LTC4412
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For more information www.linear.com/LTC4412
Typical applicaTion
DescripTion
Low Loss PowerPath™
Controller in ThinSOT
The LT C
®
4412 controls an external P-channel MOSFET to
create a near ideal diode function for power switchover
or load sharing. This permits highly efficient OR’ing of
multiple power sources for extended battery life and low
self-heating. When conducting, the voltage drop across
the MOSFET is typically 20mV. For applications with a
wall adapter or other auxiliary power source, the load is
automatically disconnected from the battery when the
auxiliary source is connected. Tw o or more LTC4412s
may be interconnected to allow load sharing between
multiple batteries or charging of multiple batteries from
a single charger.
The wide supply operating range supports operation
from one to six Li-Ion cells in series. The low quiescent
current (11µA typical) is independent of the load current.
The gate driver includes an internal voltage clamp for
MOSFET protection.
The STAT pin can be used to enable an auxiliary P-channel
MOSFET power switch when an auxiliary supply is
detected. This pin may also be used to indicate to a mi-
crocontroller that an auxiliary supply is connected.
The
control (CTL) input enables the user to force the primary
MOSFET off and the STAT pin low.
The LTC4412 is available in a low profile (1mm) ThinSOT
package.
LTC4412 vs Schottky Diode
Forward Voltage Drop
FeaTures
applicaTions
n Very Low Loss Replacement for Power Supply
OR’ing Diodes
n Minimal External Components
n Automatic Switching Between DC Sources
n Simplifies Load Sharing with Multiple Batteries
n Low Quiescent Current: 11µA
n 3V to 28V AC/DC Adapter Voltage Range
n 2.5V to 28V Battery Voltage Range
n Reverse Battery Protection
n Drives Almost Any Size MOSFET for Wide Range of
Current Requirements
n MOSFET Gate Protection Clamp
n Manual Control Input
n Low Profile (1mm) ThinSOT™ Package
n Cellular Phones
n Notebook and Handheld Computers
n Digital Cameras
n USB-Powered Peripherals
n Uninterruptible Power Supplies
n Logic Controlled Power Switch
Figure 1. Automatic Switchover of Load Between a Battery and a Wall Adapter
VIN
GND
CTL
SENSE
GATE
STAT
LTC4412 COUT
TO LOAD
STATUS OUTPUT
LOW WHEN WALL
ADAPTER PRESENT
470k
4412 F01
VCC
BATTERY
CELL(S)
WALL
ADAPTER
INPUT
FORWARD VOLTAGE (V)
0.02
0
CURRENT (A)
1
CONSTANT
RON
4412 F01b
0.5
CONSTANT
VOLTAGE SCHOTTKY
DIODE
LTC4412
L, LT , LT C , LT M , Linear Technology and the Linear logo are registered trademarks and
PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
LTC4412
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For more information www.linear.com/LTC4412
pin conFiguraTionabsoluTe MaxiMuM raTings
Supply Voltage (VIN) .................................. –14V to 36V
Voltage from VIN to SENSE ........................ – 28V to 28V
Input Voltage
CTL ........................................................–0.3V to 36V
SENSE .................................................... –14V to 36V
Output Voltage
GATE ..................... –0.3V to the Higher of VIN + 0.3V
or SENSE + 0.3V
STAT ......................................................–0.3V to 36V
Operating Junction Temperature Range
(Note 2) ........................................... – 55°C to 150°C
Storage Temperature Range ...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
(Note 1)
VIN 1
GND 2
CTL 3
6 SENSE
5 GATE
4 STAT
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 230°C/W
orDer inForMaTion
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4412ES6#PBF LTC4412ES6#TRPBF LTA 2 6-Lead Plastic TSOT-23 –40°C to 85°C
LTC4412IS6#PBF LTC4412IS6#TRPBF LTA 2 6-Lead Plastic TSOT-23 –40°C to 85°C
LTC4412HS6#PBF LTC4412HS6#TRPBF LTA 2 6-Lead Plastic TSOT-23 –40°C to 150°C
LTC4412MPS6#PBF LTC4412MPS6#TRPBF LTA 2 6-Lead Plastic TSOT-23 –55°C to 150°C
LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4412ES6 LTC4412ES6#TR LTA 2 6-Lead Plastic TSOT-23 –40°C to 85°C
LTC4412IS6 LTC4412IS6#TR LTA 2 6-Lead Plastic TSOT-23 –40°C to 85°C
