1646I [Linear]
CompactPCI Dual Hot Swap Controller; CompactPCI的双通道热插拔控制器
| 型号： | 1646I |
| 厂家： | 
Linear |
| 描述： | CompactPCI Dual Hot Swap Controller |
| 文件： | 总20页 (文件大小：400K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1646
CompactPCI Dual
Hot Swap Controller
U
DESCRIPTIO
FEATURES
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. Elec-
tronic circuit breakers protect both supplies against
overcurrentfaultconditions.ThePWRGDoutputindicates
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.
■
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
U
APPLICATIO S
The LTC1646 is available in the 16-pin narrow SSOP
package.
■
CompactPCI Bus Removable Boards
, 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.
U
TYPICAL APPLICATIO
COMPACT PCI COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
CIRCUIT CARD
CONNECTOR
(FEMALE)
R2
Z2
Z1
0.007Ω
Q1
1%
IRF7413
5V
5A
5V
R1
2.7Ω
1.8Ω
Q2
LONG 5V
3.3V
0.005Ω, 1%
IRF7413
3.3V
7.6A
0.1µF
0.1µF
R4
10Ω
R5
LONG 3.3V
BD_SEL#
R3
10Ω
1k, 5%
V(I/O)
C1
0.01µF
8
9
10
7
12
11
5
3V
3V
GATE 3V
5V
5V
5V
OUT
IN
SENSE
OUT
IN
SENSE
1.2k
V(I/O)
3k
1k
10k
2
1
15
3
OFF/ON
FAULT
TIMER
0.1µF
3k
3V
OUT
LTC1646
4
HEALTHY#
PCI_RST#
PWRGD
3k
16
RESETIN
RESETOUT
GND
6
PRECHARGE
13
DRIVE
14
18Ω
1k
18Ω
12Ω
4.7nF
3V
5V
IN
IN
GROUND
I/O PIN 1
MMBT2222A
PRECHARGE OUT
1V ±10%
3V
5V
IN
3.3V
10k
I
= ± 55mA
OUT
RESET#
10Ω
DATA LINE EXAMPLE
I/O
PCI
BRIDGE
(21154)
DATA BUS
DATA BUS
1646 F01
Z1, Z2: BZX84C6V2
Figure 1
1646fa
1
LTC1646
W W U W
U
W
U
ABSOLUTE AXI U RATI GS
(Note 1)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
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:
RESETOUT
TIMER
1
2
3
4
5
6
7
8
16 RESETIN
15 OFF/ON
FAULT
14
13
12
11
10
9
DRIVE
PWRGD
PRECHARGE
5V
5V
IN
OUT
GND
5V
SENSE
3V
GATE
3V
OUT
3V
IN
SENSE
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
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 135°C/W
ORDER PART NUMBER
GN PART MARKING
LTC1646CGN
LTC1646IGN
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 T = 25°C. V
= 5V and V
= 3.3V unless otherwise noted.
A
5VIN
3VIN
SYMBOL PARAMETER
Supply Current
CONDITIONS
MIN
TYP
MAX
UNITS
I
V
OFF/ON = 0V
●
1.5
4
mA
DD
5VIN
V
Undervoltage Lockout
5V
3V
●
●
2.3
2.3
2.50
2.55
2.7
2.7
V
V
LKO
IN
IN
V
Foldback Current Limit Voltage
V
V
V
V
= (V
– V
– V
– V
– V
), V
), V
), V
), V
= 0V, TIMER = 0V
= 4V, TIMER = 0V
= 0V, TIMER = 0V
= 2V, TIMER = 0V
●
●
●
●
15
50
15
50
20
55
20
55
30
65
30
65
mV
mV
mV
mV
FB
FB
FB
FB
FB
5VIN
5VIN
3VIN
3VIN
5VSENSE
5VSENSE
3VSENSE
3VSENSE
5VOUT
5VOUT
3VOUT
3VOUT
= (V
= (V
= (V
V
Circuit Breaker Trip Voltage
V
V
= (V
= (V
– V
– V
), V
), V
= 5V, TIMER Open
= 3.3V, TIMER Open
●
●
50
50
56
56
65
65
mV
mV
CB
OC
SS
CP
CB
CB
5VIN
3VIN
5VSENSE
3VSENSE
5VOUT
3VOUT
t
t
I
Overcurrent Fault Response Time
(V
(V
– V
– V
) = 100mV, TIMER Open
) = 100mV, TIMER Open
●
●
10
10
21
21
30
30
µs
µs
5VIN
3VIN
5VSENSE
3VSENSE
Short-Circuit Fault Response Time (V
(V
– V
– V
) = 200mV, TIMER Open
) = 200mV, TIMER Open
●
●
0.145
0.145
1
1
