Datasheet LTC1473 Datasheet (Linear Technology)

LTC1473

FEATURES

■

Power Path Management for Systems with Multiple DC Sources

■

All N-Channel Switching to Reduce Power Losses and System Cost

■

Switches and Isolates Sources Up to 30V

■

Adaptive High Voltage Step-Up Regulator for N-Channel Gate Drive

■

Capacitor Inrush and Short-Circuit Current Limited

■

User-Programmable Timer to Limit Switch Dissipation

■

Small Footprint: 16-Pin Narrow SSOP

U

APPLICATIO S

■

Notebook Computers

■

Portable Instruments

■

Handi-Terminals

■

Portable Medical Equipment

■

Portable Industrial Control Equipment

Dual PowerPath

TM

Switch Driver

U

DESCRIPTIO

The LTC®1473 provides a power management solution for single and dual battery notebook computers and other portable equipment. The LTC1473 drives two sets of backto-back N-channel MOSFET switches to route power to the input of the main system switching regulator. An internal boost regulator provides the voltage to fully enhance the logic level N-channel MOSFET switches.

The LTC1473 senses current to limit surge currents both into and out of the batteries and the system supply capacitor during switch-over transitions or during fault conditions. A user-programmable timer monitors the time the MOSFET switches are in current limit and latches them off when the programmed time is exceeded.

A unique “2-diode mode” logic ensures system start-up regardless of which input receives power first.

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

PowerPath is a trademark of Linear Technology Corporation.

TYPICAL APPLICATION

BAT1

MMBD2838LTI

DCIN

C

TIMER

4700pF

1µF

BAT2

*COILCRAFT 1812LS-105XKBC

1µF

FROM POWER

MANAGEMENT

1mH*

MMBD914LTI

U

MBRD340

Si9926DY

LTC1473

1

IN1

2

3

4

5

6

7

8

IN2

DIODE

TIMER

+

V

GG

SW

GND

µP

GA1

SAB1

GB1

SENSE

GA2

SAB2

GB2

16

15

14

13

+

12

–

11

10

9

Si9926DY

R

SENSE

0.04Ω

INPUT OF SYSTEM HIGH EFFICIENCY DC/DC SWITCHING REGULATOR (LTC1735, ETC)

C

OUT

1473 TA01

1

LTC1473

TOP VIEW

GN PACKAGE

16-LEAD NARROW PLASTIC SSOP

1 2 3 4 5 6 7 8

16 15 14 13 12 11 10

9

IN1 IN2

DIODE

TIMER

V

+

V

GG

SW

GND

GA1 SAB1 GB1 SENSE

+

SENSE

–

GA2 SAB2 GB2

ABSOLUTE MAXIMUM RATINGS

(Note 1)

DCIN, BAT1, BAT2 Supply Voltage .............. –0.3 to 32V

SENSE+, SENSE–, V+..................................–0.3 to 32V

GA1, GB1, GA2, GB2 ................................... –0.3 to 42V

SAB1, SAB2.................................................– 0.3 to 32V

SW, VGG......................................................– 0.3 to 42V

IN1, IN2, DIODE........................................–0.3V to 7.5V

Junction Temperature (Note 2)............................. 125°C

Operating Temperature Range

Commercial .............................................0°C to 70°C

Industrial ........................................... –40°C to 85°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. Test circuit, V+ = 20V, unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

+

V I

S

V

GS +

V

UVLO

+

V

UVLOHYS

V

HIDIGIN

V

LODIGIN

I

IN

V

GS(ON)

V

GS(OFF)

+

I

BSENSE

–

I

BSENSE

V

SENSE

I

PDSAB

I

TIMER

V

TIMER

t

ON

t

OFF

t

D1

t

D2

f

OVGG

2

WW

W

U

W

PACKAGE/ORDER INFORMATION

ORDER PART

NUMBER

LTC1473CGN LTC1473IGN

GN PART MARKING

1473 1473I

T

= 125°C, θJA = 150°C/W

JMAX

Consult factory for Military grade parts.

