LINER LTC1646 Compactpci dual hot swap controller Datasheet

LTC1646
CompactPCI Dual
Hot Swap Controller
DESCRIPTIO
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FEATURES
■
■
Allows Safe Board Insertion and Removal from a
Live, CompactPCITM Bus
Controls 3.3V and/or 5V Supplies
Programmable Foldback Current Limit During
Power-Up
Dual Level Circuit Breakers Protect Supplies from
Overcurrent and Short-Circuit Faults
LOCAL_PCI_RST# Logic On-Chip
PRECHARGE Output Biases I/O Pins During Card
Insertion and Extraction
User Programmable Supply Voltage Power-Up Rate
15V High Side Drive for External N-Channel
MOSFETS
PWRGD, RESETOUT and FAULT Outputs
■
CompactPCI Bus Removable Boards
■
■
■
■
■
■
■
The LTC®1646 is a Hot SwapTM controller that allows a
board to be safely inserted and removed from a live
CompactPCI bus slot. Two external N-Channel transistors
control the 3.3V and 5V supplies. The supplies can be
ramped-up in current limit or a programmable rate. Electronic circuit breakers protect both supplies against
overcurrent fault conditions. The PWRGD output indicates
when all of the supply voltages are within tolerance. The
OFF/ON pin is used to cycle the board power or reset the
circuit breaker. The PRECHARGE output can be used to
bias the bus I/O pins during card insertion and extraction.
PCI_RST# is logically combined on-chip with HEALTHY#
in order to generate LOCAL_PCI_RST# which can be used
to reset the CPCI card logic if either of the supply voltages
is not within tolerance.
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APPLICATIO S
The LTC1646 is available in the 16-pin narrow SSOP
package.
, LTC and LT 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.
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TYPICAL APPLICATIO
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)
R2
0.007Ω
1%
Z2
Z1
Q1
IRF7413
5V
5A
5V
R1
0.005Ω, 1%
2.7Ω
LONG 5V
3.3V
3.3V
7.6A
0.1µF
LONG 3.3V
R3
10Ω
V(I/O)
8
3VIN
1.2k
1k
BD_SEL#
V(I/O)
R4
10Ω
3k
15
3
3k
16
PCI_RST#
12
5VIN
11
5VSENSE
OFF/ON
C1
0.01µF
5
5VOUT
TIMER
2
10k
0.1µF
3VOUT
FAULT
LTC1646
4
HEALTHY#
9
10
7
3VSENSE GATE 3VOUT
R5
1k, 5%
PWRGD
RESETIN
GND
6
3k
RESETOUT
PRECHARGE
13
18Ω
10k
10Ω
DATA BUS
PRECHARGE OUT
1V ±10%
IOUT = ± 55mA
1k
12Ω
MMBT2222A
DATA LINE EXAMPLE
DATA BUS
Z1, Z2: BZX84C6V2
DRIVE
14
4.7nF
GROUND
I/O PIN 1
18Ω
1
LOCAL_PCI_RST#
0.1µF
1.8Ω
Q2
IRF7413
3VIN
3VIN
5VIN
3.3V
5V
RESET#
I/O
PCI
BRIDGE
(21154)
1646 F01
Figure 1
1646fa
1
LTC1646
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltages: 5VIN, 3VIN ............................................... 10V
Input Voltages: (Pins 15, 16) ..................... –0.3V to 10V
Output Voltages: (Pins 1, 3, 4) .................. –0.3V to 10V
Analog Voltages and Currents:
(Pin 9) .................................... –0.3V to (3VIN + 0.3V)
(Pins 2, 5, 7, 11, 13, 14) ........ –0.3V to (5VIN + 0.3V)
(Pin 10) .......................................................... ±20mA
Operating Temperature Range:
LTC1646C ............................................... 0°C to 70°C
LTC1646I .............................................–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
RESETOUT 1
16 RESETIN
TIMER 2
15 OFF/ON
FAULT 3
14 DRIVE
PWRGD 4
13 PRECHARGE
5VOUT 5
12 5VIN
GND 6
11 5VSENSE
3VOUT 7
10 GATE
3VIN 8
9
3VSENSE
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 135°C/W
ORDER PART NUMBER
LTC1646CGN
LTC1646IGN
GN PART MARKING
1646
1646I
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V5VIN = 5V and V3VIN = 3.3V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
IDD
V5VIN Supply Current
OFF/ON = 0V
●
VLKO
Undervoltage Lockout
5VIN
3VIN
●
●
VFB
Foldback Current Limit Voltage
VFB = (V5VIN – V5VSENSE), V5VOUT = 0V, TIMER = 0V
VFB = (V5VIN – V5VSENSE), V5VOUT = 4V, TIMER = 0V
VFB = (V3VIN – V3VSENSE), V3VOUT = 0V, TIMER = 0V
VFB = (V3VIN – V3VSENSE), V3VOUT = 2V, TIMER = 0V
VCB
Circuit Breaker Trip Voltage
t OC
UNITS
1.5
4
2.3
2.3
2.50
2.55
2.7
2.7
V
V
●
●
●
●
15
50
15
50
20
55
20
55
30
65
30
65
mV
mV
mV
mV
VCB = (V5VIN – V5VSENSE), V5VOUT = 5V, TIMER Open
VCB = (V3VIN – V3VSENSE), V3VOUT = 3.3V, TIMER Open
●
●
50
50
56
56
65
65
mV
mV
Overcurrent Fault Response Time
(V5VIN – V5VSENSE) = 100mV, TIMER Open
(V3VIN – V3VSENSE) = 100mV, TIMER Open
●
●
10
10
21
21
30
30
µs
µs
t SS
Short-Circuit Fault Response Time
(V5VIN – V5VSENSE) = 200mV, TIMER Open
(V3VIN – V3VSENSE) = 200mV, TIMER Open
●
●
0.145
0.145
1
1
µs
µs
ICP
GATE Pin Output Current
OFF/ON = 0V, VGATE = 0V, TIMER = 0V
OFF/ON = 5V, VGATE = 5V, TIMER = 0V
OFF/ON = 0V, VGATE = 5V, FAULT = 0V, TIMER Open
●
●
–18
80
4
–13
200
7
–8
300
12
µA
µA
mA
mA
VGATE
External Gate Voltage
(GATE to GND)
OFF/ON = 0V, IGATE = –1µA
OFF/ON = 0V, V5VIN = 3.3V, IGATE = –1µA
●
●
12
11
15
13
16
15
V
V
VTH
Power Good Threshold Voltage
3VOUT
5VOUT
●
●
2.8
4.5
2.9
4.65
3.0
4.75
V
V
V3VONLY
No 5V Input Mode Window Voltage V3VONLY = ⎪V5VIN – V3VIN⎪, V5VOUT = V3VOUT = 3.3V
Input Low Voltage
OFF/ON, RESETIN, FAULT
●
50
120
200
mV
0.8
V
VIL
●
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LTC1646
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. V5VIN = 5V and V3VIN = 3.3V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VIH
Input High Voltage
OFF/ON, RESETIN, FAULT
●
MIN
2
VTIMER
TIMER Threshold Voltage
VTIMER , FAULT = 0V
●
1.15
IIN
OFF/ON Input Current
OFF/ON = 5V
OFF/ON = 0V
RESETIN Input Current