LTC4412HS6 LTC4412HS6#TR LTA 2 6-Lead Plastic TSOT-23 –40°C to 150°C
LTC4412MPS6 LTC4412MPS6#TR LTA 2 6-Lead Plastic TSOT-23 –55°C to 150°C
Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
LTC4412
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For more information www.linear.com/LTC4412
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
junction temperature range, unless otherwise noted specifications are at TA = 25°C, VIN = 12V, CTL and GND = 0V. Current into a pin is
positive and current out of a pin is negative. All voltages are referenced to GND, unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN,
VSENSE
Operating Supply Range VIN and/or VSENSE Must Be in This Range
for Proper Operation
l2.5 28 V
IQFL Quiescent Supply Current at Low Supply
While in Forward Regulation
VIN = 3.6V. Measure Combined Current
at VIN and SENSE Pins Averaged with
VSENSE = 3.5V and VSENSE = 3.6V (Note 3)
l11 19 µA
IQFH Quiescent Supply Current at High Supply
While in Forward Regulation
VIN = 28V. Measure Combined Current
at VIN and SENSE Pins Averaged with
VSENSE = 27.9V and VSENSE = 28V (Note 3)
l15 26 µA
IQRL Quiescent Supply Current at Low Supply
While in Reverse Turn-Off
VIN = 3.6V, VSENSE = 3.7V. Measure
Combined Current of VIN and SENSE Pins
10 19 µA
IQRH Quiescent Supply Current at High Supply
While in Reverse Turn-Off
VIN = 27.9V, VSENSE = 28V. Measure
Combined Current of VIN and SENSE Pins
16 28 µA
IQCL Quiescent Supply Current at Low Supply
with CTL Active
VIN = 3.6V, VSENSE = 0V, VCTL = 1V 7 13 µA
IQCH Quiescent Supply Current at High Supply
with CTL Active
VIN = 28V, VSENSE = 0V, VCTL = 1V 12 20 µA
ILEAK VIN and SENSE Pin Leakage Currents
When Other Pin Supplies Power
VIN = 28V, VSENSE = 0V; VSENSE = 28V, VIN = 0V
VIN = 14V, VSENSE = –14V; VSENSE = 14V, VIN = –14V
–3 0 1 µA
PowerPath Controller
VFR PowerPath Switch Forward Regulation
Voltage
VIN – VSENSE, 2.5V ≤ VIN ≤ 28V l10 20 32 mV
VRTO PowerPath Switch Reverse Turn-Off
Threshold Voltage
VSENSE – VIN, 2.5V ≤ VIN ≤ 28V l10 20 32 mV
GATE and S TAT Outputs
IG(SRC)
IG(SNK)
GATE Active Forward Regulation
Source Current
Sink Current
(Note 4)
–1
25
–2.5
50
–5
85
µA
µA
VG(ON) GATE Clamp Voltage Apply IGATE = 1µA, VIN = 12V,
VSENSE = 11.9V, Measure VIN – VGATE
6.3 7 7.7 V
VG(OFF) GATE Off Voltage Apply IGATE = –5µA, VIN = 12V,
VSENSE = 12.1V, Measure VSENSE – VGATE
0.13 0.25 V
tG(ON) GATE Turn-On Time VGS < –3V, CGATE = 1nF (Note 5) 110 175 µs
tG(OFF) GATE Turn-Off Time VGS > –1.5V, CGATE = 1nF (Note 6) 13 22 µs
IS(OFF) STAT Off Current 2.5V ≤ VIN ≤ 28V (Note 7) l–1 0 1 µA
IS(SNK) STAT Sink Current 2.5V ≤ VIN ≤ 28V (Note 7) l6 10 17 µA
tS(ON) STAT Turn-On Time (Note 8) 4.5 25 µs
tS(OFF) STAT Turn-Off Time (Note 8) 40 75 µs
CTL Input
VIL CTL Input Low Voltage 2.5V ≤ VIN ≤ 28V l0.5 0.35 V
VIH CTL Input High Voltage 2.5V ≤ VIN ≤ 28V l0.9 0.635 V
ICTL CTL Input Pull-Down Current 0.35V ≤ VCTL ≤ 28V 1 3.5 5.5 µA
HCTL CTL Hysteresis 2.5V ≤ VIN ≤ 28V 135 mV
LTC4412
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For more information www.linear.com/LTC4412
elecTrical characTerisTics
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC4412 is tested under pulsed load conditions such that TJ ≈
TA. The LTC4412E is guaranteed to meet performance specifications from
0°C to 85°C operating junction temperature range. Specifications over
the –40°C to 85°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC4412I is guaranteed over the –40°C to 85°C operating junction
temperature range. The LTC4412MP is tested and guaranteed over the
–55°C to 150°C operating junction temperature range. High junction
temperatures degrade operating lifetimes; operating lifetime is degraded
for junction temperatures greater than 125°C. Note that the maximum
ambient temperature consistent with these specifications is determined
by specific operating conditions in conjunction with board layout, the
rated package thermal impedance and other environmental factors. TJ
is calculated from the ambient temperature TA and power dissipation PD
according to the following formula: TJ = TA + (PD • ΘJA), where ΘJA =
230°C/W for the TSOT-23 package.