Supply Operating Range 4.75 30 V Supply Current V

IN1

= V

VGS Gate Supply Voltage VGS = V

DIODE

– V

GG

= 5V, V

+

IN2

= 0V, V

SENSE

+

= V

V+ Undervoltage Lockout Threshold V+ Ramping Down 2.7 3.1 3.5 V V+ Undervoltage Lockout Hysteresis 0.75 1 1.25 V Digital Input Logic High ● 2 1.6 V Digital Input Logic Low ● 1.5 0.8 V Input Current V Gate-to-Source ON Voltage I Gate-to-Source OFF Voltage I SENSE+ Input Bias Current V

SENSE– Input Bias Current V

Inrush Current Limit Sense Voltage V

SAB1, SAB2 Pull-Down Current V

Timer Source Current V

Timer Latch Threshold Voltage V Gate Drive Rise Time C Gate Drive Fall Time C Gate Drive Turn-On Delay C Gate Drive Turn-Off Delay C VGG Regulator Operating Frequency 30 kHz

= V

IN1

= I

GA1

= I

GA1

SENSE

V

SENSE

V

SENSE

SENSE–

V

SENSE–

= V

IN1

= V

V

IN1

= 0.8V, V

IN1

V

SENSE

= 0.8V, V

IN1

= 1000pF, V

GS

= 1000pF, V

GS

= 1000pF, V

GS

= 1000pF, V

GS

= V

IN2

= I

GA2

= I

GA2 +

= V

SENSE

+

= V

SENSE

+

= V

SENSE–

+

= V

SENSE

= 20V (V = 0V (V

= V

IN2

= 0.8V, V

IN2

+

– V

SENSE

= 5V ±1 µA

DIODE

= I

GB1

DIODE

IN2

= –1µA, V

GB2

= I

= 100µA, V

GB2

–

= 20V ● 24.56.5µA

–

= 0V (Note 3) ● –300 –160 –100 µA = 20V ● 24.56.5µA

–

= 0V (Note 3) ● –300 –160 –100 µA

– V

SENSE+

– V

SENSE

= 0.8V 5 20 30 µA

= 2V 30 200 300 µA

DIODE

= V

SAB1

= 2V, V

DIODE

–

= 300mV

= 2V ● 1.1 1.2 1.3 V

DIODE

= V

= 0V (Note 4) 33 µs

SAB2

= V

= 20V (Note 4) 2 µs

SAB2

= V

= 0V (Note 4) 22 µs

SAB2

= V

= 20V (Note 4) 1 µs

SAB2

= V

SAB1

–

) ● 0.15 0.20 0.25 V

–

) 0.10 0.20 0.30 V

= 0V, ● 35.58 µA

TIMER

–

= 20V ● 100 200 µA

SENSE

● 7.5 8.5 9.5 V

= 20V ● 5.0 5.7 7.0 V

SAB2

= V

= 20V ● 00.4 V

SAB2

U

ELECTRICAL CHARACTERISTICS

TEMPERATURE (°C)

–50

8.1

V

GS

GATE SUPPLY VOLTAGE (V)

8.2

8.4

8.5

8.6

0

9.0

1473 G03

8.3

–25 25 50 75 100 125

8.7

8.8

8.9

V+ = 20V V

GS = VGG

– V

+

LTC1473

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

Note 2: T dissipation P

Note 3: IS increases by the same amount as I

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

= TA + (PD)(150°C/W)

T

J

BSENSE

+

+ I

BSENSE

–

when

Note 4: Gate turn-on and turn-off times are measured with no inrush current limiting, i.e., V

4.5V and fall times are measured from 4.5V to 1V. Delay times are measured from the input transition to when the gate voltage has risen or fallen to 3V.

their common mode falls below 5V.

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

DC Supply Current vs Supply Voltage

160

140

120

100

80

60

SUPPLY CURRENT (µA)

40

20

0

V

0

5

= V

DIODE

10

= 5V

IN1

V

= 0V

IN2

V

DIODE

= V

V

IN1

V

SENSE

20

15

SUPPLY VOLTAGE (V)

= 5V

+

25

IN2

= V

= 0V

SENSE

30

–

= V

35

1473 G01

+

40

DC Supply Current vs Temperature

140

V+ = 20V

130

V

DIODE

120

110

100

90

80

SUPPLY CURRENT (µA)

70

60

50

–25 25 50 75 100 125

–50

= V

= 5V

IN1

= 0V

V

IN2

V

= 5V

DIODE

= V

IN1

IN2

= 0V

V

0 TEMPERATURE (°C)

1473 G02

= 0V. Gate rise times are measured from 1V to

SENSE

DC Supply Current vs V

500

450

400

350

300

250

SUPPLY CURRENT (µA)

200

150

100

2.5

0

|V

5

SENSE

V

7.5 | COMMON MODE(V)

SENSE

10

V

DIODE

+

– V

12.5

SENSE

= V

SENSE

15

V+ = 20V

= 5V

IN1

= 0V

V

IN2

–

= 0V

17.5

1473 • TPC02.5

20

VGS Gate-to-Source ON Voltage vs Temperature

6.0 V+ = V

5.9

5.8

5.7

5.6

5.5

5.4

5.3

GATE-TO-SOURCE ON VOLTAGE (V)

