LTC4412ES6#TRPBF Linear Technology, LTC4412ES6#TRPBF Datasheet - Page 7

IC CTRLR LOWLOS PWRPATH TSOT23-6

LTC4412ES6#TRPBF

Manufacturer Part Number
LTC4412ES6#TRPBF
Description
IC CTRLR LOWLOS PWRPATH TSOT23-6
Manufacturer
Linear Technology
Series
PowerPath™r
Datasheet

Specifications of LTC4412ES6#TRPBF

Applications
Handheld/Mobile Devices
Fet Type
P-Channel
Number Of Outputs
1
Internal Switch(s)
No
Delay Time - On
110µs
Delay Time - Off
13µs
Voltage - Supply
2.5 V ~ 28 V
Current - Supply
16µA
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
TSOT-23-6, TSOT-6
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

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APPLICATIO S I FOR ATIO
Introduction
The system designer will find the LTC4412 useful in a
variety of cost and space sensitive power control applica-
tions that include low loss diode OR’ing, fully automatic
switchover from a primary to an auxiliary source of power,
microcontroller controlled switchover from a primary to
an auxiliary source of power, load sharing between two or
more batteries, charging of multiple batteries from a
single charger and high side power switching.
External P-Channel MOSFET Transistor Selection
Important parameters for the selection of MOSFETs are
the maximum drain-source voltage V
voltage V
The maximum allowable drain-source voltage, V
must be high enough to withstand the maximum drain-
source voltage seen in the application.
The maximum gate drive voltage for the primary MOSFET
is set by the smaller of the V
clamping voltage V
monly used, but if a low supply voltage limits the gate
voltage, a sub-logic level threshold MOSFET should be
considered. The maximum gate drive voltage for the
auxiliary MOSFET, if used, is determined by the external
resistor connected to the STAT pin and the STAT pin sink
current.
As a general rule, select a MOSFET with a low enough
R
load current and an achievable V
operates in the linear region and acts like a voltage
controlled resistor. If the MOSFET is grossly undersized,
it can enter the saturation region and a large V
result. However, the drain-source diode of the MOSFET, if
forward biased, will limit V
the load current, will likely result in excessively high
MOSFET power dissipation. Keep in mind that the LTC4412
will regulate the forward voltage drop across the primary
MOSFET at 20mV if R
R
current in amps. Achieving forward regulation will mini-
mize power loss and heat dissipation, but it is not a
DS(ON)
DS(ON)
to obtain the desired V
can be calculated by dividing 0.02V by the load
GS(VT)
and on-resistance R
U
G(ON).
DS(ON)
U
A logic level MOSFET is com-
DS
IN
supply voltage or the internal
. A large V
is low enough. The required
GS
DS
. The MOSFET normally
while operating at full
W
DS(ON)
DS(MAX),
DS
, combined with
.
U
threshold
DS(MAX),
DS
may
necessity. If a forward voltage drop of more than 20mV is
acceptable then a smaller MOSFET can be used, but must
be sized compatible with the higher power dissipation.
Care should be taken to ensure that the power dissipated
is never allowed to rise above the manufacturer’s recom-
mended maximum level. The auxiliary MOSFET power
switch, if used, has similar considerations, but its V
be tailored by resistor selection. When choosing the
resistor value consider the full range of STAT pin current
(I
V
Many types of capacitors, ranging from 0.1μF to 10μF and
located close to the LTC4412, will provide adequate V
bypassing if needed. Voltage droop can occur at the load
during a supply switchover because some time is required
to turn on the MOSFET power switch. Factors that deter-
mine the magnitude of the voltage droop include the
supply rise and fall times, the MOSFET’s characteristics,
the value of C
insignificant by the proper choice of C
is inversely proportional to the capacitance. Bypass ca-
pacitance for the load also depends on the application’s
dynamic load requirements and typically ranges from 1μF
to 47μF. In all cases, the maximum droop is limited to the
drain source diode forward drop inside the MOSFET.
Caution must be exercised when using multilayer ceramic
capacitors. Because of the self resonance and high Q
characteristics of some types of ceramic capacitors, high
voltage transients can be generated under some start-up
conditions such as connecting a supply input to a hot
power source. To reduce the Q and prevent these tran-
sients from exceeding the LTC4412’s absolute maximum
voltage rating, the capacitor’s ESR can be increased by
adding up to several ohms of resistance in series with the
ceramic capacitor. Refer to Application Note 88.
The selected capacitance value and capacitor’s ESR can be
verified by observing V
age transitions during dynamic conditions over the full
load current range. This should be checked with each
power source as well. Ringing may indicate an incorrect
bypass capacitor value and/or too low an ESR.
S(SNK)
IN
and SENSE Pin Bypass Capacitors
) that may flow through it.
OUT
and the load current. Droop can be made
IN
and SENSE for acceptable volt-
OUT
LTC4412
, since the droop
GS
4412fa
7
can
IN

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