Datasheet LT4422 (Analog Devices) - 8

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Data Sheet LT4422 BLOCK DIAGRAM IN OUT 15mV REGULATOR 15mV INTERNAL UVLO BIAS VMAX SHDN STATUS (OUT > IN) GND
013
Figure 13. Block Diagram THEORY OF OPERATION
The LT4422 is a single positive voltage ideal diode, utilizing a P-channel power MOSFET with a RON of 50m 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 300mA, the internal MOSFET is fully on, and the forward voltage drop is governed by the ohmic relationship of I ⠂ LOAD RON. Typical on-resistance (50mΩ) 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 low dropout power path. The LT4422 is placed in shutdown mode by driving SHDN low. In shutdown, the device consumes very little quiescent current (typically less than 500nA). It is important to note that the SHDN input, while disabling the LT4422 and reducing its current consumption, does not disconnect the load from the input since the internal MOSFET’s body diode is ever-present. External MOSFETs may be added to configure load-switching applications. STATUS is an open drain output intended to indicate power path conditions. STATUS is designed for connection to a power supply through a pull-up resistor. STATUS pulls low whenever the internal power path is disabled. STATUS may pull low for the following reasons. First, driving SHDN low pulls STATUS low. Second, when the power path is reverse biased (the OUT voltage exceeds the IN voltage by at approximately 20mV), STATUS also pulls low. When the power path is enabled, the STATUS pull-down is removed.
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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 Diode-OR Layout and Thermal Considerations Typical Application High-Load Current Application Reverse Input Voltage Protection Related Parts Outline Dimensions Ordering Guide