Note 3: This results in the same supply current as would be observed with
an external P-channel MOSFET connected to the LTC4412 and operating in
forward regulation.
Note 4: VIN is held at 12V and GATE is forced to 10.5V. SENSE is set at
12V to measure the source current at GATE. SENSE is set at 11.9V to
measure sink current at GATE.
Note 5: VIN is held at 12V and SENSE is stepped from 12.2V to 11.8V to
trigger the event. GATE voltage is initially VG(OFF).
Note 6: VIN is held at 12V and SENSE is stepped from 11.8V to 12.2V to
trigger the event. GATE voltage is initially internally clamped at VG(ON).
Note 7: STAT is forced to VIN – 1.5V. SENSE is set at VIN – 0.1V to
measure the off current at STAT. SENSE is set VIN + 0.1V to measure the
sink current at STAT.
Note 8: STAT is forced to 9V and VIN is held at 12V. SENSE is stepped
from 11.8V to 12.2V to measure the STAT turn-on time defined when ISTAT
reaches one half the measured IS(SNK). SENSE is stepped from 12.2V to
11.8V to measure the STAT turn-off time defined when ISTAT reaches one
half the measured IS(SNK) .
LTC4412
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For more information www.linear.com/LTC4412
Typical perForMance characTerisTics
TEMPERATURE (°C)
–75
–25
25
75
125
175
15
20
25
V
FR
(mV)
Supply Voltage
V
FR
vs Temperature and
4412 G01
V
IN
= 2.5V
V
IN
= 28V
TEMPERATURE (°C)
–75
–25
25
75
125
175
15
20
25
V
RTO
(mV)
Supply Voltage
V
RTO
vs Temperature and
4412 G02
V
IN
= 2.5V
V
IN
= 28V
TEMPERATURE (°C)
–75
–25
25
75
125
175
0.95
1.00
1.05
1.10
1.15
CURRENT (µA)
Current vs Temperature
Normalized Quiescent Supply
4412 G03
3.6V ≤ V
IN
≤ 28V
TEMPERATURE (°C)
–75
–25
25
75
125
175
–0.4
–0.35
–0.3
–0.25
–0.2
CURRENT (µA)
I
LEAK
vs Temperature
4412 G04
TEMPERATURE (°C)
–75
–25
25
75
125
175
6.85
6.95
7.05
VOLTAGE (V)
V
G(ON)
vs Temperature
4412 G05
8V ≤ V
IN
≤ 28V
I
GATE
= 1µA
TEMPERATURE (°C)
–75
–25
25
75
125
175
0.00
0.10
0.20
0.30
VOLTAGE (V)
V
G(OFF)
vs Temperature and I
GATE
4412 G06
I
GATE
= –10µA
I
GATE
= –5µA
I
GATE
= 0µA
2.5V ≤ V
IN
≤ 28V
TEMPERATURE (°C)
–75
–25
25
75
125
175
94
100
106
TIME (µs)
t
G(ON)
vs Temperature
4412 G07
3.6V ≤ V
IN
≤ 28V
C
GATE
= 1nF
TEMPERATURE (°C)
–75
–25
25
75
125
175
12.0
12.5
13.0
TIME (µs)
t
G(OFF)
vs Temperature
4412 G08
3.6V ≤ V
IN
≤ 28V
C
GATE
= 1nF
TEMPERATURE (°C)
–75
–25
25
75
125
175
10.0
10.5
11.0
11.5
CURRENT (µA)
I
S(SNK)
vs Temperature and V
IN
4412 G09
V
STAT
= V
IN
– 1.5V
V
IN
= 28V
V
IN
= 2.5V
LTC4412
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pin FuncTions
VIN (Pin 1): Primary Input Supply Voltage. Supplies power
to the internal circuitry and is one of two voltage sense
inputs to the internal analog controller (The other input
to the controller is the SENSE pin). This input is usually
supplied power from a battery or other power source which
supplies current to the load. This pin can be bypassed to
ground with a capacitor in the range of 0.1µF to 10µF if
needed to suppress load transients.
