BAV20W 查看數據表（PDF） - Linear Technology
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BAV20W Datasheet PDF : 24 Pages
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LT8300
Applications Information
Tables 2 and 3 show some recommended diodes and
Zener diodes.
Table 2. Recommended Zener Diodes
PART
VZENER POWER
(V)
(W)
CASE VENDOR
MMSZ5266BT1G
68
0.5 SOD-123 On Semi
MMSZ5270BT1G
91
0.5 SOD-123
CMHZ5266B
CMHZ5267B
68
0.5 SOD-123 Central
75
0.5 SOD-123 Semiconductor
BZX84J-68
68
0.5 SOD323F NXP
BZX100A
100
0.5 SOD323F
Table 3. Recommended Diodes
PART
VREVERSE
I (A)
(V)
CASE VENDOR
BAV21W
0.625 200 SOD-123 Diodes Inc.
BAV20W
0.625 150 SOD-123
The recommended approach for designing an RC snubber
is to measure the period of the ringing on the SW pin when
the power switch turns off without the snubber and then
add capacitance (starting with 100pF) until the period of
the ringing is 1.5 to 2 times longer. The change in period
will determine the value of the parasitic capacitance, from
which the parasitic inductance can be determined from
the initial period, as well. Once the value of the SW node
capacitance and inductance is known, a series resistor can
be added to the snubber capacitance to dissipate power
and critically dampen the ringing. The equation for deriving
the optimal series resistance using the observed periods
( tPERIOD and tPERIOD(SNUBBED)) and snubber capacitance
(CSNUBBER) is:
CPAR
=
CSNUBBER
tPERIOD(SNUBBED)
tPERIOD
2
−
1
L PAR
=
tPERIOD 2
CPAR • 4π2
RSNUBBER =
LPAR
CPAR
Note that energy absorbed by the RC snubber will be
converted to heat and will not be delivered to the load.
In high voltage or high current applications, the snubber
may need to be sized for thermal dissipation.
Undervoltage Lockout (UVLO)
A resistive divider from VIN to the EN/UVLO pin imple-
ments undervoltage lockout (UVLO). The EN/UVLO pin
falling threshold is set at 1.223V with 16mV hysteresis.
In addition, the EN/UVLO pin sinks 2.5µA when the volt-
age at the pin is below 1.223V. This current provides user
programmable hysteresis based on the value of R1. The
programmable UVLO thresholds are:
VIN(UVLO + )
=
1.239V • (R1+
R2
R2)
+
2.5µA
•
R1
VIN(UVLO − )
=
1.223V • (R1+
R2
R2)
Figure 7 shows the implementation of external shutdown
control while still using the UVLO function. The NMOS
grounds the EN/UVLO pin when turned on, and puts the
LT8300 in shutdown with quiescent current less than 2µA.
VIN
R1
EN/UVLO
LT8300
R2
GND
8300 F07
RUN/STOP
CONTROL
(OPTIONAL)
Figure 7. Undervoltage Lockout (UVLO)
8300f
15
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