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PDF LTC4217 Data sheet ( Hoja de datos )
| Número de pieza | LTC4217 | |
| Descripción | 2A Integrated Hot Swap Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Small Footprint
n 25mΩ MOSFET and 7.5mΩ RSENSE
n Wide Operating Voltage Range: 2.9V to 26.5V
n Adjustable, 5% Accurate Current Limit
n Current and Temperature Monitor Outputs
n Overtemperature Protection
n Adjustable Current Limit Timer Before Fault
n Powergood and Fault Outputs
n Adjustable Inrush Current Control
n 2% Accurate Undervoltage and Overvoltage
Protection
n Available in 20-Lead TSSOP and 16-Lead
5mm × 3mm DFN Packages
APPLICATIONS
n RAID Systems
n Server I/O Cards
n Industrial
LTC4217
2A Integrated Hot Swap
Controller
DESCRIPTION
The LTC®4217 is an integrated solution for Hot Swap™
applications that allows a board to be safely inserted and
removed from a live backplane. The part integrates a Hot
Swap controller, power MOSFET and current sense resistor
in a single package for small form factor applications. A
dedicated 12V version (LTC4217-12) contains preset 12V
specific thresholds, while the standard LTC4217 allows
adjustable thresholds.
The LTC4217 provides separate inrush current control
and an accurate (5%) 2A current limit with current fold-
back limiting. The current limit threshold can be adjusted
dynamically using an external pin. Additional features
include a current monitor output that amplifies the sense
resistor voltage for ground referenced current sensing
and a MOSFET temperature monitor output. Thermal limit,
overvoltage, undervoltage and powergood monitoring are
also provided.
L, LT, LTC and LTM 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
12V, 1.5A Card Resident Application
12V
VDD OUT
+
VOUT
12V
UV 12V 330μF 1.5A
AUTO
RETRY
LTC4217DHC-12
FLT PG
10k
0.1μF
TIMER
INTVCC
IMON
GND
20k
ADC
4217 TA01a
VIN
10V/DIV
IIN
0.1A/DIV
VOUT
10V/DIV
PG
10V/DIV
Power-Up Waveforms
25ms/DIV
4217 TA01b
4217fb
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LTC4217
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VDD = 12V unless otherwise noted.
IDD vs VDD
2.0
1.8
85°C
1.6
25°C
1.4
–40°C
1.2
1.0
0
5 10 15 20 25 30
VDD (V)
4217 G01
INTVCC Load Regulation
3.5
3.0
VDD = 5V
2.5 VDD = 3.3V
2.0
1.5
1.0
0.5
0
0 –2 –4 –6 –8 –10 –12 –14
ILOAD (mA)
4217 G02
UV Low-High Threshold vs
Temperature
1.234
1.232
1.230
1.228
1.226
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
4217 G03
UV Hysteresis vs Temperature
0.10
Timer Pull-Up Current vs
Temperature
–110
Current Limit Delay
(tPHL(ILIM) vs Overdrive)
1000
–105
0.08
–100
0.06
–95
100
10
1
0.04
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
4217 G04
Current Limit Threshold Foldback
2.5
2.0
1.5
1.0
0.5
0
0 0.2 0.4 0.6 0.8 1.0 1.2
FB VOLTAGE (V)
4217 G07
–90
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
4217 G05
Current Limit Adjustment
(IOUT vs RSET)
2.5
2.0
1.5
1.0
0.5
0
1k
10k 100k 1M 10M
RSET (Ω)
4217 G08
0.1
0
2468
OUTPUT CURRENT (A)
10
4217 G06
ISET Resistor vs Temperature
22
21
20
19
18
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
4217 G09
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LTC4217
APPLICATIONS INFORMATION
LTC4217
GATE
CP
2.2nF
*OPTIONAL
RC TO LOWER
INRUSH CURRENT
4217 F03
Figure 3. Compensation for Small CLOAD
will turn off the switch. These include an input overvoltage
(OV pin), overcurrent circuit breaker (SENSE pin) or over
temperature. Normally the switch is turned off with a 250μA
current pulling down the GATE pin to ground. With the
switch turned off, the OUT voltage drops which pulls the
FB pin below its threshold. PG then pulls low to indicate
output power is no longer good.
If VDD drops below 2.65V for greater than 5μs or INTVCC
drops below 2.5V for greater than 1μs, a fast shutdown
of the switch is initiated. The GATE is pulled down with a
170mA current to the OUT pin.
Overcurrent Fault
The LTC4217 features an adjustable current limit with
foldback that protects against short circuits or excessive
load current. To prevent excessive power dissipation in the
switch during active current limit, the available current is
reduced as a function of the output voltage sensed by the
FB pin. A graph in the Typical Performance curves shows
the current limit versus FB voltage.
An overcurrent fault occurs when the current limit circuitry
has been engaged for longer than the time-out delay set
by the TIMER. Current limiting begins when the MOSFET
current reaches 0.5A to 2A (depending on the foldback).
The GATE pin is then brought down with a 170mA GATE-
to-OUT current. The voltage on the GATE is regulated in
order to limit the current to less than 2A. At this point, a
circuit breaker time delay starts by charging the external
timing capacitor from the TIMER pin with a 100μA pull-up
current. If the TIMER pin reaches its 1.2V threshold, the
internal switch turns off (with a 250μA current from GATE
to ground). Included in the Typical Performance Curves is
a graph of the Safe Operating Area for the MOSFET. From
this graph one can determine the MOSFET’s maximum
time in current limit for a given output power.
Tying the TIMER pin to INTVCC will force the part to use
the internally generated (circuit breaker) delay of 2ms.
In either case the FLT pin is pulled low to indicate an
overcurrent fault has turned off the pass MOSFET. For a
given the circuit breaker time delay, the equation for setting
the timing capacitor’s value is as follows:
CT = tCB • 0.083(μF/ms)
After the switch is turned off, the TIMER pin begins dis-
charging the timing capacitor with a 2μA pull-down current.
When the TIMER pin reaches its 0.2V threshold, an internal
100ms timer is started. After the 100ms delay, the switch
is allowed to turn on again if the overcurrent fault has been
cleared. Bringing the UV pin below 0.6V and then high will
clear the fault. If the TIMER pin is tied to INTVCC then the
switch is allowed to turn on again (after an internal 100ms
delay) if the overcurrent fault is cleared.
Tying the FLT pin to the UV pin allows the part to self-
clear the fault and turn the MOSFET on as soon as TIMER
pin has ramped below 0.2V. In this auto-retry mode the
LTC4217 repeatedly tries to turn on after an overcurrent
at a period determined by the capacitor on the TIMER pin.
The auto-retry mode also functions when the TIMER pin
is tied to INTVCC.
The waveform in Figure 4 shows how the output latches
off following a short circuit. The current in the MOSFET
is 0.5A as the timer ramps up.
Current Limit Adjustment
The default value of the active current limit is 2A. The
current limit threshold can be adjusted lower by placing
VOUT
10V/DIV
IOUT
1A/DIV
ΔVGATE
10V/DIV
TIMER
2V/DIV
1ms/DIV
4217 F04
Figure 4. Short-Circuit Waveform
4217fb
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC4217.PDF ] | |
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