GND (Pin 2): Ground. Provides a power return for all the
internal circuits.
CTL (Pin 3): Digital Control Input. A logical high input
(VIH) on this pin forces the gate to source voltage of the
primary P-channel MOSFET power switch to a small voltage
(VGOFF). This will turn the MOSFET off and no current will
flow from the primary power input at VIN if the MOSFET
is configured so that the drain to source diode does not
forward bias. A high input also forces the STAT pin to
sink 10µA of current (IS(SNK)). If the STAT pin is used to
control an auxiliary P-channel power switch, then a second
active source of power, such as an AC wall adaptor, will
be connected to the load (see Applications Information).
An internal current sink will pull the CTL pin voltage to
ground (logical low) if the pin is open.
STAT (Pin 4): Open-Drain Output Status Pin. When the
SENSE pin is pulled above the VIN pin with an auxiliary
power source by about 20mV or more, the reverse turn-
off threshold (VRTO) is reached. The STAT pin will then go
from an open state to a 10µA current sink (IS(SNK)). The
STAT pin current sink can be used, along with an external
resistor, to turn on an auxiliary P-channel power switch
and/or signal the presence of an auxiliary power source
to a microcontroller.
GATE (Pin 5): Primary P-Channel MOSFET Power Switch
Gate Drive Pin. This pin is directed by the power controller
to maintain a forward regulation voltage (VFR) of 20mV
between the VIN and SENSE pins when an auxiliary power
source is not present. When an auxiliary power source
is connected, the GATE pin will pull up to the SENSE pin
voltage, turning off the primary P-channel power switch.
SENSE (Pin 6): Power Sense Input Pin. Supplies power
to the internal circuitry and is a voltage sense input to the
internal analog controller (The other input to the controller
is the VIN pin). This input is usually supplied power from
an auxiliary source such as an AC adapter or back-up
battery which also supplies current to the load.
block DiagraM
–
+
1 6
SOURCE
POWER
VOLTAGE/CURRENT
REFERENCE
0.5V
POWER
LINEAR GATE
DRIVER AND
VOLTAGE CLAMP
A1
VIN SENSE
ANALOG CONTROLLER
–
+
C1
3
2
CTL
3.5µA
ON/OFF
10µA
*DRAIN-SOURCE DIODE OF MOSFET
STATUS
OUTPUT
4412 BD
ON/OFF
STAT
VCC
GATE
4
5
GND
OUTPUT
TO LOAD
SELECTOR
–
+
PRIMARY
SUPPLY
–
+
AUXILIARY
SUPPLY
–
+
LTC4412
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operaTion
Operation can best be understood by referring to the Block
Diagram, which illustrates the internal circuit blocks along
with the few external components, and the graph that
accompanies Figure 1. The terms primary and auxiliary
are arbitrary and may be changed to suit the application.
Operation begins when either or both power sources are
applied and the CTL control pin is below the input low
voltage of 0.35V (VIL). If only the primary supply is pres-
ent, the Power Source Selector will power the LTC4412
from the VIN pin. Amplifier A1 will deliver a current to
the Analog Controller block that is proportional to the
voltage difference in the VIN and SENSE pins. While the
voltage on SENSE is lower than VIN – 20mV (VFR), the
Analog Controller will instruct the Linear Gate Driver and
Voltage Clamp block to pull down the GATE pin voltage
and turn on the external P-channel MOSFET. The dynamic
pull-down current of 50µA (IG(SNK)) stops when the GATE
voltage reaches ground or the gate clamp voltage. The
gate clamp voltage is 7V (VG(ON)) below the higher of VIN
or VSENSE. As the SENSE voltage pulls up to VIN – 20mV,
the LTC4412 will regulate the GATE voltage to maintain
a 20mV difference between VIN and VSENSE which is also
the VDS of the MOSFET. The system is now in the forward
regulation mode and the load will be powered from the
primary supply. As the load current varies, the GATE volt-
age will be controlled to maintain the 20mV difference. If
the load current exceeds the P-channel MOSFET’s ability
to deliver the current with a 20mV VDS the GATE voltage
will clamp, the MOSFET will behave as a fixed resistor
and the forward voltage will increase slightly. While the
MOSFET is on the STAT pin is an open circuit.
When an auxiliary supply is applied, the SENSE pin will be
pulled higher than the VIN pin through the external diode.
