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PDF LTC4419 Data sheet ( Hoja de datos )
| Número de pieza | LTC4419 | |
| Descripción | 18V Dual Input Micropower PowerPath Prioritizer | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC4419
18V Dual Input Micropower
PowerPath Prioritizer
Features
Description
nn Selects Highest Priority Valid Supply from Two Inputs
nn Wide 1.8V to 18V Operating Range
nn Internal Dual 2Ω, 0.5A Switches
nn Low 3.6µA Operating Current
nn Low 320nA V2 Current When V1 Connected to OUT
nn Blocks Reverse and Cross Conduction Currents
nn Reverse Supply Protection to –15V
nn V2 Freshness Seal/Ship Mode
nn ±1.5% Accurate Adjustable Switchover Threshold
nn Two Auxiliary ±2.3% Accurate Voltage Comparators
nn Overcurrent and Thermal Protection
nn Thermally Enhanced 10-Pin 3mm × 3mm DFN
and 12-Lead Exposed Pad MSOP Packages
Applications
nn Low Power Battery Backup
nn Portable Equipment
nn Point-of-Sale (POS) Equipment
The LTC®4419 is a dual input monolithic PowerPath™
prioritizer with low operating current, that provides backup
switchover for keeping critical circuitry alive during brown
out and power loss conditions. Unlike diode-OR products,
little current is drawn from the inactive supply even if its
voltage is greater than the active supply.
Internal 2Ω, current limited PMOS switches provide power
path selection from a primary input (V1) or a backup input
(V2) to the output. An adjustable voltage monitor set via
an external resistive divider provides flexibility in setting
the V1 to V2 switchover threshold. When primary input V1
drops, the ADJ monitor input causes OUT to be switched
to V2. Fast non-overlap switchover circuitry prevents both
reverse and cross conduction while minimizing output
droop.
The LTC4419 has two auxiliary comparators with open-
drain outputs that provide flexible voltage monitoring. The
V2ON output indicates if V2 is powering OUT. Freshness
seal mode prevents V2 battery discharge during storage
or shipment.
L, LT, LTC, LTM, 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.
Typical Application
5V
WALL
ADAPTER
C1
10µF
1M
237k
121k
V1 OUT
ADJ CMPOUT1
CMP1 CMPOUT2
LTC4419
OUT
1M 1M
V1UV
V2UV
+
7.4V
Li-Ion
V2
4.02M
V2ON
CMP2
280k
GND
4419 TA01a
V2ON
SWITCHOVER
THRESHOLD: V1 < 4V (V1 FALLING)
V1UV THRESHOLD: V1 < 4.4V (V1 FALLING)
V2UV THRESHOLD: V2 < 6V (V2 FALLING)
Typical Switchover Waveforms
V2
2V/DIV
V1
2V/DIV
OUT
COUT = 10µF
ILOAD = 100mA
SWITCHOVER
THRESHOLD
50µs/DIV
4419 TA01b
For more information www.linear.com/LTC4419
4419f
1
1 page  
LTC4419
Typical Performance Characteristics (TA = 25°C, V1 = V2 = 3.6V unless otherwise indicated).
