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LTC1473 Dual PowerPathTM Switch Driver
FEATURES
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DESCRIPTIO
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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
The LTC(R)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.
APPLICATIO S
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Notebook Computers Portable Instruments Handi-Terminals Portable Medical Equipment Portable Industrial Control Equipment
TYPICAL APPLICATION
MBRD340
Si9926DY BAT1 MMBD2838LTI 1 DCIN FROM POWER MANAGEMENT P 2 3 4 CTIMER 4700pF 1F 1F 1mH* 5 6 7 8 MMBD914LTI LTC1473 IN1 IN2 DIODE TIMER V+ VGG SW GND GA1 SAB1 GB1 16 15 14 RSENSE 0.04 INPUT OF SYSTEM HIGH EFFICIENCY DC/DC SWITCHING REGULATOR (LTC1735, ETC)
13 SENSE + 12 SENSE - 11 GA2 10 SAB2 9 GB2
BAT2 *COILCRAFT 1812LS-105XKBC Si9926DY
1473 TA01
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COUT
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LTC1473
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW IN1 1 IN2 2 DIODE 3 TIMER 4 V+ 5 VGG 6 SW 7 GND 8 16 GA1 15 SAB1 14 GB1 13 SENSE + 12 SENSE - 11 GA2 10 SAB2 9 GB2
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) ............................. 125C Operating Temperature Range Commercial ............................................. 0C to 70C Industrial ........................................... - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1473CGN LTC1473IGN GN PART MARKING 1473 1473I
GN PACKAGE 16-LEAD NARROW PLASTIC SSOP TJMAX = 125C, JA = 150C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. Test circuit, V + = 20V, unless otherwise specified.
SYMBOL V+ IS VGS V +UVLO V +UVLOHYS VHIDIGIN VLODIGIN IIN VGS(ON) VGS(OFF) IBSENSE + IBSENSE - VSENSE IPDSAB ITIMER VTIMER t ON t OFF t D1 t D2 fOVGG PARAMETER Supply Operating Range Supply Current VGS Gate Supply Voltage V + Undervoltage Lockout Threshold V + Undervoltage Lockout Hysteresis Digital Input Logic High Digital Input Logic Low Input Current Gate-to-Source ON Voltage Gate-to-Source OFF Voltage SENSE + Input Bias Current SENSE - Input Bias Current Inrush Current Limit Sense Voltage SAB1, SAB2 Pull-Down Current Timer Source Current Timer Latch Threshold Voltage Gate Drive Rise Time Gate Drive Fall Time Gate Drive Turn-On Delay Gate Drive Turn-Off Delay VGG Regulator Operating Frequency VIN1 = VIN2 = VDIODE = 5V IGA1 = IGA2 = IGB1 = IGB2 = - 1A, VSAB1 = VSAB2 = 20V IGA1 = IGA2 = IGB1 = IGB2 = 100A, VSAB1 = VSAB2 = 20V VSENSE + = VSENSE - = 20V VSENSE + = VSENSE - = 0V (Note 3) VSENSE + = VSENSE - = 20V VSENSE + = VSENSE - = 0V (Note 3) VSENSE - = 20V (VSENSE + - VSENSE -) VSENSE - = 0V (VSENSE + - VSENSE -) VIN1 = VIN2 = VDIODE = 0.8V VIN1 = VIN2 = 0.8V, VDIODE = 2V VIN1 = 0.8V, VIN2 = VDIODE = 2V, VTIMER = 0V, VSENSE + - VSENSE - = 300mV VIN1 = 0.8V, VIN2 = VDIODE = 2V CGS = 1000pF, VSAB1 = VSAB2 = 0V (Note 4) CGS = 1000pF, VSAB1 = VSAB2 = 20V (Note 4) CGS = 1000pF, VSAB1 = VSAB2 = 0V (Note 4) CGS = 1000pF, VSAB1 = VSAB2 = 20V (Note 4)
q q q q q q q q q q q
CONDITIONS VIN1 = VDIODE = 5V, VIN2 = 0V, VSENSE = VSENSE = 20V VGS = VGG - V+ V + Ramping Down
+ -
MIN 4.75
q q
TYP 100
MAX 30 200 9.5 3.5 1.25 0.8 1 7.0 0.4 6.5 - 100 6.5 - 100 0.25 0.30 30 300 8 1.3
UNITS V A V V V V V A V V A A A A V V A A A V s s s s kHz
7.5 2.7 0.75 2
8.5 3.1 1 1.6 1.5
5.0 2 - 300 2 - 300 0.15 0.10 5 30 3 1.1
5.7 0 4.5 - 160 4.5 - 160 0.20 0.20 20 200 5.5 1.2 33 2 22 1 30
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LTC1473
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD)(150C/W) Note 3: IS increases by the same amount as IBSENSE + + IBSENSE - when their common mode falls below 5V. Note 4: Gate turn-on and turn-off times are measured with no inrush current limiting, i.e., VSENSE = 0V. Gate rise times are measured from 1V to 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.
TYPICAL PERFORMANCE CHARACTERISTICS
DC Supply Current vs Supply Voltage
160 140 VDIODE = VIN1 = 5V VIN2 = 0V
SUPPLY CURRENT (A)
SUPPLY CURRENT (A)
100 80 60 40 20 0 0 5 VSENSE + = VSENSE - = V + 10 15 20 25 30 SUPPLY VOLTAGE (V) 35 40 VDIODE = 5V VIN1 = VIN2 = 0V
110 100 90 80 70 60 50 - 50 - 25 25 50 75 0 TEMPERATURE (C) 100 125 VDIODE = 5V VIN1 = VIN2 = 0V
SUPPLY CURRENT (A)
120
VGS Gate-to-Source ON Voltage vs Temperature
6.0
VGS GATE-TO-SOURCE ON VOLTAGE (V)
V + = VSAB =20V
5.9 5.8
SUPPLY VOLTAGE (V)
4.5 4.0 3.5 3.0 2.5 2.0 1.5 - 25 25 50 75 0 TEMPERATURE (C) 100 125 1.0 - 50 - 25
VGS GATE SUPPLY VOLTAGE (V)
5.7 5.6 5.5 5.4 5.3 5.2 5.1 - 50
UW
1473 G01
DC Supply Current vs Temperature
140 130 120 VDIODE = VIN1 = 5V VIN2 = 0V V + = 20V
500 450 400 350 300 250 200 150 100
DC Supply Current vs VSENSE
V+ = 20V VDIODE = VIN1 = 5V VIN2 = 0V VSENSE + - VSENSE - = 0V
0
2.5
5 7.5 10 12.5 15 17.5 20 |VSENSE| COMMON MODE(V)
1473 * TPC02.5
1473 G02
Undervoltage Lockout Threshold (V +) vs Temperature
5.5 5.0 START-UP THRESHOLD SHUTDOWN THRESHOLD 9.0 8.9 8.8 8.7 8.6 8.5 8.4 8.3 8.2 25 50 75 0 TEMPERATURE (C) 100 125
VGS Gate Supply Voltage vs Temperature
V + = 20V VGS = VGG - V +
8.1 - 50
- 25
25 50 75 0 TEMPERATURE (C)
100
125
1473 G04
1473 G05
1473 G03
3
LTC1473 TYPICAL PERFORMANCE CHARACTERISTICS
Turn-Off Delay and Gate Fall Time vs Temperature
TURN-OFF DELAY AND GATE FALL TIME (s)
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6
TURN-ON DELAY AND GATE RISE TIME (s)
V + = 20V CLOAD = 1000pF VSAB = 20V GATE FALL TIME
RISE AND FALL TIME (s)
TURN-OFF DELAY
0.4 - 50
- 25
25 50 75 0 TEMPERATURE (C)
Logic Input Threshold Voltage vs Temperature
1.9
LOGIC INPUT THRESHOLD VOLTAGE (V)
1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 - 50 - 25 25 50 75 0 TEMPERATURE (C) 100 125 VLOW VHIGH
1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 - 50 - 25 25 50 75 0 TEMPERATURE (C) 100 125 VLOW VHIGH
TIMER LATCH THRESHOLD VOLTAGE (V)
LOGCI INPUT THRESHOLD VOLTAGE (V)
V + = 5V
Timer Source Current vs Temperature
8.5 8.0 V + = 20V TIMER = 0V
175 150
TIMER SOURCE CURRENT (A)
SENSE PIN CURRENT (A)
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 - 50 - 25 25 50 75 0 TEMPERATURE (C) 100 125
4
UW
100
1473 G07
1473 G10
Turn-On Delay and Gate Rise Time vs Temperature
45 40 35 30 25 20 15 10 5 0 - 50 - 25 25 50 75 0 TEMPERATURE (C) 100 125 TURN-ON DELAY V + = 20V CLOAD = 1000pF VSAB = 0V
40 35 30 25 20 15 10 5 0
Rise and Fall Time vs Gate Capacitive Loading
GATE RISE TIME
RISE TIME VSAB = 0V
FALL TIME VSAB = 20V 10 100 1000 GATE CAPACITIVE LOADING (pF) 10000
1473 G08
125
1473 G06
Logic Input Threshold Voltage vs Temperature
1.9 V + = 20V 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12
Timer Latch Threshold Voltage vs Temperature
V + = 20V
1.10 - 50
- 25
25 50 75 0 TEMPERATURE (C)
100
125
1473 G11
1473 G12
Sense Pin Source Current IBSENSE vs VSENSE
V+ = 20V VDIODE = VIN1 = 5V VIN2 = 0V VSENSE + - VSENSE - = 0V
125 100 75 50 25 0 -25 0 2.5 5
7.5 10 12.5 VSENSE (V)
15
17.5 20
1473 * TPC14
1473 G13
LTC1473
PIN FUNCTIONS
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 1F capacitor. VGG (Pin 6): Gate Driver Supply. This high voltage supply is intended only for driving the internal micropower gate drive circuitry. Do not load this pin with any external circuitry. Bypass this pin with at least 1F. 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. 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 (VSENSE + - VSENSE -) exceeds 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.
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LTC1473 FUNCTIONAL DIAGRA W