GS

5.2

V

5.1

–50

=20V

SAB

–25 25 50 75 100 125

0 TEMPERATURE (°C)

1473 G04

Undervoltage Lockout Threshold (V+) vs Temperature

5.5

5.0

4.5

4.0

3.5

3.0

2.5

SUPPLY VOLTAGE (V)

2.0

1.5

1.0 –50

START-UP

THRESHOLD

SHUTDOWN

THRESHOLD

–25 25 50 75 100 125

0 TEMPERATURE (°C)

VGS Gate Supply Voltage vs Temperature

1473 G05

3

LTC1473

TEMPERATURE (°C)

–50

1.10

TIMER LATCH THRESHOLD VOLTAGE (V)

1.12

1.16

1.18

1.20

0

1.28

1473 G12

1.14

–25 25 50 75 100 125

1.22

1.24

1.26

V+ = 20V

W

U

TYPICAL PERFORMANCE CHARACTERISTICS

Turn-Off Delay and Gate Fall Time vs Temperature

2.2

+

= 20V

V

= 1000pF

C

2.0

LOAD

V

= 20V

SAB

1.8

1.6

1.4

1.2

1.0

0.8

0.6

TURN-OFF DELAY AND GATE FALL TIME (µs)

0.4 –25 25 50 75 100 125

–50

GATE FALL

TIME

TURN-OFF

DELAY

0 TEMPERATURE (°C)

Logic Input Threshold Voltage vs Temperature

1.9

V+ = 5V

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

LOGIC INPUT THRESHOLD VOLTAGE (V)

1.0 –25 25 50 75 100 125

–50

0 TEMPERATURE (°C)

V

HIGH

LOW

1473 G07

1473 G10

Turn-On Delay and Gate Rise Time vs Temperature

45

+

= 20V

V

40

35

30

25

20

15

10

5

TURN-ON DELAY AND GATE RISE TIME (µs)

0

= 1000pF

C

LOAD

V

= 0V

SAB

–25 25 50 75 100 125

–50

0 TEMPERATURE (°C)

GATE RISE

TIME

TURN-ON

DELAY

Logic Input Threshold Voltage vs Temperature

1.9 V+ = 20V

1.8

V

HIGH

LOW

1.7

1.6

1.5

1.4

1.3

1.2

1.1

LOGCI INPUT THRESHOLD VOLTAGE (V)

1.0

–25 25 50 75 100 125

–50

0 TEMPERATURE (°C)

1473 G06

1473 G11

Rise and Fall Time vs Gate Capacitive Loading

40

35

30

25

20

15

10

RISE AND FALL TIME (µs)

5

0

10

RISE TIME

= 0V

V

SAB

FALL TIME

= 20V

V

SAB

100 1000 10000

GATE CAPACITIVE LOADING (pF)

Timer Latch Threshold Voltage vs Temperature

1473 G08

4

TIMER SOURCE CURRENT (µA)

Timer Source Current vs Temperature

8.5 V+ = 20V

TIMER = 0V

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0

–25 25 50 75 100 125

–50

0 TEMPERATURE (°C)

1473 G13

Sense Pin Source Current I

vs V

BSENSE

175

150

125

100

75

50

25

SENSE PIN CURRENT (µA)

0

–25

2.5

0

SENSE

5

7.5 V

V+ = 20V V

DIODE

V

IN2

V

SENSE

10

SENSE

= 0V

(V)

= V

+

12.5

– V

IN1

SENSE

= 5V

15

–

= 0V

17.5

1473 • TPC14

20

UUU

PIN FUNCTIONS

LTC1473

IN1 (Pin 1): Logic Input of Gate Drivers GA1 and GB1. IN1 is disabled when IN2 is high or DIODE is low.

IN2 (Pin 2): Logic Input of Gate Drivers GA2 and GB2. IN2 is disabled when IN1 is high or DIODE is low.

DIODE (Pin 3): “2-Diode Mode” Logic Input. DIODE overrides IN1 and IN2 by forcing the two back-to-back external N-channel MOSFET switches to mimic two diodes.

TIMER (Pin 4): Fault Timer. A capacitor connected from this pin to GND programs the time the MOSFET switches are allowed to be in current limit. To disable this function, Pin 4 can be grounded.

V+ (Pin 5): Input Supply. Bypass this pin with at least a 1µF capacitor.

VGG (Pin 6): Gate Driver Supply. This high voltage supply is intended only for driving the internal micropower gate drive circuitry.

circuitry

SW (Pin 7): Open Drain of an internal N-Channel MOSFET Switch. This pin drives the bottom of the VGG switching regulator inductor which is connected between this pin and the V+ pin.

