FeaTures
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LTC4235
Dual 12V Ideal Diode-OR
and Single Hot Swap Controller
with Current Monitor
DescripTion
The
LTC
®
4235
offers ideal diode-OR and Hot Swap
TM
functions for two 12V power rails by controlling external
N-channel MOSFETs. MOSFETs acting as ideal diodes
replace two high power Schottky diodes and the associ-
ated heat sinks, saving power and board area. A Hot Swap
control MOSFET allows a board to be safely inserted and
removed from a live backplane by limiting inrush current.
The supply output is also protected against short-circuit
faults with a foldback current limit and circuit breaker.
The LTC4235 regulates the forward voltage drop across
the MOSFETs to ensure smooth current transfer from one
supply to the other without oscillation. The ideal diodes
turn on quickly to reduce the load voltage droop during
supply switchover. If the input supply fails or is shorted,
a fast turn-off minimizes reverse-current transients.
A current sense amplifier translates the voltage across the
sense resistor to a ground referenced signal. The LTC4235
allows turn-on/off control, and reports fault and power
good status for the supply.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Hot
Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of
their respective owners. Protected by U.S. Patents, including 7920013, 8022679.
Ideal Diode-OR and Inrush Current Control for
Redundant Supplies
Low Loss Replacement for Power Schottky Diodes
Enables Safe Board Insertion into a Live Backplane
9V to 14V Operation
Current Monitor Output
Controls N-Channel MOSFETs
Limits Peak Fault Current in ≤ 1µs
Adjustable Current Limit with Foldback
Adjustable Current Limit Fault Delay
0.5µs Ideal Diode Turn-On and Turn-Off Time
Smooth Switchover without Oscillation
Fault and Power Good Outputs
LTC4235-1: Latch Off After Fault
LTC4235-2: Automatic Retry After Fault
20-Pin 4mm x 5mm QFN Package
applicaTions
n
n
n
Redundant Power Supplies
High Availability Systems and Servers
Telecom and Network Infrastructure
Typical applicaTion
Ideal Diode-OR with Hot Swap Application
12V
0.1µF
12V
0.1µF
13.7k
2k
LTC4235
CPO1 IN1 DGATE1 CPO2
ON
IN2 DGATE2
REG
SiR158DP
IN2
SiR158DP
0.1µF
SENSE
+
SENSE
–
HGATE OUT
FAULT
PWRGD
IMON
EN
INTV
CC
0.1µF
GND
D2OFF
FTMR
0.1µF
4235 TA01a
Smooth Supply Switchover
0.003
SiR158DP
+
12V
7A
C
LOAD
IN1
1V/DIV
IN2
1V/DIV
I
IN1
2A/DIV
I
IN2
2A/DIV
200ms/DIV
4235 TA01b
IN1
ADC
For more information
www.linear.com/LTC4235
1
4235f
LTC4235
absoluTe MaxiMuM raTings
(Notes 1, 2)
Supply Voltages
IN1, IN2.................................................. –0.3V to 24V
INTV
CC
..................................................... –0.3V to 7V
REG ...........................SENSE
+
– 5V to SENSE
+
+ 0.3V
Input Voltages
ON, D2OFF,
EN
...................................... –0.3V to 24V
FTMR .....................................–0.3V to INTV
CC
+ 0.3V
SENSE
+
, SENSE
–
................................... –0.3V to 24V
Output Voltages
IMON ....................................................... –0.3V to 7V
FAULT, PWRGD
...................................... –0.3V to 24V
CPO1, CPO2 (Note 3) ............................. –0.3V to 35V
DGATE1, DGATE2 (Note 3) ..................... –0.3V to 35V
HGATE (Note 4) ..................................... –0.3V to 35V
OUT ....................................................... –0.3V to 24V
Average Currents
FAULT, PWRGD
....................................................5mA
INTV
CC
...............................................................10mA
Operating Ambient Temperature Range
LTC4235C ................................................ 0°C to 70°C
LTC4235I .............................................–40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
pin conFiguraTion
TOP VIEW
DGATE1
HGATE
CPO1
OUT
16
PWRGD
15
FAULT
21
14 ON
13 D2OFF
12 REG
11 IMON
7
DGATE2
8
CPO2
9 10
FTMR
EN
20 19 18 17
SENSE
–
1
SENSE
+
2
IN1 3
INTV
CC
4
GND 5
IN2 6
UFD PACKAGE
20-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W (NOTE 5)
EXPOSED PAD (PIN 21) PCB GND CONNECTION OPTIONAL
orDer inForMaTion
LEAD FREE FINISH
LTC4235CUFD-1#PBF
LTC4235CUFD-2#PBF
LTC4235IUFD-1#PBF
LTC4235IUFD-2#PBF
TAPE AND REEL
LTC4235CUFD-1#TRPBF
LTC4235CUFD-2#TRPBF
LTC4235IUFD-1#TRPBF
LTC4235IUFD-2#TRPBF
PART MARKING
42351
42352
42351
42352
PACKAGE DESCRIPTION
20-Lead (4mm x 5mm) Plastic QFN
20-Lead (4mm x 5mm) Plastic QFN
20-Lead (4mm x 5mm) Plastic QFN
20-Lead (4mm x 5mm) Plastic QFN
TEMPERATURE RANGE
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
4235f
For more information
www.linear.com/LTC4235
LTC4235
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted.
