LT4351CMS#TRPBF Linear Technology, LT4351CMS#TRPBF Datasheet - Page 10

• Manufacturer Part Number: LT4351CMS#TRPBF
• Description: IC CTRLR MOSFET DIODE-OR 10MSOP
• Manufacturer: Linear Technology

Specifications of LT4351CMS#TRPBF

• Applications: Paralleled/Redundant Power Supplies
• Fet Type: N-Channel
• Number Of Outputs: 1
• Internal Switch(s): No
• Delay Time - Off: 600ns
• Voltage - Supply: 1.2 V ~ 18 V
• Current - Supply: 1.4mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Delay Time - On: -

LT4351
UV
APPLICATIONS INFORMATION
In that case, the resistor values are set by:
Hysteresis helps prevent erratic behavior due to the noise
on V
dipping when the MOSFETs first turn on and draw down
the voltage on the V
switch turning on and drawing current from the V
pacitors. Use low ESR capacitors for V
Note that because the UV pin uses current hysteresis,
placing a capacitor on UV to ground to filter noise will
reduce the effective hysteresis. Filtering can be achieved
by splitting the R2 resistor, as shown in Figure 4.
To defeat undervoltage fault detection, the UV pin should
be tied higher than 0.33V. UV can be tied to V
V
grounding the OV pin. Do not exceed V
External Shutdown
To externally turn off the MOSFETs, such as to disable the
supply, use an open-collector transistor pulling down on
the UV pin. Note this will not turn off the boost regulator
which will continue to operate.
10
Figure 5. Graphical Representation of the UV and OV Functions
IN
FAULT
R3 =
R2 =
R1=
< 9V. Overvoltage fault detection can be defeated by
IN
REFERRED
+ UV
OV
UV
. Two of the most common noise sources are: V
INPUT
FAULT
FAULT
OV
I
HYST
UV
V
UVHYST
UV
FAULT
HYST
UV
–
FAULT
V
UV
OV
OVERVOLTAGE FILTERED FAULT
OV
UNDERVOLTAGE HYSTERESIS
• UV
FAULT
FAULT
UNDERVOLTAGE FAULT:
(
OVERVOLTAGE FAULT:
• UV
IN
GATE CONTROLLED
– V
BY V
capacitors, and the boost regulator
FAULT
GATE LOW
GATE LOW
FAULT
UV
IN
• V
– V
OV
OUT
– V
• R3
UV
)
• R3
IN
4351 F05
IN
and OUT filtering.
OV
REFERRED
V
V
OV
OV
.
> 0.3V
= 0.3V
IN
provided
UV
REFERRED
V
V
V
UV
UV
UV
IN
= 0.33V
= 0.3V
< 0.3V
ca-
IN
Boost Regulator
The boost regulator will start working as soon as V
greater than 0.85V. The regulator will supply all the cur-
rent for the gate drive amplifier. While the amplifier itself
requires only about 3mA, larger current pulses are required
when charging the MOSFET gate. The reservoir capacitor
on V
The regulator performance is relatively insensitive to the
inductor value. The inductor value does control the fre-
quency of operation. A 4.7µH inductor is recommended
for V
greater than 10V. Several inductors that work well with
the LT4351 are listed in Table 1. Many different sizes and
shapes are available. Consult each manufacturer for more
detailed information and for their entire selection of related
parts. The switching frequency for the boost regulator is
around 1MHz so ferrite core inductors should be used
to obtain the best efficiency. The inductor must handle a
peak current of 0.7A minimum and have a DC resistance
of 0.5Ω or less. Shielded inductors are recommended to
reduce the noise due to inductive switching.
Table 1. Recommended Inductors
PART NUMBER
LPS3314-472ML
LPS4012-103ML
744029004
744042100
SD3112-4R7-R
SD3118-100-R
DD
IN
voltages less than 10V and 10µH for V
will provide this current (Figure 6).
QSW
LT4351
IND (µH)
GND
SW
4.7
4.7
4.7
10
10
10
Figure 6
V
IN
L1
D2
DCR (mΩ)
D1
175
350
200
150
246
295
4351 F06
C
V
DD
DD
Coilcraft
847-639-6400
www.coilcraft.com
Würth Elektronik
www.we-online.com
Coiltronics
www.coiltronics.com
VENDOR
IN
voltages
IN
4351fc
is