The Power Source Selector will power the LTC4412 from
the SENSE pin. As the SENSE voltage pulls above VIN –
20mV, the Analog Controller will instruct the Linear Gate
Driver and Voltage Clamp block to pull the GATE voltage
up to turn off the P-channel MOSFET. When the voltage
on SENSE is higher than VIN + 20mV (VRTO), the Analog
Controller will instruct the Linear Gate Driver and Voltage
Clamp block to rapidly pull the GATE pin voltage to the
SENSE pin voltage. This action will quickly finish turning
off the external P-channel MOSFET if it hasn’t already
turned completely off. For a clean transition, the reverse
turn-off threshold has hysteresis to prevent uncertainty.
The system is now in the reverse turn-off mode. Power to
the load is being delivered through the external diode and
no current is drawn from the primary supply. The external
diode provides protection in case the auxiliary supply is
below the primary supply, sinks current to ground or is
connected reverse polarity. During the reverse turn-off
mode of operation the STAT pin will sink 10µA of current
(IS(SNK)) if connected. Note that the external MOSFET is
wired so that the drain to source diode will momentarily
forward bias when power is first applied to VIN and will
become reverse biased when an auxiliary supply is applied.
When the CTL (control) input is asserted high, the external
MOSFET will have its gate to source voltage forced to a
small voltage VG(OFF) and the STAT pin will sink 10µA of
current if connected. This feature is useful to allow control
input switching of the load between two power sources
as shown in Figure 4 or as a switchable high side driver
as shown in Figure 7. A 3.5µA internal pull-down current
(ICTL) on the CTL pin will insure a low level input if the pin
should become open.
LTC4412
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applicaTions inForMaTion
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 VDS(MAX), threshold
voltage VGS(VT) and on-resistance RDS(ON).
The maximum allowable drain-source voltage, VDS(MAX),
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 VIN supply voltage or the internal
clamping voltage VG(ON).
A logic level MOSFET is commonly
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
RDS(ON) to obtain the desired VDS while operating at full
load current and an achievable VGS. The MOSFET nor-
mally 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 VDS may
result. However, the drain-source diode of the MOSFET,
if forward biased, will limit VDS. A large VDS, combined
with 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 RDS(ON) is low enough. The required
RDS(ON) can be calculated by dividing 0.02V by the load
current in amps. Achieving forward regulation will minimize
power loss and heat dissipation, but it is not a necessity.
If a forward voltage drop of more than 20mV is accept-
able 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 VGS
can be tailored by resistor selection. When choosing the
resistor value consider the full range of STAT pin current
(IS(SNK) ) that may flow through it.
VIN and SENSE Pin Bypass Capacitors
Many types of capacitors, ranging from 0.1µF to 10µF and
located close to the LTC4412, will provide adequate VIN
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 determine
the magnitude of the voltage droop include the supply rise
and fall times, the MOSFET’s characteristics, the value of
COUT and the load current. Droop can be made insignificant
by the proper choice of COUT, since the droop is inversely
proportional to the capacitance. Bypass capacitance 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 transients
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 VIN and SENSE for acceptable
voltage 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.
LTC4412
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applicaTions inForMaTion
VIN and SENSE Pin Usage
Since the analog controller’s thresholds are small (±20mV),
the VIN and SENSE pin connections should be made in a
way to avoid unwanted I • R drops in the power path. Both
pins are protected from negative voltages.
GATE Pin Usage
The GATE pin controls the external P-channel MOSFET
connected between the VIN and SENSE pins when the
load current is supplied by the power source at VIN. In
this mode of operation, the internal current source, which
is responsible for pulling the GATE pin up, is limited to
a few microamps (IG(SRC)). If external opposing leakage
currents exceed this, the GATE pin voltage will reach the
clamp voltage (VGON) and VDS will be smaller. The internal
current sink, which is responsible for pulling the GATE pin
down, has a higher current capability (IG(SNK)). With an
auxiliary supply input pulling up on the SENSE pin and
exceeding the VIN pin voltage by 20mV (VRTO), the device
enters the reverse turn-off mode and a much stronger
current source is available to oppose external leakage
currents and turn off the MOSFET (VGOFF).
While in forward regulation, if the on resistance of the
MOSFET is too high to maintain forward regulation, the
GATE pin will maximize the MOSFET’s VGS to that of the
clamp voltage (VGON). The clamping action takes place
between the higher of VIN or VSENSE and the GATE pin.
Status Pin Usage
During normal operation, the open-drain STAT pin can be
biased at any voltage between ground and 28V regard-
less of the supply voltage to the LTC4412. It is usually
connected to a resistor whose other end connects to a
voltage source. In the forward regulation mode, the STAT
pin will be open (IS(OFF)). When a wall adaptor input or
other auxiliary supply is connected to that input, and the
voltage on SENSE is higher than VIN + 20mV (VRTO), the
system is in the reverse turn-off mode. During this mode of
operation the STAT pin will sink 10µA of current (IS(SNK)).