GND (Pin 8): Ground. GA2, GB2 (Pins 11, 9): Switch Gate Drivers. GA2 and GB2

drive the gates of the second back-to-back external N-channel switches.

. Bypass this pin with at least 1µF.

Do not load this pin with any external

SAB2 (Pin 10): Source Return. The SAB2 pin is connected to the sources of SW A2 and SW B2. A small pull-down current source returns this node to 0V when the switches are turned off.

SENSE– (Pin 12): Inrush Current Input. This pin should be connected directly to the bottom (output side) of the low value current sense resistor in series with the two input power selector switch pairs, SW A1/B1 and SW A2/B2, for detecting and controlling the inrush current into and out of the power supply sources and the output capacitor.

SENSE+ (Pin 13): Inrush Current Input. This pin should be connected directly to the top (switch side) of the low value current sense resistor in series with the two input power selector switch pairs, SW A1/B1 and SW A2/B2, for detecting and controlling the inrush current into and out of the power supply sources and the output capacitor. Current limit is invoked when (V ±0.2V.

GA1, GB1 (Pins 16, 14): Switch Gate Drivers. GA1 and GB1 drive the gates of the first back-to-back external N-channel switches.

SAB1 (Pin 15): Source Return. The SAB1 pin is connected to the sources of SW A1 and SW B1. A small pull-down current source returns this node to 0V when the switches are turned off.

SENSE

+

– V

SENSE

–

) exceeds

5

LTC1473

UU

W

FUNCTIONAL DIAGRA

1

IN1

IN2

2

DIODE

3

+

V

5.5µA

TIMER

4

INRUSH

CURRENT

SENSE

SW A1/B1

GATE

DRIVERS

SW A2/B2

GATE

DRIVERS

GA1

16

SAB1

15

GB1

14

+

SENSE

13

–

SENSE

12

GA2

11

SAB2

10

GB2

9

V

SW

GND

TO

GATE

DRIVERS

+

V

5

6

GG

7

V

GG

SWITCHING

REGULATOR

8

900k

+

–

1.20V

R

LATCH

S

1473 FD

6

U

OPERATION

LTC1473

The LTC1473 is responsible for low-loss switching and isolation at the “front end” of the power management system, where up to two battery packs can be connected and disconnected seamlessly. Smooth switching between input power sources is accomplished with the help of lowloss N-channel switches. They are driven by special gate drive circuitry which limits the inrush current in and out of the battery packs and the system power supply capacitors.

All N-Channel Switching

The LTC1473 drives external back-to-back N-channel MOSFET switches to direct power from two sources: the primary battery and the secondary battery or a battery and a wall unit. (N-channel MOSFET switches are more cost effective and provide lower voltage drops than their Pchannel counterparts.)

Gate Drive (VGG) Power Supply

The gate drive for the low-loss N-channel switches is supplied by an internal micropower boost regulator which is regulated at approximately 8.5V above V+, up to 37V maximum. In two battery systems, the LTC1473 V+ pin is diode ORed through three external diodes connected to the three main power sources, DCIN, BAT1 and BAT2. Thus, VGG is regulated at 8.5V above the highest power source and will provide the overdrive required to fully enhance the MOSFET switches.

For maximum efficiency the top of the boost regulator inductor is connected to V+ as shown in Figure 1. C1 provides filtering at the top of the 1mH switched inductor, L1, which is housed in a small surface mount package. An internal diode directs the current from the 1mH inductor to the VGG output capacitor C2.

Inrush and Short-Circuit Current Limiting

The LTC1473 uses an adaptive inrush current limiting scheme to reduce current flowing in and out of the two main power sources and the following system’s input capacitor during switch-over transitions. The voltage across a single small valued resistor, R

, is measured to

SENSE

ascertain the instantaneous current flowing through the

two switch pairs, SW A1/B1 and SW A2/B2, during the transitions.

Figure 2 shows a block diagram of a switch driver pair, SW A1/B1. A bidirectional current sensing and limiting circuit determines when the voltage drop across R

SENSE

reaches

±200mV. The gate-to-source voltage, VGS, of the appro- priate switch is limited during the transition period until the inrush current subsides, generally within a few milliseconds, depending upon the value of the following system’s input capacitor.

This scheme allows capacitors and MOSFET switches of differing sizes and current ratings to be used in the same system without circuit modifications.

