AL8821

Document number: DS37671 Rev. 1 - 2

10 of 14

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January 2015

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AL8821

VIN OVP Protection

AL8821 has an internal over voltage protection to protect IC from excessive input voltage. When the voltage applied at VIN pin exceeds 39V, it will

VCC Regulator

The VCC pin requires a capacitor C3 for stable operation and to store the charge for the large GATE switching currents. Choose a 10V rated low

ESR, X7R or X5R, ceramic capacitor for best performance. A 4.7µF capacitor will be adequate for many applications. Place the capacitor close to

the IC to minimize the trace length to the VCC pin and to the IC ground.

An internal current limit on the VCC output protects the excessive on-chip power dissipation. The VCC pin has set the output to 5V (typ.) to protect

the internal FETs from excessive power dissipation caused by not being fully enhanced. If the VCC pin is used to drive extra circuits beside the

AL8821, the extra loads should be limited to less than 8mA.

applications, it is recommended to use an aluminum electrolytic capacitor with greater than 220µF capacitance.

Compensation Capacitor C4

In applications powered by electronic transformer, the input voltage can change roughly in one cycle of AC power frequency. A 1µF ceramic

capacitor C4 connected from COMP pin to ground help to stabilize the control loop of the regulator.

Diode Selection

For maximum efficiency and performance, the rectifiers (D5) should be fast low capacitance Schottky diodes with low reverse leakage at

maximum operating voltage and temperature. With its low power dissipation, the Schottky diode outperforms other silicon diodes and increases

overall efficiency.

Over Temperature Protection

A over temperature protection feature is to protect the AL8821 from excessive heat damage. When the junction temperature exceeds +160ºC, the

internal FET will be turned off. When junction temperature drops below +120ºC, IC will turn on both FETs and return to normal operation.