LT8300
applicaTions inForMaTion
Tables 2 and 3 show some recommended diodes and
Zener diodes.
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.
Table 2. Recommended Zener Diodes
V
ZENER
(V)
POWER
(W)
PART
CASE
VENDOR
Undervoltage Lockout (UVLO)
MMSZ5266BT1G
MMSZ5270BT1G
CMHZ5266B
CMHZ5267B
BZX84J-68
BZX100A
68
91
0.5
0.5
0.5
0.5
0.5
0.5
SOD-123 On Semi
SOD-123
A resistive divider from V to the EN/UVLO pin imple-
IN
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:
68
SOD-123 Central
Semiconductor
75
SOD-123
68
SOD323F NXP
SOD323F
100
Table 3. Recommended Diodes
V
REVERSE
1.239V •(R1+ R2)
PART
I (A)
0.625
0.625
(V)
CASE
VENDOR
V
=
=
+ 2.5µA •R1
IN(UVLO+ )
R2
1.223V •(R1+ R2)
R2
BAV21W
BAV20W
200
150
SOD-123 Diodes Inc.
SOD-123
V
IN(UVLO− )
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
capacitanceandinductanceisknown,aseriesresistorcan
be added to the snubber capacitance to dissipate power
andcriticallydampentheringing.Theequationforderiving
the optimal series resistance using the observed periods
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.
V
IN
R1
R2
EN/UVLO
LT8300
RUN/STOP
CONTROL
(OPTIONAL)
GND
( t
and t
) is:
) and snubber capacitance
PERIOD(SNUBBED)
PERIOD
(C
8300 F07
SNUBBER
CSNUBBER
Figure 7. Undervoltage Lockout (UVLO)
CPAR
=
2
t
PERIOD(SNUBBED)
− 1
tPERIOD
2
tPERIOD
LPAR
=
CPAR • 4π2
LPAR
CPAR
RSNUBBER
=
8300f
15
Linear [ Linear ]
