L8565G-S08-R datasheet(8/13 Pages) UTC

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L8565

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

8 of 13

www.unisonic.com.tw

QW-R114-004.d



FUNCTIONAL DESCRIPTION(Cont.)

4.1 Brown-Out Protection (BOP)

Input Brown-out occurs if the input voltage VIN falls below the minimum input voltage of the design (i.e. 85V for

universal input voltage range) and the VCC has not entered into the VCC under voltage lockout level yet. For a system

without BOP, the boost converter will increasingly draw a higher current from the mains at a given output power

which may exceed the maximum design values of the input current. The UTC L8565 limits internally the current

drawn from the mains and therefore also limits the input power. The difference of input and output power will result in

decreasing output voltage. If the condition prolongs, the decreasing VOUT will terminate in output under voltage

condition (OUV, 50% of rated), and the IC will be shut down (See section 4.5).

Fig. 8 shows the occurrence of BOP in respect to the ISENSE voltage.

The VIN threshold for BOP to occur is dependent on the voltage at ISENSE and thus the output power. The rated

output power with a minimum VIN (VIN(MIN)) is

0.6

INMIN

OUT

)

rated

(

Due to the internal parameter tolerance, the maximum power with VIN(MIN) before BOP occurs is

INMIN

OUT

(max)

And the BOP takes over the normal operation under rated output power latest at an input voltage of

OUT

BOPMAX

)

rated

(

4.2 Soft Over Current Control (SOC)

The UTC L8565 is designed not to support any output power that corresponds to a voltage lower than -0.73V at

the ISENSE pin. A further increase in the inductor current, which results in a lower ISENSE voltage, will activate the Soft

Over Current Control (SOC). This is a soft control as it does not directly switch off the gate drive like the PCL. It acts

on the nonlinear gain block to result in a reduced PWM duty cycle.

4.3 Peak Current Limit (PCL)

The UTC L8565 is equipped with a cycle by cycle peak current protection feature. It is active when the voltage at

pin 5 (ISENSE) reaches -1.08V. This voltage is amplified by OP1 with a factor of -1.43 and connected to comparator

C2 with a reference voltage of 1.5V as shown in Fig. 9. A deglitcher with 300ns after the comparator improves noise

immunity to the activation of this protection.

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