This will result in a voltage change across the resistor,
depending on the resistance, which is useful to turn on an
auxiliary P-channel MOSFET or signal to a microcontroller
that an auxiliary power source is connected. External
leakage currents, if significant, should be accounted for
when determining the voltage across the resistor when
the STAT pin is either on or off.
Control Pin Usage
This is a digital control input pin with low threshold voltages
(VIL,VIH) for use with logic powered from as little as 1V.
During normal operation, the CTL pin can be biased at any
voltage between ground and 28V, regardless of the supply
voltage to the LTC4412. A logical high input on this pin
forces the gate to source voltage of the primary P-channel
MOSFET power switch to a small voltage (VGOFF). This
will turn the MOSFET off and no current will flow from the
primary power input at VIN if the MOSFET is configured
so that the drain to source diode is not forward biased.
The high input also forces the STAT pin to sink 10µA of
current (IS(SNK)). See the Typical Applications for various
examples on using the STAT pin. A 3.5µA internal pull-
down current (ICTL) on the CTL pin will insure a logical
low level input if the pin should be open.
Protection
Most of the application circuits shown provide some
protection against supply faults such as shorted, low or
reversed supply inputs. The fault protection does not protect
shorted supplies but can isolate other supplies and the load
from faults. A necessary condition of this protection is for
all components to have sufficient breakdown voltages. In
some cases, if protection of the auxiliary input (sometimes
referred to as the wall adapter input) is not required, then
the series diode or MOSFET may be eliminated.
Internal protection for the LTC4412 is provided to prevent
damaging pin currents and excessive internal self heating
during a fault condition. These fault conditions can be
a result of any LTC4412 pins shorted to ground or to a
power source that is within the pin’s absolute maximum
voltage limits. Both the VIN and SENSE pins are capable
of being taken significantly below ground without current
drain or damage to the IC (see Absolute Maximum Voltage
Limits). This feature allows for reverse-battery condition
without current drain or damage. This internal protection
is not designed to prevent overcurrent or overheating of
external components.
LTC4412
10
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For more information www.linear.com/LTC4412
Typical applicaTions
Figure 2. Automatic Switchover of Load Between a Battery and a
Wall Adapter with Auxiliary P-Channel MOSFET for Lowest Loss
Figure 3. Automatic Switchover of Load Between
a Battery and a Wall Adapter in Comparator Mode
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
PRIMARY
P-CHANNEL
MOSFET
COUT
TO LOAD
STATUS OUTPUT
DROPS WHEN A
WALL ADAPTER
IS PRESENT
470k
4412 F02
BATTERY
CELL(S)
WALL
ADAPTER
INPUT
*
*
AUXILIARY
P-CHANNEL
MOSFET
*DRAIN-SOURCE DIODE OF MOSFET
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
BATTERY
CHARGER
P-CHANNEL
MOSFET
COUT
TO LOAD
STATUS OUTPUT
IS LOW WHEN A
WALL ADAPTER
IS PRESENT
470k
*DRAIN-SOURCE DIODE OF MOSFET
4412 F03
VCC
BATTERY
CELL(S)
*
WALL
ADAPTER
INPUT
Automatic PowerPath Control
The applications shown in Figures 1, 2 and 3 are automatic
ideal diode controllers that require no assistance from a
microcontroller. Each of these will automatically connect
the higher supply voltage, after accounting for certain
diode forward voltage drops, to the load with application
of the higher supply voltage.
Figure 1 illustrates an application circuit for automatic
switchover of a load between a battery and a wall adapter
or other power input. With application of the battery, the
load will initially be pulled up by the drain-source diode
of the P-channel MOSFET. As the LTC4412 comes into
action, it will control the MOSFET’s gate to turn it on and
reduce the MOSFET’s voltage drop from a diode drop to
20mV. The system is now in the low loss forward regula-
tion mode. Should the wall adapter input be applied, the
Schottky diode will pull up the SENSE pin, connected to
the load, above the battery voltage and the LTC4412 will
turn the MOSFET off. The STAT pin will then sink current
indicating an auxiliary input is connected. The battery is
now supplying no load current and all the load current
flows through the Schottky diode. A silicon diode could
be used instead of the Schottky, but will result in higher
power dissipation and heating due to the higher forward
voltage drop.