BAT1 BAT2DCIN

BAT1

V

LTC1473

GG

LTC1473

TO GATE

DRIVERS

SW A1

GA1

6V

+

(8.5V + V

)

V

GG

SWITCHING

REGULATOR

Figure 1. VGG Switching Regulator

SW B1

GB1

V

SENSE

THRESHOLD

BIDIRECTIONAL

INRUSH CURRENT

SENSING AND

SAB1

6V

SW A/B

GATE

DRIVERS

R

SENSE

+

± 200mV

LIMITING

+

V

GG

SW

GND

L1 1mH

V

SENSE

C2 1µF 50V

+

–

1473 F02

1473 F01

C

C1 1µF 50V

OUTPUT LOAD

OUT

Figure 2. SW A1/B1 Inrush Current Limiting

7

LTC1473

U

WUU

APPLICATIONS INFORMATION

After the transition period, the VGS of both MOSFETs in the selected switch pair rises to approximately 5.6V. The gate drive is set at 5.6V to provide ample overdrive for standard logic-level MOSFET switches without exceeding their maximum VGS rating.

In the event of a fault condition the current limit loop will limit the inrush current into the short. At the instant the MOSFET switch is in current limit, i.e., when the voltage drop across R timing. It will continue to time as long as the MOSFET switch is in current limit. Eventually the preset time will lapse and the MOSFET switch will latch off. The latch is reset by deselecting the gate drive input. Fault time-out is programmed by an external capacitor connected between the TIMER pin and ground.

POWER PATH SWITCHING CONCEPTS

Power Source Selection

is ±200mV, a fault timer will start

SENSE

Switches SW A1/B1 and SW A2/B2 direct power from either batteries to the input of the DC/DC switching regulator. Each of the switches is controlled by a TTL/CMOS compatible input that can interface directly with a power management system µP.

Using Tantalum Capacitors

The inrush (and “outrush”) current of the system DC/DC regulator input capacitor is limited by the LTC1473, i.e., the current flowing both in and out of the capacitor during transitions from one input power source to another is limited. In many applications, this inrush current limiting makes it feasible to use smaller tantalum surface mount capacitors in place of larger aluminum electrolytics.

Note: The capacitor manufacturer should be consulted for specific inrush current specifications and limitations and some experimentation may be required to ensure compliance with these limitations under all possible operating conditions.

The LTC1473 drives low-loss switches to direct power in the main power path of a single or dual rechargeable battery system, the type found in many notebook computers and other portable equipment.

Figure 3 is a conceptual block diagram that illustrates the main features of an LTC1473 dual battery power management system starting with the three main power sources and ending at the output load (i.e.: system DC/DC regulator).

DCIN

SW A1/B1

BAT1

SW A2/B2

BAT2

LTC1473

INRUSH CURRENT LIMITING

Back-to-Back Switch Topology

The simple SPST switches shown in Figure 3 actually consist of two back-to-back N-channel switches. These low-loss N-channel switch pairs are housed in 8-pin SO and SSOP packaging and are available from a number of manufacturers. The back-to-back topology eliminates the problems associated with the inherent body diodes in power MOSFET switches and allows each switch pair to

OUTPUT LOAD

+

POWER

MANAGEMENT

µP

HIGH

IN

EFFICIENCY

DC/DC SWITCHING REGULATOR

C

12V

5V

3.3V

8

1473 F03

Figure 3. LTC1473 PowerPath Conceptual Diagram

LTC1473

U

WUU

APPLICATIONS INFORMATION

block current flow in either direction when both switches are turned off.

The back-to-back topology also allows for independent control of each half of the switch pair which facilitates bidirectional inrush current limiting and the so-called “2-diode mode” described in the following section.

The 2-Diode Mode

Under normal operating conditions, both halves of each switch pair are turned on and off simultaneously. For example, when the input power source is switched from BAT1 to BAT2 in Figure 4, both gates of switch pair SW A1/B1 are normally turned off and both gates of switch pair SW A2/B2 are turned on. The back-to-back body diodes in switch pair, SW A1/B1, block current flow in or out of the BAT1 input connector.

In the “2-diode mode,” only the first half of each power path switch pair, i.e., SW A1 and SW A2, are turned on; and the second half, i.e., SW B1 and SW B2 are turned off. These two switch pairs now act simply as two diodes connected to the two main input power sources as illustrated in Figure 4. The power path diode with the highest input voltage passes current through to the output load (i.e. input of the DC/DC converter) to ensure that the power

management µP is powered even under start-up or abnor- mal operating conditions. (An undervoltage lockout circuit defeats this mode when the V+ pin drops below approximately 3.2V. The supply to V+ comes from the main power sources, DCIN, BAT1 and BAT2 through three external diodes as shown in Figure 1.)

The 2-diode mode is asserted by applying an active low to the DIODE input.

COMPONENT SELECTION

N-Channel Switches

The LTC1473 adaptive inrush current limiting circuitry permits the use of a wide range of logic-level N-Channel MOSFET switches. A number of dual, low R

DS(ON)

N-channel switches in 8-lead surface mount packages are available that are well suited for LTC1473 applications.

