LT3750
Capacitor Charger
Controller
FEATURES
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DESCRIPTIO
Charges Any Size Capacitor
Easily Adjustable Output Voltage
Drives High Current NMOS FETs
Primary-Side Sense—No Output Voltage Divider
Necessary
Wide Input Range: 3V to 24V
Drives Gate to V
CC
– 2V
Available in 10-Lead MS Package
APPLICATIO S
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Emergency Warning Beacons
Professional Photoflash Systems
Security/Inventory Control Systems
High Voltage Power Supply
Electric Fences
Detonators
The LT
®
3750 is a flyback converter designed to rapidly
charge large capacitors to a user-adjustable target volt-
age. A patented boundary mode control scheme* mini-
mizes transition losses and reduces transformer size. The
transformer turns ratio and two external resistors easily
adjust the output voltage.* A low 78mV current sense
accurately limits peak switch current and also helps to
maximize efficiency. With a wide input voltage range, the
LT3750 can operate from a variety of power sources. A
typical application can charge a 100µF capacitor to 300V
in less than 300ms.
The CHARGE pin gives full control of the LT3750 to the
user. The DONE pin indicates when the capacitor has
reached its programmed value and the part has stopped
charging.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents, including 6518733, 6636021.
TYPICAL APPLICATIO
V
TRANS
10µF
300V, 6A Capacitor Charger
T1
1:10
56µF
×2
D1
V
OUT
300V
•
•
+
100µF
300
V
TRANS
= 18V
250
V
TRANS
= 6V
200
V
OUT
(V)
150
100
V
CC
12V
10µF
100k
V
CC
DONE
V
TRANS
RV
OUT
RDCM
LT3750
GATE
SOURCE
60.4k
43k
OFF ON
CHARGE
M1
GND
RBG
12mΩ
2.49k
100pF
3750 TA01a
50
0
0
0.1
0.2
0.3
TIME (SECONDS)
0.4
0.5
3750 TA03c
U
6A Charge Time
V
TRANS
= 12V
3750fa
U
U
1
LT3750
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
TRANS
DONE
CHARGE
V
CC
GND
1
2
3
4
5
10
9
8
7
6
RBG
RV
OUT
RDCM
GATE
SOURCE
V
CC
, V
TRANS
, GATE, DONE, CHARGE ...................... 24V
RBG ....................................................................... 1.5V
SOURCE ................................................................... 1V
Current into RDCM Pin ........................................
±1mA
Current into RV
OUT
Pin ........................................
±1mA
Current into DONE Pin .........................................
±1mA
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/ W
ORDER PART NUMBER
LT3750EMS
MS PART MARKING
LTBQD
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
CC
= V
TRANS
= 5V unless otherwise specified.
PARAMETER
Minimum V
CC
Minimum V
TRANS
V
CC
Quiescent Current
V
TRANS
Quiescent Current
CHARGE Pin Current
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0V
Not Switching, CHARGE = 5V
Not Switching, CHARGE = 0V
CHARGE = 24V
CHARGE = 5V
CHARGE = 0V
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
●
MIN
TYP
2.8
2.5
1.6
140
24
19
0.87
MAX
3
3
2.5
1
250
1
UNITS
V
V
mA
µA
µA
µA
µA
µA
µA
V
V
µs
V
mV
nA
mV
mV
V
V
µA
µs
ns
CHARGE Pin Enable Voltage
CHARGE Pin Disable Voltage
Minimum CHARGE Pin Low Time
V
OUT
Comparator Trip Voltage
V
OUT
Comparator Overdrive
RBG Pin Bias Current
DCM Comparator Trip Voltage
Current Limit Comparator Trip Voltage
DONE Output Signal High
DONE Output Signal Low
DONE Pin Leakage Current
NMOS Minimum On Time
GATE Rise Time
GATE High Voltage
GATE Turn Off Propagation Delay
C
GATE
= 1nF, V
CC
= 5V
C
GATE
= 1nF, V
CC
= 24V
C
GATE
= 1nF
High→Low→High
Measured RBG Pin
1µs Pulse Width, Measured on RBG Pin
RBG = 1.2V
Measured as V
DRAIN
– V
TRANS
, R
DCM
= 43k (Note 3)
100kΩ to 5V
100kΩ to 5V
DONE = 2.5V
1
1.1
20
0.2
1.215
0.6
1.24
30
70
36
78
5
0.1
0.6
50
1.265
500
80
88
0.2
0.2
●
●
●
5
68
4.9
3
22
3.8
22.6
100
4.5
23.5
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 LT3750E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Refer to Block Diagram for V
DRAIN
definition.
