Datasheet LT8390 (Analog Devices) - 24

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APPLICATIONS INFORMATION ISMON Current Monitor
VOUT The ISMON pin provides a buffered monitor output of the LT8390 R3 current flowing through the ISP/ISN current sense resistor, FB RIS. The VISMON voltage is calculated as V(ISP-ISN) • 10 + R4 0.25V. Since the ISMON pin has the same 0.25V offset as the CTRL pin, the master LT8390 ISMON pin can be 8390 F15 directly tied to the slave LT8390 CTRL pin for equal current
Figure 15. Feedback Resistor Connection
sharing in parallel applications. capacitors, the output voltage may overshoot a lot during
Load Switch Control
load transient event. Once the FB pin hits its overvoltage The LOADEN and LOADTG pins provide high side PMOS threshold 1.1V, the LT8390 stops switching by turning load switch control. The LOADEN pin accepts a logic level off TG1, BG1, TG2, and BG2, and also turns off LOADTG ON/OFF signal and then drives the LOADTG pin to turn on to disconnect the output load for protection. The output or off the high side PMOS load switch, thereby connect- overvoltage threshold can be set as: ing or disconnecting the LT8390 power output from the system output. When the LOADEN pin is forced low, the VOUT(OVP) = 1.1V • R3+R4 R4 LT8390 turns off TG1 and TG2, turns on BG1 and BG2, disconnects the V To provide the output short-circuit detection and protec- C pin from all internal loads, and turns off LOADTG. The LOADEN pin should not be left open (tie tion, the output short threshold can be set as: to INTVCC or VREF if not used). VOUT(SHORT) = 0.25V • R3+R4
High Side PMOS Load Switch Selection
R4 A high side PMOS load switch is recommended in some
Power GOOD (PGOOD) Pin
LT8390 applications requiring load switch control. The high side PMOS load switch is typically selected for drain-source The LT8390 provides an open-drain status pin, PGOOD, voltage V which is pulled low when V DS, gate-source threshold voltage VGS(TH), and FB is within ±10% of the 1.00V continuous drain current I regulation voltage. The PGOOD pin is allowed to be pulled D. For proper operations, VDS rating should exceed the output regulation voltage set by up by an external resistor to INTVCC or an external voltage the FB pin, the absolute value of V source of up to 6V. GS(TH) should be less than 3V, and ID rating should be above IOUT(MAX).
Soft-Start and Short-Circuit Protection Programming Output Voltage and Thresholds
As shown in Figure 8 and explained in the Operation sec- The LT8390 has a voltage feedback pin FB that can be used tion, the SS pin can be used to program the output voltage to program a constant-voltage output. The output voltage soft-start by connecting an external capacitor from the SS can be set by selecting the values of R3 and R4 (Figure pin to ground. The internal 12.5µA pull-up current charges 15) according to the following equation: up the capacitor, creating a voltage ramp on the SS pin. As the SS pin voltage rises linearly from 0.25V to 1V (and V beyond), the output voltage rises smoothly into its final OUT = 1V • R3 +R4 R4 voltage regulation. The soft-start time can be calculated as: In addition, the FB pin also sets output overvoltage C t SS threshold, PGOOD upper and lower thresholds, and out- SS = 1V • 12.5µA put short threshold. For an application with small output 8390fa 24 For more information www.linear.com/LT8390 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts