SCY99080CDWR2G 데이터 시트보기 (PDF) - ON Semiconductor

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SCY99080CDWR2G

High Performance Switch-Mode Power Supply Controller for Backlight and LLC Converters

ON Semiconductor 

DDA002C

Voltage−Controlled Oscillator

The VCO section features a high−speed circuitry allowing

operation from 60 kHz up to 1 MHz. However, as there is an

internal division by two, it creates Q and Q outputs. The final

effective signal on the outputs Lgd, Hgd, Lgs and Hgs

Vdd

therefore switches between 30 kHz and 500 kHz. The VCO

is configured in such a way that if the feedback pin voltage

goes down, the switching frequency goes up. Figure 35

shows simplified architecture of the VCO.

DT

Vref

Vref = 2.5 V

Ct_DT

Vdd

Vdd

RQ

SQ

Rfmin

Vref

Ct_ T_On

Vref = 2.5 V

Vref = 1.2 V

Vdd

10 k

FB

Vref = 1.2 V

SQ

D

CLK

RQ

DT

from

internal logic

B

To drivers

A

Vref_DC_0 = 1.2 V

R_Fmax

Vref_FB_Fault = 6 V

Vdd

Skip

FB_Fault

To_FB_Fault_Timer

Dgs

Vref

On_time_clamp

Vref = 2.5 V

Ct_Dgs

SR_B

To SR drivers

SR_A

Figure 35. Simplified VCO Architecture

The VCO conversion characteristic is shown in Figure 36.

The FB fault is detected in case the feedback voltage is

higher than 6 V. This will happen if the converter is

overloaded or the feedback path is not closed i.e. a broken

optocoupler. The internal fault timer starts to count once the

FB fault is detected and it latches off the controller if the fault

lasts more than 50 ms. To overcome triggering of the FB

fault protection during the application start, the FB timer is

disabled until the soft−start period ends (VSS > 1.9 V).

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