2
U
V
V
ns
3750fa
W
U
U
W W
W
LT3750
TYPICAL PERFOR A CE CHARACTERISTICS
V
CC
Pin Current
1.8
225
V
TRANS
= 24V
CHARGE PIN CURRENT (µA)
V
TRANS
PIN CURRENT (µA)
1.7
V
CC
PIN CURRENT (mA)
V
CC
= 24V
1.6
V
CC
= 12V
1.5
V
CC
= 3V
1.4
1.3
–50 –25
50
25
0
75
TEMPERATURE (°C)
CHARGE Pin Enable/Disable
Voltage
0.9
0.8
160
CHARGE PIN VOLTAGE (V)
DONE PIN VOLTAGE (mV)
0.7
0.6
CHARGE PIN ENABLE
GATE PIN VOLTAGE (V)
CHARGE PIN DISABLE
0.5
0.4
0.3
0.2
–50
–25
50
25
75
0
TEMPERATURE (°C)
60
1.240
CURRENT LIMIT COMPARATOR TRIP VOLTAGE (mV)
DCM Comparator Trip Voltage
DCM COMPARATOR TRIP VOLTAGE (mV)
V
OUT
COMPARATOR TRIP VOLTAGE (V)
R
DCM
= 43k
50
40
30
20
10
–50
–25
50
25
0
75
TEMPERATURE (°C)
U W
100
3750 G01
V
TRANS
Pin Current
45
40
35
30
25
20
15
10
5
125
100
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
0
CHARGE Pin Current
–50°C
200
V
TRANS
= 12V
175
V
TRANS
= 3V
150
25°C
125°C
125
0
4
8
12
16
V
CHARGE
(V)
20
24
3750 G02
3750 G03
DONE Output Signal Low
25
GATE High Voltage
V
CC
= 24V
V
DONE
= 5V
R
DONE
= 100k
20
140
15
V
CC
= 12V
10
120
100
5
V
CC
= 5V
100
125
80
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3750 G04
3750 G05
3750 G06
V
OUT
Comparator Trip Voltage
Current Limit Comparator Trip
Voltage
82
1.236
80
1.232
78
1.228
76
1.224
74
100
125
1.220
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
72
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
3750 G07
3750 G08
3750 G09
3750fa
3
LT3750
PI FU CTIO S
V
TRANS
(Pin 1):
Transformer Supply Pin. Powers the
primary coil of the transformer as well as internal circuitry
that performs boundary mode detection. Bypass at the pin
with a 1µF to 10µF capacitor. Bypass the primary winding
of the transformer with a large capacitor.
DONE (Pin 2):
Open Collector Indication Pin. When target
output voltage is reached, an NPN transistor turns on.
Requires a pull-up resistor or current source. Any fault
conditions such as thermal shutdown or undervoltage
lockout will also turn on the NPN.
CHARGE (Pin 3):
Charge Pin. Initiates a new charge cycle
when brought high or discontinues charging and puts part
into shutdown when low. To properly enable the device, a
step input with a minimum ramp rate of 1V/µs is required.
Drive to 1.1V or higher to enable the device; drive below
0.2V to disable the device.
V
CC
(Pin 4):
Input Supply Pin. Bypass locally with a
ceramic capacitor. A 1µF to 10µF ceramic capacitor should
be sufficient for most applications.
GND (Pin 5):
Ground Pin. Connect directly to local ground
plane.
SOURCE (Pin 6):
Source Pin. Senses NMOS drain current.
Connect NMOS source terminal and current sense resistor
to this pin. The current limit is 78mV/R
SENSE
.
GATE (Pin 7):
Gate Pin. Connect NMOS gate terminal to
this pin. Internal gate driver will drive voltage to within
V
CC
– 2V during each switching cycle.
RDCM (Pin 8):
Discontinuous Mode Sense Pin. Senses
when current in transformer has decayed to zero and ini-
tiates a new charge cycle if output voltage target has not
been reached. Place a resistor between this pin and the drain
of the NMOS. A good choice is a 43k, 5% resistor.
RV
OUT
(Pin 9):
Output Voltage VI Converter Pin. Develops
a current proportional to output capacitor voltage. Con-
nect a resistor between this pin and the drain of the NMOS.
RBG (Pin 10):
Output Voltage Sense Pin. Senses the
voltage across the RBG resistor, which is proportional to
the current flowing into the R
VOUT
pin. When voltage
equals 1.24V, charging is disabled and DONE pin goes
low. Connect a resistor (2.5k or less is recommended)
from this pin to GND. A 2.49k, 1% resistor is a good
choice.
4
U
U
U
3750fa
LT3750
BLOCK DIAGRA
R
DONE
2
DONE
2.8V
+
–
V
CC
UVLO
V
CC
V
TRANS
UVLO
2.5V
+
–
TSD
ONE
SHOT
V
TRANS
DIE
TEMP
160°C
M1
ENABLE
Q Q
S R
+
–
3
CHARGE
ONE
SHOT
GND
5
10
RBG
R
BG
W
V
TRANS
1
V
TRANS
T1
1:N
D1
•
V
OUT
RV
OUT
R
VOUT
9
+
C
OUT
•
DCM
COMPARATOR
+
–
+–
36mV
RDCM
R
DCM
8
V
TRANS
V
DRAIN
V
CC
4
7
M1
S
R
Q
GATE
+
+
V
OUT
COMPARATOR
SOURCE
6
–
1.24V
CURRENT LIMIT
COMPARATOR
–
+
–
78mV
R
SENSE
3750 BD
3750fa
5
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