16 GA1 SW A1/B1 GATE DRIVERS 15 SAB1 14 GB1 13 SENSE + 12 SENSE - 11 GA2 SW A2/B2 GATE DRIVERS INRUSH CURRENT SENSE 10 SAB2 9 GB2 TIMER 4 R
IN1 IN2
DIODE
VGG SW
GND
6
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V+
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1 2
3 V+
5.5A
TO GATE DRIVERS 5 6 7 VGG SWITCHING REGULATOR 900k
+
S
LATCH
-
1.20V
8
1473 FD
LTC1473
OPERATION
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, RSENSE, is measured to ascertain the instantaneous current flowing through the
VGG SW A/B GATE DRIVERS
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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 RSENSE reaches 200mV. The gate-to-source voltage, VGS, of the appropriate 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.
DCIN LTC1473 BAT1 BAT2
V+
L1 1mH TO GATE DRIVERS (8.5V + V +) VGG SW VGG SWITCHING REGULATOR C1 1F 50V C2 1F 50V
GND
1473 F01
Figure 1. VGG Switching Regulator
SW A1 BAT1 SW B1 RSENSE
OUTPUT LOAD
+
COUT GA1 6V SAB1 6V GB1 VSENSE + 200mV THRESHOLD VSENSE -
BIDIRECTIONAL INRUSH CURRENT SENSING AND LIMITING
LTC1473
1473 F02
Figure 2. SW A1/B1 Inrush Current Limiting
7
LTC1473
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 RSENSE is 200mV, a fault timer will start 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 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). 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 P. 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.
DCIN SW A1/B1 BAT1 SW A2/B2 BAT2 INRUSH CURRENT LIMITING
LTC1473
Figure 3. LTC1473 PowerPath Conceptual Diagram
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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.
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 12V 5V 3.3V
+
CIN
HIGH EFFICIENCY DC/DC SWITCHING REGULATOR
POWER MANAGEMENT P
1473 F03
LTC1473
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 P is powered even under start-up or abnormal 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 RDS(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, VDS(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 SW B1 OUTPUT LOAD SW A1 BAT1 ON OFF SW A2 BAT2 ON OFF SW B2 RSENSE 12V 5V 3.3V
LTC1473
Figure 4. LTC1473 PowerPath Switches in 2-Diode Mode
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HIGH EFFICIENCY DC/DC SWITCHING REGULATOR
POWER MANAGEMENT P
1473 F04
9
LTC1473
APPLICATIONS INFORMATION
As a general rule, select the switch with the lowest RDS(ON) 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, RSENSE 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 2x or 3x 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 0.033 sense resistor, RSENSE, using the following formula: RSENSE = (200mV)/IINRUSH 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, CTIMER A fault timer capacitor, CTIMER, is used to program the time 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. 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 5.5A current source starts charging CTIMER through the TIMER pin. When the voltage across CTIMER reaches 1.2V an internal 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 3x to 5x 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. The following example illustrates the calculation of CTIMER. Assume the maximum battery voltage is 20V, the system supply capacitor is 68F, 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: tSW(MAX) = tSW(MAX) = (VBAT(MAX))(CIN(DC/DC)) IINRUSH - ILOAD (20)(68F) = 340s 6A - 2A
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Multiplying 3 by 340s 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 CTIMER can be calculated using the following formula:
CTIMER = 1.02ms
))
5.5A = 4700pF 1.20V
Therefore, CTIMER should be 4700pF.
