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PDF LTC4225-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC4225-2 | |
| Descripción | Dual Ideal Diode and Hot Swap Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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Features
n Power Path and Inrush Current Control for
Redundant Supplies
n Low Loss Replacement for Power Schottky Diodes
n Allows Safe Hot Swapping from a Live Backplane
n 2.9V to 18V Operating Range
n Controls N-Channel MOSFETs
n Limits Peak Fault Current in ≤1µs
n 0.5µs Turn-On and Reverse Turn-Off Time
n Adjustable Current Limit with Circuit Breaker
n Smooth Switchover without Oscillation
n Adjustable Current Limit Fault Delay
n Fault and Power Status Output
n LTC4225-1: Latch Off After Fault
n LTC4225-2: Automatic Retry After Fault
n 24-Lead 4mm × 5mm QFN and SSOP Packages
Applications
n Redundant Power Supplies
n Supply Holdup
n MicroTCA Systems and Servers
n Telecom Networks
n Power Prioritizer
LTC4225-1/LTC4225-2
Dual Ideal Diode and
Hot Swap Controller
Description
The LTC®4225 offers ideal diode and Hot Swap™ functions
for two power rails by controlling external series connected
N-channel MOSFETs. MOSFETs acting as ideal diodes
replace two high power Schottky diodes and the associ-
ated heat sinks, saving power and board area. Hot Swap
control MOSFETs allow boards to be safely inserted and
removed from a live backplane by limiting inrush current.
The supply output is also protected against short-circuit
faults with a fast acting current limit and internal timed
circuit breaker.
The LTC4225 regulates the forward voltage drop across
the back-to-back MOSFETs to ensure smooth current
transfer from one supply to the other without oscillation.
The ideal diodes turn on quickly to reduce the load voltage
droop during supply switch-over. If the input supply fails
or is shorted, a fast turn-off minimizes reverse-current
transients.
The LTC4225 allows independent on/off control, and reports
fault and power good status for the supply. The LTC4225-1
features a latch-off circuit breaker, while the LTC4225-2
provides automatic retry after a fault.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Typical Application
µTCA Application
0.004Ω Si7336ADP Si7336ADP
12V
0.1µF
PLUG-IN
CARD 1
12V
7.6A
137k
CPO1
IN1 SENSE1 DGATE1 HGATE1 OUT1
ON1 FAULT1
20k
INTVCC
0.1µF
GND
LTC4225
PWRGD1
EN1
TMR1
TMR2
47nF
47nF
PLUG-IN
CARD 2
20k
137k
12V
ON2
CPO2
IN2
0.1µF
SENSE2 DGATE2
EN2
PWRGD2
FAULT2
HGATE2 OUT2
0.004Ω Si7336ADP Si7336ADP
BACKPLANE
12V
7.6A
422512 TA01a
Power Dissipation vs Load Current
3.0
2.5
2.0 DIODE
(SBG1025L)
1.5
POWER SAVED
1.0
0.5
0
0
MOSFET
(Si7336ADP)
24 6
LOAD CURRENT (A)
8
422512 TA01
422512f
1
1 page  
LTC4225-1/LTC4225-2
Typical Performance Characteristics TA = 25°C, VIN = 12V, unless otherwise noted.
