LINEAR TECHNOLOGY LTC4350 Technical data

FEATURES

LTC4350

Hot Swappable

Load Share Controller

U

DESCRIPTIO

■

Build N + 1 Redundant Supply

■

Hot SwapTM 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

U

APPLICATIO S

■

Servers and Network Equipment

■

Telecom and Base Station Equipment

■

Distributed Power Systems

U

TYPICAL APPLICATIO

5V Load Share (5A per Module)

+

SENSE

+

OUT

SUD50N03-07

The LTC®4350 is a load share controller that allows
systems 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.

, LTC and LT are registered trademarks of Linear Technology Corporation.

Hot Swap is a trademark of Linear Technology Corporation.

0.010Ω

V

OUT

+

SHARE BUS

–

V

OUT

VICOR*

VI-J30-CY

SENSE

SENSE

VICOR*

VI-J30-CY

SENSE

51Ω 100Ω

0.1µF

0.1µF

43.2k

274k

12.1k

121k

0.1µF

TRIM

470k

–

–

OUT

+

+

OUT

43.2k

274k

0.1µF

TRIM

470k

–

–

OUT

*LOAD SHARING CIRCUIT WORKS WITH MOST POWER SUPPLIES THAT HAVE A SENSE

12.1k121k

0.1µF

SUD50N03-07

51Ω 100Ω

0.1µF

0.1µF

0.1µF

–

34k

34k

R+R

LTC4350

1000pF

0.010Ω

R+R

LTC4350

1000pF

STATUS STATUS

–

STATUS STATUS

+

OR FB PIN

GATE

V

CC

UV

OV
TIMER

GAIN COMP1 GND COMP2

GATE

V

CC

UV

OV
TIMER

GAIN COMP1 GND COMP2

37.4k

FB

I

OUT

SB

R

SET

4.7µF

150Ω

FB

I

OUT

SB

R

SET

4.7µF

150Ω

12.1k

100Ω

37.4k

12.1k

100Ω

4350 TA01

4350fa

1

Note 1: A

LTC4350

WW

W

U

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Supply Voltage (VCC) ............................................... 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

, STATUS ........................................... – 0.3V to 17V

OUT

R

.......................................................................

SET

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

–0.3V to 1V

U

W

U

PACKAGE/ORDER INFORMATION

TOP VIEW

1

UV

2

OV

3

TIMER

4

GAIN

5

COMP2

6

COMP1

7

SB

8

GND

GN PACKAGE

16-LEAD PLASTIC SSOP

T

= 150°C, θJA = 135°C/W

JMAX

Consult LTC marketing for parts specified with wider operating temperature ranges.

16

15

14

13

12

11

10

9

V

CC

STATUS

GATE

+

R

–

R

I

OUT

R

SET

FB

ORDER PART

NUMBER

LTC4350CGN
LTC4350IGN

GN PART MARKING

4350
4350I

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
DC Characteristics

I

CC

V

LKOH

V

LKOL

V

FB

V

FBLIR

V

FBLOR

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

VCC Supply Current UV = V
VCC Undervoltage Lockout High ● 2.36 2.45 2.52 V
VCC Undervoltage Lockout Low ● 2.24 2.34 2.44 V
FB Pin Voltage 0°C to 85°C (LTC4350I) or 0°C to 70°C (LTC4350C) 1.208 1.220 1.236 V

FB Line Regulation VCC = 3.3V to 12V, COMP1 = 1.240V 0.02 0.05 %/V
FB Load Regulation COMP1 = 2V ● –0.0008 –0.1 %

UV Pin Threshold High Going Threshold ● 1.215 1.244 1.258 V

OV Pin Threshold High Going Threshold ● 1.203 1.220 1.250 V

TIMER Pin Threshold ● 1.18 1.22 1.26 V
TIMER Pin Current TIMER On, V

GAIN Pin Voltage R
GAIN Pin Offset R
SB Pin Minimum Voltage 28 mV
SB Pin Maximum Voltage VCC = 3.3V ● 2.4 2.7 2.9 V

