LTC1645
Dual-Channel Hot Swap
Controller/Power Sequencer
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
s
Allows Safe Board Insertion and Removal from a
Live Backplane
Programmable Power Supply Sequencing
Programmable Electronic Circuit Breaker
User-Programmable Supply Voltage Power-Up and
Power-Down Rate
High Side Drivers for External N-Channel FETs
Controls Supply Voltages from 1.2V to 12V
Ensures Proper Power-Up Behavior
Undervoltage Lockout
Glitch Filter Protects Against Spurious RESET Signals
APPLICATIO S
s
s
s
Hot Board Insertion
Power Supply Sequencing
Electronic Circuit Breaker
The LTC
®
1645 is a 2-channel Hot Swap
TM
controller that
allows a board to be safely inserted and removed from a
live backplane. Using external N-channel pass transistors,
the supply voltages can be ramped at a programmable
rate. Two high side switch drivers control the N-channel
gates for supply voltages ranging from 1.2V to 12V. The
two channels can be set to ramp up and down separately,
or they can be programmed to rise and fall simultaneously,
ensuring power supply tracking at the two outputs.
Programmable electronic circuit breakers protect against
shorts at either output. The RESET output can be used to
generate a system reset when a supply voltage falls below
a user-programmed voltage. An additional spare com-
parator is available for monitoring a second supply
voltage.
The LTC1645 is available in the 8- and 14-pin SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN2
5V and 3.3V Hot Swap
0.005Ω* IRF7413
5V and 3.3V Hot Swap Waveforms
+
V
OUT2
3.3V
5A
C
LOAD2
V
OUT1
5V
5A
C
LOAD1
0.005Ω*
V
IN1
IRF7413
ON
5V/DIV
+
10Ω
10Ω
0.01µF
25V
7
8
5
10k
GND
4
1645 TA01
GATEn
10V/DIV
CONNECTOR 2
CONNECTOR 1
0.01µF
25V
1
2
3
6
V
OUT2
5V/DIV
SENSE1 GATE1
V
CC1
ON
V
CC2
SENSE2 GATE2
LTC1645
(8-LEAD)
V
OUT1
5V/DIV
ON
GND
BACKPLANE PLUG-IN CARD
*LRF1206-01-R005-J (IRC)
U
U
U
1
LTC1645
ABSOLUTE
AXI U
RATI GS
Supply Voltage (V
CC1
, V
CC2
) ................................. 13.2V
Input Voltage
FB, ON, COMP
+
..................... – 0.3V to (V
CC1
+ 0.3V)
TIMER ................................................. – 0.3V to 2.5V
SENSE1 ..................... (V
CC1
– 0.7V) to (V
CC1
+ 0.3V)
SENSE2 ...................... (V
CC1
– 0.7V) to (V
CC2
+ 0.3V)
Output Voltage
RESET, COMPOUT, FAULT .....................– 0.3V to 16V
GATE1, GATE2 ................. Internally Limited (Note 3)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
CC2
1
SENSE2 2
GATE2 3
GND 4
8
7
6
5
V
CC1
SENSE1
GATE1
ON
ORDER PART
NUMBER
LTC1645CS8
LTC1645IS8
S8 PART MARKING
1645
1645I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
2.375V
≤
V
CC1
≤
12V, 1.2V
≤
V
CC2
≤
12V unless otherwise noted (Note 2).
SYMBOL
I
CC1
I
CC2
V
LKO1
V
LKO2
V
LKHn
V
FB
∆V
FB
V
FBHST
V
COMP
∆V
COMP
V
COMPHST
PARAMETER
V
CC1
Supply Current
V
CC2
Supply Current
V
CC1
Undervoltage Lockout
V
CC2
Undervoltage Lockout
V
CCn
Undervoltage Lockout Hysteresis
FB Pin Voltage Threshold
FB Pin Threshold Line Regulation
FB Pin Voltage Threshold Hysteresis
COMP
+
Pin Voltage Threshold
COMP
+
Pin Threshold Line Regulation
COMP
+
Pin Voltage Threshold Hysteresis
High to Low
High to Low, V
CC1
= 2.375V to 12V
q
q
CONDITIONS
ON = V
CC1
= 5V, V
CC2
= 3.3V
ON = V
CC1
= 5V, V
CC2
= 3.3V
High to Low
High to Low
High to Low
High to Low, V
CC1
= 2.375V to 12V
q
q
q
q
DC Characteristics
1.1
0.28
2.16
1.06
1.226
2.23
1.12
25
q
q
2
U
U
W
W W
U
W
(Note 1)
Output Current
GATE1, GATE2 ...............................................