LTC1473
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. 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 1F to filter switching transients. The VGG output capacitor, C2, provides storage and filtering for the VGG output and should be at least 1F and rated for 50V operation. C1 and C2 can be ceramic capacitors.
LTC1473
TO GATE DRIVERS
*COILCRAFT 1812LS-105 XKBC. (708) 639-6400
Figure 5. VGG Step-Up Switching Regulator
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DCIN
BAT1
BAT2
V+
L1* 1mH (8.5V + V +) VGG SW VGG SWITCHING REGULATOR C1 1F 50V
C2 1F 50V
GND
1473 F05
11
LTC1473
TYPICAL APPLICATIONS
Input Power Routing Circuit for Microprocessor Controlled Dual Battery Dual Chemistry System
Si9926DY
16 15 14 13 RSENSE 0.033 12 11 10 9
LTC1473 GA1 SAB1 GB1 SENSE + SENSE - GA2 SAB2 GB2
1 IN1 2 IN2 3 DIODE 4 5 6 7 8
TIMER V+ VGG SW GND
Si9926DY
BAT2 8.4V Li-Ion
BAT1 12V NiCd
DCIN
* COILCRAFT 1812LS-105XKBC
12
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Si9926DY
MMBD2838LT1 750k CTIMER 4700pF CTIMER 4700pF
500k
C7 1F
C8 1F
L1* 1mH
LTC1473 16 IN1 GA1 2 IN2 15 SAB1 3 14 DIODE GB1 4 + 13 TIMER SENSE 12 5+ V SENSE - 11 6 VGG GA2 10 7 SW SAB2 9 8 GND GB2 1
RSENSE 0.033
MMBD914LT1
Si9926DY
POWER MANAGEMENT P
HIGH EFFICIENCY DC/DC SWITCHING REGULATOR
SMBus MBRD340
1473 TA02
BATTERY CHARGER
LTC1473
TYPICAL APPLICATIONS
Complete Front End Including Battery Charger and DC/DC Converter with Automatic Switchover Between Battery and DCIN
C2, 0.1F COSC 57pF 1 CSS, 0.1F RC, 10k CC2, 51pF CC 330pF 2 3 4 5 COSC RUN/SS ITH SFB TG BOOST SW VIN 16 15 14 D1 CMDSH-3 C4 0.1F L1* 10H RSENSE 0.015 COUT 100F 10V x3 SGND Q1 Si4412DY CIN 22F 35V x2
C1 100pF
C5 1000pF
74C00
13 12
7 3 6
10 9
1
2
4
5 14
D3 6.8V
1 R6 900k 1% R7 130k 1% R8 427k 1% R9 113k 1% 2 3 4
OUT A V-
OUT B V+ REF HYST
8 7 6 5 R10 50k 1% R11 1132k 1% R12 3k 1% C9 0.1F R13 5.1k 1%
LTC1442
IN + A IN - B
*SUMIDA CDRH125-10 **COILCRAFT 1812LS-105XKBC ***COILTRONICS CTX20-4 C16 220pF RSENSE 0.033 8.4V Li-Ion BATTERY
U
+
13 LTC1735 12 INTVCC SGND 11 6 BG VOSENSE 10 7 - SENSE PGND 9 8 SENSE + EXTVCC VOUT
+
C3 4.7F 16V
Q2 Si4412DY
+
VOUT 5V/3.5A R1 105k 1% C6 100pF
D2 MBRS140T3
R2 20k 1%
Si9926DY
11
MMBD2838LT1 1 2 3 IN1 IN2
LTC1473 GA1 SAB1 GB1 SENSE
16 15 14 RSENSE 0.033
8 4 5 4700pF CTIMER C7 1F 6 C8 1F 7 L2** 1mH 8
DIODE TIMER V+ VGG SW GND
+ 13
SENSE - GA2 SAB2 GB2
12 11 10 9
R5 500k
DCIN D4 MBRD340 RSENSE 0.033 D5 MBRD340 1 2,3 L3*** 20H 1,4 C11 0.47F 2 3 4 5 6 7 8 9 10 11 12 R18, 200, 1% GND SW BOOST GND GND UV GND GND VCC1 VCC2 VCC3 24 23 22 21 20 C12 10F C13 10F
Si9926DY
R14 510 C10 1F
D6 MBR0540T
19 PROG LT (R)1511 18 GND VC 17 OVP UVOUT 16 CLP GND 15 CLN COMP2 14 COMP1 BAT 13 SENSE SPIN
R15 1k C15 0.33F
