LT3751
Capacitor Charger
Controller with Regulation
FEATURES
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DESCRIPTION
The LT
®
3751 is a high input voltage capable flyback con-
troller designed to rapidly charge a large capacitor to a
user-adjustable target voltage set by the transformer turns
ratio and three external resistors. An optional feedback pin
can be used to provide a low noise high-voltage regulated
output.
The LT3751 has an integrated rail-to-rail MOSFET gate
driver that allows for efficient operation down to 4.75V.
A low 106mV differential current sense threshold voltage
accurately limits the peak switch current. Added protec-
tion is achieved with user-selectable overvoltage and
undervoltage lockouts for both V
CC
and V
TRANS
. A typical
application can charge a 1000μF capacitor to 500V in less
than one second.
The CHARGE pin is used to initiate a new charge cycle and
provides ON/OFF control. The
DONE
pin indicates when the
capacitor has reached its programmed value and the part
has stopped charging. The
FAULT
pin indicates when the
LT3751 has shut down due to either V
CC
or V
TRANS
voltage
exceeding the user-programmed supply tolerances.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
6518733 and 6636021.
Charges Any Size Capacitor
Low Noise Output in Voltage Regulation Mode
Stable Operation Under a No-Load Condition
Integrated 2A MOSFET Gate Driver with Rail-to-Rail
Operation for V
CC
≤ 8V
Selectable 5.6V or 10.5V Internal Gate Drive
Voltage Clamp
User-Selectable Over/Undervoltage Detect
Easily Adjustable Output Voltage
Primary or Secondary Side Output Voltage Sense
Wide Input V
CC
Voltage Range (5V to 24V)
Available in a 20-Pin QFN 4mm
×
5mm
APPLICATIONS
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High Voltage Regulated Supply
High Voltage Capacitor Charger
Professional Photoflash Systems
Emergency Strobe
Security/Inventory Control Systems
Detonators
TYPICAL APPLICATION
DANGER HIGH VOLTAGE! OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY
V
TRANS
24V
T1
1:10
330μF
2
40.2k
RV
TRANS
RDCM
CHARGE
CLAMP
RV
OUT
V
CC
LT3751
HVGATE
LVGATE
CSP
CSN
FB
RBG
732Ω
3751 TA01a
D1
Regulation Mode Load Regulation
and Efficiency vs Load Current
500V
0 TO 150mA
500
90
10μF
×2
18.2k
40.2k
•
•
+
100μF
498
OUTPUT VOLTAGE (V)
84
EFFICIENCY (%)
OFF ON
V
CC
24V
0.47μF
496
78
TO
DONE
MICRO
FAULT
374k
UVLO1
V
TRANS
475k
OVLO1
374k
UVLO2
V
CC
475k
OVLO2
GND
10μF
V
CC
6mΩ
715k
494
72
492
OUTPUT VOLTAGE
EFFICIENCY
490
0
50
100
LOAD CURRENT (mA)
66
10nF
1.74k
60
150
3751 TA01b
3751f
1
LT3751
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
RV
TRANS
UVLO1
RDCM
16 RV
OUT
15 NC
21
14 RBG
13 HVGATE
12 LVGATE
11 V
CC
7
CLAMP
8
FB
9 10
CSN
CSP
NC
V
CC
, CHARGE, CLAMP ..............................................24V
DONE, FAULT
............................................................24V
LVGATE (Note 8) .......................................................24V
V
CC
– LVGATE..............................................................8V
HVGATE ................................................................Note 9
RBG, CSP CSN ............................................................2V
,
FB ...............................................................................5V
Current into
DONE
Pin ...........................................±1mA
Current into
FAULT
Pin ...........................................±1mA
Current into RV
TRANS
Pin .......................................±1mA
Current into RV
OUT
Pin.........................................±10mA
Current into RDCM Pin ........................................±10mA
Current into UVLO1 Pin..........................................±1mA
Current into UVLO2 Pin..........................................±1mA
Current into OVLO1 Pin..........................................±1mA
Current into OVLO2 Pin..........................................±1mA
Maximum Junction Temperature........................... 125°C
Operating Temperature Range (Note 2).. –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
20 19 18 17
OVLO1 1
UVLO2 2
OVLO2 3
FAULT
4
DONE
5
CHARGE 6
UFD PACKAGE
20-PIN (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE TIED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3751EUFD#PBF
LT3751IUFD#PBF
LEAD BASED FINISH
LT3751EUFD
LT3751IUFD
TAPE AND REEL
LT3751EUFD#TRPBF
LT3751IUFD#TRPBF
TAPE AND REEL
LT3751EUFD#TR
LT3751IUFD#TR
PART MARKING*
3751
3751
PART MARKING*
3751
3751
PACKAGE DESCRIPTION
20-Lead (4mm
×
5mm) Plastic QFN
20-Lead (4mm
×
5mm) Plastic QFN
PACKAGE DESCRIPTION
20-Lead (4mm
×
5mm) Plastic QFN