Figure 2 illustrates an application circuit for automatic
switchover of load between a battery and a wall adapter
that features lowest power loss. Operation is similar
to Figure 1 except that an auxiliary P-channel MOSFET
replaces the diode. The STAT pin is used to turn on the
MOSFET once the SENSE pin voltage exceeds the battery
voltage by 20mV. When the wall adapter input is applied,
the drain-source diode of the auxiliary MOSFET will turn
on first to pull up the SENSE pin and turn off the primary
MOSFET followed by turning on of the auxiliary MOSFE
T
.
Once the auxiliary MOSFET has turned on the voltage drop
across it can be very low depending on the MOSFE
T’s
characteristics.
Figure 3 illustrates an application circuit for the automatic
switchover of a load between a battery and a wall adapter
in the comparator mode. It also shows how a battery char-
ger can be connected. This circuit differs from Figure 1
in the way the SENSE pin is connected. The SENSE pin is
connected directly to the auxiliary power input and not the
load. This change forces the LTC4412’s control circuitry
to operate in an open-loop comparator mode. While the
battery supplies the system, the GATE pin voltage will be
forced to its lowest clamped potential, instead of being
regulated to maintain a 20mV drop across the MOSFET.
This has the advantages of minimizing power loss in the
MOSFET by minimizing its RON and not having the influence
of a linear control loop’s dynamics. A possible disadvantage
is if the auxiliary input ramps up slow enough the load
voltage will initially droop before rising. This is due to the
LTC4412
11
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For more information www.linear.com/LTC4412
Typical applicaTions
SENSE pin voltage rising above the battery voltage and
turning off the MOSFET before the Schottky diode turns
on. The factors that determine the magnitude of the voltage
droop are the auxiliary input rise time, the type of diode
used, the value of COUT and the load current.
Ideal Diode Control with a Microcontroller
Figure 4 illustrates an application circuit for microcon-
troller monitoring and control of two power sources. The
microcontroller’s analog inputs, perhaps with the aid of a
resistor voltage divider, monitors each supply input and
commands the LTC4412 through the CTL input. Back-to-
back MOSFETs are used so that the drain-source diode will
not power the load when the MOSFET is turned off (dual
MOSFETs in one package are commercially available).
With a logical low input on the CTL pin, the primary input
supplies power to the load regardless of the auxiliary
voltage. When CTL is switched high, the auxiliary input
will power the load whether or not it is higher or lower
than the primary power voltage. Once the auxiliary is
on, the primary power can be removed and the auxiliary
will continue to power the load. Only when the primary
voltage is higher than the auxiliary voltage will taking
CTL low switch back to the primary power, otherwise
the auxiliary stays connected. When the primary power
is disconnected and VIN falls below VLOAD, it will turn
on the auxiliary MOSFET if CTL is low, but VLOAD must
stay up long enough for the MOSFET to turn on. At a
minimum, COUT capacitance must be sized to hold up
VLOAD until the transition between the sets of MOSFETs
is complete. Sufficient capacitance on the load and low
or no capacitance on VIN will help ensure this. If desired,
this can be avoided by use of a capacitor on VIN to ensure
that VIN falls more slowly than VLOAD.
Load Sharing
Figure 5 illustrates an application circuit for dual battery
load sharing with automatic switchover of load from
batteries to wall adapter. Whichever battery can supply
the higher voltage will provide the load current until it is
discharged to the voltage of the other battery. The load will
then be shared between the two batteries according to the
capacity of each battery. The higher capacity battery will
provide proportionally higher current to the load. When
a wall adapter input is applied, both MOSFETs will turn
off and no load current will be drawn from the batteries.
The STAT pins provide information as to which input is
supplying the load current. This concept can be expanded
to more power inputs.