R16 300 C14 1F
R17 4.93k
R19 200 1%
+
C17 10F
R20 395k 0.1% R21 164k 0.1%
1473 TA03
13
LTC1473
TYPICAL APPLICATION
5V
SUPPLY V1 10k 1M 1M 3 8 1 2 1F D1 MMBD2838LT1
+ -
5 4 6
+
7
-
C6 4700pF
1M 1M 10k SUPPLY V2 *1812LS-105XKBC, COILCRAFT
14
U
Protected Automatic Switchover Between Two Supplies
1
LT1121-5 3
8 Q1 Si9926DY
LT1490 1 2 3 4 5 6 LTC1473 IN1 IN2 DIODE TIMER V+ VGG SW GND GA1 SAB1 GB1 SENSE + 16 15 14 13 R3 0.033 OUT
12 SENSE - GA2 SAB2 GB2 11 10 9
+ C7
1F
L1*, 1mH
7 8
+ C5
1F
Q2 Si9926DY
1473 TA04
LTC1473
PACKAGE DESCRIPTION
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
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.
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 13 12 11 10 9
0.009 (0.229) REF
0.229 - 0.244 (5.817 - 6.198)
0.150 - 0.157** (3.810 - 3.988)
1 0.015 0.004 x 45 (0.38 0.10) 0 - 8 TYP 0.053 - 0.068 (1.351 - 1.727)
23
4
56
7
8 0.004 - 0.0098 (0.102 - 0.249)
0.008 - 0.012 (0.203 - 0.305)
0.0250 (0.635) BSC
GN16 (SSOP) 1098
15
LTC1473
TYPICAL APPLICATIONS
Protected Hot SwapTM Switchover Between Two Supplies
OTHER 5V LOGIC SUPPLY LONG PIN 100k SUPPLY V1 5V D1 MMBD2838LT1 Q1 Si4936DY DOCKING CONNECTOR 5V
100k C6 4700pF C7 1F L1*, 1mH C5 1F SUPPLY V2 12V
*1812LS-105XKBC, COILCRAFT SHORT PIN
Hot Swap is a trademark of Linear Technology Corporation.
RELATED PARTS
PART NUMBER
LTC1155 LTC1161 LTC1473L LTC1479 LT1505 LT1510 LT1511 LTC1628 LTC1735
DESCRIPTION
Dual High Side Micropower MOSFET Driver Quad Protected High Side MOSFET Driver Dual PowerPath Switch Driver PowerPath Controller for Dual Battery Systems Synchronous Constant-Voltage/Constant-Current Battery Charger Constant-Voltage/Constant-Current Battery Charger 3A Constant-Voltage/Constant-Current Battery Charger 2-Phase Dual Synchronous Step-Down Controller High Efficiency Synchronous Switching Regulator
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
U
1 2 3 4 5 6 7 8
LTC1473 IN1 IN2 DIODE TIMER V+ VGG SW GND GA1 SAB1 GB1
16 15 14 R3 0.1
13 SENSE + SENSE - GA2 SAB2 GB2 12 11 10 9
OUT
LONG PIN
Q2 Si4936DY ON
1473 * TA05
COMMENTS
Internal Charge Pump Requires No External Components Rugged, Designed for Harsh Environment Low Voltage Version of the LTC1473; Operates with 3.3V Input Designed to Interface with a Power Management P Up to 6A Charge Current; High Efficiency; Adaptive Current Limiting Up to 1.5A Charge Current for Lithium-Ion, NiCd and NiMH Batteries High Efficiency, Minimal External Components to Fast Charge Lithium, NiMH and NiCd Batteries Minimum Input Capacitors; 4.5V VIN 36V Constant Frequency, VIN 36V, Fault Protection
1473fa LT/TP 0400 REV A 2K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1997

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