Datasheet

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LTC4370

4370f

Typical applicaTion

FeaTures DescripTion

Two-Supply Diode-OR

Current Balancing Controller

The LTC

4370 is a two-supply current sharing controller

which incorporates MOSFET ideal diodes. The diodes

block reverse and shoot-through currents during start-up

and fault conditions. Their forward voltage is adjusted to

share the load currents between supplies. Unlike other

sharing methods, neither a share bus nor trim pins on

the supply are required.

The maximum MOSFET voltage drop can be set with a

resistor. A fast gate turn-on reduces the load voltage

droop during supply switchover. If the input supply fails

or is shorted, a fast turn-off minimizes reverse current

transients.

The controller operates with supplies from 2.9V to 18V.

For lower rail voltages, an external supply is needed at

the V

pin. Enable inputs can be used to turn off the

MOSFET and put the controller in a low current state.

Status outputs indicate whether the MOSFETs are on or

off. The load sharing function can be disabled to turn the

LTC4370 into a dual ideal diode controller.

12V, 10A Load Share Current Sharing Error vs Supply Difference

applicaTions

Shares Load Between Two Supplies

Eliminates Need for Active Control of

Input Supplies

No Share Bus Required

Blocks Reverse Current

No Shoot-Through Current During Start-Up or Faults

0V to 18V High Side Operation

Enable Inputs

MOSFET On Status Outputs

Dual Ideal Diode Mode

16-Lead DFN (4mm × 3mm) and MSOP Packages

Redundant Power Supplies

High Availability Systems and Servers

Telecom and Network Infrastructure

L, LT, LTC , LT M, Linear Technology and the Linear logo are registered trademarks and

PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks

are the property of their respective owners. Protected by U.S. Patents, including 7920013 and

8022679. Additional patent pending.

SUM85N03-06P

*OPTIONAL, FOR FAST TURN-ON

SUM85N03-06P

GATE1CPO1

CPO2

GND

EN1

EN2

RANGE

4370 TA01

INA

12V

INB

12V

0.1µF

OUT

12V, 10A

39nF*

IN1

FETON1

COMP

FETON2

OUT1

OUT2

GATE2

IN2

LTC4370

2mΩ

0.18µF

INA

– V

INB

(mV)

–750

–20

SHARING ERROR (I

VINA

–

VINB

)/I

(%)

–10

–500 –250 2500 500

–15

–5

750

4370 TA01b

Summary of content (20 pages)

