LINEAR TECHNOLOGY LT3750 Technical data

FEATURES

■

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 VCC – 2V

■

Available in 10-Lead MS Package

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APPLICATIO S

■

Emergency Warning Beacons

■

Professional Photoflash Systems

■

Security/Inventory Control Systems

■

High Voltage Power Supply

■

Electric Fences

■

Detonators

LT3750

Capacitor Charger

Controller

U

DESCRIPTIO

The LT®3750 is a flyback converter designed to rapidly
charge large capacitors to a user-adjustable target volt­age. A patented boundary mode control scheme* mini­mizes 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

300V, 6A Capacitor Charger

V

TRANS

10µF

V

V
12V

CC

100k

10µF

OFF ON

TRANS

V

CC

DONE

LT3750

CHARGE

GND RBG

U

RV

OUT

RDCM

GATE

SOURCE

2.49k 100pF

56µF
×2

60.4k

43k

3750 TA01a

•

T1

1:10

M1

12mΩ

D1

•

V

OUT

300V

+

100µF

(V)

OUT

V

300

250

200

150

100

V

50

0

0

6A Charge Time

= 18V

TRANS

V

TRANS

0.1 0.2 0.3 0.4
TIME (SECONDS)

V

TRANS

= 12V

= 6V

0.5

3750 TA03c

3750fa

1

LT3750

WWWU

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UU

W

(Note 1)

VCC, V

RBG ....................................................................... 1.5V

SOURCE ................................................................... 1V

Current into RDCM Pin ........................................ ±1mA

Current into RV

, GATE, DONE, CHARGE ...................... 24V

TRANS

Pin ........................................ ±1mA

OUT

V

TRANS

DONE

CHARGE

V

GND

Current into DONE Pin ......................................... ±1mA

Operating Temperature Range (Note 2) .. – 40°C to 85°C

Storage Temperature Range ................ –65°C to 150°C

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum V
Minimum V
VCC Quiescent Current Not Switching, CHARGE = 5V 1.6 2.5 mA

V

TRANS

CHARGE Pin Current CHARGE = 24V 24 µA

CHARGE Pin Enable Voltage
CHARGE Pin Disable Voltage
Minimum CHARGE Pin Low Time High→Low→High 20 µs
V

OUT

V

OUT

RBG Pin Bias Current RBG = 1.2V 70 500 nA
DCM Comparator Trip Voltage Measured as V
Current Limit Comparator Trip Voltage
DONE Output Signal High 100kΩ to 5V 4.9 5 V
DONE Output Signal Low 100kΩ to 5V 0.1 0.2 V
DONE Pin Leakage Current DONE = 2.5V 0.2 µA
NMOS Minimum On Time 0.6 µs
GATE Rise Time 50 ns
GATE High Voltage C

GATE Turn Off Propagation Delay C

CC

TRANS

Quiescent Current Not Switching, CHARGE = 5V 140 250 µA

Comparator Trip Voltage Measured RBG Pin
Comparator Overdrive 1µs Pulse Width, Measured on RBG Pin 30 mV

A

Not Switching, CHARGE = 0V 1 µA

Not Switching, CHARGE = 0V 1 µA

CHARGE = 5V 19 µA
CHARGE = 0V 1 µA

= 1nF, VCC = 5V 3 3.8 4.5 V

GATE

= 1nF, VCC = 24V 22 22.6 23.5 V

C

GATE

= 1nF 100 ns

GATE

The ● denotes specifications which apply over the full operating

= 25°C. VCC = V

– V

DRAIN

ORDER PART NUMBER MS PART MARKING

LT3750EMS

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.

= 5V unless otherwise specified.

TRANS

, R

TRANS

= 43k (Note 3)

DCM

TOP VIEW

1
2
3
4

CC

5

MS PACKAGE

10-LEAD PLASTIC MSOP

T

= 125°C, θJA = 120°C/ W

JMAX

●

●

●

●

0.2 0.6 V

●

1.215 1.24 1.265 V

●

●

53680 mV

68 78 88 mV

10

RBG

9

RV

OUT

RDCM

8

GATE

7

SOURCE

6

LTBQD

2.8 3 V

2.5 3 V

0.87 1.1 V

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.

2

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.

