NOT RECOMMENDED FOR NEW DESIGNS
Contact Linear Technology for Potential Replacement
LTC4350
Hot Swappable
Load Share Controller
DescripTion
The LTC
®
4350 is a load share controller that allows sys-
tems to equally load multiple power supplies connected
in parallel. The output voltage of each supply is adjusted
using the SENSE
+
input until all currents match the share
bus. The LTC4350 also isolates supply failures by turning
off the series pass transistors and identifying the failed
supply. The failed supply can then be removed and replaced
with a new unit without turning off the system power. The
LTC4350 is available in a 16-pin narrow SSOP package.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot
Swap and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
FeaTures
n
n
n
n
n
n
n
Build N + 1 Redundant Supply
Hot Swap™ Power Supplies
Isolates Supply Failures from Output
Eliminates ORing Diodes
Identifies and Localizes Output Low, Output High
and Open-Circuit Faults
Output Voltages from 1.5V to 12V
16-Lead Narrow SSOP Package
applicaTions
n
n
n
Servers and Network Equipment
Telecom and Base Station Equipment
Distributed Power Systems
Typical applicaTion
5V Load Share (5A per Module)
SENSE
+
OUT
+
SUD50N03-07
0.010
V
OUT+
SHARE BUS V
OUT–
51
0.1µF
VICOR*
VI-J30-CY
274k
43.2k
0.1µF
100
R
+
R
–
37.4k
12.1k
STATUS
GATE
V
CC
UV
FB
I
OUT
LTC4350
STATUS
SB
0.1µF
TRIM
470k
SENSE
–
OUT
–
SENSE
+
OUT
+
121k
12.1k
0.1µF
OV
TIMER
GAIN COMP1
R
SET
GND COMP2
1000pF
34k
4.7µF
150
100
SUD50N03-07
0.010
51
0.1µF
VICOR*
VI-J30-CY
274k
43.2k
0.1µF
100
R
+
R
–
37.4k
12.1k
STATUS
GATE
V
CC
UV
FB
I
OUT
LTC4350
STATUS
SB
0.1µF
TRIM
470k
SENSE
–
OUT
–
121k
12.1k
0.1µF
OV
TIMER
GAIN COMP1
R
SET
GND COMP2
4.7µF
150
100
1000pF
34k
*LOAD SHARING CIRCUIT WORKS WITH MOST POWER SUPPLIES THAT HAVE A SENSE
+
OR FB PIN
4350 TA01
4350fb
LTC4350
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
UV
OV
TIMER
GAIN
COMP2
COMP1
SB
GND
1
2
3
4
5
6
7
8
16 V
CC
15 STATUS
14 GATE
13 R
+
12 R
–
11 I
OUT
10 R
SET
9
FB
Supply Voltage (V
CC
) ................................................17V
Input Voltage
TIMER ................................................... –0.3V to 1.2V
R
+
, R
–
(Note 2) ...................................... –0.3V to 17V
FB ......................................................... –0.3V to 5.3V
OV, UV ....................................................... –0.3V to 17V
Output Voltage
COMP1 .................................................... –0.3V to 6V
COMP2 .................................................... –0.3V to 3V
GAIN, SB............................................... –0.3V to 5.6V
GATE (Note 3) ............................................ –0.3V to 20V
I
OUT
, STATUS ............................................. –0.3V to 17V
R
SET
............................................................. –0.3V to 1V
Operating Temperature Range
LTC4350C ................................................ 0°C to 70°C
LTC4350I .............................................–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
T
JMAX
= 150°C,
θ
JA
= 135°C/W
orDer inForMaTion
LEAD FREE FINISH
LTC4350CGN#PBF
LTC4350IGN#PBF
TAPE AND REEL
LTC4350CGN#TRPBF
LTC4350IGN#TRPBF
PART MARKING
4350
4350I
PACKAGE DESCRIPTION
16-Lead Plastic SSOP
16-Lead Plastic SSOP
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V unless otherwise noted.
SYMBOL
I
CC
V
LKOH
V
LKOL
V
FB
V
FBLIR
V
FBLOR
PARAMETER
V
CC
Supply Current
V
CC
Undervoltage Lockout High
V
CC
Undervoltage Lockout Low
FB Pin Voltage
FB Line Regulation
FB Load Regulation
0°C to 85°C (LTC4350I) or 0°C to 70°C (LTC4350C)
–40°C to 85°C (LTC4350I)
V
CC
= 3.3V to 12V, COMP1 = 1.240V
COMP1 = 2V
COMP1 = 0.64V
l
l
elecTrical characTerisTics
CONDITIONS
UV = V
CC
DC Characteristics
MIN
l
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TYP
1.6
2.45
2.34
1.220
1.220
0.02
–0.0008
0.003
MAX
2.0
2.52
2.44
1.236
1.244
0.05
–0.1
0.1
UNITS
mA
V
V
V
V
%/V
%
%
1.0
2.36
2.24
1.208
1.196
4350fb
LTC4350
elecTrical characTerisTics
SYMBOL
V
UVTH
V
OVTH
V
TM
I
TM
V
G
V
GO
V
SB(MIN)
V
SB(MAX)
I
SB(MAX)
R
SB
V
E/A2OFF
PARAMETER
UV Pin Threshold
OV Pin Threshold
TIMER Pin Threshold
TIMER Pin Current
GAIN Pin Voltage
GAIN Pin Offset
SB Pin Minimum Voltage
SB Pin Maximum Voltage
SB Pin Maximum Current
SB Pin Resistor Value
E/A2 Offset
V
SB
– V
GAIN
V
CC
= 3.3V, R
SET
= 100Ω
V
CC
= 12V, R
SET
= 100Ω
V
CC
= 5V, R
SET
= 1000Ω
V
CC
= 5V, R
SET
= 100Ω
R
SET
= 50Ω, V
IOUT
= 1.1V
V
R+
– V
R+
V
GATE
– V
CC
Gate On, V
GATE
= 0V
I
OUT
= 3mA
V
CC
= 3.3V
V
CC
= 12V
V
SB
= 0V
l
l
l
l
l
l
l
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 5V unless otherwise noted.
CONDITIONS
High Going Threshold
Low Going Threshold
High Going Threshold
Low Going Threshold
TIMER On, V
TIMER
= 0V
TIMER On, V
TIMER
= 0V, V
OV
> V
OVTH
R
GAIN
= 25k, (V
R+
– V
R–
) = 100mV
R
GAIN
= 25k, (V
R+
– V
R–
) = 0mV
l
l
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l
l
MIN
1.215
1.205
1.203
1.180
1.18
–1.75
–5.30
2.3
0
2.4
5.6
–8
14
8
0.94
0.94
TYP
1.244
1.220
1.220
1.205
1.22
–2
–6
2.5
0.02
2
2.7
7.8
–33
20
25
1
1
0.001
0.001
MAX
1.258
1.237
1.250
1.229
1.26
–2.3
–6.7
2.7
0.20
8
2.9
10.5
–41
33
50
1.03
1.03
0.5
0.5
21
40
12.7
–12
1.2
UNITS
V
V
V
V
V
µA
µA
V
V
mV
V
V
mA
kΩ
mV
V
V
V
V
mA
mV
V
µA
V
DC Characteristics
V
RSET(MAX)
R
SET
Pin Maximum Voltage
V
RSET(MIN)
R
SET
Pin Minimum Voltage
I
RSET(MAX)
V
RCTH
∆V
GATE
I
GATE
V
SOL
R
SET
Pin Maximum Current
Reverse Current Threshold
External N-Channel Gate Drive
GATE Pin Current
STATUS Pin Output Low
18
10
10.8
–8
0.1
20
30
12
–10
0.3
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
R
+
and R
–
could be at 17V while V
CC
= 0V.
Note 3:
An internal clamp limits the GATE pin to a minimum of 10.8V
above V
CC
. Driving this pin to voltages beyond the clamp may damage the
part.
