AL1666 datasheet(9/16 Pages) DIODES

9 / 16 page

AL1666

Document number: DS42417 Rev. 1 - 2

9 of 16

www.diodes.com

December 2019

AL1666

Application Information (continued)

Protections

1. Output Open Protection (OVP)

The output voltage is reflected by the voltage on t

ransformer’s auxiliary winding. Both FB pin and VCC pin of IC integrate over voltage protection

function. When there is a rapid line and load transient, the output voltage may exceed the regulated value. If VCC exceeds VCC_OVP, the VCC over

voltage protection will be triggered, switch will be turned off and VCC will be discharged. Once VCC is below VOPR_MIN, the IC will shut down and be

powered on again by BUS voltage through start up resistor. If VFB exceeds VFB_CV, the FB over voltage protection will be triggered, switch will be

turned off and VCC will be latched for 16s, then VCC will be discharged. Once VCC is below VOPR_MIN, the IC will shut down and be powered on

again by BUS voltage through start up resistor. Power dissipation is low when FB over voltage protection happens.

Thus, output over voltage depends on the minimum voltage between both OVP

protections’ limitation. It can be gotten by below formula.

OVP

CC OVP

FB CV

AUX

Min













Where VOVP is the output over voltage setting; R5 and R6, shown as Figure 1, divide reflected voltage.

NAUX is the turns of auxiliary wind; NS is turns of the secondary wind. VCC_OVP is OVP Voltage of VCC.

2. Output Short Protection (OSP)

When the output is shorted, the output voltage is clamped to zero. The output voltage of the auxiliary winding, which is proportional to the output

winding, will drop down too. If VFB drops below 0.4V, the output short protection will be triggered, the device cannot detect the tOFF time, and the

device controls the system operation at 4kHz low frequency.

3. Over Current Protection (OCP)

The AL1666 has a built-in cycle by cycle over current protection of primary inductor current. When CS pin voltage reaches the voltage VCS_CLAMP,

switch will be turned off until next switch period. The maximum peak current (IPEAK (MAX)) of the inductor can be calculated as below:

��_��=

VCS_CLAMP

RCS

Where VCS_CLAMP means primary current clamp voltage that is 2V.

RCS is current sense resister which is shown as Figure 1.

4. Secondary Diode/Primary Windings/Secondary Windings Short Protection

The CS voltage will be high when Secondary Diodes/Primary windings/Secondary windings are Shorted. If CS is higher than VCS_OCP, the

protection will be triggered, switch will be turned off and VCC will be latched for 16s, then VCC will be discharged. Once VCC is below VOPR_MIN, the

IC will shut down and power on again by the BUS voltage through the startup resistor. Power dissipation is low when output short protection

happens.

5. Thermal Fold-Back Protection (TFP)

The AL1666 has thermal fold-back function: it adopts self-adaptive control method which can prevent the system from breaking down caused by

over temperature. The overheating temperature is set at +150°C. When the temperature of the IC is higher than this point; the device will decrease

the voltage reference of the

CS linearly till OTP happens. By this way, the device can limit system’s input power at high ambient temperature,

preventing system’s temperature increases further.

6. Over Temperature Protection (OTP)

The AL1666 has built-in Over Temperature Protection (OTP) function. When the temperature goes up to +180°C, the over temperature protection

is triggered, which leads to VCC UVLO. When OTP recovers, the system can be restarted.

AL1666 Fiches technique(PDF) 9 Page - Diodes Incorporated

AL1666 Fiches technique(HTML) 9 Page - Diodes Incorporated

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Fiches technique Télécharger

Lien URL