AL1672 datasheet(8/14 Pages) DIODES

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AL1672

Document number: DS39344 Rev. 1 - 2

8 of 14

www.diodes.com

July 2017

AL1672

Functional Description and Application Information (Cont.)

Where VOVP is the output over voltage setting; R5 and R6 is shown as Figure.1, it is the resistor divider from auxiliary winding;

NAUX is the turns of L2 auxiliary winding; NP is turns of L2 main winding. 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. Once VCC is below VOPR_MIN, the IC will shut down and power on again by the BUS voltage through the start up

resistor.

3. Over Current Protection (OCP)

The AL1672 has a build-in cycle by cycle over current protection of primary inductor current. When CS pin voltage reaches the voltage VCS_OCP,

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





CS OCP

PEAK MAX



------------------------------------------------ (3)

Where VCS_OCP means primary current clamp voltage that is 1.25V.

RCS is current sense resister which is shown as figure1.

4. Thermal Fold-Back Protection (TFP)

The AL1672 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 +145°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 increase further.

5. Over Temperature Protection (OTP)

The AL1672 has build-in over temperature protection (OTP) function. When the temperature goes up to +165°C, the over temperature protection

will be triggered, which leads to a latch mode protection. When OTP happens, the system need to be powered off and on again to restart.

Output Constant-Current Control

According to the definition of mean output current, the mean output current can be obtained as below.

O MEAN









 

 



------------------------------------------------ (4)

arcsin

RMS

 



------------------------------------------------ (5)

Where IO_MEAN is the mean output current; IP is the peak current of inductance; VIN_RMS is the rate input voltage; VO is the output voltage;

It can be described by following formula:

REF

R dt









 





------------------------------------------------ (6)

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