TYP
MAX
UNITS
V
1.25
1.35
V
●
●
±0.08
±0.08
±10
±10
µA
µA
RESETIN = 5V
RESETIN = 0V
●
●
±0.08
±0.08
±10
±10
µA
µA
5VSENSE Input Current
5VSENSE = 5V, 5VOUT = 0V
●
66
100
µA
3VSENSE Input Current
3VSENSE = 3.3V, 3VOUT = 0V
●
66
100
µA
3VIN Input Current
3VIN = 3.3V
●
460
1000
µA
5VOUT Input Current
5VOUT = 5V, OFF/ON = 0V
●
0.9
1.5
mA
3VOUT Input Current
3VOUT = 3.3V, OFF/ON = 0V
●
0.9
1.5
mA
ITIMER
TIMER Pin Current
OFF/ON = 0V, VTIMER = 0V
OFF/ON = 5V, VTIMER = 5V
●
–5
6.6
–3
µA
mA
RDIS
5VOUT Discharge Impedance
3VOUT Discharge Impedance
OFF/ON = 5V
OFF/ON = 5V
●
●
120
120
220
220
Ω
Ω
VOL
Output Low Voltage
FAULT, PWRGD, RESETOUT, I = 2mA
●
0.25
0.4
V
VPXG
PRECHARGE Reference Voltage
VPRECHARGE, V5VIN = 5V and 3.3V
●
1.00
1.10
V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
–7
0.90
Note 2: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
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TYPICAL PERFOR A CE CHARACTERISTICS
12
11
11
10
10
9
9
8
7
6
5
4
3
1.8
1.7
SUPPLY CURRENT (mA)
12
8
7
6
5
4
3
2
2
0
0
1
3
2
4
OUTPUT VOLTAGE (V)
5
1646 G01
0
1
3
2
OUTPUT VOLTAGE (V)
4
1.6
1.5
1.4
1.3
1.2
1.1
RSENSE = 0.005Ω
1
RSENSE = 0.007Ω
1
0
5VIN Supply Current vs
Temperature
3.3V Current Foldback Profile
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
5V Current Foldback Profile
5
1646 G02
1.0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G03
1646fa
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LTC1646
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TYPICAL PERFOR A CE CHARACTERISTICS
5VIN Undervoltage Lockout
Voltage vs Temperature
3VIN Undervoltage Lockout
Voltage vs Temperature
2.60
2.55
LOW-TO-HIGH TRANSITION
2.50
HIGH-TO-LOW TRANSITION
2.45
2.40
–50
–25
0
25
50
TEMPERATURE (°C)
75
60
LOW-TO-HIGH TRANSITION
2.55
HIGH-TO-LOW TRANSITION
2.50
2.45
2.40
–50
100
–25
0
25
50
TEMPERATURE (°C)
75
1646 G04
30
3VOUT = 0V
10
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
58
57
56
55
54
53
52
51
–25
0
25
50
TEMPERATURE (°C)
75
21.00
20.75
20.50
20.25
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G10
100
58
57
56
55
54
53
52
51
50
–50
100
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G09
Gate Current vs Temperature
170
–10
160
–11
150
GATE CURRENT (µA)
SHORT-CIRCUIT FAULT RESPONSE TIME (ns)
21.25
75
59
5VIN/3VIN Short-Circuit Fault
Response Time vs Temperature
21.50
0
25
50
TEMPERATURE (°C)
1646 G08
5VIN/3VIN Overcurrent Fault
Response Time vs Temperature
21.75
–25
60
1646 G07
20.00
–50
10
3VIN Circuit Breaker Trip Voltage
vs Temperature
59
50
–50
100
22.00
5VOUT = 0V
20
1646 G06
CIRCUIT BREAKER TRIP VOLTAGE (mV)
40
20
30
0
–50
100
60
CIRCUIT BREAKER TRIP VOLTAGE (mV)
FOLDBACK CURRENT LIMIT VOLTAGE (mV)
60
50
40
5VIN Circuit Breaker Trip Voltage
vs Temperature
3VOUT = 2V
5VOUT = 4V
50
1646 G05
3VIN Foldback Current Limit
Voltage vs Temperature
OVERCURRENT FAULT RESPONSE TIME (µs)
FOLDBACK CURRENT LIMIT VOLTAGE (mV)
UNDERVOLTAGE LOCKOUT VOLTAGE (V)
UNDERVOLTAGE LOCKOUT VOLTAGE (V)
2.60
5VIN Foldback Current Limit
Voltage vs Temperature
140
130
120
–12
–13
–14
110
100
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G11
–15
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G12
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LTC1646
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TYPICAL PERFOR A CE CHARACTERISTICS
Gate ISINK vs Temperature
15.5
3.00
FAULT = 0V
POWER GOOD THRESHOLD VOLTAGE (V)
10
I = –1µA
5VIN = 5V
15.0
GATE VOLTAGE (V)
9
GATE ISINK (mA)
Power Good Threshold Voltage vs
Temperature (3VOUT)
Gate Voltage vs Temperature
8
7
14.5
14.0
13.5
5VIN = 3.3V
6
13.0
5
–50
–25
0
25
50
TEMPERATURE (°C)
75
12.5
–50
100
–25
0
25
50
TEMPERATURE (°C)
75
1646 G13
2.90
2.85
2.80
–50
100
–25
0
25
50
TEMPERATURE (°C)
75
1646 G14
4.75
100
1646 G15
5VSENSE Input Current vs
Temperature
Timer Threshold Voltage vs
Temperature
Power Good Threshold Voltage vs
Temperature (5VOUT)
1.30
70
4.70
4.65
4.60
4.55
5VSENSE INPUT CURRENT (µA)
69
TIMER THRESHOLD VOLTAGE (V)
POWER GOOD THRESHOLD VOLTAGE (V)
2.95
1.28
1.26
1.24
1.22
68
67
66
65
64
63
62
61
4.50
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1.20
–50
–25
0
25
50
TEMPERATURE (°C)
75
1646 G16
3VIN INPUT CURRENT (µA)
3VSENSE INPUT CURRENT (µA)
69
66
65
64
63
62
480
–4.00
475
–4.25
470
465
460
455
450
61
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G19
75
445
–50
100
Timer Current vs Temperature
TIMER CURRENT (µA)
70
67
0
25
50
TEMPERATURE (°C)
1646 G18
3VIN Input Current vs Temperature
68
–25
1646 G17
3VSENSE Input Current vs
Temperature
60
–50
60
–50
100
–4.50
–4.75
–5.00
–5.25
–5.50
–5.75
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G20
–6.00
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1646 G21
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LTC1646
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TYPICAL PERFOR A CE CHARACTERISTICS
RESETOUT, PWRGD and FAULT
Output Low Voltage vs ISINK
5VOUT/3VOUT Discharge
Impedance vs Temperature
180
3VOUT/5VOUT DISCHARGE IMPEDANCE (Ω)
1.0
OUTPUT LOW VOLTAGE (V)
0.9
90°C
0.8
0.7
25°C
0.6
0.5
–45°C
0.4
0.3
0.2
0.1
0
0
1
2
3
ISINK (mA)
4
5
160
140
120
100
80
60
40
20
0
–50
–25
0
25
50
TEMPERATURE (°C)
1646 G22
75
100
1646 G23
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PI FU CTIO S
RESETOUT (Pin 1): Open Drain Digital Output. Connect
the CPCI LOCAL_PCI_RST# signal to the RESETOUT pin.
RESETOUT is the logical combination of RESETIN and
PWRGD (see Table 4).
TIMER (Pin 2): Current Fault Inhibit Timing Input. Connect
a capacitor from TIMER to GND. With the chip turned off,
the TIMER pin is internally held at GND. When the chip is
turned on, a 5µA pull-up current source is connected to
TIMER. Current limit and voltage compliance faults will be
ignored until the voltage at the TIMER pin is greater than
1.25V.
FAULT (Pin 3): Open Drain Digital I/O. FAULT is pulled low
when a current limit fault is detected. Faults are ignored
while the voltage at the TIMER pin is less than 1.25V. Once
the TIMER cycle is complete, FAULT will pull low and the
chip will latch off in the event of an overcurrent fault. The
chip will remain latched in the off state until the OFF/ON pin
is cycled high then low or the power is cycled.
Forcing the FAULT pin low with an external pull-down will
cause the chip to be latched into the off state after a 21µs
deglitching time.
PWRGD (Pin 4) :Open Drain Power Good Digital Output.
Connect the CPCI HEALTHY# signal to the PWRGD pin.
PWRGD remains low while V3VOUT ≥ 2.9V and V5VOUT ≥
4.65V. When either of the supplies falls below its power
good threshold voltage, PWRGD will go high after a 50µs
deglitching time.
5VOUT (Pin 5): 5V Output Sense. The PWRGD pin will not
pull low until the 5VOUT pin voltage exceeds 4.65V. If no 5V
input supply is available, tie the 5VOUT pin to the 3VOUT pin
in order to disable the 5VOUT power good function.
GND (Pin 6): Chip Ground
3VOUT (Pin 7): 3.3V Output Sense. The PWRGD pin will not
pull low until the 3VOUT pin voltage exceeds 2.90V. If no
3.3V input supply is available, tie the 3VOUT pin to the
5VOUT pin.
3VIN (Pin 8): 3.3V Supply Sense Input. An undervoltage
lockout circuit prevents the switches from turning on
when the voltage at the 3VIN pin is less than 2.5V. If no 3.3V
input supply is available, connect a diode between 5VIN
and 3VIN (tie anode to 5VIN and cathode to 3VIN ). See
Figure 11.
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LTC1646
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PI FU CTIO S
3VSENSE (Pin 9): 3.3V Current Limit Set. With a sense
resistor placed in the supply path between 3VIN and
3VSENSE, the GATE pin voltage will be adjusted to maintain
a constant voltage across the sense resistor and a constant current through the switch while the TIMER pin
voltage is less than 1.25V. A foldback feature makes the
current limit decrease as the voltage at the 3VOUT pin
approaches GND.
When the TIMER pin voltage is greater than 1.25V, the
circuit breaker function is enabled. If the voltage across
the sense resistor exceeds 56mV but is less than 150mV,
the circuit breaker is tripped after a 21µs time delay. In the
event the sense resistor voltage exceeds 150mV, the
circuit breaker trips immediately and the chip latches off.
To disable the 5V current limit, short 5VSENSE and 5VIN
together.
When the TIMER pin voltage exceeds 1.25V, the circuit
breaker function is enabled. If the voltage across the sense
resistor exceeds 56mV, the circuit breaker is tripped after
a 21µs time delay. In the event the sense resistor voltage
exceeds 150mV, the circuit breaker trips immediately and
the chip latches off. To disable the 3.3V current limit,
3VSENSE and 3VIN can be shorted together.
5VIN (Pin 12): 5V Supply Sense Input. An undervoltage
lockout circuit prevents the GATE pin voltage from
ramping up when the voltage at the 5VIN pin is less than
2.5V. If no 5V input supply is available, tie the 5VIN pin to
the 3VIN pin.
GATE (Pin 10): High Side Gate Drive for the External 3.3V
and 5V N-Channel pass transistors. Requires an external
series RC network for the current limit loop compensation
and setting the minimum ramp-up rate. During power-up,
the slope of the voltage rise at the GATE is set by the 13µA
current source connected to the internal charge pump and
the external capacitor connected to GND or by the 3.3V or
5V current limit and the bulk capacitance on the 3VOUT or
5VOUT supply lines. During power-down, the slope of the
ramp down voltage is set by the 200µA current source
connected to GND and the external GATE capacitor.
The voltage at the GATE pin will be modulated to maintain
a constant current when either the 3V or 5V supplies go
into current limit while the TIMER pin voltage is less than
1.25V. If a current fault occurs after the TIMER pin voltage
exceeds 1.25V, the GATE pin is immediately pulled to
GND.
5VSENSE (Pin 11): 5V Current Limit Set. With a sense
resistor placed in the supply path between 5VIN and
5VSENSE, the GATE pin voltage will be adjusted to maintain
a constant voltage across the sense resistor and a constant current through the switch while the TIMER pin
voltage is less than 1.25V. A foldback feature makes the
current limit decrease as the voltage at the 5VOUT pin
approaches GND.
PRECHARGE (Pin 13): Precharge Monitor Input. An onchip error amplifier with a 1V reference servos the DRIVE
pin voltage to keep the precharge node at 1V. If the
precharge function is not being used, tie the PRECHARGE
pin to GND.