The maximum allowable drain-source voltage, V

DS(MAX)

, of the two switch pairs, SW A1/B1 and SW A2/B2 must be high enough to withstand the maximum DC supply voltage. If the DC supply is in the 20V to 28V range, use 30V MOSFET switches. If the DC supply is in the 10V to 18V range, and is well regulated, then 20V MOSFET switches will suffice.

DCIN

BAT1

BAT2

SW A1

ON

SW B1

R

SENSE

OFF

SW A2

ON

Figure 4. LTC1473 PowerPath Switches in 2-Diode Mode

SW B2

OFF

LTC1473

+

C

IN

EFFICIENCY

DC/DC SWITCHING REGULATOR

POWER

MANAGEMENT

OUTPUT LOAD

HIGH

µP

12V

5V

3.3V

1473 F04

9

LTC1473

U

WUU

APPLICATIONS INFORMATION

As a general rule, select the switch with the lowest R and able to withstand the maximum allowable VDS. This will minimize the heat dissipated in the switches while increasing the overall system efficiency. Higher switch resistances can be tolerated in some systems with lower current requirements, but care should be taken to ensure that the power dissipated in the switches is never allowed to rise above the manufacturers’ recommended level.

Inrush Current Sense Resistor, R

A small valued sense resistor (current shunt) is used by the two switch pair drivers to measure and limit the inrush or short-circuit current flowing through the conducting switch pair.

The inrush current limit should be set at approximately 2× or 3× the maximum required output current. For example, if the maximum current required by the DC/DC converter is 2A, an inrush current limit of 6A is set by selecting a

0.033Ω sense resistor, R mula:

SENSE

, using the following for-

DS(ON)

The fault time delay is programmed with an external capacitor between the TIMER pin and GND. At the instant the MOSFET switch enters current limit, a 5.5µA current source starts charging C When the voltage across C latch is set and the MOSFET switch is turned off. To reset the latch, the logic input of the MOSFET gate driver is deselected.

The fault time delay should be programmed as large as possible, at least 3× to 5× the maximum switching transition period, to avoid prematurely tripping the protection circuit. Conversely, for the protection circuit to be effective, the fault time delay must be within the safe operating area of the MOSFET switches, as stated in the manufacturer’s data sheet.

The maximum switching transition period happens during a cold start, when a fully charged battery is connected to an unpowered system. The inrush current charging the system supply capacitor to the battery voltage determines the switching transition period.

through the TIMER pin.

TIMER

reaches 1.2V an internal

TIMER

R

Note that the voltage drop across the resistor in this example is only 66mV under normal operating conditions. Therefore, the power dissipated in the resistor is extremely small (132mW), and a small 1/4W surface mount resistor can be used in this application (the resistor will tolerate the higher power dissipation during current limit for the duration of the fault time-out). A number of small valued surface mount resistors are available that have been specifically designed for high efficiency current sensing applications.

Programmable Fault Timer Capacitor, C

A fault timer capacitor, C duration the MOSFET switches are allowed to be in continuous current limit.

In the event of a fault condition, the MOSFET switch is driven into current limit by the inrush current limit loop. The MOSFET switch operating in current limit is in a high dissipation mode and can fail catastrophically if not promptly terminated.

= (200mV)/I

SENSE

INRUSH

TIMER

, is used to program the time

TIMER

The following example illustrates the calculation of C Assume the maximum battery voltage is 20V, the system supply capacitor is 68µF, the inrush current limit is 6A and the maximum current required by the DC/DC converter is 2A. Then, the maximum switching transition period is calculated using the following formula:

(V

t

SW(MAX)

t

SW(MAX)

Multiplying 3 by 340µs gives 1.02ms, the minimum fault delay time. Make sure this delay time does not fall outside of the safe operating area of the MOSFET switch dissipating 60W (6A • 20V/2). Using this delay time the C be calculated using the following formula:

C

Therefore, C

= 1.02ms = 4700pF

TIMER

BAT(MAX)

=

= = 340µs

TIMER

I

(20)(68µF)

6A – 2A

should be 4700pF.

INRUSH

5.5µA

)

1.20V

)(C

IN(DC/DC)

– I

LOAD

)

TIMER.

TIMER

can

10

LTC1473

U

WUU

APPLICATIONS INFORMATION

VGG Regulator Inductor and Capacitors

The VGG regulator provides a power supply voltage 8.5V higher than any of the three main power source voltages to allow the control of N-channel MOSFET switches. This micropower, step-up voltage regulator is powered by the highest potential available from the three main power sources for maximum regulator efficiency.

