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PDF LTC4420 Data sheet ( Hoja de datos )
| Número de pieza | LTC4420 | |
| Descripción | 18V Dual Input Micropower PowerPath Prioritizer | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Selects Highest Priority Valid Supply from Two
Inputs
n Wide 1.8V to 18V Operating Range
n Internal Dual 2Ω, 0.5A Switches
n Low 3.6µA Operating Current
n Low 320nA V2 Current When V1 Connected to OUT
n Blocks Reverse and Cross Conduction Currents
n Reverse Supply Protection to –15V
n Built-In V2 Test with Optional V2 Disconnect
n V2 Freshness Seal/Ship Mode
n ±1.5% Accurate Adjustable Switchover Threshold
n ±2.3% Accurate V2 Monitor and Comparator
n Overcurrent and Thermal Protection
n Thermally Enhanced 12-Pin 3mm × 3mm
DFN and 12-Lead Exposed Pad MSOP Packages
Applications
n Low Power Battery Backup
n Portable Equipment
n Point-of-Sale (POS) Equipment
LTC4420
18V Dual Input Micropower
PowerPath Prioritizer with
Backup Supply Monitoring
Description
The LTC®4420 is a dual input monolithic PowerPath™
prioritizer, with low operating current, that provides
backup switchover for keeping critical circuitry alive dur-
ing brownout 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. Two adjustable voltage monitors
set via external resistive dividers provide flexibility in set-
ting V1 to V2 switchover and V2 undervoltage thresholds.
V1 is monitored continuously while V2 supply monitoring
includes controllable low duty cycle UV monitoring. When
primary input V1 drops, the ADJ monitor causes OUT to
be switched to V2. When V2 drops, it is disconnected from
OUT if V2DIS is low. Fast non-overlap switchover circuitry
prevents reverse and cross conduction while minimizing
output droop.
Auxiliary voltage monitor CMP1 provides flexible voltage
monitoring and output V2OK provides V2 undervoltage
status. 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
+
10µF
7.4V
Li-Ion
1M
237k
121k
4.02M
280k
V1 OUT
ADJ CMPOUT1
CMP1 V2OK
LTC4420
V2 V2DIS
V2UV V2TEST
GNDSW
GND
1M
V1UV
OUT
1M
V2OK
V2
2V/DIV
V1
2V/DIV
TYPICAL VALUES:
SWITCHOVER THRESHOLD: V1 < 4V (V1 FALLING)
V1UV THRESHOLD: V1 < 4.4V (V1 FALLING)
4420 TA01a V2OK THRESHOLD: V2 < 6V (V2 FALLING)
Typical Switchover Waveforms
V2 MONITORING
INTERVAL
SWITCHOVER
THRESHOLD
V2 UNDERVOLTAGE
AND DISCONNECT
COUT = 10µF
ILOAD = 100mA
20ms/DIV
OUT
4420 TA01b
For more information www.linear.com/LTC4420
4420f
1
1 page  
Typical Performance Characteristics
(TA = 25°C, V1 = V2 = 3.6V unless otherwise indicated)
Output Current Limit vs Temperature
Output Current IOUT Response for
Different Shorting Impedances
1.40 3.0 1.2Ω
2.2Ω
1.30 2.5 3.3Ω
3.9Ω
1.20
5Ω
2.0
1.10 1.5
1.00 1.0
0.90 0.5
0.80
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4420 G10
0
40µs/DIV
4419 G11
LTC4420
IOUT vs VOUT for Different Input
Supply Voltages
1.2
1.0
FOLDBACK
VIN = 1.8V
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
1
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
4419 G13
Freshness Seal Current vs
V2 Voltage and Temperature
250
1.8V
3.6V
200
5V
≥6V
V1 = 0V
150
100
50
0
–50 –25
0
25 50 75 100
TEMPERATURE (°C)
4420 G14
Switchover from a Higher to a
Lower Voltage
COUT = 10µF
V1 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
4420 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
4420 G17
For more information www.linear.com/LTC4420
4420f
5
5 Page 
LTC4420
Applications Information
In order to limit output rising slew rate dVOUT/dt, size:
COUT
≥
ILIM
dVOUT
dt
(9)
as the LTC4420 limits OUT charging current to ILIM until
OUT approaches the input supply to within ILIM • RON,
where RON is the channel switch resistance. Refer to the
Thermal Protection and Maximum COUT section to deter-
mine maximum allowed COUT.
Inductive Effects
Parasitic inductance and resistance can impact circuit
performance by causing overshoot and undershoot of input
and output voltages when the LTC4420 turns off. Parasitic
inductance in the power path causes positive-going
overshoot on the input and a negative-going undershoot
on the output. Another cause of positive input overshoot is
R-L-C tank ringing during hot plug of an input supply. Input
overshoot is most pronounced when the total resistance
of the input tank is low. Care must be taken to ensure over
voltage transients do not exceed the Absolute Maximum
ratings of the LTC4420. Additionally, parasitic resistance
and inductance can cause input undershoot (droop)
during power path turn on. If severe enough, undershoot
can temporarily invalidate a supply and cause repeated
power up cycles (motorboating) or unwanted switchover
between sources.
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.
Second, use a bypass capacitor at the input to limit input
voltage overshoot during LTC4420 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 LTC4420 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
LTC4420’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 resister RSN2 to
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 LTC4420 to clamp negative
ringing if the OUT pin rings below –0.3V.
LPAR1
V1
LTC4420
V1 OUT
LPAR2
RSN1 OPTIONAL
0.5Ω
CSN1
5µF
RSN2 OPTIONAL
1Ω
COUT1
1µF
D1
1N5818
OUT
COUT2
10µF
4420 F03
Figure 3. Recommended Inductive Transient Suppression Circuitry
For more information www.linear.com/LTC4420
4420f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC4420.PDF ] | |
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