SB Pin Maximum Current V
SB Pin Resistor Value ● 14 20 33 kΩ
E/A2 Offset VSB – V

CC

–40°C to 85°C (LTC4350I) 1.196 1.220 1.244 V

COMP1 = 0.64V

Low Going Threshold

Low Going Threshold

= 0V ● –1.75 – 2 –2.3 µA

TIMER

TIMER On, V

= 25k, (V

GAIN

= 25k, (V

GAIN

VCC = 12V ● 5.6 7.8 10.5 V

= 0V ● –8 –33 –41 mA

SB

GAIN

= 0V, VOV > V

TIMER

+

– V

R

+

– V

R

–

R

–

R

OVTH

) = 100mV ● 2.3 2.5 2.7 V
) = 0mV ● 0 0.02 0.20 V

● 1.0 1.6 2.0 mA

● 0.003 0.1 %

● 1.205 1.220 1.237 V

● 1.180 1.205 1.229 V

● – 5.30 – 6 – 6.7 µA

● 82550 mV

2

4350fa

LTC4350

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
DC Characteristics

V

RSET(MAX)RSET

V

RSET(MIN)RSET

I

RSET(MAX)RSET

V

RCTH

∆V

GATE

I

GATE

V

SOL

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: R

Pin Maximum Voltage VCC = 3.3V, R

V

Pin Minimum Voltage VCC = 5V, R

V

Pin Maximum Current R
Reverse Current Threshold V
External N-Channel Gate Drive V
GATE Pin Current Gate On, V
STATUS Pin Output Low I

+

and R– could be at 17V while VCC = 0V.

OUT

= 100Ω ● 0.94 1 1.03 V

– V

SET

= 100Ω ● 0.94 1 1.03 V

SET

= 1000Ω ● 0.001 0.5 V

SET

= 100Ω ● 0.001 0.5 V

SET

= 1.1V ● 18 20 21 mA

IOUT

+

R

CC

= 0V ● –8 –10 –12 µA

GATE

● 10 30 40 mV

● 10.8 12 12.7 V

= 12V, R

CC

= 5V, R

CC

= 50Ω, V

SET

+

– V

R

GATE

= 3mA ● 0.1 0.3 1.2 V

Note 3: An internal clamp limits the GATE pin to a minimum of 10.8V
above V

. Driving this pin to voltages beyond the clamp may damage the

CC

part.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

3.5

3.0

2.5

(mA)

CC

I

2.0

1.5

ICC vs V

TA = 25°C

CC

ICC vs Temperature UV Threshold vs V

1.66

1.64

1.62

1.60

(mA)

CC

I

1.58

1.56

VCC = 5V

1.250
TA = 25°C

1.245

1.240

1.235

1.230

UV THRESHOLD (V)

1.225

1.220

CC

1.0
02

4

VCC (V)

10

8

6

12

14

4350 G01

1.54
–50

–25 0

UV Threshold vs Temperature OV Threshold vs V

1.255
VCC = 5V

1.250

1.245

1.240

1.235

1.230

UV THRESHOLD (V)

1.225

1.220

1.215

–50

–25

02550

TEMPERATURE (°C)

75 100

4350 G04

1.222
TA = 25°C

1.220

1.218

1.216

1.214

1.212

1.210

OV THRESHOLD (V)

1.208

1.206

1.204

1.202

02

25 75

TEMPERATURE (°C)

CC

8

6

4

VCC (V)

50 100

4350 G02

12

14

4350 G05

10

1.215
02

6

4

VCC (V)

OV Threshold vs Temperature

1.225

VCC = 5V

1.220

1.215

1.210

OV THRESHOLD (V)

1.205

1.200

–50

02550

–25

TEMPERATURE (°C)

8

10

14

12

4350 G03

75 100

4350 G06

4350fa

3

LTC4350

VCC (V)

02

2.2

GAIN (V)

2.4

2.7

4

8

10

4350 G09

2.3

2.6

2.5

6

12

14

R

GAIN

= 25k

(V

R

+

– V

R

–

) = 100mV

T

A

= 25°C

UW

TYPICAL PERFOR A CE CHARACTERISTICS

FB vs V

CC

1.230
TA = 25°C

1.225

1.220

FB (V)

1.215

1.210
02

4

VCC (V)

10

8

6

12

14

4350 G07

Gain Pin Voltage vs Temperature ∆V

2.7
R

= 25k

GAIN

+

–

– V

) = 100mV

(V

R

R

= 5V

V

CC

2.6

2.5

GAIN (V)

