LTC1473L
Dual Low Voltage
PowerPath
TM
Switch Driver
FEATURES
s
s
s
DESCRIPTIO
s
s
s
s
s
Power Path Management for Systems
with Multiple DC Sources
Switches and Isolates Sources from 3.3V to 10V
All N-Channel Switching to Reduce Power Losses
and System Cost
Built-In Step-Up Regulator for N-Channel Gate Drive
Capacitor Inrush and Short-Circuit Current Limited
User-Programmable Timer Prevents Overdissipation
During Current Limiting
Undervoltage Lockout Prevents Operation with Low
Inputs
Small Footprint: 16-Pin Narrow SSOP
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.
, 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
Portable Computers
Portable Instruments
Fault Tolerant Computers
Battery-Backup Systems
3.3V/5V Power Management
TYPICAL APPLICATIO
DCIN
3.3V
3.3V to 4-Cell NiMH Backup Switch
Si9926DY
BAT54C
LOGIC
DRIVEN
V
BAT1
4× NiMH
1
2
3
4
5
6
LTC1473L
IN1
IN2
DIODE
TIMER
V
+
V
GG
SW
GND
GA1
SAB1
GB1
SENSE
+
SENSE
–
GA2
SAB2
GB2
16
15
14
13
12
11
10
9
R
SENSE
0.04Ω
C
TIMER
2000pF
1mH*
1µF
1µF
7
8
* COILCRAFT 1812LS-105XKBC
Si9926DY
U
+
C
OUT
3.3V OR
V
BAT1
1473 TA01
U
U
1
LTC1473L
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
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
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
ORDER PART
NUMBER
LTC1473LCGN
GN PART MARKING
1473L
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Military and Industrial grade parts.
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.
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
GS
Regulator Operating Frequency
(Note 4)
(Note 4)
V
IN1
= V
IN2
= V
DIODE
= 5V
I
GA1
= I
GA2
= I
GB1
= I
GB2
= – 1µA, V
SAB1
= V
SAB2
= 5V
I
GA1
= I
GA2
= I
GB1
= I
GB2
= 100µA, V
SAB1
= V
SAB2
= 5V
V
SENSE +
= V
SENSE –
= 10V (Note 3)
V
SENSE +
= V
SENSE –
= 0V (Note 5)
V
SENSE +
= V
SENSE –
= 10V (Note 3)
V
SENSE +
= V
SENSE –
= 0V (Note 5)
V
SENSE –
= 10V (V
SENSE +
– V
SENSE –
) (Note 3)
V
SENSE –
= 0V (V
SENSE +
– V
SENSE –
)
V
IN1
= V
IN2
= V
DIODE
= 0.4V, V
+
= 10V (Note 3)
V
IN1
= V
IN2
= 0.4V, V
DIODE
= 2V
V
IN1
= 0.4V, V
IN2
= V
DIODE
= 2V, V
TIMER
= 0V,
V
SENSE +
– V
SENSE –
= 300mV
V
IN1
= 0.4V, V
IN2
= V
DIODE
= 2V
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 6)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 5V (Note 6)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 0V (Note 6)
C
GS
= 1000pF, V
SAB1
= V
SAB2
= 5V (Note 6)
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
IN1
= V
DIODE
= 5V, V
IN2
= 0V, V
SENSE +
= V
SENSE –
= 5V
V
GS
= V
GG
– V
+
, 2.8V
≤
V
+
≤
10V (Note 3)
V
+
Ramping Down
q
q
q
MIN
2.8
TYP
100
MAX
9
200
9.5
2.8
UNITS
V
µA
V
V
mV
V
7.5
2.3
2
8.5
2.5
70
0.9
0.6
0.4
±1
7.0
0.4
10
– 75
10
– 75
0.25
0.30
35
300
9
1.25
4.5
2
– 300
2
– 300
0.15
0.10
5
30
3
1.05
5.6
0
4.5
– 175
4.5
– 175
0.20
0.20
20
140
6
1.16
33
2
22
1
30
2
U
V
µA
V
V
µA
µA
µA
µA
V
V
µA
µA
µA
V
µs
µs
µs
µs
kHz
W
U
U
W W
W
LTC1473L
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:
Some tests are performed under more stringent conditions to
ensure reliable operation over the entire supply voltage range.
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.
