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LTC1473L
1
The LTC
1473L provides reliable and efficient switching
between two DC power sources. This device drives two
external sets of back-to-back N-channel MOSFET switches
to route power to the input of a low voltage system. An
internal boost regulator provides the voltage to fully en-
hance the logic-level N-channel MOSFET switches while
an internal undervoltage lock-out circuit keeps the system
alive down to 2.8V.
The LTC1473L senses current to limit inrush between the
batteries and the system supply capacitor during switch-
over transitions or during fault conditions. A user-pro-
grammable timer monitors the time the MOSFET switches
are in current limit and latches them off when the pro-
grammed time is exceeded.
A unique "2-diode" logic mode ensures system start-up
regardless of which input receives power first.
s
Portable Computers
s
Portable Instruments
s
Fault Tolerant Computers
s
Battery-Backup Systems
s
3.3V/5V Power Management
, LTC and LT are registered trademarks of Linear Technology Corporation.
s
Power Path Management for Systems
with Multiple DC Sources
s
Switches and Isolates Sources from 3.3V to 10V
s
All N-Channel Switching to Reduce Power Losses
and System Cost
s
Built-In Step-Up Regulator for N-Channel Gate Drive
s
Capacitor Inrush and Short-Circuit Current Limited
s
User-Programmable Timer Prevents Overdissipation
During Current Limiting
s
Undervoltage Lockout Prevents Operation with Low
Inputs
s
Small Footprint: 16-Pin Narrow SSOP
Dual Low Voltage
PowerPath
TM
Switch Driver
PowerPath is a trademark of Linear Technology Corporation.
3.3V to 4-Cell NiMH Backup Switch
IN1
IN2
DIODE
TIMER
V
+
V
GG
SW
GND
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
GA1
SAB1
GB1
SENSE
+
SENSE
GA2
SAB2
GB2
LTC1473L
C
OUT
R
SENSE
0.04
1
F
1mH*
Si9926DY
BAT54C
1473 TA01
DCIN
3.3V
V
BAT1
4
NiMH
LOGIC
DRIVEN
3.3V OR
V
BAT1
C
TIMER
2000pF
Si9926DY
1
F
+
* COILCRAFT 1812LS-105XKBC
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
LTC1473L
2
ABSOLUTE AXI U
RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
(Note 1)
ELECTRICAL CHARACTERISTICS
ORDER PART
NUMBER
LTC1473LCGN
T
JMAX
= 125
C,
JA
= 150
C/ W
Consult factory for Military and Industrial grade parts.
SENSE
+
, SENSE
, V
+
.................................. 0.3 to 10V
GA1, GB1, GA2, GB2 ................................... 0.3 to 20V
SAB1, SAB2 ................................................. 0.3 to 10V
SW, V
GG
...................................................... 0.3 to 20V
IN1, IN2, DIODE ........................................... 0.3V to 7V
Junction Temperature (Note 2) ............................. 125
C
Operating Temperature Range ..................... 0
C to 70
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
GN PART MARKING
1473L
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
+
Supply Operating Range
2.8
9
V
I
S
Supply Current
V
IN1
= V
DIODE
= 5V, V
IN2
= 0V, V
SENSE
+
= V
SENSE
= 5V
q
100
200
A
V
GS
V
GS
Gate Supply Voltage
V
GS
= V
GG
V
+
, 2.8V
V
+
10V (Note 3)
q
7.5
8.5
9.5
V
V
+
UVLO
V
+
Undervoltage Lockout Threshold
V
+
Ramping Down
q
2.3
2.5
2.8
V
V
+
UVLOHYS
V
+
Undervoltage Lockout Hysteresis
70
mV
V
HIDIGIN
Digital Input Logic High
(Note 4)
q
2
0.9
V
V
LODIGIN
Digital Input Logic Low
(Note 4)
q
0.6
0.4
V
I
IN
Input Current
V
IN1
= V
IN2
= V
DIODE
= 5V
1
A
V
GS(ON)