DRIVE (Pin 14): Precharge Base Drive Output. Provides
base drive for an external NPN emitter-follower which in
turn biases the PRECHARGE node. If the precharge function is not being used, allow the DRIVE pin to float.
OFF/ON (Pin 15): Digital Input. Connect the CPCI BD_SEL#
signal to the OFF/ON pin. When the OFF/ON pin is pulled
low, the GATE pin is pulled high by a 13µA current source.
When the OFF/ON pin is pulled high the GATE pin will be
pulled to ground by a 200µA current source.
The OFF/ON pin is also used to reset the electronic circuit
breaker. If the OFF/ON pin is cycled high and low following
the trip of the circuit breaker, the circuit breaker is reset,
and a normal power-up sequence will occur.
RESETIN (Pin 16): Digital Input. Connect the CPCI
PCI_RST# signal to the RESETIN pin. Pulling RESETIN low
will cause the RESETOUT pin to pull low.
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LTC1646
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TEST DIAGRA
V3VONLY No 5V Input Mode Window Voltage
V3VONLY = ⎟ 5VIN – 3VIN ⎢ 5VOUT = 3VOUT = 3.3V, 3VIN = 3.3V
V3VONLY
V5VIN
3.3V
–V3VONLY
5V
PWRGD
0V
1646 T01
W
UW
TI I G DIAGRA S
tOC Overcurrent Fault Detect
FALL TIME ≤ 1µs, 5VIN = 5V, 3VIN = 3.3V
5V
V5VSENSE OR 3.3V
100mV
OR
V3VSENSE
tOC
FAULT
1V
1646 T02
tSC Short-Circuit Fault Detect
FALL TIME ≤ 30ns, 5VIN = 5V, 3VIN = 3.3V
5V
V5VSENSE OR 3.3V
200mV
OR
V3VSENSE
tSC
FAULT
1V
1646 T03
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LTC1646
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BLOCK DIAGRA
5VIN
5VSENSE
12
11
GATE
10
VGG
5VOUT
+–
3VIN
9
8
+
7
5
–+
55mV
55mV
+–
–
Q1
200µA
–+
–
+
+
–
–
150mV
+–
3VOUT 5VOUT
3VOUT
13µA
+
3VSENSE
Q2
Q3
150mV
2.5V
UVL
–+
2.5V
UVL
CP3
+
OFF/ON 15
–
FAULT 3
REF
Q7
CP4
+
PWRGD 4
LOGIC
–
Q6
1 RESETOUT
REF
Q4
RESETIN 16
5Vin
5µA
+
TIMER 2
1V
Q5
–
6
GND
14
13
DRIVE
PRECHARGE
1646 BD
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Hot Circuit Insertion
When a circuit board is inserted into a live CompactPCI
(CPCI) slot, the supply bypass capacitors on the board can
draw huge supply transient currents from the CPCI power
bus as they charge up. The transient currents can cause
glitches on the power bus, causing other boards in the
system to reset.
The LTC1646 is designed to turn a board’s supply voltages
on and off in a controlled manner, allowing the board to be
safely inserted or removed from a live CPCI slot without
glitching the system power supplies. The chip also protects the supplies from shorts, precharges the bus I/O pins
during insertion and extraction and monitors the supply
voltages.
The LTC1646 is specifically designed for CPCI applications where the chip resides on the plug-in board.
LTC1646 Feature Summary
1. Allows safe board insertion and removal from a CPCI
backplane.
2. Controls 5V and 3.3V CPCI supplies.
3. Current limit during power-up: the supplies are allowed
to power up in current limit. This allows the chip to
power up boards with widely varying capacitive loads
without tripping the circuit breaker. The maximum
allowable power-up time is programmable using the
TIMER pin and an external capacitor.
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4. Programmable foldback current limit: a programmable
analog current limit with a value that depends on the
output voltage. If the output is shorted to ground, the
current limit drops to keep power dissipation and
supply glitches to a minimum.
5. Dual-level, programmable 5V and 3.3V circuit breakers:
this feature is enabled when the TIMER pin voltage
exceeds 1.25V. If either supply exceeds current limit
for more than 21µs, the circuit breaker will trip, the
supplies will be turned off, and the FAULT pin is pulled
low. In the event that either supply exceeds three times
the set current limit, all supplies will be turned off and
the FAULT pin is pin is pulled low without delay.
6. 15V high side drive for external 3.3V and 5V N-channel
MOSFETs.
7. PWRGD output: monitors the voltage status of the
supply voltages.
8. PCI_RST# combined on-chip with HEALTHY# to create
LOCAL_PCI_RST# output. If HEALTHY# deasserts,
LOCAL_PCI_RST# is asserted independent of
PCI_RST#.
9. Precharge output: on-chip reference and amplifier provide 1V for biasing bus I/O connector pins during CPCI
card insertion and extraction.
10. Space saving 16-pin SSOP package.
PCI Power Requirements
CPCI systems may require up to four power rails: 5V, 3.3V,
12V and –12V. The LTC1646 is designed for CPCI applications which only use the 5V and/or 3.3V supplies. The
tolerance of the supplies as measured at the components
on the plug-in card is summarized in Table 1.
Table 1. PCI Power Supply Requirements
SUPPLY
TOLERANCE
CAPACITIVE LOAD
5V ±5%
< 3000µF
3.3V ±0.3V
< 3000µF
5V
3.3V
The main 3.3V and 5V inputs to the LTC1646 come from
the medium length power pins. The long 3.3V, 5V connector pins are shorted to the medium length 5V and 3.3V
connector pins on the CPCI plug-in card and provide early
power for the LTC1646’s precharge circuitry, the V(I/O)
pull-up resistors and the PCI bridge chip. The BD_SEL#
signal is connected to the OFF/ON pin while the PWRGD
pin is connected to the HEALTHY# signal. The HEALTHY#
signal is combined with the PCI_RST# signal on-chip to
generate the LOCAL_PCI_RST# signal which is available
at the RESETOUT pin.
The power supplies are controlled by placing external
N-channel pass transistors in the 3.3V and 5V power
paths.
Resistors R1 and R2 provide current fault detection and
R5 and C1 provide current control loop compensation.
Resistors R3 and R4 prevent high frequency oscillations
in Q1 and Q2.
When the CPCI card is inserted, the long 5V and 3.3V
connector pins and GND pins make contact first. The
LTC1646’s precharge circuit biases the bus I/O pins to 1V
during this stage of the insertion (Figure 2). The 5V and
3.3V medium length pins make contact during the next
stage of insertion, but the slot power is disabled as long
as the OFF/ON pin is pulled high by the 1.2k pull-up
resistor to V(I/O). During the final stage of board insertion,
the BD_SEL# short connector pin makes contact and the
OFF/ON pin can be pulled low. This enables the pass
transistors to turn on and a 5µA current source is connected to the TIMER pin.
