TOP243 View Datasheet(PDF) - Power Integrations, Inc
Part Name
Description
MFG CO.
'TOP243' PDF : 52 Pages View PDF
TOP242-250
A high V is required to take full advantage of the wider DC
OR
MAX
of TOPSwitch-GX. An RCD clamp provides tighter clamp
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
voltage tolerance than a Zener clamp and allows a VOR as high as
150 V. RCD clamp dissipation can be minimized by reducing
worldwide conducted EMI limits.
the external current limit as a function of input line voltage (see Transformer Design
Figure 21 and 35). The RCD clamp is more cost effective than It is recommended that the transformer be designed for
the Zener clamp but requires more careful design (see quick maximum operating flux density of 3000 Gauss and a peak flux
design checklist).
density of 4200 Gauss at maximum current limit. The turns ratio
Output Diode
should be chosen for a reflected voltage (V ) no greater than
OR
135 V when using a Zener clamp, or 150 V (max) when using
The output diode is selected for peak inverse voltage, output RCD clamp with current limit reduction with line voltage
current, and thermal conditions in the application (including (overload protection).
heatsinking, air circulation, etc.). The higher DCMAX of
TOPSwitch-GX along with an appropriate transformer turns ratio
For designs where operating current is significantly lower than
can allow the use of a 60 V Schoktty diode for higher efficiency the default current limit, it is recommended to use an externally
on output voltages as high as 15 V (see Figure 41. A 12 V, 30 W set current limit close to the operating peak current to reduce
design using a 60 V Schottky for the output diode). General pIenakffoluxrdmensaitytainod pneak&powTera(sbeelFeiguroesf20Canod 3n4)t. eIn nts
most applications, the tighter current limit tolerance, higher
Bias Winding Capacitor
Due to the low frequency operation at no-load a 1 µF bias
winding capacitor is recommended.
80
70
ProdTuOcPStwiStche-IIl(enocjitttoer)r Guide
1
60
Soft-Start
50
Generally a power supply experiences maximum stress at
40
start-up before the feedback loop achieves regulation. For a
period of 10 ms the on-chip soft-start linearly increases the duty
30
Data Sheets 2
Application Notes 3
cycle from zero to the default DCMAX at turn on. In addition, the
primary current limit increases from 85% to 100% over the same
period. This causes the output voltage to rise in an orderly
manner allowing time for the feedback loop to take control of the
duty cycle. This reduces the stress on the TOPSwitch-GX
MOSFET, clamp circuit and output diode(s), and helps prevent
transformer saturation during start-up. Also soft-start limits the
20
-10
0
-10
-20
0.15
Design Ideas 4
EN55022B (QP)
EN55022B (AV)
Design Tools 5
1
10
30
amount of output voltage overshoot, and in many applications
eliminates the need for a soft-finish capacitor.
Frequency (MHz)
Figure 46a.QTOuPSawitlcih-tIIyFuall Rnandge ERMI eScalniability 6
(100 kHz, no jitter).
EMI
The frequency jitter feature modulates the switching frequency
80
Package Information 7
over a narrow band as a means to reduce conducted EMI peaks
70
TOPSwitch-GX (with jitter)
associated with the harmonics of the fundamental switching
frequency. This is particularly beneficial for average detection
mode. As can be seen in Figure 46, the benefits of jitter increase
D6P0 A-Switch
50
DC-DC
Seminar
8
with the order of the switching harmonic due to an increase in
40
frequency deviation.
LinkSwitch & Tin30ySwitch-II AC-DC Seminar 9
20
The FREQUENCY pin of TOPSwitch-GX offers a switching
frequency option of 132 kHz or 66 kHz. In applications that TOP-1S0 witch-GX AC-DC Seminar 10
require heavy snubbers on the drain node for reducing high
0
Sales Representatives and Distributors 11 frequency radiated noise (for example, video noise sensitive
-10
applications such as VCR, DVD, monitor, TV, etc.), operating at
-20
EN55022B (QP)
EN55022B (AV)
66 kHz will reduce snubber loss resulting in better efficiency.
0.15
1
10
30
Also, in applications where transformer size is not a concern, use
of the 66 kHz option will provide lower EMI and higher
Frequency (MHz)
efficiency. Note that the second harmonic of 66 kHz is still
below 150 kHz, above which the conducted EMI specifications
get much tighter.
Figure 46b. TOPSwitch-GX Full Range EMI Scan (132 kHz,
with jitter) with Identical Circuitry and
Conditions.
30 H
9/02
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