µs
µs
5VIN
3VIN
5VSENSE
3VSENSE
GATE Pin Output Current
OFF/ON = 0V, V
OFF/ON = 5V, V
OFF/ON = 0V, V
= 0V, TIMER = 0V
= 5V, TIMER = 0V
= 5V, FAULT = 0V, TIMER Open
●
–18
80
4
–13
200
7
–8
300
12
µA
µA
mA
GATE
GATE
GATE
●
V
V
External Gate Voltage
(GATE to GND)
OFF/ON = 0V, I
OFF/ON = 0V, V
= –1µA
= 3.3V, I
●
●
12
11
15
13
16
15
V
V
GATE
TH
GATE
= –1µA
5VIN
GATE
Power Good Threshold Voltage
3V
5V
●
●
2.8
4.5
2.9
4.65
3.0
4.75
V
V
OUT
OUT
V
V
No 5V Input Mode Window Voltage
Input Low Voltage
V
= ⎪V
– V
⎪, V
= V = 3.3V
3VOUT
●
●
50
120
200
0.8
mV
V
3VONLY
IL
3VONLY
5VIN
3VIN
5VOUT
OFF/ON, RESETIN, FAULT
1646fa
2
LTC1646
ELECTRICAL CHARACTERISTICS
The
●
denotes the specifications which apply over the full operating
= 5V and V = 3.3V unless otherwise noted.
temperature range, otherwise specifications are at T = 25°C. V
A
5VIN
3VIN
SYMBOL PARAMETER
CONDITIONS
OFF/ON, RESETIN, FAULT
, FAULT = 0V
MIN
2
TYP
MAX
UNITS
V
V
Input High Voltage
●
●
V
V
IH
TIMER Threshold Voltage
OFF/ON Input Current
V
1.15
1.25
1.35
TIMER
TIMER
I
OFF/ON = 5V
OFF/ON = 0V
●
●
±0.08
±0.08
±10
±10
µA
µA
IN
RESETIN Input Current
RESETIN = 5V
RESETIN = 0V
●
●
±0.08
±0.08
±10
±10
µA
µA
5V
3V
Input Current
Input Current
5V
3V
= 5V, 5V = 0V
OUT
●
●
●
●
●
●
66
66
100
100
1000
1.5
µA
µA
SENSE
SENSE
SENSE
SENSE
= 3.3V, 3V
= 0V
OUT
3V Input Current
3V = 3.3V
460
0.9
0.9
µA
IN
IN
5V
3V
Input Current
Input Current
5V
3V
= 5V, OFF/ON = 0V
mA
mA
OUT
OUT
OUT
OUT
= 3.3V, OFF/ON = 0V
1.5
I
TIMER Pin Current
OFF/ON = 0V, V
OFF/ON = 5V, V
= 0V
= 5V
–7
–5
6.6
–3
µA
mA
TIMER
TIMER
TIMER
R
DIS
5V
3V
Discharge Impedance
Discharge Impedance
OFF/ON = 5V
OFF/ON = 5V
●
●
120
120
220
220
Ω
Ω
OUT
OUT
V
V
Output Low Voltage
FAULT, PWRGD, RESETOUT, I = 2mA
, V = 5V and 3.3V
●
●
0.25
1.00
0.4
V
V
OL
PRECHARGE Reference Voltage
V
0.90
1.10
PXG
PRECHARGE 5VIN
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
5V Supply Current vs
IN
5V Current Foldback Profile
3.3V Current Foldback Profile
Temperature
12
11
10
9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
12
11
10
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
R
= 0.005Ω
1
R
= 0.007Ω
1
SENSE
SENSE
0
0
0
1
2
3
4
5
–50
–25
0
25
50
75
100
0
1
2
3
4
5
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1646 G02
1646 G03
1646 G01
1646fa
3
LTC1646
U W
TYPICAL PERFOR A CE CHARACTERISTICS
5V Undervoltage Lockout
3V Undervoltage Lockout
5V Foldback Current Limit
IN
IN
IN
Voltage vs Temperature
Voltage vs Temperature
Voltage vs Temperature
2.60
2.55
2.50
2.45
2.40
2.60
2.55
2.50
2.45
2.40
60
50
40
30
20
10
0
LOW-TO-HIGH TRANSITION
5V
= 4V
OUT
HIGH-TO-LOW TRANSITION
LOW-TO-HIGH TRANSITION
HIGH-TO-LOW TRANSITION
5V
= 0V
OUT
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G04
1646 G05
1646 G06
3V Foldback Current Limit
5V Circuit Breaker Trip Voltage
3V Circuit Breaker Trip Voltage
IN
IN
IN
Voltage vs Temperature
vs Temperature
vs Temperature
60
50
40
30
20
10
0
60
59
58
57
56
55
54
53
52
51
50
60
59
58
57
56
55
54
53
52
51
50
3V
= 2V
OUT
3V
= 0V
OUT
