Diodes are an essential component in many systems, but using them for reverse-connection protection in automotive and other power applications has one weakness: Their forward voltage drop (which can be as low as 0.3 V for a Schottky device) wastes valuable power while the diode’s self-heating due to resistive loss can significantly limit current-handling and operating range. That’s where a clever analog topology called the “ideal” diode can provide major benefits (obviously, it’s not perfect with 0-Ω on-resistance and thus no voltage drop or dissipation, but it comes surprisingly close).
The just-introduced LTC4376 from Analog Devices is an ideal diode rated at 7 A, targeting nominal 12-V automotive battery protection as well as redundant power supplies, portable battery devices, and computer systems and servers. Although internally far more complex than a diode, it’s externally a simple-to-use, three-terminal device in its basic operating configuration—input, output, and ground (Fig. 1).
1. The LTC4376 7-A ideal diode needs just three connections in its basic operating mode. Remaining package pins support shutdown and other operating modes for additional in-circuit flexibility.
The internal 15-mΩ on-resistance N-channel MOSFET replaces a discrete Schottky diode when used in diode-OR and high-current diode applications, thus reducing power consumption, heat dissipation, and even PC board area. A diode of equivalent current-handling rating would be far larger than its 16-pin 5- × 4-mm DFN package (Fig. 2).
2. As load current increases, the span between the dissipation of this ideal diode and a standard Schottky diode becomes more dramatic and consequential.
In operation, the LTC4376 controls the forward voltage drop across the MOSFET to ensure smooth current delivery without oscillation, even at light loads. If a power source fails or is shorted, a fast turn-off minimizes reverse-current transients. The LTC4376 also easily ORs power sources to increase total system reliability.
Operating current is just 150 μA, and a shutdown pin allows users to invoke a corresponding mode that reduces the quiescent current to 9 μA. The pin can also control the forward current path when an external MOSFET is used in series with the internal MOSFET in a back-to-back configuration.
Operating voltage range is 4 to 40 V with reverse-input protection to –40 V. In addition to the many tables and graphs showing performance under various conditions, the datasheet provides examples of how this ideal diode can be used in a basic circuit, as well as with added features such as undervoltage lockout (UVLO). Versions of the LTC4376 are available for 0 to +70°C, −40 to +85°C, and −40 to +125°C operation; the DC2705A evaluation board is also available. Pricing (1000-piece lots) begins at $2.55.