Figure 4. Microcontroller Monitoring and Control
of Tw o Power Sources
Figure 5. Dual Battery Load Sharing with Automatic
Switchover of Load from Batteries to Wall Adapter
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
*DRAIN-SOURCE DIODE OF MOSFET
PRIMARY
P-CHANNEL MOSFETS
COUT
TO LOAD
4412 F04
AUXILIARY POWER
SOURCE INPUT
*
*
*
*
PRIMARY
POWER
SOURCE INPUT
AUXILIARY
P-CHANNEL MOSFETS
470k
MICROCONTROLLER
0.1µF
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412 COUT
TO LOAD
STATUS IS HIGH
WHEN BAT1 IS
SUPPLYING
LOAD CURRENT
WHEN BOTH STATUS LINES ARE
HIGH, THEN BOTH BATTERIES ARE
SUPPLYING LOAD CURRENTS. WHEN
BOTH STATUS LINES ARE LOW THEN
WALL ADAPTER IS PRESENT
STATUS IS HIGH
WHEN BAT2 IS
SUPPLYING
LOAD CURRENT
470k
4412 F05
VCC
BAT1
WALL
ADAPTER
INPUT
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
470k
VCC
BAT2
*
*
*DRAIN-SOURCE DIODE OF MOSFET
LTC4412
12
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For more information www.linear.com/LTC4412
Typical applicaTions
Multiple Battery Charging
Figure 6 illustrates an application circuit for automatic
dual battery charging from a single charger. Whichever
battery has the lower voltage will receive the charging
current until both battery voltages are equal, then both
will be charged. When both are charged simultaneously,
the higher capacity battery will get proportionally higher
current from the charger. For Li-Ion batteries, both batteries
will achieve the float voltage minus the forward regulation
voltage of 20mV. This concept can apply to more than
two batteries. The STAT pins provide information as to
which batteries are being charged. For intelligent control,
the CTL pin input can be used with a microcontroller and
back-to-back MOSFETs as shown in Figure 4. This allows
complete control for disconnection of the charger from
either battery.
High Side Power Switch
Figure 7 illustrates an application circuit for a logic con-
trolled high side power switch.
When the CTL pin is a logical
low, the LTC4412 will turn on the MOSFET. Because the
SENSE pin is grounded, the LTC4412 will apply maximum
clamped gate drive voltage to the MOSFET. When the CTL
pin is a logical high, the LTC4412 will turn off the MOSFET
by pulling its gate voltage up to the supply input voltage
and thus deny power to the load. The MOSFET is con-
nected with its source connected to the power source. This
disables the drain-source diode from supplying voltage
to the load when the MOSFET is off. Note that if the load
is powered from another source, then the drain-source
diode can forward bias and deliver current to the power
supply connected to the VIN pin.
Figure 6. Automatic Dual Battery Charging
from Single Charging Source
Figure 7. Logic Controlled High Side Power Switch
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
TO LOAD OR
PowerPath
CONTROLLER
TO LOAD OR
PowerPath
CONTROLLER
STATUS IS HIGH
WHEN BAT1 IS
CHARGING
STATUS IS HIGH
WHEN BAT2 IS
CHARGING
470k
4412 F06
VCC
*
*
BAT1
BATTERY
CHARGER
INPUT
470k
VCC
BAT2
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
*DRAIN-SOURCE DIODE OF MOSFET
0.1µF
VIN
GND
CTL
SENSE
GATE
STAT
1
2
3
6
5
4
LTC4412
P-CHANNEL
MOSFET
SUPPLY
INPUT
LOGIC
INPUT
COUT
*
TO LOAD
4412 F07
*DRAIN-SOURCE DIODE OF MOSFET
0.1µF
LTC4412
13
4412fb
For more information www.linear.com/LTC4412
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
revision hisTory
REV DATE DESCRIPTION PAGE NUMBER
B 02/15 Added H and MP-grade options. Throughout
(Revision history begins at Rev B)
LTC4412
14
4412fb
For more information www.linear.com/LTC4412
LINEAR TECHNOLOGY CORPORATION 2002
LT 0215 REV B • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC4412
relaTeD parTs
package DescripTion
PART NUMBER DESCRIPTION COMMENTS
LTC1473 Dual PowerPath Switch Driver Switches and Isolates Sources Up to 30V
LTC1479 PowerPath Controller for Dual Battery Systems Complete PowerPath Management for Tw o Batteries; DC Power Source,
Charger and Backup
LTC1558/LTC1559 Back-Up Battery Controller with Programmable Output Adjustable Backup Voltage from 1.2V NiCd Button Cell,
Includes Boost Converter
LT
®
1579 300mA Dual Input Smart Battery Back-Up Regulator Maintains Output Regulation with Dual Inputs, 0.4V Dropout at 300mA
LTC1733/LTC1734 Monolithic Linear Li-Ion Chargers Thermal Regulation, No External MOSFET/Sense Resistor
LTC1960 Dual Battery Charger Selector with SPI Complete Dual Battery Charger/Selector System, 36-Lead SSOP
LTC1998 2.5µA, 1% Accurate Programmable Battery Detector Adjustable Trip Voltage/Hysteresis, ThinSOT
LTC4350 Hot Swappable Load Share Controller Allows N + 1 Redundant Supply, Equally Loads Multiple Power Supplies
Connected in Parallel
LTC4410 USB Power Manager in ThinSOT Enables Simultaneous Battery Charging and
Operation of USB Component Peripheral Devices
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3) S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