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G07
1646 G08
1646 G09
5V /3V Overcurrent Fault
5V /3V Short-Circuit Fault
IN IN
Response Time vs Temperature
IN
IN
Response Time vs Temperature
Gate Current vs Temperature
22.00
21.75
21.50
21.25
21.00
20.75
20.50
20.25
20.00
170
160
150
140
130
120
110
100
–10
–11
–12
–13
–14
–15
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G10
1646 G11
1646 G12
1646fa
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LTC1646
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Power Good Threshold Voltage vs
Gate ISINK vs Temperature
Gate Voltage vs Temperature
Temperature (3V
)
OUT
10
9
15.5
15.0
14.5
14.0
13.5
13.0
12.5
3.00
2.95
2.90
2.85
2.80
FAULT = 0V
I = –1µA
5V = 5V
IN
8
7
5V = 3.3V
IN
6
5
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G13
1646 G14
1646 G15
Power Good Threshold Voltage vs
Temperature (5V
Timer Threshold Voltage vs
Temperature
5V
Input Current vs
SENSE
)
Temperature
OUT
4.75
4.70
4.65
4.60
4.55
4.50
1.30
1.28
1.26
1.24
1.22
1.20
70
69
68
67
66
65
64
63
62
61
60
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G16
1646 G17
1646 G18
3V
Input Current vs
SENSE
Temperature
3V Input Current vs Temperature
IN
Timer Current vs Temperature
70
69
68
67
66
65
64
63
62
61
60
480
475
470
465
460
455
450
445
–4.00
–4.25
–4.50
–4.75
–5.00
–5.25
–5.50
–5.75
–6.00
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1646 G19
1646 G20
1646 G21
1646fa
5
LTC1646
U W
TYPICAL PERFOR A CE CHARACTERISTICS
RESETOUT, PWRGD and FAULT
5V /3V
Discharge
OUT
OUT
Output Low Voltage vs I
Impedance vs Temperature
SINK
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
180
160
140
120
100
80
90°C
25°C
–45°C
60
40
20
0
0
1
2
3
4
5
–50
–25
0
25
50
75
100
I
(mA)
TEMPERATURE (°C)
SINK
1646 G22
1646 G23
U
U
U
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).
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.
TIMER(Pin2):CurrentFaultInhibitTimingInput.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.
5VOUT (Pin 5): 5V Output Sense. The PWRGD pin will not
pulllowuntilthe5VOUT pinvoltageexceeds4.65V. Ifno5V
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
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
chipwillremainlatchedintheoffstateuntiltheOFF/ONpin
is cycled high then low or the power is cycled.
3VOUT (Pin7):3.3VOutputSense.ThePWRGDpinwillnot
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
whenthevoltageatthe3VIN pinislessthan2.5V.Ifno3.3V
input supply is available, connect a diode between 5VIN
and 3VIN (tie anode to 5VIN and cathode to 3VIN ). See
Figure 11.
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.
1646fa
6
LTC1646
U
U
U
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 con-
stant 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
breakerfunctionisenabled. Ifthevoltageacrossthesense
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.
PRECHARGE (Pin 13): Precharge Monitor Input. An on-
chip 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.
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.
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 func-
tion is not being used, allow the DRIVE pin to float.
OFF/ON(Pin15):DigitalInput.ConnecttheCPCIBD_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 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.
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#signaltotheRESETINpin.PullingRESETINlow
will cause the RESETOUT pin to pull low.
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 con-
stant 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.
1646fa
7
LTC1646
W
TEST DIAGRA
V
No 5V Input Mode Window Voltage
3VONLY
V
= ⎟ 5V – 3V ⎢ 5V
= 3V
= 3.3V, 3V = 3.3V
IN
3VONLY
IN IN
OUT
OUT
V
3VONLY
3.3V
V
5VIN
–V
3VONLY
5V
PWRGD
1646 T01
0V
W U
W
TI I G DIAGRA S
t
OC
Overcurrent Fault Detect
FALL TIME ≤ 1µs, 5V = 5V, 3V = 3.3V
IN IN
5V
OR 3.3V
V
V
5VSENSE
OR
3VSENSE
100mV
t
OC
FAULT
1V
1646 T02
t
SC
Short-Circuit Fault Detect
FALL TIME ≤ 30ns, 5V = 5V, 3V = 3.3V
IN IN
5V
OR 3.3V
V
V
5VSENSE
OR
3VSENSE
200mV
t
SC
FAULT
1V
1646 T03
1646fa
8
LTC1646
W
BLOCK DIAGRA
5V
5V
3V
3V
3V
5V
IN
SENSE
SENSE
9
IN
OUT
OUT
GATE
10
12
11
8
7
5
V
GG
5V
3V
OUT
OUT
13µA
+–
+
+
+ –
55mV
55mV
+–
+ –
Q2
Q3
–
–
Q1
200µA
+
–
+
–
150mV
150mV
+–
+ –
2.5V
UVL
2.5V
UVL
C
P3
+
OFF/ON 15
–
FAULT
3
REF
Q7
Q6
C
P4
+
–
PWRGD
4
LOGIC
1
RESETOUT
REF
Q4
RESETIN 16
5V
in
5µA
+
–
1V
TIMER
2
Q5
1646 BD
6
14
13
PRECHARGE
GND
DRIVE
U
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APPLICATIO S I FOR ATIO
Hot Circuit Insertion
The LTC1646 is specifically designed for CPCI applica-
tions where the chip resides on the plug-in board.
When a circuit board is inserted into a live CompactPCI
(CPCI)slot, thesupplybypasscapacitorsontheboardcan
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.
LTC1646 Feature Summary
1. Allows safe board insertion and removal from a CPCI
backplane.
2. Controls 5V and 3.3V CPCI supplies.
TheLTC1646isdesignedtoturnaboard’ssupplyvoltages
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 pro-
tectsthesuppliesfromshorts,prechargesthebusI/Opins
during insertion and extraction and monitors the supply
voltages.
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.
The main 3.3V and 5V inputs to the LTC1646 come from
the medium length power pins. The long 3.3V, 5V connec-
tor 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.
5. Dual-level,programmable5Vand3.3Vcircuitbreakers:
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.
The power supplies are controlled by placing external
N-channel pass transistors in the 3.3V and 5V power
paths.
6. 15V high side drive for external 3.3V and 5V N-channel
MOSFETs.
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.
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#.
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
resistortoV(I/O). Duringthefinalstageofboardinsertion,
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 con-
nected to the TIMER pin.
9. Precharge output: on-chip reference and amplifier pro-
vide 1V for biasing bus I/O connector pins during CPCI
card insertion and extraction.
10. Space saving 16-pin SSOP package.
PCI Power Requirements
CPCIsystemsmayrequireuptofourpowerrails:5V,3.3V,
12V and –12V. The LTC1646 is designed for CPCI applica-
tions 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.
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:
Table 1. PCI Power Supply Requirements
SUPPLY
5V
TOLERANCE
5V ±5%
CAPACITIVE LOAD
<3000µF
ILIMIT(5V)
ILIMIT(3V)
dV 13µA
=
,or =
,or =
(1)
dt
C1
CLOAD(5VOUT)
CLOAD(3VOUT)
3.3V
3.3V ±0.3V
<3000µF
whichever is slower.
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
Power-Up Sequence
The LTC1646 is specifically designed for hot swapping
CPCI boards. The typical application is shown in Figure 1.
low and LOCAL_PCI_RST# is free to follow PCI_RST#.
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U
GATE
10V/DIV
GATE
10V/DIV
5V
3V
OUT
OUT
5V
3V
OUT
OUT
5V/DIV
5V/DIV
TIMER
5V/DIV
TIMER
5V/DIV
BD_SEL#
5V/DIV
BD_SEL#
5V/DIV
HEALTHY#
5V/DIV
HEALTHY#
5V/DIV
LCL_PCI_RST#
5V/DIV
LCL_PCI_RST#
5V/DIV
PRECHARGE
5V/DIV
PRECHARGE
5V/DIV
20ms/DIV
1646 F02
10ms/DIV
1646 F03
Figure 2. Normal Power-Up Sequence
Figure 3. Normal Power-Down Sequence
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:
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
oftheoutputvoltagesdipsbelowitsthreshold,HEALTHY#
pulls high and LOCAL_PCI_RST# will be asserted low.
CLOAD(XVOUT) • XVOUT
ILIMIT(XVOUT) – ILOAD(XVOUT)
tON (XVOUT) = 2 •
(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
maximumsafeoperatingareaofthepasstransistorduring
a short-circuit. The timer period for the LTC1646 is given
by:
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.
CTIMER •1.25V
tTIMER
=
(3)
5µA
Timer
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.
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
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Table 2. t
C
vs C
TIMER
TIMER
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.
t
C
t
TIMER
TIMER
TIMER
TIMER
0.01µF
0.022µF
0.033µF
0.047µF
0.068µF
0.082µF
0.1µF
2.5ms
5.5ms
8.25ms
11.8ms
17ms
0.22µF
0.33µF
0.47µF
0.68µF
0.82µF
1µF
55ms
82.5ms
118ms
170ms
205ms
250ms
After power-up (TIMER pin voltage >1.25V), the 5V and
3.3V supplies are protected from overcurrent and short-
circuit 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).
20.5ms
25ms
The TIMER pin is immediately pulled low when BD_SEL#
goes high.
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.
5V –5V
IN
SENSE
50mV/DIV
Inordertopreventexcessivepowerdissipationinthepass
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
10V/DIV
GATE
FAULT
5V/DIV
5V/DIV
5V
OUT
3V
OUT
2V/DIV
10µs/DIV
1646 F05
TIMER
1V/DIV
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
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
10ms/DIV
1646 F04
Figure 4. Power-Up into a Short on 3.3V Output
shown in Figure 1, a sense resistor is connected between
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U
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.
5V –5V
IN
SENSE
100mV/DIV
I
R
LOAD(MAX)
SENSE
1
2
GATE
10V/DIV
5V
IN
3
4
12
5V
11
5V
SENSE
IN
+
–
FAULT
5V/DIV
V
LTC1646*
CB
–
+
V
V
V
= 65mV
= 56mV
= 50mV
CB(MAX)
CB(NOM)
CB(MIN)
5µs/DIV
1646 F06
*ADDITIONAL DETAILS
OMITTED FOR CLARITY
1646 F07
Figure 6. Short-Circuit Fault on 5V
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:
Figure 7. Circuit Breaker Equivalent
Circuit for Calculating R
SENSE
Two other parameters affect the value of the sense resis-
tor. 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.
55mV
RSENSE(XVOUT)
(4)
(5)
ILIMIT(XVOUT)
=
20mV
RSENSE(XVOUT)
IFOLDBACK(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. I
and I
I
vs R
I
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).ThemaximumvalueforRSENSE inthis
case is expressed by Equation 6:
LIMIT(XVOUT)
(Ω)
FOLDBACK(XVOUT)
SENSE
R
SENSE
LIMIT(XVOUT)
FOLDBACK(XVOUT)
0.005
0.006
0.007
0.008
0.009
0.01
11A
9.2A
7.9A
6.9A
6.1A
5.5A
4A
3.3A
2.9A
2.5A
2.2A
2A
VCB(MIN)
ITRIP(MAX)
RSENSE(MAX)
=
(6)
The second step is to determine the nominal value of the
where XVOUT = 3VOUT or 5VOUT
.
sense resistor which is dependent on its tolerance
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APPLICATIO S I FOR ATIO
(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:
VCB(MAX)
RSENSE(MIN)
ITRIP(MAX,NEW)
=
=
VCB(MAX)
65mV
=
= 9.8A
RSENSE(MAX)
⎡
⎤
0.0065
RTOL
100
⎛
⎜
⎝
⎞
⎟
⎠
RSENSE(N0M) • 1–
RSENSE(NOM)
=
⎢
⎥
⎦
RTOL
100
⎛
⎜
⎝
⎞
⎟
⎠
⎣
(7)
1+
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
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:
ILOAD(MAX)
.
.
Output Voltage Monitor
The status of both 5V and 3.3V output voltages is moni-
toredbythepowergoodfunction.Inaddition,thePCI_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
HI
LO
HI
LO
LO
HI
VCB(MAX)
RSENSE(MIN)
LO
HI
ITRIP(MAX,NEW)
=
(8)
HI
LO
⎡
⎤
RTOL
100
⎛
⎜
⎝
⎞
⎟
⎠
where RSENSE(MIN) = RSENSE(NOM) • 1–
If either of the output voltages drop below the power good
thresholdformorethan50µs,theHEALTHY#signalwillbe
pulledhighandtheLOCAL_PCI_RST#signalwillbepulled
low.
⎢
⎥
⎦
⎣
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:
Precharge
The PRECHARGE input and DRIVE output pins are in-
tended 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
applicationsthatneedprechargevoltagesgreaterthan1V.
Table 5 lists suggested resistor values for R1 and R2 vs
precharge voltage for the application circuits shown in
Figures 8 and 9.
VCB(MIN)
ITRIP(MAX)
50mV
6.8A
RSENSE(MAX)
=
=
= 0.0074Ω
The nominal sense resistor value is (Equation 7):
RSENSE(MAX)
0.0074Ω
RSENSE(NOM)
=
=
= 0.007Ω
RTOL
100
5
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
1+
1+
100
And the new current-limit trip point is Equation 8:
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Table 5. R1 and R2 Resistor Values vs Precharge Voltage
Other CompactPCI Applications
V
R1
R2
V
R1
R2
PRECHARGE
PRECHARGE
The LTC1646 can be easily configured for applications
whereno5Vsupplyispresentbysimplytying the5VIN and
5VSENSE pins to the 3VIN pin and tying the 5VOUT pin to the
3VOUT pin (Figure 10).
1.5V
1.4V
1.3V
1.2V
1.1V
1V
18Ω
18Ω
18Ω
18Ω
18Ω
18Ω
9.09Ω
7.15Ω
5.36Ω
3.65Ω
1.78Ω
0Ω
0.9V
0.8V
0.7V
0.6V
0.5V
16.2Ω
14.7Ω
12.1Ω
11Ω
1.78Ω
3.65Ω
5.11Ω
7.15Ω
9.09Ω
9.09Ω
LTC1646*
PRECHARGE DRIVE
LTC1646*
GND
6
GND PRECHARGE
13
DRIVE
14
13
14
6
18Ω
1k
18Ω
1k
4.7nF
4.7nF
R2
12Ω
12Ω
R1
R2
MMBT2222A
R1
MMBT2222A
PRECHARGE OUT
PRECHARGE OUT
3V
IN
3V
IN
R1
R1 + R2
• 1V
V
=
V
=
• 1V
PRECHARGE
PRECHARGE
R1 + R2
R1
1646 F08
1646 F09
*ADDITIONAL DETAILS OMITTED FOR CLARITY
*ADDITIONAL DETAILS OMITTED FOR CLARITY
Figure 8. Precharge Voltage <1V Application Circuit
Figure 9. Precharge Voltage >1V Application Circuit
COMPACT PCI COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
CIRCUIT CARD
CONNECTOR
(FEMALE)
Z1
0.005Ω
1%
IRF7413
1
2
3.3V
7.6A
OUT
3.3V
3
4
0.1µF
LONG 3.3V
1.8Ω
10Ω
V(I/O)
1k
0.010µF
0.1µF
8
3V
IN
9
10
7
12
IN
11
5
1.2k
3V
GATE 3V
5V
5V
5V
OUT
SENSE
OUT
SENSE
1k
10k
3V
2
1
15
3
BD_SEL#
OFF/ON
FAULT
TIMER
V(I/O)
3k
3k
OUT
LTC1646
4
3k
HEALTHY#
PCI_RST#
PWRGD
16
RESETIN
RESETOUT
GND
6
PRECHARGE
13
DRIVE
14
18Ω
1k
4.7nF
18Ω
12Ω
3V
IN
GROUND
I/O PIN 1
PRECHARGE OUT
MMBT2222A
1V ±10%
3.3V
RESET#
1k
I
= ± 55mA
OUT
3V
IN
10Ω
DATA LINE EXAMPLE
I/O
PCI
BRIDGE
(21154)
DATA BUS
DATA BUS
Z1: BZX84C6V2
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
5V
IN
IRF7413
2
1
5V
OUT
5V
3
4
LONG
5V
2.7Ω
10Ω
BAV16W
1k
0.1µF
0.01µF
8
9
SENSE
12
11
10
GATE 5V
5
7
3V 3V
IN
5V
5V
3V
IN
SENSE
OUT OUT
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.
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
additiontooneormorelarge-valuebulkbypasscapacitors
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.
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
andreinserttheCPCIboardinordertoresettheLTC1646’s
circuit breakers.
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 connec-
tor, results in a fast rising edge applied on the 3.3V and the
5V line of the LTC1646.
PUSH-
BUTTON
SWITCH
V(I/0)
COMPACT PCI
BACKPLANE
CONNECTOR
(MALE)
COMPACT PCI
CIRCUIT CARD
CONNECTOR
(FEMALE)
1.2k
BD_SEL#
15
6
OFF/ON
1k
100Ω
LTC1646
LONG GND
GND
1646 F12
Figure 12. BD_SEL# Pushbutton Toggle Switch
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LTC1646
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APPLICATIO S I FOR ATIO
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Since there is no bulk capacitance to damp the parasitic
trace inductance, supply voltage transients excite para-
sitic 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 sinu-
soidal 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 induc-
tance. This is shown schematically in Figure 13 and a
recommended layout of the transient protection devices
around the LTC1646 is shown in Figure 14.
5V
IN
VIAS TO
GND PLANE
TZ1
C2
C3
In these applications, there are two methods for eliminat-
ing 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
capacitorsinthesenetworksarechosentobe10× to100×
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
LTC1646*
TZ2
GND
3V
IN
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
1646 F14
Figure 14. Recommended Layout for
Transient Protection Components
R2
0.007Ω
Q1
IRF7413
V
5V
IN1
OUT
5V
AT 5A
R6 2.7Ω
R1
0.005Ω
Q2
LONG 5V
IRF7413
V
3V
OUT
AT 7.6A
IN2
3.3V
R7 1.8Ω
LONG 3.3V
C1
0.01µF
R3
10Ω
R4
10Ω
R5
1k
8
9
10
7
12
11
5
3V
IN
3V
SENSE
GATE 3V
5V
IN
5V
SENSE
5V
OUT
OUT
Z1
LTC1646**
GND
Z2
C2
C3
0.1µF
0.1µF
1646 F13
6
Z1, Z2: BZX84C6V2
**ADDITIONAL DETAILS OMITTED FOR CLARITY
Figure 13. Place Transient Protection Device Close to the LTC1646
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LTC1646
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APPLICATIO S I FOR ATIO
PCB Layout Considerations
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
thePCboard.For1ouncecopperfoilplating,ageneralrule
is 1A of DC current per via, making sure the via is properly
dimensioned so that solder completely fills any void. For
otherplatingthicknesses, checkwithyourPCBfabrication
facility.
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
thesenseresistor, thepowerMOSFET, andtheGATEdrive
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 tempera-
tures. Since the sheet resistance of 1 ounce copper foil is
approximately0.5mΩ/■,trackresistancesaddupquickly
in high current applications. Thus, to keep PCB track
resistance and temperature rise to a minimum, the sug-
gested 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
componentmentionedthroughouttheLTC1646datasheet.