The current in each pass transistor increases until it
reaches the current limit for each supply. The 5V and 3.3V
supplies are then allowed to power up based on one of the
following power-up rates:
ILIMIT (3 V)
ILIMIT (5 V)
dV 13µA
=
, or =
, or =
(1)
dt
C1
C LOAD(5 VOUT )
C LOAD(3 VOUT )
whichever is slower.
Power-Up Sequence
The LTC1646 is specifically designed for hot swapping
CPCI boards. The typical application is shown in Figure 1.
Current limit faults are ignored while the TIMER pin
voltage is ramping up and is less than 1.25V. Once both
supply voltages are within tolerance, HEALTHY# will pull
low and LOCAL_PCI_RST# is free to follow PCI_RST#.
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GATE
10V/DIV
GATE
10V/DIV
5VOUT
3VOUT
5V/DIV
5VOUT
3VOUT
5V/DIV
TIMER
5V/DIV
TIMER
5V/DIV
BD_SEL#
5V/DIV
BD_SEL#
5V/DIV
HEALTHY#
5V/DIV
LCL_PCI_RST#
5V/DIV
HEALTHY#
5V/DIV
LCL_PCI_RST#
5V/DIV
PRECHARGE
5V/DIV
PRECHARGE
5V/DIV
20ms/DIV
10ms/DIV
1646 F02
Figure 2. Normal Power-Up Sequence
Power-Down Sequence
When BD_SEL# is pulled high, a power-down sequence
begins (Figure 3).
Internal switches are connected to each of the output
supply voltage pins to discharge the bypass capacitors to
ground. The TIMER pin (Pin 2) is immediately pulled low.
The GATE pin (Pin 10) is pulled down by a 200µA current
source to prevent the load currents on the 3.3V and 5V
supplies from going to zero instantaneously in order to
prevent glitching the power supply voltages. When either
of the output voltages dips below its threshold, HEALTHY#
pulls high and LOCAL_PCI_RST# will be asserted low.
Once the power-down sequence is complete, the CPCI
card may be removed from the slot. During extraction, the
precharge circuit will continue to bias the bus I/O pins at
1V until the 5V and 3.3V long connector pin connections
are separated.
Timer
During a power-up sequence, a 5µA current source is
connected to the TIMER pin and current limit faults are
ignored until the voltage exceeds 1.25V. This feature
1646 F03
Figure 3. Normal Power-Down Sequence
allows the chip to power up CPCI boards with widely
varying capacitive loads on the supplies. The power-up
time for either of the two outputs is given by:
tON (XVOUT ) = 2 •
CLOAD(XVOUT) • XVOUT
ILIMIT(XVOUT) – ILOAD(XVOUT)
(2)
Where XVOUT = 5VOUT or 3VOUT. For example, for
CLOAD(5VOUT) = 2000µF, ILIMIT = 7A, and ILOAD = 5A, the
5VOUT turn-on time will be ~10ms. By substituting the
variables in Equation 2 with the appropriate values, the
turn-on time for the 3VOUT output can also be calculated.
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 for the LTC1646 is given
by:
tTIMER =
C TIMER • 1.25V
5µA
(3)
As a design aid, the timer period as a function of the timing
capacitor using standard values from 0.01µF to 1µF is
shown in Table 2.
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Table 2. t TIMER vs CTIMER
CTIMER
tTIMER
CTIMER
tTIMER
0.01µF
2.5ms
0.22µF
55ms
0.022µF
5.5ms
0.33µF
82.5ms
0.033µF
8.25ms
0.47µF
118ms
0.047µF
11.8ms
0.68µF
170ms
0.068µF
17ms
0.82µF
205ms
0.082µF
20.5ms
1µF
250ms
0.1µF
25ms
The TIMER pin is immediately pulled low when BD_SEL#
goes high.
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 prevents voltage glitches at the
input supply when powering up into a short circuit.
After power-up (TIMER pin voltage >1.25V), the 5V and
3.3V supplies are protected from overcurrent and shortcircuit conditions by dual-level circuit breakers. If the
sense resistor voltage of either supply current exceeds
56mV but is less than 150mV, an internal timer is started.
If the supply is still overcurrent after 21µs, the circuit
breaker trips and both supplies are turned off (Figure 5).
Short-Circuit Protection
During a normal power-up sequence, if the TIMER pin is
done ramping and a supply is still in current limit, all of the
pass transistors will be immediately turned off and FAULT
(Pin 3) will be pulled low as shown in Figure 4.
In order to prevent excessive power dissipation in the pass
transistors 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.
GATE
5V/DIV
5VIN – 5VSENSE
50mV/DIV
GATE
10V/DIV
FAULT
5V/DIV
5VOUT
3VOUT
2V/DIV
10µs/DIV
TIMER
1V/DIV
1646 F05
Figure 5. Overcurrent Fault on 5V
BD_SEL#
5V/DIV
If a short-circuit occurs and the sense resistor voltage of
either supply current exceeds 150mV, the circuit breakers
trip without delay and the chip latches off (Figure 6). The
chip will stay in the latched-off state until OFF/ON (Pin 15)
is cycled high then low, or the 5VIN (Pin 12) power supply
is cycled.
LCL_PCI_RST#
5V/DIV
HEALTHY#
5V/DIV
FAULT
5V/DIV
10ms/DIV
Figure 4. Power-Up into a Short on 3.3V Output
1646 F04
The current limit and the foldback current level for the 5V
and 3.3V outputs are both a function of the external sense
resistor (R1 for 3VOUT and R2 for 5VOUT, see Figure 1). As
shown in Figure 1, a sense resistor is connected between
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Calculating RSENSE
An equivalent circuit for one of the LTC1646’s circuit
breakers useful in calculating the value of the sense
resistor is shown in Figure 7. To determine the most
appropriate value for the sense resistor first requires the
maximum current required by the load under worst-case
conditions.
5VIN –5VSENSE
100mV/DIV
ILOAD(MAX)
GATE
10V/DIV
5VIN
1
RSENSE
3
4
11
5VSENSE
12
5VIN
+
–
FAULT
5V/DIV
–
5µs/DIV
2
VCB
LTC1646*
+
1646 F06
Figure 6. Short-Circuit Fault on 5V
*ADDITIONAL DETAILS
OMITTED FOR CLARITY
5VIN (Pin 12) and 5VSENSE (Pin 11) for the 5V supply. For
the 3.3V supply, a sense resistor is connected between
3VIN (Pin 8) and 3VSENSE (Pin 9). The current limit and the
current foldback current level are given by Equations 4
and 5:
ILIMIT (XVOUT) =
(4)
55mV
RSENSE(XVOUT)
IFOLDBACK(XVOUT) =
(5)
20mV
RSENSE(XVOUT)
where XVOUT = 5VOUT or 3VOUT.