±20mA
Operating Temperature Range
LTC1645C ............................................... 0°C to 70°C
LTC1645I ............................................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
V
CC2
1
SENSE2 2
GATE2 3
FAULT 4
RESET 5
FB 6
GND 7
14 V
CC1
13 SENSE1
12 GATE1
11 TIMER
10 ON
9
8
COMPOUT
COMP
+
ORDER PART
NUMBER
LTC1645CS
LTC1645IS
S PACKAGE
14-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/ W
MIN
TYP
MAX
2.0
0.4
2.3
1.18
1.250
4
1.250
4
UNITS
mA
mA
V
V
mV
V
mV
mV
V
mV
mV
1.238
1
5
1.226
1.238
1
5
LTC1645
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
2.375V
≤
V
CC1
≤
12V, 1.2V
≤
V
CC2
≤
12V unless otherwise noted (Note 2).
SYMBOL PARAMETER
V
TM
∆V
TM
I
TM
V
CB1
V
CB2
t
CBDn
I
CP
TIMER Pin Voltage Threshold
TIMER Pin Threshold Line Regulation
TIMER Pin Current
Circuit Breaker Trip Voltage 1
Circuit Breaker Trip Voltage 2
Circuit Breaker Trip Delay
GATEn Pin Output Current
V
CC1
= 2.375V to 12V
Timer On, V
TIMER
= 0.6V, V
CC1
= 5V
Timer Off, V
TIMER
= 1.5V
V
CB1
= (V
CC1
– V
SENSE1
)
V
CB2
= (V
CC2
– V
SENSE2
)
V
CBn
= (V
CCn
– V
SENSEn
) > 60mV
ON = 2.2V, V
GATEn
= V
CCn
, V
CC1
= 5V, V
CC2
= 3.3V
ON = 0.7V, V
GATEn
= V
CCn
, V
CC1
= 5V, V
CC2
= 3.3V
ON = 0.3V, V
GATEn
= V
CCn
, V
CC1
= 5V, V
CC2
= 3.3V
∆V
GATEn
= (V
GATEn
– V
CCn
)
Low to High
High to Low, Fast Pull-Down Engaged
Low to High, GATE1 Turns On
High to Low, GATE1 Turns Off
Low to High, GATE2 Turns On
High to Low, GATE2 Turns Off
V
CC1
= 5V, V
CC2
= 3.3V
RESET, FAULT, COMPOUT, I
OUT
= 1.6mA, V
CC1
= 5V
q
q
q
q
q
q
q
q
q
CONDITIONS
q
q
q
q
q
MIN
1.212
– 2.3
46
46
– 12.5
30
4.5
0.375
0.35
0.8
0.775
2
1.975
TYP
1.230
1
–2
12
50
50
1.5
– 10
40
12
0.4
0.375
0.825
0.8
2.025
2
25
±0.01
0.16
MAX
1.248
9
– 1.7
56
56
– 7.5
50
16
0.425
0.4
0.85
0.825
2.050
2.025
±2
0.4
UNITS
V
mV
µA
mA
mV
mV
µs
µA
µA
mA
V
V
V
V
V
V
V
mV
µA
V
∆V
GATEn
V
ONFPD
V
ON1
V
ON2
V
ONHYST
I
ON
V
OL
External N-Channel Gate Drive
ON Pin Fast Pull-Down Threshold
ON Pin Threshold #1
ON Pin Threshold #2
ON Pin Hysteresis
ON Pin Input Current
Output Low Voltage
q
q
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 3:
An internal zener on the GATEn pins clamps the charge pump
voltage to a typical maximum operating voltage of 22V. External overdrive
of a GATE pin (for example, from capacitive coupling of V
CCn
glitches)
beyond the internal zener voltage may damage the device. If a lower
GATEn pin clamp voltage is desired, use an external zener diode.