Table 6. N-Channel Power MOSFET Selection Guide
CURRENT LEVEL (A)
PART NUMBER
DESCRIPTION
Dual N-Channel SO-8
= 0.1Ω
MANUFACTURER
0 to 2
MMDF3N02HD
ON Semiconductor
R
DS(ON)
2 to 5
MMSF5N02HD
MTB50N06V
IRF7413
Single N-Channel SO-8
= 0.025Ω
ON Semiconductor
ON Semiconductor
International Rectifier
Vishay-Siliconix
R
DS(ON)
5 to 10
5 to 10
5 to 10
Single N-Channel DD Pak
= 0.028Ω
R
DS(ON)
Single N-Channel SO-8
= 0.01Ω
R
DS(ON)
Si4410DY
Single N-Channel SO-8
= 0.01Ω
R
DS(ON)
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
5A
LR120601R028F
WSL1206R028
0.028Ω, 0.5W, 1% Resistor
0.011Ω, 0.5W, 1% Resistor
IRC-TT
Vishay-Dale
LR120601R011F
WSL2010R011
IRC-TT
Vishay-Dale
7.6A
10A
WSL2512R007
WSL2512R005
0.007Ω, 1W, 1% Resistor
0.005Ω, 1W, 1% Resistor
Vishay-Dale
Vishay-Dale
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LTC1646
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APPLICATIO S I FOR ATIO
Table 8. Manufacturers’ Web Site
MANUFACTURER
International Rectifier
ON Semiconductor
IRC-TT
WEB SITE
www.irf.com
www.onsemi.com
www.irctt.com
www.vishay.com
www.vishay.com
www.diodes.com
Vishay-Dale
Vishay-Siliconix
Diodes, Inc.
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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
.009
(0.229)
REF
16 15 14 13 12 11 10 9
.254 MIN
.150 – .165
.229 – .244
.150 – .157**
(5.817 – 6.198)
(3.810 – 3.988)
.0165 ± .0015
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
2
3
4
5
6
7
8
.015 ± .004
(0.38 ± 0.10)
× 45°
.0532 – .0688
(1.35 – 1.75)
.004 – .0098
(0.102 – 0.249)
.007 – .0098
(0.178 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
.0250
(0.635)
BSC
.008 – .012
GN16 (SSOP) 0204
(0.203 – 0.305)
TYP
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
19
LTC1646
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TYPICAL APPLICATIO
CURRENT FLOW
TO LOAD
CURRENT FLOW
TO LOAD
SENSE
RESISTOR
SO-8
D
D
D
D
G
S
S
S
V
V
OUT
5V
IN
W
W
5V
R3
R5
VIA
TRACK WIDTH W:
0.03" PER AMPERE
ON 1 OZ Cu FOIL
C1
LTC1646*
CURRENT FLOW
TO SOURCE
VIA TO GND
C
TIMER
GND
W
GND
*ADDITIONAL DETAILS OMITTED FOR CLARITY
DRAWING IS NOT TO SCALE!
1646 F15
Figure 15. Recommended Layout for Power MOSFET, Sense Resistor, and Gate Components
RELATED PARTS
PART NUMBER
LTC1421
DESCRIPTION
COMMENTS
Hot Swap Controller
Dual Supplies from 3V to 12V, Additionally –12V
Single Supply Hot Swap in SO-8 from 3V to 12V
Negative High Voltage Supplies from –10V to –80V
Supplies from 9V to 80V, Autoretry/Latches Off
3V to 15V, Overvoltage Protection Up to 33V
3.3V, 5V, 12V, –12V Supplies for PCI Bus
3.3V, 5V, ±12V Local Reset Logic and Precharge
Operates from 1.2V to 12V, Power Sequencing
Dual ON Pins for Supplies from 3V to 15V
Single Supply, 2.5V to 16.5V, MSOP
LTC1422
Hot Swap Controller
LT1640AL/LT1640AH
LT1641/LT1641-1
LTC1642
Negative Voltage Hot Swap Controllers in SO-8
Positive Voltage Hot Swap Controller in SO-8
Fault Protected Hot Swap Controller
PCI Bus Hot Swap Controllers
CompactPCI Hot Swap Controller
2-Channel Hot Swap Controller
Dual Hot Swap Controller
LTC1643L/LTC1643L-1/LTC1643H
LTC1644
LTC1645
LTC1647
LTC4211
Hot Swap Controller with Multifunction Current Control
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LT 1205 REV A • PRINTED IN USA
20 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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