As a design aid, the current limit and foldback level for
commonly used values for RSENSE is shown in Table 3.
Table 3. ILIMIT(XVOUT) and IFOLDBACK(XVOUT) vs RSENSE
RSENSE (Ω)
ILIMIT(XVOUT)
IFOLDBACK(XVOUT)
0.005
11A
4A
0.006
9.2A
3.3A
0.007
7.9A
2.9A
0.008
6.9A
2.5A
0.009
6.1A
2.2A
0.01
5.5A
2A
where XVOUT = 3VOUT or 5VOUT.
VCB(MAX) = 65mV
VCB(NOM) = 56mV
VCB(MIN) = 50mV
1646 F07
Figure 7. Circuit Breaker Equivalent
Circuit for Calculating RSENSE
Two other parameters affect the value of the sense resistor. First is the tolerance of the LTC1646’s circuit breaker
threshold. The LTC1646’s nominal circuit breaker
threshold is VCB(NOM) = 56mV; however, it exhibits a
–6mV/+9mV tolerance due to process variations. Second
is the tolerance (RTOL) in the sense resistor. Sense
resistors are available in RTOLs of ±1%, ±2% and ±5%
and exhibit temperature coefficients of resistance (TCRs)
between ±75ppm/°C and ±100ppm/°C. How the sense
resistor changes as a function of temperature depends on
the I2R power being dissipated by it.
The first step in calculating the value of RSENSE is based on
ITRIP(MAX) and the lower limit for the circuit breaker
threshold, VCB(MIN). The maximum value for RSENSE in this
case is expressed by Equation 6:
RSENSE(MAX) =
VCB(MIN)
ITRIP(MAX)
(6)
The second step is to determine the nominal value of the
sense resistor which is dependent on its tolerance
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(RTOL = ±1%, ±2% or ±5%) and standard sense resistor
values. Equation 7 can be used to calculate the nominal
value from the maximum value found by Equation 6:
RSENSE(NOM) =
RSENSE(MAX)
⎛ RTOL⎞
1+ ⎜
⎟
⎝ 100 ⎠
(7)
Often, the result of Equation 7 may not yield a standard
sense resistor value. In this case, two sense resistors with
the same RTOL can be connected in parallel to yield
RSENSE(NOM).
The last step requires calculating a new value for
ITRIP(MAX)(ITRIP(MAX, NEW)) based on a minimum value for
RSENSE (RSENSE(MIN)) and the upper limit for the circuit
breaker threshold, VCB(MAX). Should the calculated value
for ITRIP(MAX, NEW) be much greater than the design value
for ITRIP(MAX), a larger sense resistor value should be
selected and the process repeated. The new value for
ITRIP(MAX, NEW) is given by Equation 8:
ITRIP(MAX,NEW)
VCB(MAX)
=
RSENSE(MIN)
(8)
⎡ ⎛ RTOL⎞ ⎤
where RSENSE(MIN) = RSENSE(NOM) • ⎢1 – ⎜
⎟⎥
⎣ ⎝ 100 ⎠ ⎦
Example: A 5V supply exhibits a nominal 5A load with a
maximum load current of 6.8A (ILOAD(MAX) = 6.8A), and
sense resistors with ±5% RTOL will be used. According to
Equation 6, VCB(MIN) = 50mV and RSENSE(MAX) is given by:
RSENSE(MAX) =
VCB(MIN)
ITRIP(MAX)
=
50mV
= 0.0074Ω
6.8A
The nominal sense resistor value is (Equation 7):
RSENSE(NOM) =
RSENSE(MAX) 0.0074Ω
=
= 0.007Ω
⎛ RTOL⎞
⎛ 5 ⎞
1+ ⎜
⎟ 1+ ⎜
⎟
⎝ 100 ⎠
⎝ 100⎠
And the new current-limit trip point is Equation 8:
ITRIP(MAX,NEW) =
VCB(MAX)
=
RSENSE(MIN)
VCB(MAX)
65mV
=
= 9.8A
⎡ ⎛ RTOL⎞ ⎤ 0.0065
RSENSE(N0M) • ⎢1 – ⎜
⎟⎥
⎣ ⎝ 100 ⎠ ⎦
Since ITRIP(MAX, NEW) > ILOAD(MAX), a larger value for
RSENSE should be selected and the process repeated again
to lower ITRIP(MAX, NEW) without substantially affecting
ILOAD(MAX).
Output Voltage Monitor
The status of both 5V and 3.3V output voltages is monitored by the power good function. In addition, the PCI_RST#
signal is logically combined on-chip with the HEALTHY#
signal to create LOCAL_PCI_RST# (see Table 4).
Table 4. LOCAL_PCI_RST# Truth Table
PCI_RST#
HEALTHY#
LOCAL_PCI_RST#
LO
LO
LO
LO
HI
LO
HI
LO
HI
HI
HI
LO
If either of the output voltages drop below the power good
threshold for more than 50µs, the HEALTHY# signal will be
pulled high and the LOCAL_PCI_RST# signal will be pulled
low.
Precharge
The PRECHARGE input and DRIVE output pins are intended for use in generating the 1V precharge voltage that
is used to bias the bus I/O connector pins during board
insertion. The LTC1646 is also capable of generating
precharge voltages other than 1V. Figure 8 shows a circuit
that can be used in applications requiring a precharge
voltage less than 1V. The circuit in Figure 9 can be used for
applications that need precharge voltages greater than 1V.
Table 5 lists suggested resistor values for R1 and R2 vs
precharge voltage for the application circuits shown in
Figures 8 and 9.
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Table 5. R1 and R2 Resistor Values vs Precharge Voltage
VPRECHARGE
R1
R2
VPRECHARGE
1.5V
18Ω
9.09Ω
1.4V
18Ω
1.3V
1.2V
Other CompactPCI Applications
R1
R2
0.9V
16.2Ω
1.78Ω
7.15Ω
0.8V
14.7Ω
3.65Ω
18Ω
5.36Ω
0.7V
12.1Ω
5.11Ω
18Ω
3.65Ω
0.6V
11Ω
7.15Ω
1.1V
18Ω
1.78Ω
0.5V
9.09Ω
9.09Ω
1V
18Ω
0Ω
The LTC1646 can be easily configured for applications
where no 5V supply is present by simply tying the 5VIN and
5VSENSE pins to the 3VIN pin and tying the 5VOUT pin to the
3VOUT pin (Figure 10).
