Overview
The LT4321HUF#TRPBF, produced by Analog Devices Inc., is a dual ideal diode bridge controller designed to enable Power over Ethernet (PoE) powered devices (PDs) to receive power from RJ-45 data pairs, spare pairs, or both. This controller replaces the traditional eight diodes in a passive PoE rectifier bridge with eight N-channel MOSFETs, enhancing thermal design and increasing delivered power. The LT4321 features an internal charge pump that allows for an all-NMOS bridge, eliminating the need for larger and more costly PMOS switches. It supports both 2-pair and 4-pair applications and includes high impedance input sense pins to prevent reverse current on unused pairs.
Key Specifications
| Parameter | Conditions | Min | Typ | Max | Units |
|---|---|---|---|---|---|
| Operating Supply Range | |IN12 – IN36|, |IN45 – IN78|, OUTP | 20 | 80 | V | |
| Undervoltage Lockout (VUVLO) | OUTP – OUTN | 15 | 17 | 18 | V |
| Total Supply Current in Detect Region (IS(DET)) | mA | ||||
| EN Pull-Down Resistance (Active High) | OUTP = 55V | 160 | 250 | 310 | kΩ |
| Digital Input High (VIH) | EN, EN | 2.6 | V | ||
| Digital Input Low (VIL) | EN, EN | 0.5 | V | ||
| Topside Forward Regulation Voltage (∆VSD) | INn – OUTP | 2 | 10 | 18 | mV |
| Bottom Comparator Turn-On Threshold | INn – OUTN | –30 | –15 | 0 | mV |
| Bottom Comparator Turn-Off Threshold | INn – OUTN | 2 | 15 | 30 | mV |
| Operating Ambient Temperature Range | –40°C to 125°C | °C | |||
| Package Type | 16-Lead 4mm × 4mm Plastic QFN |
Key Features
- Ideal Diode Bridge Mode: The LT4321 saves power by activating MOSFETs in place of power path diodes, enhancing efficiency and reducing thermal issues.
- Internal Charge Pump: Allows for an all-NMOS bridge, eliminating the need for larger and more costly PMOS switches.
- High Impedance Input Sense Pins: Prevents reverse current on unused pairs, ensuring reliable operation.
- Fast Turn-Off: Minimizes reverse current transients in case of power source failure or short circuits.
- Support for 2-Pair and 4-Pair Applications: Flexible design to accommodate various PoE configurations.
- Tolerance to Transients: The LT4321 operates through hot-plugs, input short-circuits, common mode shift, and PCB leakage without enabling the MOSFETs unnecessarily.
Applications
- Power over Ethernet (PoE) Devices: Ideal for PoE powered devices (PDs) that require efficient and reliable power delivery from Ethernet cables.
- Networking Equipment: Suitable for use in switches, routers, and other network devices that support PoE.
- Industrial Automation: Can be used in industrial automation systems where reliable and efficient power delivery is critical.
- IoT Devices: Applicable for Internet of Things (IoT) devices that require power over Ethernet connections.
Q & A
- What is the primary function of the LT4321?
The LT4321 is a dual ideal diode bridge controller that enables PoE powered devices to receive power from Ethernet cables efficiently.
- What type of MOSFETs does the LT4321 use?
The LT4321 uses eight N-channel MOSFETs to replace the traditional diodes in a passive PoE rectifier bridge.
- What is the operating supply range of the LT4321?
The operating supply range of the LT4321 is from 20V to 80V.
- What is the purpose of the internal charge pump in the LT4321?
The internal charge pump allows for an all-NMOS bridge, eliminating the need for larger and more costly PMOS switches.
- How does the LT4321 handle reverse current on unused pairs?
The LT4321 prevents reverse current on unused pairs through its high impedance input sense pins.
- What happens in case of a power source failure or short circuit?
In case of a power source failure or short circuit, the LT4321 minimizes reverse current transients with a fast turn-off mechanism.
- Does the LT4321 support both 2-pair and 4-pair PoE applications?
Yes, the LT4321 supports both 2-pair and 4-pair PoE applications.
- What is the operating ambient temperature range of the LT4321?
The operating ambient temperature range of the LT4321 is from –40°C to 125°C.
- What type of package does the LT4321 come in?
The LT4321 comes in a 16-Lead 4mm × 4mm Plastic QFN package.
- Is the LT4321 tolerant to hot-plugs and other transients?
Yes, the LT4321 is tolerant to hot-plugs, input short-circuits, common mode shift, and PCB leakage.