2.4

2.3

FB vs Temperature Gain PIn Voltage vs V

1.230

VCC = 5V

1.225

1.220

FB (V)

1.215

1.210

(V)

GATE

∆V

13

12

11

10

9

8

7

–50

GATE

TA = 25°C

02550

–25

TEMPERATURE (°C)

vs V

CC

75 100

4350 G08

(V)

GATE

∆V

13.0

12.5

12.0

11.5

∆V

vs Temperature

GATE

VCC = 5V

CC

2.2

–50

U

02550

–25

TEMPERATURE (°C)

75 100

4350 G10

UU

6

0

24

PI FU CTIO S

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.

81214

610

VCC (V)

4350 G11

11.0
–50

02550

–25

TEMPERATURE (°C)

75 100

4350 G12

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

) from VCC is connected to the

TIMER

TIMER pin and the voltage starts to ramp up with a slope
given by: dV/dt = I

TIMER/CT

. 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 • CT)/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.

4350fa

4

LTC4350

U

UU

PI FU CTIO S

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 repre­sents a diode voltage up from the voltage at the R
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 compen­sation 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.

GND (Pin 8): Chip Ground.

FB (Pin 9): Analog Error Amplifier Input (E/A1). This pin is

used to monitor the output supply voltage with an external
resistive divider. The FB pin voltage is compared to 1.220V
reference. The difference between the FB pin voltage and
the reference is amplified and output on the COMP1 pin.

R

(Pin 10): Analog Output Pin. The I

SET

OUT

converts the voltage at the COMP2 pin (down a diode
voltage) to the R
external resistor (R
ground is (COMP2 – V

pin. Therefore, the current through the

SET

) placed between the R

SET

DIODE

)/R

. This current is used to

SET

SET

adjust the output voltage.

I

(Pin 11): Analog Output Pin. The current flowing into

OUT

the I
pin that was set by the external resistor R

pin is equal to the current flowing out of the R

OUT

. This current

SET

is used to adjust the output supply voltage by modifying
the voltage sensed by the power supply’s internal voltage
feedback circuitry.

pin.

SET

amplifier

pin and

SET

R– (Pin 12): Analog Input Pin. With a sense resistor placed
in the supply path between the R+ and R– pins, the power
supply current is measured as a voltage drop between R
and R–. This voltage is measured by the I

SENSE

block and

+

multiplied at the GAIN pin.

+

(Pin 13): Analog Input Pin. With a sense resistor placed

R

in the supply path between the R
supply current is measured as a voltage drop between R
and R–. This voltage is measured by the I

+

and R– pins, the power

block and

SENSE

+

multiplied at the GAIN pin.

GATE (Pin14): The high side gate drive for the external
N-Channel power FET. An internal charge pump provides
the gate drive necessary to drive the FETs. The slope of the
voltage rise or fall at the GATE is set by an external
capacitor connected between GATE and GND, and the
10µA charge pump output current. When the undervoltage
lockout circuit monitoring V

trips, the OV pin is pulled

CC

high or the UV pin is pulled low, the GATE pin is immedi­ately pulled to GND.

STATUS (Pin 15): Open-Drain Digital Output. The STA­TUS pin has an open-drain output to GND. This pin is
pulled low to indicate a fault has occurred in the system.
There are three types of faults. The first is a undervoltage
lockout on VCC or the UV pin is low while the output
voltage is active. The second is when the COMP2 pin is
above 1.5V or below 0.5V and the voltage on the GAIN pin
is greater than 100mV. The final failure is when the OV pin
is high. The three faults will activate the pull-down on the
STATUS pin after a timing cycle.

VCC (Pin 16): The Positive Supply Input, Ranging from

3.3V to 12V for Normal Operation. ICC is typically 1.6mA.
An undervoltage lockout circuit disables the chip until the
voltage at VCC is greater than 2.47V. A 0.1µF bypass
capacitor is required on the VCC pin. If the VCC pin is tied
to the same power supply output that is being adjusted,
then a 51Ω decoupling resistor is needed to hold up the
supply during a short to ground on the supply output. V

CC

must be greater than or equal to the supply that is
connected to the R+ and R– pins.

4350fa

5