TYPICAL PERFOR A CE CHARACTERISTICS
V
CC1
Supply Current vs Voltage
3.0
2.5
2.0
T
A
= 25°C
I
CC1
(mA)
I
CC2
(mA)
2.0
V
CC1
= 2.375V
1.5
1.0
V
CC1
= 12V
0.5
0
1
2
3
4
5
7 8
V
CC2
(V)
6
9 10 11 12
1645 G02
I
CCn
(mA)
1.5
V
CC2
= 1.5V
1.0
V
CC2
= 12V
0.5
0
2
3
4
5
6 7 8
V
CC1
(V)
9
10 11 12
1645 G01
U W
V
CC2
Supply Current vs Voltage
3.5
3.0
2.5
T
A
= 25°C
Supply Current vs Temperature
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–40 –20
I
CC2
V
CC1
= 5V
V
CC2
= 3.3V
I
CC1
40
20
60
0
TEMPERATURE (°C)
80
100
1645 G03
3
LTC1645
TYPICAL PERFOR A CE CHARACTERISTICS
GATE Voltage vs Supply Voltage
25
16.0
T
A
= 25°C
15.4
GLITCH FILTER TIME (µs)
20
GATEn (V)
GATEn (V)
15
10
5
0
2
3
4
5
6 7 8 9
HIGHEST V
CC
(V)
RESET, FAULT, COMPOUT Output
Voltage vs Temperature
450
400
SINK CURRENT = 3mA
V
CC1
= 5V
800
700
OUTPUT VOLTAGE (mV)
FAST PULL-DOWN CURRENT (mA)
OUTPUT VOLTAGE (mV)
350
300
250
200
150
SINK CURRENT = 1.6mA
100
50
0
–40
–20
0
20
40
60
TEMPERATURE (°C)
80
100
4
U W
1645 G04
1645 G07
GATE Voltage vs Temperature
V
CC1
= 5V
15.8 V
CC2
= 3.3V
15.6
100
90
80
70
60
50
40
30
20
10
0
40
20
0
60
TEMPERATURE (°C)
80
100
Glitch Filter Time
vs Feedback Transient
T
A
= 25°C
15.2
15.0
14.8
14.6
14.4
14.2
10 11 12
14.0
–40 – 20
0
40
80 120 160 200 240
FEEDBACK TRANSIENT (mV)
280
1645 G05
1645 G06
RESET, FAULT, COMPOUT Output
Voltage vs V
CC1
T
A
= 25°C
18
Fast Pull-Down Current vs V
CC1
T
A
= 25°C
17 V
CC2
= 1.5V
16
15
14
13
12
11
10
9
600
500
SINK CURRENT = 3mA
400
300
200
100
0
2
3
4
5
6 7 8
V
CC1
(V)
9
10 11 12
1645 G08
SINK CURRENT = 1.6mA
8
2
3
4
5
6 7 8
V
CC1
(V)
9
10 11 12
1645 G09
LTC1645
PI FU CTIO S
V
CC2
(Pin 1/Pin 1):
Positive Supply Input. V
CC2
can range
from 1.2V to 12V for normal operation. I
CC2
is typically
0.2mA. An undervoltage lockout circuit disables the
LTC1645 whenever the voltage at V
CC2
is less than 1.12V.
SENSE2 (Pin 2/Pin 2):
V
CC2
Circuit Breaker Set Pin. With
a sense resistor placed in the supply path between V
CC2
and SENSE2, the circuit breaker trips when the voltage
across the resistor exceeds 50mV for more than 1.5µs. If
the circuit breaker trip current is set to twice the normal
operating current, only 25mV is dropped across the sense
resistor during normal operation. To disable the circuit
breaker, short V
CC2
and SENSE2 together.