SYMBOL
Supplies
V
IN
I
IN
V
INTVCC
V
INTVCC(UVL)
Input Supply Range
Input Supply Current
Internal Regulator Voltage
Internal V
CC
Undervoltage Lockout
I = 0, –500µA
INTV
CC
Rising
l
l
l
l
l
elecTrical characTerisTics
PARAMETER
CONDITIONS
MIN
9
TYP
MAX
14
UNITS
V
mA
V
V
mV
2.7
4.5
2.1
30
5
2.2
60
4
5.5
2.3
90
∆V
INTVCC(HYST)
Internal V
CC
Undervoltage Lockout
Hysteresis
Ideal Diode Control
∆V
FWD(REG)
∆V
DGATE
I
CPO(UP)
I
DGATE(FPU)
I
DGATE(FPD)
I
DGATE2(DN)
t
ON(DGATE)
t
OFF(DGATE)
t
PLH(DGATE2)
∆V
SENSE(TH)
V
SENSE
+
(UVL)
Forward Regulation Voltage
(V
INn
– V
SENSE
+)
External N-Channel Gate Drive
(V
DGATEn
– V
INn
)
CPOn Pull-Up Current
DGATEn Fast Pull-Up Current
DGATEn Fast Pull-Down Current
DGATE2 Off Pull-Down Current
DGATEn Turn-On Delay
DGATEn Turn-Off Delay
D2OFF Low to DGATE2 High
Current Limit Sense Voltage Threshold
(V
SENSE
+ – V
SENSE
–)
SENSE
+
Undervoltage Lockout
OUT = 11V
OUT = 0V
SENSE
+
Rising
∆V
FWD
= 0.15V; I = 0, –1µA
CPO = IN = 12V
∆V
FWD
= 0.2V, ∆V
DGATE
= 0V, CPO = 17V
∆V
FWD
= –0.2V, ∆V
DGATE
= 5V
D2OFF = 2V, ∆V
DGATE2
= 2.5V
∆V
FWD
= 0.2V , C
DGATE
= 10nF
∆V
FWD
= –0.2V, C
DGATE
= 10nF
l
l
l
2
10
–50
15
12
–90
–1.5
1.5
28
14
–120
mV
V
µA
A
A
l
l
l
l
50
100
0.25
0.2
50
200
0.5
0.5
100
27.5
10.8
2
90
1.3
100
14
4.8
–13
4
350
10.8
240
1
20
40
20
150
20
µA
µs
µs
µs
mV
mV
V
mV
mA
µA
V
V
µA
mA
mA
V
mV
µs
µs
µs
µs
ms
µs
Hot Swap Control
l
l
l
l
22.5
5.8
1.8
10
0.3
10
10
3.6
–7
1
100
10.2
110
25
8.3
1.9
50
0.8
40
12
4.2
–10
2
200
10.5
170
0.5
10
20
10
∆V
SENSE
+
(HYST)
SENSE
+
Undervoltage Lockout
Hysteresis
I
SENSE
+
I
SENSE–
∆V
HGATE
∆V
HGATE(H)
I
HGATE(UP)
I
HGATE(DN)
I
HGATE(FPD)
V
OUT(PGTH)
∆V
OUT(PGHYST)
t
PHL(SENSE)
t
OFF(HGATE)
t
D(HGATE)
t
P(HGATE)
SENSE
+
Pin Current
SENSE
–
Pin Current
External N-Channel Gate Drive
(V
HGATE
– V
OUT
)
Gate High Threshold (V
HGATE
– V
OUT
)
External N-Channel Gate Pull-Up Current Gate Drive On, HGATE = 0V
External N-Channel Gate Pull-Down
Current
External N-Channel Gate Fast Pull-Down
Current
OUT Power Good Threshold
OUT Power Good Hysteresis
Sense Voltage (SENSE
+
– SENSE
–
)
High to HGATE Low
ON Low to HGATE Low
EN
High to HGATE Low
SENSE
+
Low to HGATE Low
ON High,
EN
Low to HGATE Turn-On
Delay
ON to HGATE Propagation Delay
ON = Step 0.8V to 2V
∆V
SENSE
= 200mV, C
HGATE
= 10nF
Gate Drive Off, OUT = 12V,
HGATE = OUT + 5V
Fast Turn-Off, OUT = 12V,
HGATE = OUT + 5V
OUT Rising
SENSE
+
= 12V
SENSE