LTC1473

+

)

TO GATE

DRIVERS

(8.5V + V

Three external components are required by the VGG regulator: L1, C1 and C2, as shown in Figure 5.

L1 is a small, low current, 1mH surface mount inductor. C1 provides filtering at the top of the 1mH switched inductor and should be at least 1µF to filter switching transients. The VGG output capacitor, C2, provides storage and filtering for the VGG output and should be at least 1µF and rated for 50V operation. C1 and C2 can be ceramic capacitors.

BAT1 BAT2DCIN

+

V

L1* 1mH

V

GG

SW

C1 1µF 50V

V

GG

SWITCHING

REGULATOR

GND

*COILCRAFT 1812LS-105 XKBC. (708) 639-6400

Figure 5. VGG Step-Up Switching Regulator

C2 1µF 50V

1473 F05

11

LTC1473

U

TYPICAL APPLICATIONS

Input Power Routing Circuit for Microprocessor Controlled Dual Battery Dual Chemistry System

R

SENSE

0.033Ω

Si9926DY

DCIN

Si9926DY

LTC1473

16

GA1

15

SAB1

14

GB1

13

+

SENSE

12

–

SENSE

11

GA2

10

SAB2

9

GB2

BAT2

8.4V

Li-Ion

IN1 IN2

DIODE

TIMER

V

SW

GND

V

GG

+

BAT1

12V

NiCd

1 2 3

C

TIMER

4700pF

4

5

6

7

8

SMBus

750k

500k

POWER MANAGEMENT µP

MMBD2838LT1

C7

1µF

LTC1473

1

IN1

2

IN2

3

C

TIMER

4700pF

C8

L1* 1mH

MMBD914LT1

DIODE

4

TIMER

5

+

V

6

V

GG

7

SW

8

GND

HIGH EFFICIENCY

DC/DC SWITCHING

REGULATOR

MBRD340

SAB1

SENSE

SAB2

GA1

GB1

GA2

GB2

16

15

14

13

+

12

–

11

10

9

Si9926DYSi9926DY

R

SENSE

0.033Ω

1473 TA02

* COILCRAFT 1812LS-105XKBC

12

BATTERY CHARGER

LTC1473

U

TYPICAL APPLICATIONS

Complete Front End Including Battery Charger and DC/DC Converter with Automatic Switchover Between Battery and DCIN