4350fb
LTC4350
Typical perForMance characTerisTics
I
CC
vs V
CC
3.5
T
A
= 25°C
1.66
1.64
1.62
I
CC
(mA)
1.60
1.58
1.5
1.56
1.54
–50
UV THRESHOLD (V)
I
CC
vs Temperature
V
CC
= 5V
1.250
1.245
1.240
1.235
1.230
1.225
1.220
–25
50
25
0
TEMPERATURE (°C)
75
100
4350 G02
UV Threshold vs V
CC
T
A
= 25°C
3.0
I
CC
(mA)
2.5
2.0
1.0
0
2
4
8
6
V
CC
(V)
10
12
14
1.215
0
2
4
4350 G01
8
6
V
CC
(V)
10
12
14
4350 G03
UV Threshold vs Temperature
1.255
1.250
1.245
UV THRESHOLD (V)
1.240
1.235
1.230
1.225
1.220
1.215
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4350 G04
1.222
V
CC
= 5V
1.220
1.218
OV THRESHOLD (V)
OV Threshold vs V
CC
T
A
= 25°C
OV Threshold vs Temperature
1.225
V
CC
= 5V
1.220
OV THRESHOLD (V)
1.216
1.214
1.212
1.210
1.208
1.206
1.204
1.202
0
2
4
8
6
V
CC
(V)
10
12
14
1.215
1.210
1.205
1.200
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4350 G06
4350 G05
1.230
FB vs V
CC
T
A
= 25°C
1.230
FB vs Temperature
2.7
V
CC
= 5V
1.225
GAIN (V)
2.6
Gain PIn Voltage vs V
CC
R
GAIN
= 25k
(V
R+
– V
R–
) = 100mV
T
A
= 25°C
1.225
2.5
FB (V)
1.220
FB (V)
1.220
2.4
1.215
1.215
2.3
1.210
0
2
4
8
6
V
CC
(V)
10
12
14
1.210
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4350 G08
2.2
0
2
4
4350 G07
8
6
V
CC
(V)
10
12
14
4350 G09
4350fb
LTC4350
Typical perForMance characTerisTics
Gain Pin Voltage vs Temperature
2.7
R
GAIN
= 25k
(V
R+
– V
R–
) = 100mV
V
CC
= 5V
13
12
11
∆V
GATE
(V)
GAIN (V)
2.5
10
9
8
2.3
2.2
–50
7
6
11.0
–50
12.5
∆V
GATE
(V)
∆V
GATE
vs V
CC
T
A
= 25°C
13.0
∆V
GATE
vs Temperature
V
CC
= 5V
2.6
12.0
2.4
11.5
–25
0
25
50
TEMPERATURE (°C)
75
100
4350 G10
0
2
4
8
6
V
CC
(V)
10
12
14
4350 G11
–25
0
25
50
TEMPERATURE (°C)
75
100
4350 G12
pin FuncTions
UV (Pin 1):
Undervoltage Pin. The threshold is set at 1.244V
with a 24mV hysteresis. When the UV pin is pulled high,
the charge pump ramps the GATE pin. When the UV pin
is pulled low, the GATE pin will be pulled low.
OV (Pin 2):
Overvoltage Pin. The threshold is set at 1.220V
with a 15mV hysteresis. When the OV pin is pulled high,
the GATE pin is pulled low. After a timer cycle, the STATUS
pin is pulled low until the OV pin is pulled low.
TIMER (Pin 3):
Analog System Timing Generator Pin.
This pin is used to set the delay before the load sharing
turns on after the UV pin goes high. The other use for
the TIMER pin is to delay the indication of a fault on the
STATUS pin.
When the timer is off, an internal N-channel shorts the
TIMER pin to ground. When the timer is turned on, a 2µA
or 6µA timer current (I
TIMER
) from V
CC
is connected to the
TIMER pin and the voltage starts to ramp up with a slope
given by: dV/dt = I
TIMER
/C
T
. When the voltage reaches the
trip point (1.220V), the timer will be reset by pulling the
TIMER pin back to ground. The timer period is given by:
(1.220V • C
T
)/I
TIMER
.
GAIN (Pin 4):
Analog Output Pin. The voltage across the
R
+
and R
–
pins is divided by a 1k resistor and sourced as
a current from the GAIN pin. An external resistor on the
GAIN pin determines the voltage gain from the current
sense resistor to the GAIN pin.
COMP2 (Pin 5):
Analog Output Pin. This pin is the output
of the share bus error amplifier E/A2. (A compensation
capacitor between this pin and ground sets the crossover
frequency for the power supply adjustment loop.) In most
cases, this pin operates between 0.5V to 1.5V and repre-
sents a diode voltage up from the voltage at the R
SET
pin.
It is clamped at 3V. During start-up, this pin is clamped to
ground. After a timer cycle (and if the GATE pin is high),
the COMP2 pin is released.
COMP1 (Pin 6):
Analog Output Pin. This pin is the output
of the voltage regulating error amplifier E/A1. A com-
pensation capacitor between this pin and ground sets
the crossover frequency of the share bus loop. This pin
operates a diode voltage up from the voltage at the SB
pin and is clamped at 8.4V.
SB (Pin 7):
Analog Output Pin. This pin drives the share
bus used to communicate the value of shared load current
between several power supplies. There is an amplifier that
drives this pin a diode below the COMP1 pin using an internal
NPN as a pull-up and a 20k resistor as a pull-down.
4350fb
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