Gate-to-Source ON Voltage
I
GA1
= I
GA2
= I
GB1
= I
GB2
= 1
A, V
SAB1
= V
SAB2
= 5V
q
4.5
5.6
7.0
V
V
GS(OFF)
Gate-to-Source OFF Voltage
I
GA1
= I
GA2
= I
GB1
= I
GB2
= 100
A, V
SAB1
= V
SAB2
= 5V
q
0
0.4
V
I
BSENSE
+
SENSE
+
Input Bias Current
V
SENSE
+
= V
SENSE
= 10V (Note 3)
q
2
4.5
10
A
V
SENSE
+
= V
SENSE
= 0V (Note 5)
q
300
175
75
A
I
BSENSE
SENSE
Input Bias Current
V
SENSE
+
= V
SENSE
= 10V (Note 3)
q
2
4.5
10
A
V
SENSE
+
= V
SENSE
= 0V (Note 5)
q
300
175
75
A
V
SENSE
Inrush Current Limit Sense Voltage
V
SENSE
= 10V (V
SENSE
+
V
SENSE
) (Note 3)
0.15
0.20
0.25
V
V
SENSE
= 0V (V
SENSE
+
V
SENSE
)
0.10
0.20
0.30
V
I
PDSAB
SAB1, SAB2 Pull-Down Current
V
IN1
= V
IN2
= V
DIODE
= 0.4V, V
+
= 10V (Note 3)
5
20
35
A
V
IN1
= V
IN2
= 0.4V, V
DIODE
= 2V
30
140
300
A
I
TIMER
Timer Source Current
V
IN1
= 0.4V, V
IN2
= V
DIODE
= 2V, V
TIMER
= 0V,
q
3
6
9
A
V
SENSE
+
V
SENSE
= 300mV
V
TIMER
Timer Latch Threshold Voltage
V
IN1
= 0.4V, V
IN2
= V
DIODE
= 2V
q
1.05
1.16
1.25
V
t
ON
Gate Drive Rise Time
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 6)
33
s
t
OFF
Gate Drive Fall Time
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 5V (Note 6)
2
s
t
D1
Gate Drive Turn-On Delay
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 6)
22
s
t
D2
Gate Drive Turn-Off Delay
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 5V (Note 6)
1
s
f
OVGG
V
GS
Regulator Operating Frequency
30
kHz
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. Test circuit, V
+
= 5V, unless otherwise specified.
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
LTC1473L
3
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: Some tests are performed under more stringent conditions to
ensure reliable operation over the entire supply voltage range.
ELECTRICAL CHARACTERISTICS
Note 4: Digital inputs include: IN1, IN2 and DIODE.
Note 5: I
S
increases by the same amount as I
BSENSE
+
+ I
BSENSE
when
their common mode falls below 5V.
Note 6: 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. Results are not tested, but guaranteed by design.
DC Supply Current
vs Supply Voltage
V
GS
Gate-to-Source ON Voltage
vs Temperature
DC Supply Current vs V
SENSE
V
SENSE
COMMON MODE (V)
0
SUPPLY CURRENT (
A)
1473 G03
5
6
7
10
1
2
3
4
8
9
400
350
300
250
200
150
100
50
0
V
+
= 5V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE
+
V
SENSE
= 0V
V
GS
Gate Supply Voltage
vs Temperature
TEMPERATURE (
C)
60 40 20
20
40
60
80
0
5.1
V
GS
GATE-TO-SOURCE ON VOLTAGE (V)
5.2
5.4
5.5
5.6
6.0
1473 G04
5.3
100
5.7
5.8
5.9
V
+
= V
SAB
= 10V
SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT (
A)
50
150
10
1473 G01
0
2
4
5
6
7
8
9
1
3
250
100
200
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
DIODE
= 5V
V
IN1
= V
IN2
= 0V
V
SENSE+
= V
SENSE
= V
+
TEMPERATURE (
C)
40
60
8.1
V
GS
GATE SUPPLY VOLTAGE (V)
8.2
8.4
8.5
8.6
0
9.0
1473 G06
8.3
20
20
40
60
80
100
8.7
8.8
8.9
V
+
= 5V
V
GS
= V
GG
V
+
DC Supply Current
vs Temperature
Undervoltage Lockout Threshold (V
+
)
vs Temperature
TEMPERATURE (
C)
50
50
SUPPLY CURRENT (
A)
60
80
90
100
0
140
1473 G02
70
25
25
50
75
100
110
120
130
V
+
= 5V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
TEMPERATURE (
C)
60
2.25
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
2.30
2.40
2.45
2.50
2.75
2.60
20
20
40
1473 G05
2.35
2.65
2.70
2.55
40
0
60
80
100
START-UP
THRESHOLD
SHUTDOWN
THRESHOLD
