Datasheet LT4423 (Analog Devices) - 8

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Data Sheet LT4423 BLOCK DIAGRAM IN OUT 15mV REGULATOR 15mV INTERNAL UVLO BIAS VMAX SHDN STATUS (OUT > IN) THERMAL SHUTDOWN GND
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THEORY OF OPERATION
The LT4423 is a single positive voltage ideal diode, utilizing two integrated back-to-back P-channel power MOSFETs with a RON of 200mΩ. The IN pins form the anode, while the OUT pins form the cathode and are typically connected in parallel with other diode cathodes in an ORing configuration. By applying an input power supply to IN, between 1.9V and 28V, a load can be powered at OUT. An internal gate drive amplifier (see Block Diagram) attempts to regulate the forward (IN - OUT) voltage drop to 15mV. The MOSFET gate overdrive voltage adjusts to maintain the 15mV drop. At load currents above approximately 75mA, the internal MOSFETs are fully on, and the forward voltage drop is governed by the ohmic relationship of I ⠂ LOAD RON. Typical on-resistance (200mΩ) is achieved when IN ≥ 4V. Below IN = 4V, diminishing gate drive causes RON to increase, as shown in the Typical Performance Curves. Operating with high RON and high currents will cause large forward drops and temperature rise. If the OUT voltage exceeds the IN voltage by approximately 20mV, the internal power MOSFET turns off quickly through a fast comparator, disabling the power path. Once disabled, OUT is disconnected from IN. The LT4423 is placed in shutdown mode by driving SHDN low. In shutdown, the device consumes very little quiescent current (typically less than 500nA), the power path disables, and OUT is disconnected from IN. Driving SHDN high enables the power path, connecting the load at OUT to the input power supply connected to IN. Integrated thermal protection disconnects the power path when the junction temperature exceeds 160°C (typical). While the power path is disabled due to the overtemperature condition, the device remains active and consumes power. Once the device cools down to about 145°C, the power path is restored (assuming the OUT voltage does not exceed the IN voltage by approximately 20mV, and the device has not been placed into shutdown mode by driving SHDN low).
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Rev. 0 8 of 18 Document Outline Features Applications General Description Simplified Application Diagram TABLE OF CONTENTS Revision History Specifications Absolute Maximum Ratings Pin Configurations and Function Descriptions Typical Performance Characteristics Block Diagram Theory of Operation Applications Information USB PD 3.0 and Back-Up Battery Supply Automatic Power Path Control 5V Power Ride-Through High-Voltage Load Switch with Load Sharing and Undervoltage Lockout Layout and Thermal Considerations Typical Applications High-Load Current Application Reverse Input Voltage Protection Related parts Outline Dimensions Ordering Guide