Output Current Limit vs
Temperature
1.40
1.30
1.20
1.10
1.00
0.90
0.80
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4419 G10
DOiuftfpeuret nCtuSrrheonrttiInOgUTImRpeesdpaonncseesfor
3.0
1.2Ω
2.5
2.2Ω
3.3Ω
3.9Ω
2.0 5.0Ω
1.5
1.0
0.5
0
40µs/DIV
4419 G11
ISOuUpTpvlys VVoOlUtTagfoersDifferent Input
1.2
FOLDBACK
VIN = 1.8V
1.0
VIN = 3.6V
VIN = 5V
CURRENT
0.8 LIMIT
0.6 OHMIC
0.4
0.2
0
012345
VOUT (V)
4419 G12
Switch RON vs Temperature
5
5V
3.6V
2V
4
3
2
Freshness Seal Current
vs V2 Voltage and Temperature
250
1.8V
3.6V
200
5V
≥6V
V1 = 0V
150
100
50
1
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4419 G13
0
–50 –25
0
25 50 75 100
TEMPERATURE (°C)
4419 G14
Switchover from a Higher to a
Lower Voltage
V1
COUT = 10µF
IOUT = 200mA
OUT
2V/DIV
V2
DISCONNECT FROM V1
CONNECT TO V2
3ms/DIV
4419 G15
Output Voltage and Current
Waveforms During Switchover
V2 10V
V1 6V
2V/DIV
IOUT
0.5A/DIV
OUT
COUT = 10µF
C1 = C2 = 10µF
ILOAD = 50mA
10µs/DIV
4419 G16
V1 Reverse Voltage Blocking with
V2 Powering OUT
V2
5V/DIV
6V
V1
10V/DIV
–10V
10V
IOUT
0.5A/DIV
20ms/DIV
ILOAD = 50mA
4419 G17
For more information www.linear.com/LTC4419
4419f
5
5 Page 
LTC4419
Applications Information
LPAR1
V1
LTC4419
V1 OUT
RSN1 OPTIONAL
0.5Ω
CSN1
5µF
LPAR2
RSN2 OPTIONAL
1Ω
COUT1
1µF
D1
1N5818
OUT
COUT2
10µF
4419 F03
Figure 3. Recommended Inductive Transient Suppression Circuitry
The first step to avoid these issues is to minimize parasitic
inductance and resistance in the power path. Guidelines
are given in the layout section for minimizing parasitic
inductance on the printed circuit board (PCB). External
to the PCB, twist the power and ground wires together to
minimize inductance.
damp R-L-C ringing if required. Size COUT2 to obtain the
required total output capacitance. Also add a diode between
OUT and ground close to the LTC4419 to clamp negative
ringing if the OUT pin rings below –0.3V.
Increasing CMP1 and CMP2 Hysteresis
Second, use a bypass capacitor at the input to limit input
voltage overshoot during LTC4419 power path turn off. A
few micro farads is sufficient for most applications. When
hot plugging supplies with large parasitic inductances, it
is possible for the R-L-C tank to ring to more than twice
the nominal supply voltage. Wall adapters and batteries
typically have enough loss (i.e. series resistance) to prevent
ringing of this magnitude. However, if this is a problem,
snub input capacitor CSN1 with resistor RSN1, typically
0.5Ω. Place this network close to the supply pin.
Third, if an input capacitor is not permissible, use a TVS
(such as SMAJ16CA) in applications when supply pin
transients can exceed 24V. Use a bidirectional TVS in
applications requiring reverse input protection. Note that
a TVS does not address droop and motorboating, which
are solved only by input bypassing.
During normal operation, the LTC4419 limits power path
current to < 1.6A and internal circuitry prevents OUT from
ringing below ground during power path turn off. This is
also true for output shorts when the short is close to the
LTC4419’s OUT pin. However, if the output is shorted
through a long wire, current in the wire inductance (LPAR2
in Figure 3) builds up due to the discharge of COUT1 and
can be much higher than 1.6A. This current causes the
OUT pin to ring below its −0.3V absolute maximum rating
once COUT1 has been fully discharged. For this special
case, split the output capacitor between COUT1 and COUT2
and make COUT1 small. Snub COUT1 with resistor RSN2 to
In some applications, built-in CMP1 hysteresis may be insuf-
ficient. In such cases, CMP1 hysteresis can be increased
as shown in Figure 4. Hysteresis at the monitored input
VMON with R8 present and assuming R9 << R8 is given by:
VHYST
=
VHYSTC
•
R3
R1||R3||R8
+
VPU
•
R3
R8
(10)
where VHYSTC and VTHC are found in the Electrical Character-
istics table and are typically 10mV and 0.387V respectively.
Account for supply VPU and resistor R8 when calculating
rising and falling thresholds of monitored input VMON.
Supply Impedance and ADJ Comparator Hysteresis
VMON
R3
CMP1
VPU
R1
LTC4419
R9
CMPOUT1
R8
4419 F04
Figure 4. Increasing CMP1 Hysteresis
In some applications, V1 could be supplied by a battery
pack with high ESR or through a long cable with appreciable
series resistance. Load current, IOUT, flowing through this
resistance reduces the monitored V1 voltage by:
∆V1 = IOUT • RESR
(11)
For more information www.linear.com/LTC4419
4419f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC4419.PDF ] | |
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