LTC1473
Dual PowerPath
TM
Switch Driver
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
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
®
1473 provides a power management solution for
single and dual battery notebook computers and other
portable equipment. The LTC1473 drives two sets of back-
to-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
s
s
s
s
s
Notebook Computers
Portable Instruments
Handi-Terminals
Portable Medical Equipment
Portable Industrial Control Equipment
TYPICAL APPLICATION
MBRD340
Si9926DY
BAT1
MMBD2838LTI
1
DCIN
FROM POWER
MANAGEMENT
µP
2
3
4
C
TIMER
4700pF
1µF
1µF
1mH*
5
6
7
8
MMBD914LTI
LTC1473
IN1
IN2
DIODE
TIMER
V
+
V
GG
SW
GND
GA1
SAB1
GB1
SENSE
16
15
14
R
SENSE
0.04Ω
INPUT OF SYSTEM
HIGH EFFICIENCY DC/DC
SWITCHING REGULATOR
(LTC1735, ETC)
+
13
SENSE
–
GA2
SAB2
GB2
12
11
10
9
C
OUT
BAT2
*COILCRAFT 1812LS-105XKBC
Si9926DY
1473 TA01
U
U
U
1
LTC1473
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
IN1 1
IN2 2
DIODE 3
TIMER 4
V
+
5
V
GG
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, V
GG
...................................................... – 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
ORDER PART
NUMBER
LTC1473CGN
LTC1473IGN
GN PART MARKING
1473
1473I
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ 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 = 25°C.
Test circuit, V
+
= 20V, unless otherwise specified.
SYMBOL
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
PARAMETER
Supply Operating Range
Supply Current
V
GS
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
V
GG
Regulator Operating Frequency
V
IN1
= V
IN2
= V
DIODE
= 5V
I
GA1
= I
GA2
= I
GB1
= I
GB2
= – 1µA, V
SAB1
= V
SAB2
= 20V
I
GA1
= I
GA2
= I
GB1
= I
GB2
= 100µA, V
SAB1
= V
SAB2
= 20V
V
SENSE +
= V
SENSE –
= 20V
V
SENSE +
= V
SENSE –
= 0V (Note 3)
V
SENSE +
= V
SENSE –
= 20V
V
SENSE +
= V
SENSE –
= 0V (Note 3)
V
SENSE –
= 20V (V
SENSE +
– V
SENSE –
)
V
SENSE –
= 0V (V
SENSE +
– V
SENSE –
)
V
IN1
= V
IN2
= V
DIODE
= 0.8V
V
IN1
= V
IN2
= 0.8V, V
DIODE
= 2V
V
IN1
= 0.8V, V
IN2
= V
DIODE
= 2V, V
TIMER
= 0V,
V
SENSE +
– V
SENSE –
= 300mV
V
IN1
= 0.8V, V
IN2
= V
DIODE
= 2V
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 4)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 20V (Note 4)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 4)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 20V (Note 4)
q
q
q
q
q
q
q
q
q
q
q
CONDITIONS
V
IN1
= V
DIODE
= 5V, V
IN2
= 0V, V
SENSE +
= V
SENSE –
= 20V
V
GS
= V
GG
– V
+
V
+
Ramping Down
q
q
MIN
4.75
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
35
350
9
1.3
UNITS
V
µA
V
V
V
V
V
µA
V
V
µA
µA
µA
µA
V
V
µA
µA
µA
V
µs
µs
µs
µs
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
2
U
W
U
U
W W
W
LTC1473
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
)(150°C/W)
Note 3:
I
S
increases by the same amount as I
BSENSE +
+ I
BSENSE –
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., V
SENSE
= 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
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
100
80
60
40
20
0
0
5
V
SENSE +
= V
SENSE –
= V
+
10 15 20 25 30
SUPPLY VOLTAGE (V)
35
40
V
DIODE
= 5V
V
IN1
= V
IN2
= 0V
110
100
90
80
70
60
50
– 50
– 25
25
50
75
0
TEMPERATURE (°C)
100
125
V
DIODE
= 5V
V
IN1
= V
IN2
= 0V
SUPPLY CURRENT (µA)
120
V
GS
Gate-to-Source ON Voltage
vs Temperature
6.0
V
GS
GATE-TO-SOURCE ON VOLTAGE (V)
V
+
= V
SAB
=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
V
GS
GATE SUPPLY VOLTAGE (V)
5.7
5.6
5.5
5.4
5.3
5.2
5.1
– 50
U W
1473 G01
DC Supply Current
vs Temperature
140
130
120
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
+
= 20V
500
450
400
350
300
250
200
150
100
DC Supply Current vs V
SENSE
V
+
= 20V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE +
– V
SENSE –
= 0V
0
2.5
7.5 10 12.5 15 17.5 20
|V
SENSE
| COMMON MODE(V)
5
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
V
GS
Gate Supply Voltage
vs Temperature
V
+
= 20V
V
GS =
V
GG
– 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 (µs)
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 (µs)
V
+
= 20V
C
LOAD
= 1000pF
V
SAB
= 20V
GATE FALL
TIME
RISE AND FALL TIME (µs)
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
V
LOW
V
HIGH
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
V
LOW
V
HIGH
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 (µA)
SENSE PIN CURRENT (µA)
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
U W
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
C
LOAD
= 1000pF
V
SAB
= 0V
40
35
30
25
20
15
10
5
0
Rise and Fall Time
vs Gate Capacitive Loading
GATE RISE
TIME
RISE TIME
V
SAB
= 0V
FALL TIME
V
SAB
= 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
I
BSENSE
vs V
SENSE
V
+
= 20V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE +
– V
SENSE –
= 0V
125
100
75
50
25
0
–25
0
2.5
5
7.5 10 12.5
V
SENSE
(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 over-
rides 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.
V
GG
(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 1µF.
SW (Pin 7):
Open Drain of an internal N-Channel MOSFET
Switch. This pin drives the bottom of the V
GG
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. Cur-
rent limit is invoked when (V
SENSE +
– V
SENSE –
) 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.
U
U
U
5
