TOP264EGSLASHVG datasheet(20/36 Pages) POWERINT

20 / 36 page

Rev. B 03/10

TOP264-271

www.powerint.com

frequency. This is particularly beneficial for average detection

mode. As can be seen in Figures 26 and 27, the benefits of jitter

increase with the order of the switching harmonic due to an

increase in frequency deviation. The FREQUENCY pin offers a

switching frequency option of 132 kHz or 66 kHz. In applications

that require heavy snubber on the drain node for reducing high

frequency radiated noise (for example, video noise sensitive

applications such as VCRs, DVDs, monitors, TVs, etc.), operating

at 66 kHz will reduce snubber loss, resulting in better efficiency.

Also, in applications where transformer size is not a concern, use

of the 66 kHz option will provide lower EMI and higher efficiency.

Note that the second harmonic of 66 kHz is still below 150 kHz,

above which the conducted EMI specifications get much tighter.

For 10 W or below, it is possible to use a simple inductor in place

of a more costly AC input common mode choke to meet

worldwide conducted EMI limits.

Transformer Design

It is recommended that the transformer be designed for

maximum operating flux density of 3000 Gauss and a peak flux

density of 4200 Gauss at maximum current limit. The turns ratio

should be chosen for a reflected voltage (V

OR) no greater than

135 V when using a Zener clamp or 150 V (max) when using an

RCD clamp with current limit reduction with line voltage (overload

protection). For designs where operating current is significantly

lower than the default current limit, it is recommended to use an

externally set current limit close to the operating peak current to

reduce peak flux density and peak power (see Figure 17).

Standby Consumption

Frequency reduction can significantly reduce power loss at light

or no load, especially when a Zener clamp is used. For very low

secondary power consumption, use a TL431 regulator for

feedback control. A typical TOP264-271 circuit automatically

enters MCM mode at no load and the low frequency mode at

light load, which results in extremely low losses under no-load

or standby conditions.

High Power Designs

The TOP264-271 family contains parts that can deliver up to

162 W. High power designs need special considerations.

Guidance for high power designs can be found in the Design

Guide for TOP264-271 (AN-47).

TOP264-271 Layout Considerations

The TOP264-271 has multiple pins and may operate at high

power levels. The following guidelines should be carefully

followed.

Primary Side Connections

Use a single point (Kelvin) connection at the negative terminal of

the input filter capacitor for the SOURCE pin and bias winding

return. This improves surge capabilities by returning surge

currents from the bias winding directly to the input filter

capacitor. The CONTROL pin bypass capacitor should be

located as close as possible to the SOURCE and CONTROL

pins, and its SOURCE connection trace should not be shared

by the main MOSFET switching currents. All SOURCE pin

referenced components connected to the VOLTAGE MONITOR

(V pin) or EXTERNAL CURRENT LIMIT (X pin) pins should also

be located closely between their respective pin and SOURCE.

Once again, the SOURCE connection trace of these components

should not be shared by the main MOSFET switching currents.

It is very critical that SOURCE pin switching currents are returned

to the input capacitor negative terminal through a separate trace

that is not shared by the components connected to CONTROL,

VOLTAGE MONITOR or EXTERNAL CURRENT LIMIT pins. This

is because the SOURCE pin is also the controller ground

reference pin. Any traces to the V, X or C pins should be kept

as short as possible and away from the DRAIN trace to prevent

noise coupling. VOLTAGE MONITOR resistors (R

LS in Figures

13, 14, 18, 21, 22, 25, 29) and primary side OVP circuit

components V

ZOV/ROV in Figures (28, 29) should be located close

to the V pin to minimize the trace length on the V pin side.

Resistors connected to the V or X pin should be connected as

close to the bulk cap positive terminal as possible while routing

these connections away from the power switching circuitry. In

addition to the 47

mF CONTROL pin capacitor, a high frequency

bypass capacitor (C

BP) in parallel should be used for better noise

immunity. The feedback optocoupler output should also be

Figure 27. TOPSwitch-JX Full Range EMI Scan (132 kHz With Jitter) With

Identical Circuitry and Conditions.

-20

-10

0.15

Frequency (MHz)

EN55022B (QP)

EN55022B (AV)

EN55022B (QP)

EN55022B (AV)

-20

-10

0.15

Frequency (MHz)

TOPSwitch-JX (with jitter)

Figure 26. Fixed Frequency Operation Without Jitter.

TOP264EG/VG 数据表(PDF) 20 Page - Power Integrations, Inc.

TOP264EG/VG 数据表(HTML) 20 Page - Power Integrations, Inc.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

数据表下载