GATE2 (Pin 3/Pin 3):
Channel 2 High Side Gate Drive.
Connect to the gate of an external N-channel MOSFET. An
internal charge pump guarantees at least 4.5V of gate
drive. The charge pump is powered by the higher of V
CC1
and V
CC2
. When the ON pin exceeds 2V, GATE2 is turned
on by connecting a 10µA current source from the charge
pump output to the GATE2 pin and the voltage starts to
ramp up with a slope dv/dt = 10µA/C
GATE2
. While the ON
pin is below 2V but above 0.4V, a 40µA current source
pulls GATE2 toward ground. If the ON pin is below 0.4V,
the circuit breaker trips or the undervoltage lockout circuit
trips, the GATE2 pin is immediately pulled to ground with
a 12mA (typ) current source.
FAULT (Pin 4/NA):
Circuit Breaker Fault. FAULT is an
open-drain output that pulls low when the circuit breaker
function trips. The circuit breaker is reset by pulling the ON
pin below 0.4V. An external pull-up is required to generate
a logic high at the FAULT pin. When the ON pin is low,
FAULT will release.
The circuit breaker can be programmed to automatically
reset by connecting the FAULT pin to the ON pin. In this
circuit configuration, if a logic device is driving the ON pin,
use a series resistor between the logic output and the ON
pin to prevent large currents from flowing.
RESET (Pin 5/NA):
Open-Drain RESET Output. The RESET
pin is pulled low when the voltage at the FB pin goes below
1.238V or V
CC1
is below the undervoltage lockout thresh-
old. The RESET pin goes high one timing cycle after the
voltage at the FB pin goes above the FB pin threshold. The
ON pin must remain above 0.8V during this timing cycle.
U
U
U
(14-Lead Package/8-Lead Package)
An external pull-up is required to generate a logic high at
the RESET pin.
FB (Pin 6/NA):
RESET Comparator Input. The FB pin is
used to monitor the output supply voltage with an external
resistive divider. When the voltage on the FB pin is lower
than 1.238V, the RESET pin is pulled low. A glitch filter on
the FB pin prevents fast transients from forcing RESET
low. When the voltage on the FB pin rises above the trip
point, the RESET pin goes high after one timing cycle.
GND (Pin 7/Pin 4):
Ground. Connect to a ground plane for
optimum performance.
COMP
+
(Pin 8/NA):
Spare Comparator Noninverting In-
put. When the voltage on COMP
+
is lower than 1.238V,
COMPOUT pulls low.
COMPOUT (Pin 9/NA):
Open-Drain Spare Comparator
Output. COMPOUT pulls low when the voltage on COMP
+
is below 1.238V or V
CC1
is below the undervoltage lockout
threshold. An external pull-up is required to generate a
logic high at the COMPOUT pin.
ON (Pin 10/Pin 5):
Analog Control Input. If the ON pin
voltage is below 0.4V, both GATE1 and GATE2 are imme-
diately pulled to ground. While the voltage is between 0.4V
and 0.8V, both GATE1 and GATE2 are each pulled to
ground with a 40µA current source. While the voltage is
between 0.8V and 2V, the GATE1 pull-up is turned on after
one timing cycle, but GATE2 continues to be pulled to
ground with a 40µA current source. When the voltage
exceeds 2V, both the GATE1 and GATE2 pull-ups are
turned on one timing cycle after the voltage exceeds 0.8V.
The ON pin is also used to reset the electronic circuit
breaker. If the ON pin is brought below and then above
0.4V following the trip of the circuit breaker, the circuit
breaker resets, and a normal power-up sequence occurs.
TIMER: (Pin 11/NA):
System Timing Pin. The TIMER pin
requires an external capacitor to ground to generate a
timing delay. The pin is used to set the delay before the
RESET pin goes high after the output supply voltage is
good as sensed by the FB pin. It is also used to set the delay
between the ON pin exceeding 0.8V and the GATE1 and
GATE2 pins turning on (GATE2 turns on only if the ON pin
exceeds 2V).
5
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