LT8300ES5 查看數據表（PDF） - Linear Technology
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LT8300ES5 Datasheet PDF : 24 Pages
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LT8300
Applications Information
VSW
<150V
<120V
VLEAKAGE
VSW
<150V
<120V
VLEAKAGE
VSW
<150V
<120V
VLEAKAGE
tOFF > 350ns
tSP < 250ns
No Snubber
tOFF > 350ns
tSP < 250ns
TIME
TIME
with DZ Snubber
tOFF > 350ns
tSP < 250ns
with RC Snubber
Figure 5. Maximum Voltages for SW Pin Flyback Waveform
TIME
8300 F05
Lℓ
Z
D
•
•
Lℓ
C
R
•
•
8300 F06a
DZ Snubber
Figure 6. Snubber Circuits
8300 F06b
RC Snubber
A snubber circuit is recommended for most applications.
Two types of snubber circuits shown in Figure 6 that can
protect the internal power switch include the DZ (diode-
Zener) snubber and the RC (resistor-capacitor) snubber. The
DZ snubber ensures well defined and consistent clamping
voltage and has slightly higher power efficiency, while the
RC snubber quickly damps the voltage spike ringing and
provides better load regulation and EMI performance.
Figure 5 shows the flyback waveforms with the DZ and
RC snubbers.
For the DZ snubber, proper care must be taken when
choosing both the diode and the Zener diode. Schottky
diodes are typically the best choice, but some PN diodes
can be used if they turn on fast enough to limit the leak-
age inductance spike. Choose a diode that has a reverse-
voltage rating higher than the maximum SW pin voltage.
The Zener diode breakdown voltage should be chosen to
balance power loss and switch voltage protection. The best
compromise is to choose the largest voltage breakdown.
Use the following equation to make the proper choice:
VZENER(MAX) ≤ 150V – VIN(MAX)
For an application with a maximum input voltage of 72V,
choose a 68V Zener diode, the VZENER(MAX) of which is
around 72V and below the 78V maximum.
The power loss in the clamp will determine the power rat-
ing of the Zener diode. Power loss in the clamp is highest
at maximum load and minimum input voltage. The switch
current is highest at this point along with the energy stored
in the leakage inductance. A 0.5W Zener will satisfy most
applications when the highest VZENER is chosen.
8300f
14
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