PAGE 1
LTC4370 Two-Supply Diode-OR Current Balancing Controller Features n n n n n n n n n n Description Shares Load Between Two Supplies Eliminates Need for Active Control of Input Supplies No Share Bus Required Blocks Reverse Current No Shoot-Through Current During Start-Up or Faults 0V to 18V High Side Operation Enable Inputs MOSFET On Status Outputs Dual Ideal Diode Mode 16-Lead DFN (4mm × 3mm) and MSOP Packages Applications n n n Redundant Power Supplies High Availability Systems and Servers Telecom and
PAGE 2
LTC4370 Absolute Maximum Ratings (Notes 1, 2) VIN1, VIN2, OUT1, OUT2 Voltages....................−2V to 24V VCC Voltage................................................ −0.3V to 6.5V GATE1, GATE2 Voltages (Note 3)................ −0.3V to 34V CPO1, CPO2 Voltages (Note 3).................... −0.3V to 34V RANGE Voltage.................................−0.3V to VCC + 0.3V COMP Voltage............................................... −0.3V to 3V EN1, EN2, FETON1, FETON2 Voltages..........−0.
PAGE 3
LTC4370 Electrical Characteristics The l denotes those specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN1 = VIN2 = 12V, OUT = VIN, VCC open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Supplies VIN VIN1, VIN2 Operating Range VCC(EXT) VCC External Supply Operating Range VCC(REG) VCC Regulated Voltage IIN VIN1, VIN2 Current Enabled, Higher Supply Enabled, Lower Supply Pull-Up Disabled Other VIN = 11.
PAGE 4
LTC4370 Electrical Characteristics SYMBOL PARAMETER CONDITIONS MIN IFETON FETON1, FETON2 Leakage Current At 12V l ΔVGATE(ON) MOSFET On Detect Threshold (GATE – VIN) FETON Transitions High l 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.
PAGE 5
LTC4370 Typical Performance Characteristics unless otherwise noted. 15 �VGATE Voltage vs Current 14 VIN = 18V 6 VIN = 2.
PAGE 6
LTC4370 Pin Functions COMP: Error Amplifier Compensation. Connect a capacitor from this pin to GND. The value of this capacitor should be approximately 10 to 50 times the gate capacitance (CISS) of the MOSFET switch. Maintain low board leakage on this pin for best load sharing accuracy. For example, 100nA of leakage current (equal to 1V across 10MΩ) increases the error amplifier offset by 0.7mV. Leave this pin open if only using ideal diode mode. CPO1, CPO2: Charge Pump Output.
PAGE 7
LTC4370 Functional Diagram R1 M1 VSUPPLY1 C1 13 12 VIN1 16 0.6V – EN1 + 11 GATE1 10 CPO1 OUT1 VCC DISABLE1 500k CP1 VIN2 SA1 + – VFR1 14 VCC 2.55V + + – CHARGE PUMP2 f = 3MHz + + – VCC RANGE 2 R3 VCC 500k CP5 FETON2 + VIN2 8 GATE2 EXPOSED PAD* 17 VIN2 4 GATE2 5 – OUT2 CPO2 6 + – 0.7V Z 15 TO LOAD VCC 0.
PAGE 8
LTC4370 Operation The LTC4370 controls N-channel MOSFETs, M1 and M2, to share the load between two supplies. Error amplifier EA compares OUT1 to OUT2 and sets the servo command voltages, VFR1 and VFR2, for servo amplifiers, SA1 and SA2. When enabled, each servo amplifier controls the gate of the external MOSFET to regulate its forward voltage drop (VFWD = VIN – OUT) to VFR. The combined action of EA and SA forces OUT1 to equal OUT2.
PAGE 9
LTC4370 Applications Information High availability systems often employ parallel-connected power supplies or battery feeds to achieve redundancy and enhance system reliability. ORing diodes have been a popular means of connecting these supplies at the point of load. System uptime improves further if these paralleled supplies also share the load current. VINA 5V M1 SUM85N03-06P C1 39nF EN1 CPO1 VIN1 GATE1 VCC CVCC 0.1µF GND LTC4370 RANGE R3 30.
PAGE 10
LTC4370 Applications Information diverging, and so too, the supply currents. As the supply voltages separate, the entire load current is steered to the higher supply. Now, the servo command across the higher supply’s MOSFET is folded back from the maximum to the minimum servo to minimize power dissipated in the MOSFET. The sharing capture range, ΔVIN(SH), in Figure 2a is ±500mV, set by VRANGE. Figure 2b will be discussed later in the MOSFET Selection section.
PAGE 11
LTC4370 Applications Information in the absence of load current the differential input voltage to the error amplifier is zero and the COMP current is gm(EA) • VEA(OS). Before sharing can start, the COMP voltage has to slew towards its operating point of 0.7V (when VIN1 < VIN2) or 1.24V (VIN1 > VIN2). This delay is determined by the differential input signal to the error amplifier (which is ΔVOUT = OUT1 – OUT2 = (I1 − I2) • RS), its gm and the COMP capacitor value.
PAGE 12
LTC4370 Applications Information In Figure 2b, 0.5IL • RDS(ON) is 125mV. The higher RDS(ON) rails the servo amplifier high as it cannot regulate the 25mV VFR(MIN) across the lower supply’s MOSFET. Compared to Figure 2a, the sharing capture range shrinks by 100mV (125mV – 25mV) to ±400mV. However, the ΔVIN over which currents are shared partially stays the same at 500mV + IL • RS. Even when not maximizing sharing range, IL • RDS(ON) should be kept below 75mV for optimum performance.
PAGE 13
LTC4370 Applications Information External CPO Supply The internal charge pump takes milliseconds to charge up the CPO capacitor especially during device power-up. This time can be shortened by connecting an external supply to the CPO pin. A series resistor is needed to limit the current into the internal clamp between the CPO and VIN pins. The CPO supply should also be higher than the main input supply to meet the gate drive requirements of the MOSFET. Figure 5 shows such a 3.
PAGE 14
LTC4370 Applications Information Input Transient Protection When the capacitances at the input and output are very small, rapid changes in current can cause transients that exceed the 24V absolute maximum rating of the VIN and OUT pins. In ORing applications, one surge suppressor connected from OUT to ground clamps all the inputs. In the absence of a surge suppressor, an output capacitance of 10μF is sufficient in most applications to prevent the transient from exceeding 24V.
PAGE 15
LTC4370 Applications Information PCB Layout Considerations Kelvin connection of the OUT pins to the sense resistors is important for accurate current sharing. Place the MOSFET as close as possible to the sense resistor. Keep the traces to the MOSFET wide and short to minimize resistive losses. The PCB traces associated with the power path through the MOSFET should have low resistance.
PAGE 16
LTC4370 Typical Applications Current Sharing 3.3V Supplies for 20A Output VINA 3.3V ±3% EN1 CVCC 0.1µF R3 20k M1 IRLS3034PBF C1 0.1µF CPO1 GATE1 VIN1 VCC OUT1 GND LTC4370 RANGE FETON1 R1 2mΩ FETON2 R2 2mΩ OUT2 EN2 CPO2 VIN2 GATE2 COMP C2 0.1µF VINB 3.3V ±3% OUT 20A M2 IRLS3034PBF CC 0.
PAGE 17
LTC4370 Typical Applications 12V Ideal Diode-OR by Tying RANGE to VCC (to Compare Against Load Share). Use LTC4353 if Load Share Is Not Desired VINA 12V EN1 M1 SUM85N03-06P NC CPO1 GATE1 VIN1 RANGE CVCC 0.
PAGE 18
LTC4370 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE Package 16-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1732 Rev Ø) 0.70 ±0.05 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 3.15 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) R = 0.05 TYP 9 R = 0.115 TYP 0.40 ± 0.10 16 3.30 ±0.10 3.00 ±0.
PAGE 19
LTC4370 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MS Package Package MS 16-Lead Plastic 16-Lead Plastic MSOP MSOP (Reference LTC LTC DWG DWG ## 05-08-1669 (Reference 05-08-1669Rev RevØ)Ø) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 4.039 ± 0.102 (.159 ± .004) (NOTE 3) 0.50 (.0197) BSC 0.305 ± 0.038 (.0120 ± .0015) TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 ± 0.102 (.118 ± .
PAGE 20
LTC4370 Typical Application 1.2V Load Share SUM85N03-06P VINA 1.2V EN1 39nF VIN1 CPO1 5V GATE1 OUT1 VCC 0.1µF GND LTC4370 RANGE 7.5k EN2 FETON1 2mΩ FETON2 2mΩ OUT OUT2 CPO2 VIN2 GATE2 COMP 0.18µF 39nF VINB 1.2V SUM85N03-06P 4370 TA04 Related Parts PART NUMBER DESCRIPTION COMMENTS TM LTC1473/ LTC1473L Dual PowerPath Switch Driver N-Channel, 4.75V to 30V/3.