–
= 12V
I = 0, –1µA
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
SENSE
+
UVLO
50
100
10
For more information
www.linear.com/LTC4235
3
4235f
LTC4235
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 12V, unless otherwise noted.
SYMBOL
Inputs
V
D2OFF(H,TH)
V
D2OFF(L,TH)
∆V
D2OFF(HYST)
V
ON(TH)
V
ON(RESET)
∆V
ON(HYST)
I
IN(LEAK)
V
EN(TH)
∆V
EN(HYST)
I
EN(UP)
V
FTMR(H)
V
FTMR(L)
I
FTMR(UP)
I
FTMR(DN)
D
RETRY
t
RST(ON)
Outputs
I
OUT
V
OL
V
OH
I
OH
I
PU
Current Monitor
∆V
REG
∆V
SENSE(FS)
V
IMON(OS)
G
IMON
V
IMON(MAX)
V
IMON(MIN)
R
IMON(OUT)
Floating Regulator Voltage
(V
SENSE
+ – V
REG
)
Input Sense Voltage Full Scale
(V
SENSE
+ – V
SENSE
–)
IMON Input Offset Voltage
IMON Voltage Gain
IMON Maximum Output Voltage
IMON Minimum Output Voltage
IMON Output Resistance
I
REG
= ±1µA
SENSE
+
= 12V
∆V
SENSE
= 0V
∆V
SENSE
= 20mV and 5mV
∆V
SENSE
= 70mV
∆V
SENSE
= 200µV
∆V
SENSE
= 200µV
l
l
l
l
l
l
l
elecTrical characTerisTics
PARAMETER
D2OFF Pin High Threshold
D2OFF Pin Low Threshold
D2OFF Pin Hysteresis
ON Pin Threshold Voltage
ON Pin Fault Reset Threshold Voltage
ON Pin Hysteresis
Input Leakage Current (ON, D2OFF)
EN
Pin Threshold Voltage
EN
Pin Hysteresis
EN
Pull-Up Current
FTMR Pin High Threshold
FTMR Pin Low Threshold
FTMR Pull-Up Current
FTMR Pull-Down Current
Auto-Retry Duty Cycle
ON Low to
FAULT
High
OUT Pin Current
Output Low Voltage (FAULT,
PWRGD)
Output High Voltage (FAULT,
PWRGD)
Input Leakage Current (FAULT,
PWRGD)
CONDITIONS
D2OFF Rising
D2OFF Falling
ON Rising
ON Falling
V = 5V
EN
Rising
EN
= 1V
l
l
l
l
l
l
l
l
l
l
l
l
MIN
1.21
1.19
10
1.21
0.57
40
1.185
60
–7
1.198
0.15
–80
1.3
0.07
TYP
1.235
1.215
20
1.235
0.6
80
0
1.235
110
–10
1.235
0.2
–100
2
0.15
20
MAX
1.26
1.24
30
1.26
0.63
120
±1
1.284
200
–13
1.272
0.25
–120
2.7
0.23
40
170
4
0.4
1.2
UNITS
V
V
mV
V
V
mV
µA
V
mV
µA
V
V
µA
µA
%
µs
µA
mA
V
V
V
FTMR = 1V, In Fault Mode
FTMR = 2V, No Faults
l
l
l
l
OUT = 11V, IN = 12V, ON = 2V
OUT = 13V, IN = 12V, ON = 2V
I = 1mA
I = 3mA
I = –1µA
V = 18V
l
l
l
l
l
l
l
30
100
2.5
0.15
0.4
INTV
CC
–1
–7
3.6
25
INTV
CC
– 0.5
0
–10
4.1
±1
–13
4.6
µA
µA
V
mV
Output Pull-Up Current (FAULT,
PWRGD)
V = 1.5V
±150
99
3.5
15
20
100
101
5.5
40
27
µV
V/V
V
mV
kΩ
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
All currents into device pins are positive; all currents out of
the device pins are negative. All voltages are referenced to GND unless
otherwise specified.