LTC1646*
GND
6
LTC1646*
PRECHARGE DRIVE
13
14
4.7nF
18Ω
GND
6
PRECHARGE
13
1k
DRIVE
14
4.7nF
18Ω
1k
12Ω
R1
R2
12Ω
MMBT2222A
R1
PRECHARGE OUT
R1
VPRECHARGE =
• 1V
R1 + R2
3VIN
*ADDITIONAL DETAILS OMITTED FOR CLARITY
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)
Z1
3VIN
3
0.1µF
IRF7413
3.3VOUT
7.6A
4
1.8Ω
10Ω
V(I/O)
1k
8
3VIN
1.2k
1k
BD_SEL#
15
9
10
7
3VSENSE GATE 3VOUT
12
5VIN
11
5VSENSE
OFF/ON
0.010µF
5
5VOUT
TIMER
2
10k
V(I/O)
3k
1646 F09
Figure 9. Precharge Voltage >1V Application Circuit
0.005Ω
1 1% 2
3.3V
LONG 3.3V
MMBT2222A
*ADDITIONAL DETAILS OMITTED FOR CLARITY
1646 F08
Figure 8. Precharge Voltage <1V Application Circuit
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
R2
PRECHARGE OUT
R1 + R2
VPRECHARGE =
• 1V
R1
3k
3
0.1µF
3VOUT
FAULT
LTC1646
16
PCI_RST#
3k
PWRGD
RESETIN
GND
6
RESETOUT
PRECHARGE
13
4.7nF
DRIVE
14
18Ω
1k
18Ω
12Ω
GROUND
1k
PRECHARGE OUT
1V ±10%
IOUT = ± 55mA
10Ω
3VIN
MMBT2222A
DATA LINE EXAMPLE
I/O PIN 1
DATA BUS
1
LOCAL_PCI_RST#
4
HEALTHY#
DATA BUS
Z1: BZX84C6V2
3.3V
3VIN
RESET#
I/O
PCI
BRIDGE
(21154)
1646 F10
Figure 10. 3.3V Supply Only Typical Application
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COMPACT PCI COMPACT PCI
BACKPLANE CIRCUIT CARD
CONNECTOR CONNECTOR
(MALE)
(FEMALE)
Z1
0.007Ω
5VIN
1
5V
3
LONG
5V
2 IRF7413
5VOUT
4
2.7Ω
10Ω
BAV16W
1k
0.1µF
0.01µF
8
9
12
11
10
5
7
3VIN 3VSENSE 5VIN 5VSENSE GATE 5VOUT 3VOUT
6
GND
GND
LTC1646
Z1: BZX84C6V2
1646 F11
Figure 11. 5V Supply Only Typical Application
If no 3.3V supply is present, Figure 11 illustrates how the
LTC1646 should be configured. First, 3VSENSE (Pin 9) is
connected to 3VIN (Pin 8), 3VOUT (Pin 7) is connected to
5VOUT (Pin 5) and the LTC1646’s 3VIN pin is connected
through a diode (BAV16W) to 5VIN.
For applications where the BD_SEL# connector pin is
typically grounded on the backplane, the circuit in
Figure 12 allows the LTC1646 to be reset simply by
pressing a pushbutton switch on the CPCI plug-in board.
This arrangement eliminates the requirement to extract
and reinsert the CPCI board in order to reset the LTC1646’s
circuit breakers.
PUSHBUTTON
SWITCH V(I/0)
COMPACT PCI COMPACT PCI
BACKPLANE CIRCUIT CARD
CONNECTOR CONNECTOR
(MALE)
(FEMALE)
1.2k
BD_SEL#
15
100Ω
Overvoltage Transient Protection
Good engineering practice calls for bypassing the supply
rail of any analog circuit. Bypass capacitors are often
placed at the supply connection of every active device, in
addition to one or more large-value bulk bypass capacitors
per supply rail. If power is connected abruptly, the large
bypass capacitors slow the rate of rise of the supply
voltage and heavily damp any parasitic resonance of lead
or PC trace inductance working against the supply bypass
capacitors.
The opposite is true for LTC1646 Hot Swap circuits
mounted on plug-in cards. In most cases, there is no
supply bypass capacitor present on the powered 3.3V or
5V side of the MOSFET switch. An abrupt connection,
produced by inserting the board into a backplane connector, results in a fast rising edge applied on the 3.3V and the
5V line of the LTC1646.
OFF/ON
1k
LTC1646
LONG GND
6
GND
1646 F12
Figure 12. BD_SEL# Pushbutton Toggle Switch
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Since there is no bulk capacitance to damp the parasitic
trace inductance, supply voltage transients excite parasitic resonant circuits formed by the power MOSFET
capacitance and the combined parasitic inductance from
the wiring harness, the backplane and the circuit board
traces. These ringing transients appear as a fast edge on
the 3.3V or 5V supply, exhibiting a peak overshoot to 2.5
times the steady-state value followed by a damped sinusoidal response whose duration and period is dependent
on the resonant circuit parameters. Since the absolute
maximum supply voltage of the LTC1646 is 10V, transient
protection against 3.3V and 5V supply voltage spikes and
ringing is highly recommended.
LTC1646 circuit schematics, Zener diodes and snubber
networks have been added to each 3.3V and 5V supply rail
and should be used always. These protection networks
should be mounted very close to the LTC1646’s supply
voltage using short lead lengths to minimize lead inductance. This is shown schematically in Figure 13 and a
recommended layout of the transient protection devices
around the LTC1646 is shown in Figure 14.
9
10
11
12
13
14
15
16
5VIN
TZ1
In these applications, there are two methods for eliminating these supply voltage transients: using Zener diodes to
clip the transient to a safe level and snubber networks.