3750fa

UW

V

CHARGE

(V)

0

0

CHARGE PIN CURRENT (µA)

5

15

20

25

16

45

3750 G03

10

8

4

20

12 24

30

35

40

–50°C

25°C

125°C

TEMPERATURE (°C)

–50 –25

0

GATE PIN VOLTAGE (V)

10

25

0

50

75

3750 G06

5

20

15

25

100

125

VCC = 24V

VCC = 12V

VCC = 5V

TYPICAL PERFOR A CE CHARACTERISTICS

LT3750

VCC Pin Current

1.8

1.7

1.6

1.5

PIN CURRENT (mA)

CC

V

1.4

1.3
–50 –25

VCC = 24V

VCC = 12V

VCC = 3V

25

0

TEMPERATURE (°C)

CHARGE Pin Enable/Disable
Voltage

0.9

0.8

0.7

0.6

CHARGE PIN DISABLE

0.5

CHARGE PIN ENABLE

V

Pin Current CHARGE Pin Current

TRANS

225

V

= 24V

200

V

TRANS

175

150

PIN CURRENT (µA)

TRANS

V

125

50

75

100

125

3750 G01

100

–50 –25

0

TEMPERATURE (°C)

DONE Output Signal Low

160

V

= 5V

DONE

= 100k

R

DONE

140

120

TRANS

= 12V

V

= 3V

TRANS

50

25

75

100

125

3750 G02

GATE High Voltage

0.4

CHARGE PIN VOLTAGE (V)

0.3

0.2

–50

60

50

40

30

20

DCM COMPARATOR TRIP VOLTAGE (mV)

10

–50 –25

50 100 125

–25 0

25 75

TEMPERATURE (°C)

DCM Comparator Trip Voltage

R

= 43k

DCM

50

25

0

TEMPERATURE (°C)

75

100

3750 G04

3750 G07

125

100

DONE PIN VOLTAGE (mV)

80

–50

–25 0 25 50

TEMPERATURE (°C)

V

Comparator Trip Voltage

OUT

1.240

1.236

1.232

1.228

COMPARATOR TRIP VOLTAGE (V)

1.224

OUT

V

1.220
–50 –25

25

0

TEMPERATURE (°C)

50

75 100 125

3750 G05

100

125

3750 G08

75

Current Limit Comparator Trip
Voltage

82

80

78

76

74

72

CURRENT LIMIT COMPARATOR TRIP VOLTAGE (mV)

–50 –25

0

TEMPERATURE (°C)

50

25

75

100

3750 G09

3750fa

3

125

LT3750

U

UU

PI FU CTIO S

V

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

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.

(Pin 1): Transformer Supply Pin. Powers the

TRANS

(Pin 4): Input Supply Pin. Bypass locally with a

CC

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

GATE (Pin 7): Gate Pin. Connect NMOS gate terminal to
this pin. Internal gate driver will drive voltage to within
VCC – 2V during each switching cycle.

RDCM (Pin 8): Discontinuous Mode Sense Pin. Senses
when current in transformer has decayed to zero and ini­tiates 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

(Pin 9): Output Voltage VI Converter Pin. Develops

OUT

a current proportional to output capacitor voltage. Con­nect 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
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.

pin. When voltage

VOUT

SENSE

.

4

3750fa

BLOCK DIAGRA

R

DONE

2

3

Q

RQS

CHARGE

DONE

2.8V

V

2.5V

V

TRANS

DIE

TEMP

160°C

M1
ENABLE

ONE

SHOT

CC

V

CC

UVLO

+

–

V

TRANS

UVLO

+

–

TSD

+

–

W

V

OUT

COMPARATOR

1

+

–

GND

5

V

TRANS

1.24V

LT3750

V

TRANS

D1

T1

1:N

•

R

RV

OUT

DCM

COMPARATOR

+

ONE

SHOT

–

S

QR

+

CURRENT LIMIT

COMPARATOR

RBG

10

R

BG

–

+

–

36mV

SOURCE

+
–

RDCM

V

TRANS

V

GATE

78mV

VOUT

9

R

DCM

8

V

CC

4

7

6

M1

R

3750 BD

DRAIN

SENSE

+

V

OUT

•

C

OUT

3750fa

5