20-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
3751f
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LT3751
ELECTRICAL CHARACTERISTICS
PARAMETER
V
CC
Voltage
RV
TRANS
Voltage
V
CC
Quiescent Current
RV
TRANS
, R
DCM
Quiescent Current
(Note 3)
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0.3V
(Note 4)
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0.3V
(Note 4)
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0.3V
Measured at 1mA into Pin, CHARGE = 0V
Measured at 1mA into Pin, CHARGE = 0V
CHARGE = 24V
CHARGE = 5V
CHARGE = 0V
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The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
CC
= CHARGE = 5V, CLAMP = 0V, unless otherwise noted. Individual 25kΩ
resistors tied from 5V V
TRANS
supply to RV
TRANS
, RV
OUT
, RDCM, unless otherwise noted. (Note 2)
CONDITIONS
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MIN
4.75
4.75
TYP
MAX
24
65
UNITS
V
V
mA
μA
μA
μA
μA
μA
V
V
μA
μA
μA
V
V
μs
μs
V
mV
5.5
0
35
40
0
47
0
55
60
425
60
8
1
45
1
52
1
RV
OUT
Quiescent Current
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UVLO1, UVLO2, OVLO1, OVLO2 Clamp Voltage
RV
TRANS
, RV
OUT
, R
DCM
Clamp Voltage
CHARGE Pin Current
1
1.5
0.3
20
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CHARGE Minimum Enable Voltage
CHARGE Maximum Disable Voltage
Minimum CHARGE Pin Low Time
One-Shot Clock Period
V
OUT
Comparator Trip Voltage
V
OUT
Comparator Overdrive
Measured RBG at Pin
2μs Pulse Width,
RV
TRANS
, RV
OUT
= 25kΩ
R
BG
= 0.83kΩ
Measured as V
DRAIN
– V
TRANS
, R
DCM
= 25kΩ (Note 5)
FB Pin = 0V
FB Pin = 1.3V
Current Sourced from FB Pin, Measured at FB Pin Voltage
(Note 6)
I
VCC
≤ 1μA
32
0.955
38
0.98
20
44
1.005
40
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DCM Comparator Trip Voltage
Current Limit Comparator Trip Voltage
FB Pin Bias Current
FB Pin Voltage
FB Pin Charge Mode Threshold
FB Pin Charge Mode Hysteresis
FB Pin Overvoltage Mode Threshold
FB Pin Overvoltage Hysteresis
DONE
Output Signal High
DONE
Output Signal Low
DONE
Leakage Current
FAULT
Output Signal High
FAULT
Output Signal Low
FAULT
Leakage Current
UVLO1 Pin Current
UVLO2 Pin Current
OVLO1 Pin Current
OVLO2 Pin Current
350
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600
106
11
64
1.22
1.16
55
1.34
60
5
40
5
5
40
5
900
112
15
300
1.25
1.2
1.38
mV
mV
mV
nA
V
V
mV
V
mV
V
100
7
1.19
1.12
1.29
100kΩ to 5V
100kΩ to 5V
DONE
= 5V
100kΩ to 5V
100kΩ to 5V
FAULT
= 5V
UVLO1 Pin Voltage = 1.24V
UVLO2 Pin Voltage = 1.24V
OVLO1 Pin Voltage = 1.24V
OVLO2 Pin Voltage = 1.24V
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200
200
200
200
51.5
51.5
51.5
51.5
mV
nA
V
mV
nA
μA
μA
μA
μA
48.5
48.5
48.5
48.5
50
50
50
50
3751f
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LT3751
ELECTRICAL CHARACTERISTICS
PARAMETER
UVLO1 Threshold
UVLO2 Threshold
OVLO1 Threshold
OVLO2 Threshold
Gate Minimum High Time
Gate Peak Pull-Up Current
Gate Peak Pull-Down Current
Gate Rise Time
V
CC
= 5V, LVGATE Active
V
CC
= 12V, LVGATE Inactive
V
CC
= 5V, LVGATE Active
V
CC
= 12V, LVGATE Inactive
10%
→
90%, C
GATE
= 3.3nF (Note 8)
V
CC
= 5V, LVGATE Active
V
CC
= 12V, LVGATE Inactive
90%
→
10%, C
GATE
= 3.3nF (Note 8)
V
CC
= 5V, LVGATE Active
V
CC
= 12V, LVGATE Inactive
(Note 8):
V
CC
= 5V, LVGATE Active
V
CC
= 12V, LVGATE Inactive
V
CC
= 12V, LVGATE Inactive, CLAMP Pin = 5V
V
CC
= 24V, LVGATE Inactive
C
GATE
= 3.3nF
25mV Overdrive Applied to CSP Pin
4.98
10
5
10
CONDITIONS
Measured from Pin to GND
Measured from Pin to GND
Measured from Pin to GND
Measured from Pin to GND
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The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
CC
= CHARGE = 5V, CLAMP = 0V, unless otherwise noted. Individual 25kΩ
resistors tied from 5V V
TRANS
supply to RV
TRANS
, RV
OUT
, RDCM, unless otherwise noted. (Note 2)
MIN
1.195
1.195
1.195
1.195
TYP
1.225
1.225
1.225
1.225
0.7
2.0
1.5
1.2
1.5
40
55
30
30
5
10.5
5.6
10.5
180
500
1.6
MAX
1.255
1.255
1.255
1.255
UNITS
V
V
V
V
μs
A
A
A
A
ns
ns
ns
ns
V
V
V
V
ns
mV
V
Gate Fall Time
Gate High Voltage
11.5
6.5
11.5
Gate Turn-Off Propagation Delay
Gate Voltage Overshoot
CLAMP Pin Threshold
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:
The LT3751E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design
characterization and correlation with statistical process controls. The
LT3751I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
A 60V internal clamp is connected to RV
TRANS
, RDCM, RV
OUT
,
UVLO1, UVLO2, OVLO1 and OVLO2. Resistors should be used such that
the pin currents do not exceed the Absolute Maximum Ratings.
Note 4:
Currents will increase as pin voltages are taken higher than the
internal clamp voltage.
Note 5:
Refer to Block Diagram for V
TRANS
and V
DRAIN
definitions.
Note 6:
Low noise regulation of the output voltage requires a resistive
voltage divider from output voltage to FB pin. FB pin should not be
grounded in this configuration. Refer to the Typical Application diagram for
proper FB pin configuration.
Note 7:
The feedback pin has built-in hysteresis that defines the boundary
between charge-only mode and low noise regulation mode.
Note 8:
LVGATE should be used in parallel with HVGATE when V
CC
is less
than or equal to 8V (LVGATE active). When not in use, LVGATE should be
tied to V
CC
(LVGATE inactive).
Note 9:
Do not apply a positive or negative voltage or current source to
HVGATE, otherwise permanent damage may occur.
3751f
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LT3751
TYPICAL PERFORMANCE CHARACTERISTICS
V
CC
Pin Current vs Pin Voltage
7
6
PIN CURRENT (mA)
5
4
3
2
1
0
–40°C
25°C
125°C
0
4
12
8
16
PIN VOLTAGE (V)
20
24
3751 G01
V
TRANS
Supply Current
vs Supply Voltage
150
RV
TRANS
, RV
OUT
, R
DCM
= 25k
V
CC
, CHARGE = 5V
145
I
VTRANS
= I
RVTRANS
+ I
RVOUT
+ I
RDCM
I
VTRANS
CURRENT (μA)
140
135
130
125
120
115
110
0
10
20
40
30
PIN VOLTAGE (V)
50
–40°C
25°C
125°C
60
3751 G02
CHARGE Pin Current
vs Pin Voltage
450
400
350
CURRENT (μA)
300
250
200
150
100
50
0
0
4
8
16
12
PIN VOLTAGE (V)
–40°C
25°C
125°C
20
24
3751 G03
CHARGE Pin Minimum Enable
Voltage vs Temperature
1.3
1.2
CHARGE PIN VOLTAGE (V)
CHARGE PIN VOLTAGE (V)
1.1
1.0
0.9
0.8
0.7
0.6
–40 –20
V
CC
= 5V
V
CC
= 12V
V
CC
= 24V
0
20 40 60 80
TEMPERATURE (°C)
100 120
3751 G04
CHARGE Pin Maximum Disable
Voltage vs Temperature
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
–40 –20
V
CC
= 5V
V
CC
= 12V
V
CC
= 24V
PIN LOW VOLTAGE (mV)
400
350
DONE, FAULT
Pin Voltage Low
vs Temperature
1mA SINK
300
250
200
150
100
100μA SINK
50
10μA SINK
0
20 40 60 80
TEMPERATURE (°C)
100 120
3751 G05
0
–40 –20
0
20 40 60 80
TEMPERATURE (°C)
100 120
3751 G06
V
OUT
Comparator Trip Voltage
vs Temperature
30.8
30.4
30.0
29.6
29.2
28.8
V
TRANS
= 5V
V
TRANS
= 12V
V
TRANS
= 24V
0
UVLO1 PIN VOLTAGE (V)
V
DRAIN
VOLTAGE (V)
RV
TRANS
, RV
OUT
= 25.5k (R
TOL
= 1%)
1.236
1.234
UVLO1 Trip Voltage
vs Temperature
50.5
50.4
UVLO1 PIN CURRENT (μA)
50.3
50.2
50.1
50.0
49.9
49.8
UVLO1 Trip Current
vs Temperature
1.232
1.230
1.228
1.226
V
CC
= 5V
V
CC
= 12V
V
CC
= 24V
0
20 40 60 80
TEMPERATURE (°C)
100 120
3751 G08
28.4
–40 –20
V
TRANS
= 48V
V
TRANS
= 72V
100 120
3751 G07
V
CC
= 5V
V
CC
= 12V
V
CC
= 24V
0
20 40 60 80
TEMPERATURE (°C)
100 120
3751 G09
20 40 60 80
TEMPERATURE (°C)
1.224
–40 –20
49.7
–40 –20
3751f
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