Note 3:
An internal clamp limits the DGATE and CPO pins to a minimum of
10V above and a diode below IN. Driving these pins to voltages beyond the
clamp may damage the device.
Note 4:
An internal clamp limits the HGATE pin to a minimum of 10V
above and a diode below OUT. Driving this pin to voltages beyond the
clamp may damage the device.
Note 5:
Thermal resistance is specified when the exposed pad is soldered
to a 3" x 5", four layer, FR4 board.
4235f
4
For more information
www.linear.com/LTC4235
LTC4235
Typical perForMance characTerisTics
IN Supply Current vs Voltage
3.5
3
2.5
I
SENSE
+ (mA)
I
IN
(mA)
2
1.5
1
0.5
0
0
3
6
9
V
IN
(V)
12
15
18
4235 G01
T
A
= 25°C, V
IN
= 12V, unless otherwise noted.
SENSE
+
Current vs Voltage
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
3
6
9
V
SENSE
+ (V)
12
15
18
4235 G02
OUT Current vs Voltage
3.5
3
2.5
I
OUT
(mA)
2
1.5
1
0.5
0
–0.5
0
3
6
12
9
V
OUT
(V)
15
18
4235 G03
V
SENSE
+ = V
IN
– 0.5V
V
IN
= 12V, V
SENSE
+ = 11.5V
V
OUT
= 0V
V
OUT
= 12V
Hot Swap Gate Voltage vs Current
14
12
10
∆V
HGATE
(V)
8
6
4
2
0
0
–2
–4
–6
I
HGATE
(µA)
–8
–10
–12
4235 G04
Hot Swap Gate Voltage vs IN
Voltage
14
V
OUT
= V
IN
12
10
8
∆V
HGATE
(V)
10
V
CPO
– V
IN
(V)
6
4
2
6
0
0
3
6
9
V
IN
(V)
12
15
18
4235 G05
CPO Voltage vs Current
V
OUT
= V
IN
V
IN
= 12V
12
8
4
–2
0
–20
–40
–60 –80 –100 –120 –140
I
CPO
(µA)
4235 G06
Diode Gate Voltage vs Current
12
10
8
∆V
DGATE
(V)
6
4
2
0
–2
0
–20
–40
–60 –80 –100 –120 –140
I
DGATE
(µA)
4235 G07
Diode Gate Voltage vs IN Voltage
14
V
SENSE
+ = V
IN
– 0.15V
OUTPUT LOW VOLTAGE (V)
0.6
0.5
0.4
0.3
0.2
0.1
0
FAULT, PWRGD
Output Low Voltage vs Current
V
SENSE
+ = V
IN
– 0.15V
12
V
IN
= 12V
∆V
DGATE
(V)
10
8
6
4
0
3
6
9
V
IN
(V)
12
15
18
4235 G08
0
1
2
3
CURRENT (mA)
4
5
4235 G09
For more information
www.linear.com/LTC4235
5
4235f
