Datasheet LTC4362-1, LTC4362-2 (Analog Devices) - 7

link to page 7 LTC4362-1/LTC4362-2
OPERATION
If the voltage at the IN pin exceeds 5.8V (VIN(OV)), the The LTC4362 has a CMOS compatible ON input. When internal N-channel MOSFET is turned off quickly to protect driven low, the part is enabled. When driven high, the the load. The incoming power supply must remain below internal N-channel MOSFET is turned off and the sup- 5.7V (VOUT(OV) – ∆VOV) for the duration of the start-up ply current of the LTC4362 drops to 1.5μA. The PWRGD delay to restart the OUT ramp-up. pull-down releases during this low current sleep mode, An internal sense resistor is used to implement an UVLO, overvoltage, overcurrent or thermal shutdown and overcurrent protection with a 1.5A current trip thresh- the subsequent 130ms start-up delay. After the start-up old and a 10µs glitch filter. After an overcurrent, the delay, the internal MOSFET gate starts its 3V/ms ramp-up. LTC4362-1 latches off while the LTC4362-2 restarts fol- It trips an internal gate high threshold to trigger a 65ms lowing a 130ms delay. delay. When that completes, PWRGD pulls low. The output pull-down device is capable of sinking up to 3mA allowing it to drive an optional LED. The LTC4362 has a GATEP pin that drives an optional external P-channel MOSFET to provide protection against negative voltages at IN.
APPLICATIONS INFORMATION
The typical LTC4362 application protects 2.5V to 5.5V
OUT Control
systems in portable devices from power supply overvolt- An internal charge pump enhances the internal N-channel age. The basic application circuit is shown in Figure 1. MOSFET with the OUT ramp-rate limited to 3V/ms. This Device operation and external component selection is results in an inrush current into the load capacitor C discussed in detail in the following sections. OUT of: dV V I OUT V OUT = C [ ] IN INRUSH = COUT • OUT • 3 mA /µF IN OUT 5V 5V dt 5V COUT 0.5A VIO 10µF LTC4362 R1
Overvoltage
1k D1 When power is first applied, VIN must remain below 5.7V ON PWRGD LN1351CTR (V GND IN(OV) – ∆VOV) for more than 130ms before the output is 436212 F01 turned on. If VIN then rises above 5.8V (VIN(OV)), the over- voltage comparator turns off the internal MOSFET within
Figure 1. Protection from Overvoltage and Overcurrent
1µs. After an overvoltage condition, the MOSFET is held
Start-Up
off until VIN once again remains below 5.7V for 130ms. When VIN is less than the undervoltage lockout level of
Overcurrent
2.1V, the internal N-channel MOSFET is held off and the PWRGD pull-down is high impedance. When VIN rises The overcurrent comparator protects the internal MOSFET above 2.1V and ON is held low, a 130ms delay cycle from excessive current. It trips when IOUT > 1.5A for 10µs. starts. Any undervoltage or overvoltage event at IN (VIN When the overcurrent comparator trips, the internal < 2.1V or VIN > 5.7V) restarts the delay cycle. This delay MOSFET is turned off quickly and the PWRGD pull-down allows the MOSFET to isolate the output from any input releases. The LTC4362-2 automatically tries to apply transients that occur at start-up. When the delay cycle power again after a 130ms start-up delay. The LTC4362-1 completes, the MOSFET is turned on and OUT starts its has an internal latch that maintains this off state until it is slow ramp-up. reset. To reset this latch, cycle IN below 2.1V (VIN(UVL)) Rev. B For more information www.analog.com 7 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings order information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts