window. Size the programmable soft-start so inrush into downstream bulk capacitance does not trigger short-circuit protection on every hot-plug; increasing soft-start time reduces inrush peak. Also note that 20A peak rating is a transient capability - design the continuous load budget around 8A, and confirm fault response behavior (OV, OC, OT latching versus auto-retry) against the datasheet to match your system recovery policy.
Keep the high-current loop (input pad -> internal MOSFETs -> output pad) short and wide: use at least 2 oz copper on the power layer if the full 8A is continuous, and place input ceramic decoupling close to the IN pad to suppress transients during MOSFET turn-off on fault events. Follow the Richtek datasheet footprint exactly for the VDFN-12TL leadless pads; leadless packages tolerate little solder-joint compensation, so match stencil aperture recommendations to avoid solder voiding under the thermal pad, which would degrade the thermal path computed in the thermal note above.
Compliance Information
Compliance data was not present in the retrieved web data. Richtek typically provides RoHS/green packaging status on its product page; verify against the official Richtek RT1985 product page or datasheet before finalizing compliance documentation.