Snubbers are RC networks whose time constants are
large enough to safely damp the inductance of the board’s
parasitic resonant circuits. As a starting point, the shunt
capacitors in these networks are chosen to be 10× to 100×
the power MOSFET’s COSS under bias. The value of the
series resistor (R6 and R7 in Figure 13) is then chosen to
be large enough to damp the resulting series R-L-C circuit
and typically ranges from 1Ω to 10Ω. Note that in all
VIN1
5V
LONG 5V
VIN2
3.3V
LONG 3.3V
R1
0.005Ω
8
6
5
4
3
2
1
7
3VIN
GND
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
Q1
IRF7413
5VOUT
AT 5A
Q2
IRF7413
9
10
3VSENSE GATE
Z1
3VOUT
AT 7.6A
R4
10Ω
7
12
3VOUT
5VIN
11
5VSENSE
R5
1k
5
GND
Z1, Z2: BZX84C6V2
**ADDITIONAL DETAILS OMITTED FOR CLARITY
C1
0.01µF
5VOUT
LTC1646**
C2
0.1µF
1646 F14
Figure 14. Recommended Layout for
Transient Protection Components
R3
10Ω
8
C3
TZ2
R7 1.8Ω
3VIN
VIAS TO
GND PLANE
LTC1646*
R2
0.007Ω
R6 2.7Ω
C2
6
Z2
C3
0.1µF
1646 F13
Figure 13. Place Transient Protection Device Close to the LTC1646
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LTC1646
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APPLICATIO S I FOR ATIO
In the majority of applications, it will be necessary to use
plated-through vias to make circuit connections from
component layers to power and ground layers internal to
the PC board. For 1 ounce copper foil plating, a general rule
is 1A of DC current per via, making sure the via is properly
dimensioned so that solder completely fills any void. For
other plating thicknesses, check with your PCB fabrication
facility.
PCB Layout Considerations
For proper operation of the LTC1646’s circuit breaker
function, a 4-wire Kelvin connection to the sense resistors
is highly recommended. A recommended PCB layout for
the sense resistor, the power MOSFET, and the GATE drive
components around the LTC1646 is illustrated in
Figure 15. In Hot Swap applications where load currents
can reach 10A, narrow PCB tracks exhibit more resistance
than wider tracks and operate at more elevated temperatures. Since the sheet resistance of 1 ounce copper foil is
■ , track resistances add up quickly
approximately 0.5mΩ/■
in high current applications. Thus, to keep PCB track
resistance and temperature rise to a minimum, the suggested trace width in these applications for 1 ounce
copper foil is 0.03" for each ampere of DC current.
Power MOSFET and Sense Resistor Selection
Table 6 lists some current MOSFET transistors that are
available and Table 7 lists some current sense resistors
that can be used with the LTC1646’s circuit breakers.
Table 8 lists supplier web site addresses for discrete
component mentioned throughout the LTC1646 data sheet.
Table 6. N-Channel Power MOSFET Selection Guide
CURRENT LEVEL (A)
PART NUMBER
DESCRIPTION
MANUFACTURER
0 to 2
MMDF3N02HD
Dual N-Channel SO-8
RDS(ON) = 0.1Ω
ON Semiconductor
2 to 5
MMSF5N02HD
Single N-Channel SO-8
RDS(ON) = 0.025Ω
ON Semiconductor
5 to 10
MTB50N06V
Single N-Channel DD Pak
RDS(ON) = 0.028Ω
ON Semiconductor
5 to 10
IRF7413
Single N-Channel SO-8
RDS(ON) = 0.01Ω
International Rectifier
5 to 10
Si4410DY
Single N-Channel SO-8
RDS(ON) = 0.01Ω
Vishay-Siliconix
Table 7. Sense Resistor Selection Guide
CURRENT LIMIT VALUE
PART NUMBER
DESCRIPTION
MANUFACTURER
1A
LR120601R055F
WSL1206R055
0.055Ω, 0.5W, 1% Resistor
IRC-TT
Vishay-Dale
2A
LR120601R028F
WSL1206R028
0.028Ω, 0.5W, 1% Resistor
IRC-TT
Vishay-Dale
5A
LR120601R011F
WSL2010R011
0.011Ω, 0.5W, 1% Resistor
IRC-TT
Vishay-Dale
7.6A
WSL2512R007
0.007Ω, 1W, 1% Resistor
Vishay-Dale
10A
WSL2512R005
0.005Ω, 1W, 1% Resistor
Vishay-Dale
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LTC1646
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APPLICATIO S I FOR ATIO
Table 8. Manufacturers’ Web Site
MANUFACTURER
WEB SITE
International Rectifier
www.irf.com
ON Semiconductor
www.onsemi.com
IRC-TT
www.irctt.com
Vishay-Dale
www.vishay.com
Vishay-Siliconix
www.vishay.com
Diodes, Inc.
www.diodes.com
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PACKAGE DESCRIPTIO
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.189 – .196*
(4.801 – 4.978)
.045 ±.005
16 15 14 13 12 11 10 9
.254 MIN
.009
(0.229)
REF
.150 – .165
.229 – .244
(5.817 – 6.198)
.0165 ± .0015
.150 – .157**
(3.810 – 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
.015 ± .004
× 45°
(0.38 ± 0.10)
.007 – .0098
(0.178 – 0.249)
2 3
4
5 6
7
.0532 – .0688
(1.35 – 1.75)
8
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
.008 – .012
(0.203 – 0.305)
TYP
.0250
(0.635)
BSC
GN16 (SSOP) 0204
3. DRAWING NOT TO SCALE
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1646fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LTC1646
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TYPICAL APPLICATIO
CURRENT FLOW
TO LOAD
VIN
5V
CURRENT FLOW
TO LOAD
SENSE
RESISTOR
SO-8
W
D
G
D
S
D
S
D
S
R3
TRACK WIDTH W:
0.03" PER AMPERE
ON 1 OZ Cu FOIL
VOUT
5V
W
VIA
R5
11
10
9
7
8
12
6
13
14
15
16
C1
5
4
3
2
1
LTC1646*
CTIMER
CURRENT FLOW
TO SOURCE
VIA TO GND
W
GND
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
GND
1646 F15
Figure 15. Recommended Layout for Power MOSFET, Sense Resistor, and Gate Components
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1421
Hot Swap Controller
Dual Supplies from 3V to 12V, Additionally –12V
LTC1422
Hot Swap Controller
Single Supply Hot Swap in SO-8 from 3V to 12V
LT1640AL/LT1640AH
Negative Voltage Hot Swap Controllers in SO-8
Negative High Voltage Supplies from –10V to – 80V
LT1641/LT1641-1
Positive Voltage Hot Swap Controller in SO-8
Supplies from 9V to 80V, Autoretry/Latches Off
LTC1642
Fault Protected Hot Swap Controller
3V to 15V, Overvoltage Protection Up to 33V
LTC1643L/LTC1643L-1/LTC1643H
PCI Bus Hot Swap Controllers
3.3V, 5V, 12V, –12V Supplies for PCI Bus
LTC1644
CompactPCI Hot Swap Controller
3.3V, 5V, ±12V Local Reset Logic and Precharge
LTC1645
2-Channel Hot Swap Controller
Operates from 1.2V to 12V, Power Sequencing
LTC1647
Dual Hot Swap Controller
Dual ON Pins for Supplies from 3V to 15V
LTC4211
Hot Swap Controller with Multifunction Current Control
Single Supply, 2.5V to 16.5V, MSOP
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Linear Technology Corporation
LT 1205 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2000