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
LTC1473L
4
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Turn-Off Delay and Gate Fall Time
vs Temperature
TEMPERATURE (
C)
40
60
0.4
TURN-OFF DELAY AND GATE FALL TIME (
s)
0.6
1.0
1.2
1.4
0
2.2
1473 G07
0.8
20
20
40
60
80
100
1.6
1.8
2.0
GATE FALL
TIME
V
+
= 5V
C
LOAD
= 1000pF
V
SAB
= 5V
TURN-OFF
DELAY
Rise and Fall Time
vs Gate Capacitive Loading
GATE CAPACITIVE LOADING (pF)
10
20
RISE AND FALL TIME (
s)
30
40
100
1000
10000
1473 G08
10
5
25
35
15
0
RISE TIME
V
SAB
= 0V
FALL TIME
V
SAB
= 5V
Turn-On Delay and Gate Rise Time
vs Temperature
TEMPERATURE (
C)
60
0
TURN-ON DELAY AND GATE RISE TIME (
s)
5
15
20
25
0
45
1473 G08
10
40 20
20
40
60
80
100
30
35
40
GATE RISE
TIME
V
+
= 5V
C
LOAD
= 1000pF
V
SAB
= 0V
TURN-ON
DELAY
SENSE Pin Source Current
(I
BSENSE
) vs V
SENSE
V
SENSE
(V)
SENSE PIN CURRENT (
A)
1473 G13
V
+
= 5V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE
+
V
SENSE
= 0V
0
300
250
200
150
100
50
0
50
1
2
3
4
5
6
7
8
9
10
Timer Source Current
vs Temperature
TEMPERATURE (
C)
50
4.0
TIMER SOURCE CURRENT (
A)
4.5
5.5
6.0
6.5
0
8.5
1473 G12
5.0
25
25
50
75
100
125
7.0
7.5
8.0
V
+
= 5V
TIMER = 0V
TEMPERATURE (
C)
50
1.10
TIMER LATCH THRESHOLD VOLTAGE (V)
1.12
1.16
1.18
1.20
0
1.28
1473 G11
1.14
25
25
50
75
100
125
1.22
1.24
1.26
V
+
= 5V
Timer Latch Threshold Voltage
vs Temperature
Logic Input Threshold Voltage
vs Temperature
TEMPERATURE (
C)
60
0
INPUT THRESHOLD VOLTAGE (V)
0.2
0.6
0.8
1.0
2.0
1.4
20
20
40
1473 G10
0.4
1.6
1.8
1.2
40
0
60
80
100
V
+
= 10V
V
+
= 2.8V
LTC1473L
5
PI FU CTIO S
U
U
U
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.
GB2, GA2 (Pins 9, 11): 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
valued 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
valued 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
SENSE
+
V
SENSE
) exceeds
0.2V.
IN1 (Pin 1): Logic Input of Gate Drivers GA1 and GB1. IN1
is disabled when IN2 is high or DIODE is low. During
2-diode mode, asserting IN1 disables the fault timer
function.
IN2 (Pin 2): Logic Input of Gate Drivers GA2 and GB2. IN2
is disabled when IN1 is high or DIODE is low. During
2-diode mode, asserting IN2 disables the fault timer
function.
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 di-
odes.
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): Power Supply. Bypass this pin with at least a
1
F 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 1
F.
Pin Function Table
NOMINAL (V)
ABSOLUTE MAX (V)
PIN
NAME
DESCRIPTION
MIN
TYP
MAX
MIN
MAX
1
IN1
Logic Input of Gate Drivers GA1 and GB1
0.4
1
2
0.3
7
2
IN2
Logic Input of Gate Drivers GA2 and GB2
0.4
1
2
0.3
7
3
DIODE
"2-Diode Mode" Logic Input
0.4
1
2
0.3
7
4
TIMER
Fault Timer Programs Time in Current Limit
1.16
0.3
5
5
V
+
Power Supply
2.8
9
0.3
10
6
V
GG
Gate Driver Supply
10.2
20
0.3
20
7
SW
Switch Node of Internal Boost Switching Regulator
0
20
0.3
20
8
GND
Ground
0
0
0
9
GB2
Switch Gate Driver for Switch B2
0
17
0.3
20
10
SAB2
Source Return of Switch 2
0
10
0.3
10
11
GA2
Switch Gate Driver for Switch A2
0
17
0.3
20
12
SENSE
Inrush Current Input, Low Side
0
10
0.3
10
13
SENSE
+
Inrush Current Input, High Side
0
10
0.3
10
14
GB1
Switch Gate Driver for Switch B1
0
17
0.3
20
15
SAB1
Source Return of Switch 1
0
10
0.3
10
16
GA1
Switch Gate Driver for Switch A1
0
17
0.3
20
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