Datasheet LTC4362-1, LTC4362-2 (Analog Devices) - 10

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APPLICATIONS INFORMATION
Figure 5 shows an input transient after an overcurrent. wall adaptor is mistakenly hot-plugged into the 5V device The current in LIN will cause VIN to overshoot and ava- with the USB input already live. As shown in Figure 7, a lanche the internal N-channel MOSFET to COUT. large current can build up in LIN to charge up COUT. When the internal MOSFET shuts off, this current is dumped into COUT, causing a large 40V transient. The LTC4362 limits this to a 1V rise in the output voltage. V TURN-OFF IN 10V/DIV ICABLE 10A/DIV VOUT 5V/DIV OVERCURRENT ICABLE 2A/DIV VOUT 2V/DIV 2µs/DIV 436212 F05 FIGURE 4 CIRCUIT RIN = 150mΩ, LIN = 0.7µH LOAD = 10Ω, C VIN OUT = 10µF 10V/DIV
Figure 5. Input Transient After Overcurrent
1µs/DIV 436212 F07 RIN = 150mΩ, LIN = 2µH LOAD = 10Ω Typical y, IN wil be clamped to a voltage of V COUT = 10µF (16V, SIZE 1210) OUT + 1.3•(30V BVDSS of Internal MOSFET) = 45V. The single,
Figure 7. Overvoltage Protection Waveforms
nonrepetitive, pulse of energy (EAS) absorbed by the
When 20V Plugged into 5V System
MOSFET during this avalanche breakdown with a peak current IAS is approximated by the formula: If the voltage rise at VOUT due to the discharge of the energy in LIN into COUT is not acceptable or the avalanche 1 E • L 2 capability of the MOSFET is exceeded, an additional exter- AS = IN • IAS 2 nal clamp Z1 such as the SMAJ24A can be placed between IN and GND. Figure 8 shows the resulting waveform. For LIN = 0.7µH and IAS = 3A, then EAS = 3.15µJ. This is within the IAS and EAS capabilities of the internal MOSFET. So in most instances, the LTC4362 can ride through such transients without a bypass capacitor, transient voltage ICABLE 10A/DIV suppressor or other external components at IN. V Figure 6 shows a particularly bad situation which can OUT 2V/DIV occur in a mobile device with dual power inputs. A 20V RIN LIN 20V ICABLE WALL + V – IN ADAPTOR 10V/DIV IN OUT 436212 F08 IN OUT 1µs/DIV B160 C RIN = 150mΩ, LIN = 0.7µH OUT LT4362 LOAD = 10Ω LOAD COUT = 10µF (16V, SIZE 1210) 5V + USB – GND
Figure 8. Overvoltage Protection Waveforms When
436212 F06
20V Plugged into 5V System with External IN Clamp Figure 6. Setup for Testing 20V Plugged into 5V System
Rev. B 10 For more information www.analog.com 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