IN Supply Current vs Voltage
4
3
2
1
0
0 3 6 9 12 15 18
VIN (V)
422512 G01
INTVCC Load Regulation
6
5 VIN = 12V
4
3 VIN = 3.3V
2
1
0
0 –2
–4 –6
ILOAD (mA)
–8 –10
422512 G02
CPO Voltage vs Current
12
10
8
VIN = 18V
6
4
2 VIN = 2.9V
0
–2
0 –20 –40 –60 –80 –100 –120
ICPO (µA)
422512 G03
Diode Gate Voltage vs Current
12
VOUT = VIN – 0.1V
10
8
VIN = 18V
6
4
VIN = 2.9V
2
0
–2
0 –20 –40 –60 –80 –100 –120
IDGATE (µA)
422512 G04
Circuit Breaker Trip Voltage
vs Temperature
52
51
50
49
Hot Swap Gate Voltage vs Current
14
VOUT = VIN
12 VIN = 12V
10
8
6 VIN = 2.9V
4
2
0
0 –2 –4 –6 –8 –10 –12
IHGATE (µA)
422712 G05
Active Current Limit Sense
Voltage vs Temperature
67
66
65
64
OUT Current vs Voltage
2.5
VIN = 12V
2.0
1.5
1.0
0.5
0
–0.5
0 3 6 9 12 15 18
VOUT (V)
422512 G06
Active Current Limit Delay
vs Sense Voltage
100 CHGATE = 10nF
10
1
48
–50 –25
0
25 50
TEMPERATURE (°C)
75 100
422512 G07
63
–50 –25
0
25 50
TEMPERATURE (°C)
75 100
422512 G08
0.1
50
100 150 200 250 300
SENSE VOLTAGE (VIN – VSENSE) (mV)
422512 G09
422512f
5
5 Page 
LTC4225-1/LTC4225-2
Applications Information
During a normal power-up, the ideal diode MOSFET turns
on first. As soon as the internally generated supply, INTVCC,
rises above its 2.2V undervoltage lockout threshold, the
internal charge pump is allowed to charge up the CPO
pins. Because the Hot Swap MOSFET is turned off at
power-up, OUT remains low. As a result, the ideal diode
gate drive amplifier senses a large forward drop between
the IN and OUT pins, causing it to pull up DGATE to the
CPO pin voltage.
Before the Hot Swap MOSFET can be turned on, EN must
remain low and ON must remain high for a 100ms debounce
cycle to ensure that any contact bounces during the inser-
tion have ceased. At the end of the debounce cycle, the
internal fault latches are cleared. The Hot Swap MOSFET
is then allowed to turn on by charging up HGATE with a
10µA current source from the charge pump. The voltage
at the HGATE pin rises with a slope equal to 10µA/CHG and
the supply inrush current flowing into the load capacitor,
CL, is limited to:
IINRUSH
=
CL
CHG
• 10µA
The OUT voltage follows the HGATE voltage when the
Hot Swap MOSFET turns on. If the voltage across the
current sense resistor, RS, becomes too high, the inrush
current will be limited by the internal current limiting
circuitry. Once the MOSFET gate overdrive exceeds 4.2V,
the corresponding PWRGD pin pulls low to indicate that
the power is good. Once OUT reaches the input supply
voltage, HGATE continues to ramp up. An internal 12V
clamp limits the HGATE voltage above OUT.
When both of the MOSFETs are turned on, the gate drive
amplifier controls the gate of the ideal diode MOSFET, to
servo its forward voltage drop across RS, MD and MH to
25mV. If the load current causes more than 25mV of drop,
the MOSFET gate is driven fully on and the voltage drop
across the MOSFET is equal to ILOAD • RDS(ON).
Turn-Off Sequence
The external MOSFETs can be turned off by a variety of
conditions. A normal turn-off for the Hot Swap MOSFET is
initiated by pulling the ON pin below its 1.155V threshold
IN
10V/DIV
CPO
10V/DIV
DGATE
10V/DIV
OUT
10V/DIV
20ms/DIV
422512 F02
Figure 2. Ideal Diode Controller Start-Up Waveforms
ON
5V/DIV
HGATE
10V/DIV
OUT
10V/DIV
PWRGD
10V/DIV
50ms/DIV
422512 F03
Figure 3. Hot Swap Controller Power-Up Sequence
(80mV ON pin hysteresis), or pulling the EN pin above
its 1.235V threshold. Additionally, an overcurrent fault
of sufficient duration to trip the circuit breaker also turns
off the Hot Swap MOSFET. Normally, the LTC4225 turns
off the MOSFET by pulling the HGATE pin to ground with
a 300µA current sink.
All of the MOSFETs turn off when INTVCC falls below its
undervoltage lockout threshold (2.2V). The DGATE pin is
pulled down with a 100µA current to one diode voltage
below the IN pin, while the HGATE pin is pulled down to
the OUT pin by a 200mA current.
The gate drive amplifier controls the ideal diode MOSFET
to prevent reverse current when the input supply falls
below OUT. If the input supply collapses quickly, the gate
drive amplifier turns off the ideal diode MOSFET with a
fast pull-down circuit as soon as it detects that IN is 20mV
below OUT. If the input supply falls at a more modest rate,
the gate drive amplifier controls the MOSFET to maintain
OUT at 25mV below IN.
422512f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC4225-2.PDF ] | |
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