74C00

7

3

12

R8

R6

900k

130k

427k 1%

1%

R9

R7

113k 1%

1%

*SUMIDA CDRH125-10 **COILCRAFT 1812LS-105XKBC ***COILTRONICS CTX20-4

–

+

4700pF

C

TIMER

EXTV

DCIN

C2, 0.1µF

TG

BOOST

SW

V

IN

INTV

CC

BG

PGND

CC

1µF

D4 MBRD340

R12 3k 1%

R13

5.1k 1%

+

16 15 14 13 12 11 10 9

V

OUT

MMBD2838LT1

C7

R

SENSE

0.033Ω

R14 510Ω

C10 1µF

C16 220pF

C17 10µF

1µF

Q1

Si4412DY

C4

D1

C3

4.7µF 16V

SENSE

L2**

1mH

D5 MBRD340

0.1µF

Q2

Si4412DY

1

IN1

2

IN2

3

DIODE

4

TIMER

5

V

6

V

7

SW

8

GND

C11

0.47µF

D6 MBR0540T

R18, 200Ω, 1%

R20 395k

0.1% R21

164k

0.1%

CMDSH-3

+

C8

2,3 L3***

20µH

1,4

R

0.033Ω

C

OSC

57pF

1

C

CSS, 0.1µF

R

, 10k

C

, 51pF

C

C2

C1

100pF

6

5

4

1

OUT A

2

–

V

LTC1442

3

IN+ A

4

–

B

IN

OUT B

REF

HYST

1000pF

13

12

10

9

V

C

330pF

C5

14

D3

6.8V

8

7

+

6

5

OSC

2

RUN/SS

3

I

TH

4

SFB

C

11

R10 50k 1%

R11 1132k 1%

8

500k

5 6 7

8

R5

BATTERY

SGND V

OSENSE

SENSE SENSE

8.4V

Li-Ion

LTC1735

C9

0.1µF

+

GG

+

D2 MBRS140T3

LTC1473

1

GND

2

SW

3

BOOST

4

GND

5

GND

6

UV

7

GND

8

OVP

9

CLP

10

CLN

11

COMP1

12

SENSE

L1*

10µH

C

IN

22µF 35V × 2

SAB1

SENSE

SAB2

LT

GA1

GB1

GA2

GB2

R

SENSE

0.015Ω

C

OUT

+

R15 1k

R19 200Ω 1%

R1 105k 1%

C15

0.33µF

100µF

10V

× 3

SGND

Si9926DY

16

15

14

13

+

12

–

11

10

9

Si9926DY

24

GND

23

GND

22

V

CC1

21

V

CC2

20

V

CC3

19

PROG

®

1511

18

V

C

17

UVOUT

16

GND

15

COMP2

14

BAT

13

SPIN

1473 TA03

C12 10µF

C13 10µF

R

SENSE

0.033Ω

R16 300Ω

C14 1µF

20k 1%

R2

C6 100pF

V

OUT

5V/3.5A

R17

4.93k

13

LTC1473

TYPICAL APPLICATION

5V

SUPPLY V1

10k

1M

1

5

+

6

–

1M

SUPPLY V2

1M

8

3

+

2

–

4

1M

10k

*1812LS-105XKBC, COILCRAFT

U

Protected Automatic Switchover Between Two Supplies

18

LT1121-5

3

1µF

LT1490

7

C6 4700pF

D1

MMBD2838LT1

+

C7 1µF

+

C5 1µF

L1*, 1mH

1

2

3

4

5

6

7 8

IN1

IN2

DIODE

TIMER

+

V

GG

SW

GND

LTC1473

SENSE

GA1

SAB1

GB1

GA2

SAB2

GB2

Q1

Si9926DY

16

15

14

13

+

12

–

11

10

9

Q2

Si9926DY

R3

0.033Ω

1473 TA04

OUT

14

PACKAGE DESCRIPTION

U

Dimensions in inches (millimeters) unless otherwise noted.

GN Package

16-Lead Plastic SSOP (Narrow 0.150)

(LTC DWG # 05-08-1641)

0.189 – 0.196* (4.801 – 4.978)

16

15

14

12 11 10

13

LTC1473

0.009

(0.229)

9

REF

0.015

± 0.004

(0.38 ± 0.10)

0.007 – 0.0098 (0.178 – 0.249)

0.016 – 0.050

(0.406 – 1.270)

* 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

0° – 8° TYP

× 45°

0.229 – 0.244

(5.817 – 6.198)

0.053 – 0.068

(1.351 – 1.727)

0.008 – 0.012

(0.203 – 0.305)

12

0.150 – 0.157** (3.810 – 3.988)

5

4

3

678

0.0250

(0.635)

BSC

0.004 – 0.0098 (0.102 – 0.249)

GN16 (SSOP) 1098

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.

15

LTC1473

TYPICAL APPLICATIONS

U

OTHER 5V

LOGIC

SUPPLY

SUPPLY V1

SUPPLY V2

12V

5V

*1812LS-105XKBC, COILCRAFT

100k

Protected Hot SwapTM Switchover Between Two Supplies

D1

MMBD2838LT1

C6 4700pF

C7 1µF

C5 1µF

L1*, 1mH

1

2

3

4

5

6

7 8

IN1

IN2

DIODE

TIMER

+

V

GG

SW

GND

LTC1473

GA1

SAB1

GB1

SENSE

GA2

SAB2

GB2

16

15

14

13

+

12

–

11

10

9

Q1

Si4936DY

Q2

Si4936DY

LONG PIN

R3

0.1Ω

LONG PIN

SHORT PIN

DOCKING

CONNECTOR

5V

OUT

ON

1473 • TA05

Hot Swap is a trademark of Linear Technology Corporation.

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC1155 Dual High Side Micropower MOSFET Driver Internal Charge Pump Requires No External Components LTC1161 Quad Protected High Side MOSFET Driver Rugged, Designed for Harsh Environment LTC1473L Dual PowerPath Switch Driver Low Voltage Version of the LTC1473; Operates with 3.3V Input LTC1479 PowerPath Controller for Dual Battery Systems Designed to Interface with a Power Management µP LT1505 Synchronous Constant-Voltage/Constant-Current Up to 6A Charge Current; High Efficiency; Adaptive Current Limiting

Battery Charger LT1510 Constant-Voltage/Constant-Current Battery Charger Up to 1.5A Charge Current for Lithium-Ion, NiCd and NiMH Batteries LT1511 3A Constant-Voltage/Constant-Current Battery Charger High Efficiency, Minimal External Components to Fast Charge

Lithium, NiMH and NiCd Batteries

LTC1628 2-Phase Dual Synchronous Step-Down Controller Minimum Input Capacitors; 4.5V ≤ VIN ≤ 36V LTC1735 High Efficiency Synchronous Switching Regulator Constant Frequency, VIN ≤ 36V, Fault Protection

1473fa LT/TP 0400 REV A 2K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1997

16

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

●

www.linear-tech.com