TYPICAL PERFOR A CE CHARACTERISTICS
DC Supply Current
vs Supply Voltage
250
V
SENSE +
= V
SENSE –
= V
+
200
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
150
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
110
100
90
80
70
60
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
SUPPLY CURRENT (µA)
100
V
DIODE
= 5V
V
IN1
= V
IN2
= 0V
50
0
0
1
2
3
4
5
6
7
SUPPLY VOLTAGE (V)
1473 G01
V
GS
Gate-to-Source ON Voltage
vs Temperature
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
6.0
V
GS
GATE-TO-SOURCE ON VOLTAGE (V)
V
+
= V
SAB
= 10V
5.9
5.8
5.7
5.6
5.5
5.4
5.3
5.2
5.1
– 60 – 40 –20 0
20 40 60
TEMPERATURE (°C)
80 100
1473 G04
2.65
2.60
2.55
2.50
2.45
2.40
2.35
2.30
START-UP
THRESHOLD
V
GS
GATE SUPPLY VOLTAGE (V)
U W
8
9
10
DC Supply Current
vs Temperature
140
130
120
V
+
= 5V
400
350
300
250
200
150
100
50
0
DC Supply Current vs V
SENSE
V
+
= 5V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE+
– V
SENSE–
= 0V
50
– 50
– 25
25
50
0
TEMPERATURE (°C)
75
100
0
1
2 3 4 5 6 7 8
V
SENSE
COMMON MODE (V)
9
10
1473 G02
1473 G03
Undervoltage Lockout Threshold (V
+
)
vs Temperature
2.75
2.70
9.0
8.9
8.8
8.7
8.6
8.5
8.4
8.3
8.2
80
100
V
GS
Gate Supply Voltage
vs Temperature
V
+
= 5V
V
GS
= V
GG
– V
+
SHUTDOWN
THRESHOLD
2.25
– 60 –40 –20 0 20 40 60
TEMPERATURE (°C)
8.1
20 40 60
– 60 – 40 – 20 0
TEMPERATURE (°C)
80
100
1473 G05
1473 G06
3
LTC1473L
TYPICAL PERFOR A CE 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
+
= 5V
C
LOAD
= 1000pF
V
SAB
= 5V
GATE FALL
TIME
RISE AND FALL TIME (µs)
TURN-OFF
DELAY
0.4
20 40 60
–60 –40 – 20 0
TEMPERATURE (°C)
Logic Input Threshold Voltage
vs Temperature
2.0
1.8
TIMER LATCH THRESHOLD VOLTAGE (V)
INPUT THRESHOLD VOLTAGE (V)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
– 60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
V
+
= 2.8V
V
+
= 10V
Timer Source Current
vs Temperature
8.5
8.0
TIMER SOURCE CURRENT (µA)
V
+
= 5V
TIMER = 0V
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
80
100
1473 G07
Turn-On Delay and Gate Rise Time
vs Temperature
45
40
35
30
25
20
15
10
5
0
20 40 60
– 60 – 40 – 20 0
TEMPERATURE (°C)
80
100
TURN-ON
DELAY
V
+
= 5V
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
= 5V
10
100
1000
GATE CAPACITIVE LOADING (pF)
10000
1473 G08
1473 G08
Timer Latch Threshold Voltage
vs Temperature
1.28
1.26
1.24
1.22
1.20
1.18
1.16
1.14
1.12
1.10
– 50
– 25
25
50
75
0
TEMPERATURE (°C)
100
125
V
+
= 5V
1473 G10
1473 G11
SENSE Pin Source Current
(I
BSENSE
) vs V
SENSE
300
250
200
150
100
50
0
– 50
0
1
2
3
4 5 6
V
SENSE
(V)
7
8
9
10
V
+
= 5V
V
DIODE
= V
IN1
= 5V
V
IN2
= 0V
V
SENSE+
– V
SENSE–
= 0V
1473 G12
1473 G13
LTC1473L
PI FU CTIO S
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
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.
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.
NOMINAL (V)
TYP
MAX
1
2
1
2
1
2
1.16
2.8
9
10.2
20
0
20
0
0
17
0
10
0
17
0
10
0
10
0
17
0
10
0
17
MIN
0.4
0.4
0.4
ABSOLUTE MAX (V)
MIN
MAX
– 0.3
7
– 0.3
7
– 0.3
7
– 0.3
5
– 0.3
10
– 0.3
20
– 0.3
20
0
0
– 0.3
20
– 0.3
10
– 0.3
20
– 0.3
10
– 0.3
10
– 0.3
20
– 0.3
10
– 0.3
20
Pin Function Table
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
IN1
IN2
DIODE
TIMER
V
+
V
GG
SW
GND
GB2
SAB2
GA2
SENSE
–
SENSE
+
GB1
SAB1
GA1
DESCRIPTION
Logic Input of Gate Drivers GA1 and GB1
Logic Input of Gate Drivers GA2 and GB2
“2-Diode Mode” Logic Input
Fault Timer Programs Time in Current Limit
Power Supply
Gate Driver Supply
Switch Node of Internal Boost Switching Regulator
Ground
Switch Gate Driver for Switch B2
Source Return of Switch 2
Switch Gate Driver for Switch A2
Inrush Current Input, Low Side
Inrush Current Input, High Side
Switch Gate Driver for Switch B1
Source Return of Switch 1
Switch Gate Driver for Switch A1
U
U
U
5
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