ISL6731AFBZ datasheet(13/20 Pages) RENESAS

13 / 20 page

ISL6731A, ISL6731B

FN8582 Rev 1.00

Page 13 of 20

February 13, 2015

Protection Circuits

Input Brownout, BO Protection

Brownout occurs when there is a drop in the line voltage. The BO

pin is a dual function pin. The BO pin detects the brownout

condition and shuts down the gate driver and controller. During

normal operation, the BO pin is used to compensate the effect of

the input line voltage change on the voltage loop. To keep the

harmonic distortion low, the corner frequency formed by the RBO

and CBO should be lower than 6Hz.

The BO pin is the output of the average voltage of the rectified

voltage. The PFC controller is turned off when the BO pin drops

below 0.4V. This protects the PFC power stage to enable

operation at or below brownout condition for long periods of

time. The controller resumes operation when the BO pin returns

to 0.5V.

The BO pin is usually connected to GND through a capacitor, CBO.

To avoid distortion on the VIN pin, select CBO so that:

Overcurrent Protection

The peak current limit function prevents the inductor from

saturation. The gate driver turns off when the current goes above

the current limit set point.

Overpower Protection

The overpower protection is implemented by limiting the COMP

pin voltage higher than 3.85V (typical).

Overvoltage Protection

If the voltage on the FB pin exceeds the reference voltage VREF by

about 4%, the gate driver is turned off.

If the voltage on the OVP pin exceeds the VREF by about 4.5%, the

gate driver is turned off.

The controller resumes normal operation after both OVP and FB

pin drops below VREF.

Over-Temperature Protection

The ISL6731A and ISL6731B are protected against

over-temperature conditions. When the junction temperature

exceeds +160°C, the PWM shuts down. Normal operation is

resumed when the junction temperature decreases below +135°C.

Application Guidelines

Layout Considerations

As in any high frequency switching converter, layout is very

important. Switching current from one power device to another

can generate voltage transients across the impedances of the

interconnecting bond wires and circuit traces. These

interconnecting impedances should be minimized by using wide,

short printed circuit traces. The critical components should be

located as close together as possible using ground plane

construction or single point grounding.

Figure 14 shows the critical power components; Q1, D and COUT.

To minimize the voltage overshoot, the interconnecting wires

indicated by heavy lines should be part of the ground or the

power plane in a printed circuit board. The components shown in

Figure 14 should be located as close together as possible. Please

note that the capacitors CVCC and CO each represent numerous

physical capacitors. Locate the ISL6731A or ISL6731B within 2

inches of the MOSFET, Q1. The circuit traces for the MOSFETs’

gate and source connections from the ISL6731A and ISL6731B

must be sized to handle up to 1.5A peak current.

Component Selection Guidelines

A 300W, universal input, PFC converter design is provided for

demonstration. The design method is for a continuous current

mode power factor correction boost converter with the

ISL6731B. The switching frequency is 62kHz.

Tables 3 shows the design parameters.

BOOST INDUCTOR SELECTION

First, calculate the maximum input RMS current, IINMAX.

Where

 is the converter efficiency at VRMSmin. PF is the power

factor at VRMSmin.

Assuming the current is sinusoidal and the peak-to-peak ripple at

line is 40%.

CBO 0.22F

(EQ. 6)

TABLE 3. CONVERTER DESIGN PARAMETERS

PARAMETER

CONDITIONS

MIN

TYP

MAX UNIT

VLINE

115/230 265

VAC

FLINE

POMAX

Maximum Output Power

300

THOLD

Hold Up Time

Efficiency

VLINE = 115VAC

FIGURE 14. CRITICAL CURRENT POWER COMPONENTS

COUT

GATE

VCC

CVCC

IINMAX

POMAX

 V



RMSmin

-----------------------------------

(EQ. 7)

IINMAX

300W

0.92 90V



----------------------------

3.62A

(EQ. 8)

ISL6731AFBZ Datasheet(PDF) 13 Page - Renesas Technology Corp

ISL6731AFBZ Datasheet(HTML) 13 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL