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PDF LTC1643AH Data sheet ( Hoja de datos )
| Número de pieza | LTC1643AH | |
| Descripción | PCI-Bus Hot Swap Controller | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
■ Allows Safe Board Insertion and Removal from a
Live PCI Slot
■ Works on either a Motherboard (LTC1643AH) or
CompactPCITM Card (LTC1643AL/LTC1643AL-1)
■ Controls –12V, 3.3V, 5V, 12V Supplies
■ Programmable Foldback Current Limit with
Circuit Breaker
■ User-Programmable Supply Voltage Power-Up Rate
■ High Side Drive for External N-Channel MOSFETs
■ –12V and 12V On-Chip Switches
■ Fault and Power-Good Outputs
■ Available in a Narrow 16-Lead SSOP Package
U
APPLICATIO S
■ PCI-Based Servers
■ CompactPCI Compliant Boards
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Hot Swap is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
LTC1643AL
LTC1643AL-1/LTC1643AH
PCI-Bus Hot Swap
Controller
DESCRIPTIO
TheLTC®1643AisaHotSwapTM controllerthatallowsaboard
to be safely inserted and removed from a live PCI-Bus slot.
Two external N-channel transistors control the 3.3V and 5V
supplies while on-chip switches control the –12V and 12V
supplies. All supply voltages can be ramped up at a program-
mable rate. An electronic circuit breaker protects all four
supplies against overcurrent faults. The foldback current limit
feature limits current spikes and power dissipation when
shorts occur and allows boards with large capacitances to be
powered up without tripping the circuit breaker. The PWRGD
output indicates when all of the supply voltages are within
tolerance and the FAULT output indicates an overcurrent
condition. The ON(LTC1643AH)/ON (LTC1643AL/
LTC1643AL-1) pin is used to cycle the board power or reset
the circuit breaker. The LTC1643AL-1 has the ±12V power
good comparators disabled.
The LTC1643A is available in a 16-pin narrow SSOP package.
TYPICAL APPLICATION
Hot Swappable PCI Supply
R1 Q1
0.007Ω IRF7413
R2
0.005Ω
Q2
IRF7413
R6
10Ω
SYSTEM
POWER
SUPPLY
R5
10Ω
9 10 11 3 13 12
PCI
POWER
SYSTEM
CONTROLLER
8 3VIN
GND
1
2
12VIN
VEEIN
3VSENSE GATE 3VOUT 5VIN
5VSENSE
5
ON
R3
LTC1643AH
10k 6
FAULT
R4
10k 7 PWRGD
RESET
R7
100Ω
14
5VOUT
16
12VOUT
15
VEEOUT
4
TIMER
5V
5A
3.3V
7.6A
GND
C1
0.047µF
12V
500mA
–12V
100mA
C2
0.1µF
LOGIC
RESET
1643A TA01
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1
1 page  
LTC1643AL
LTC1643AL-1/LTC1643AH
TYPICAL PERFORMANCE CHARACTERISTICS
Circuit Breaker Trip Filter Time
vs Temperature
15.50
15.25
15.00
14.75
14.50
14.25
14.00
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G13
VEEIN Supply Current
vs Temperature
0.90
0.89
0.88
0.87
0.86
0.85
0.84
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G16
VOL vs Temperature
350
I = 3mA
300
FAULT
250
200
150
PWRGD
100
50
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G19
Timer Threshold Voltage
vs Temperature
1.0
V12VIN – VTIMER
0.9
0.8
0.7
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G14
5VIN Supply Current
vs Temperature
270
268
266
264
262
260
258
256
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
LT1643A G17
12VIN Undervoltage Lockout
vs Temperature
9.515
9.510
9.505
9.500
9.495
9.490
9.485
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G20
12VIN Supply Current
vs Temperature
3.72
3.70
3.68
3.66
3.64
3.62
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G15
3VIN Supply Current
vs Temperature
275.0
272.5
270.0
267.5
265.0
262.5
260.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G18
5VIN Undervoltage Lockout
vs Temperature
2.454
2.452
2.450
2.448
2.446
2.444
2.442
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1643A G21
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5 Page 
LTC1643AL
LTC1643AL-1/LTC1643AH
APPLICATIONS INFORMATION
Timer
During a power-up sequence, a 22µA current source is
connected to the TIMER pin (Pin 4) and current limit faults
are ignored until the voltage ramps to within 0.9V of 12VIN
(Pin 1). This feature allows the chip to power up a PCI slot
that can accept boards with widely varying capacitive
loads on the supplies. The power-up time will be:
t
ON
≅
2
CSUPPLY
ILIMIT
•
−
VSUPPLY
ILOAD
For CSUPPLY = 2000µF, VSUPPLY = 5V, ILIMIT = 7A, ILOAD
= 5A, the turn-on time will be ~10ms. The timer period
should be set longer than the maximum supply turn-on
time but short enough to not exceed the maximum safe
operating area of the pass transistor during a short circuit.
The timer period will be:
tTIMER
=
CTIMER •11.1V
22µA
For CTIMER = 0.1µF, the timer period will be ~ 50ms. The
TIMER pin (Pin 4) is immediately pulled low when ON
(Pin 5) goes low.
Thermal Shutdown
The internal switches for the 12V and –12V supplies are
protected by an internal current limit and thermal shut-
down circuit. When the temperature of chip reaches
150°C, all switches will be latched off and the FAULT pin
(Pin 6) will be pulled low.
Short-Circuit Protection
During a normal power-up sequence, if the TIMER (Pin 4)
is done ramping and a supply is still in current limit, all of
the pass transistors will be immediately turned off and the
FAULT pin (Pin 6) will be pulled low as shown in Figure 4.
If a short circuit occurs after the supplies are powered up,
the shorted supply’s current will drop immediately to the
limit value (Figure 5).
If the supply remains in current limit for more than 14.6µs,
all of the supplies will be latched off. The 14.6µs delay
prevents quick current spikes—for example, from a fan
turning on—from causing false trips of the circuit breaker.
The chip will stay in the latched-off state until ON pin
(Pin 5) is cycled low then high, or the 12VIN pin (Pin 1)
power supply is cycled.
To prevent excessive power dissipation in the pass tran-
sistors and to prevent voltage spikes on the supplies
during short-circuit conditions, the current limit on each
supply is designed to be a function of the output voltage.
As the output voltage drops, the current limit decreases.
Unlike a traditional circuit breaker function where huge
currents can flow before the breaker trips, the current
foldback feature assures that the supply current will be
kept at a safe level and prevent voltage glitches when
powering up into a short.
The current limit for the 5V and 3.3V supplies is set by
placing a sense resistor between 5VIN (Pin 13) and 5VSENSE
(Pin 12) and between 3VIN (Pin 9) and 3VSENSE (Pin 10).
The current limit will be set by:
ILIMIT = 53mV/RSENSE
For a 0.005Ω resistor, the current limit will be set at 10.6A
and fold back to 1.5A when the output is shorted. For a
0.007Ω resistor, the current limit will be set at 7.6A and
fold back to 1.1A when the output is shorted.
The current limit for the internal 12V switch is set at
850mA folding back to 250mA and the –12V switch at
450mA folding back to 160mA.
In systems where it is possible to exceed the current limit
for a short amount of time, it might be necessary to
prevent the analog current loop from responding quickly
so the output voltage does not droop. This can be accom-
plished by adding an RC filter across the sense resistor as
shown in Figure 6. R4 should be 20Ω or less to prevent
offset errors. A 0.1µF capacitor gives a delay of about
1.5µs and a 1µF capacitor gives a delay of about 15µs.
CompactPCI Application
The LTC1643AL is designed for hot swapping CompactPCI
boards. The typical application is shown in Figure 7. The
3.3V, 5V, 12V and –12V inputs to the LTC1643AL come
from the medium length power pins. The long 3.3V, 5V and
V(I/O) pins power up the pull-up resistors, bus precharge
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11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1643AH.PDF ] | |
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