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3

LT1425

ELECTRICAL CHARACTERISTICS

V

IN

 = 5V, T

J

 = 25

°

C, V

SW

 Open, V

C

 = 1.4V, unless otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Load Compensation

V

RCCOMP

/

I

SW

0.45

SYNC Function

Minimum SYNC Amplitude

1.5

2.2

V

Synchronization Range

320

450

kHz

SYNC Pin Input Resistance

40

k

Power Supply

V

IN(MIN)

Minimum Input Voltage

2.8

3.1

V

I

CC

Supply Current

7.0

9.5

mA

Shutdown Mode Supply Current

15

40

µ

A

Shutdown Mode Threshold

0.4

0.9

1.3

V

TYPICAL PERFOR

M

A

N

CE CHARACTERISTICS  

U

W

Switch Saturation Voltage vs
Switch Current

TEMPERATURE (

°

C)

–50

3.1

3.0

2.9

2.8

2.7

2.6

2.5

2.4

25

75

1425 G03

–25

0

50

100

125

INPUT VOLTAGE (V)

Switch Current Limit vs
Duty Cycle

Minimum Input Voltage vs
Temperature

SWITCH CURRENT (A)

0

SWITCH SATURATION VOLTAGE (V)

1.2

1.0

0.8

0.6

0.4

0.2

0

0.6

1.0

1425 G01

0.2

0.4

0.8

1.2

1.4

125

°

C

25

°

C

–55

°

C

DUTY CYCLE (%)

0

SWITCH CURRENT LIMIT (A)

40

1425 G02

10

20 30

50 60 70 80 90 100

2.0

1.5

1.0

0.5

0

T

A

 = 25

°

C

The 

 

denotes the specifications which apply over the full operating

temperature range.

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: Feedback amplifier transconductance is R

REF

 referred.

Note 3: Voltage gain is R

REF

 referred.

Содержание LT1425

Страница 1: ...6W with no external power devices Byutilizingcurrentmodeswitchingtechniques it provides excellent AC and DC line regulation The LT1425 has a number of features not found on other switching regulator I...

Страница 2: ...tion 5V VIN 18V 0 01 0 04 V Voltage Gain Note 3 500 V V VIN Sense Error 10 25 mV Output Switch BV Output Switch Breakdown Voltage IC 5mA 35 50 V V VSW Output Switch ON Voltage ISW 1A 0 55 0 85 V ILIM...

Страница 3: ...Voltage vs Switch Current TEMPERATURE C 50 3 1 3 0 2 9 2 8 2 7 2 6 2 5 2 4 25 75 1425 G03 25 0 50 100 125 INPUT VOLTAGE V Switch Current Limit vs Duty Cycle Minimum Input Voltage vs Temperature SWITC...

Страница 4: ...Temperature SHDN Pin Input Current vs Voltage Minimum Synchronization Voltage vs Temperature TEMPERATURE C 50 300 295 290 285 280 275 270 265 25 75 1425 G07 25 0 50 100 125 SWITCHING FREQUENCY kHz TEM...

Страница 5: ...nd This pin is a clean ground The internal reference and feedback amplifier are referred to it Keep the ground path connection to RREF and the VC compensation capacitor free of large ground currents P...

Страница 6: ...VSW VC CEXT RFB RFB RREF RREF VBG Q4 D2 Q1 Q2 Q3 VIN I IM IM IFXD ENABLE 1425 EA LOAD COMPENSATION CURRENT AMPLIFIER DRIVER LOGIC 285kHz OSCILLATOR 2 6V REGULATOR SHDN FLYBACK ERROR AMPLIFIER COMP RCC...

Страница 7: ...tra transformer windings also exhibit defi ciencies The extra winding adds to the transformer s physical size and cost Dynamic response is often mediocre There is usually no method for maintaining loa...

Страница 8: ...n in the overall loop will then cause the voltage at the RREF resistor to be nearly equal to the bandgap reference VBG VBG is not present in final output voltage setting equation See Applications Info...

Страница 9: ...for fur ther details Enable Delay When the output switch shuts off the flyback pulse appears However it takes a finite time until the trans formerprimarysidevoltagewaveformapproximatelyrep resents th...

Страница 10: ...voltage terms in a single variable IIN K1 IOUT where K1 VOUT VIN Eff Switch current is converted to voltage by a sense resistor and amplified by the current sense amplifier with associ ated gain G Thi...

Страница 11: ...henewcompensationinplace Modify the original ROCOMP value if necessary to increase or decrease the effective compensation Once the proper load compensation resistor has been chosen it may be necessary...

Страница 12: ...m So the user is generally advised to arrange the snubber circuit to clamp at as high a voltage as comfortably possible observing switch breakdown such that leakage spike duration is as short as possi...

Страница 13: ...ble state whereby the top of the leakage spike is the control point and the trailing edge of the leakage spike triggers the collapse detect circuitry This will typically reduce the output volt age abr...

Страница 14: ...kage Inductance Leakage inductance on the transformer secondary reduces the effective primary to secondary turns ratio NP NS from its ideal value This will increase the output voltage target by a simi...

Страница 15: ...MIN where f Switching frequency nominally 285kHz LSEC Transformer secondary side inductance VOUT Output voltage tED Enable delay time tEN Minimum enable time tED tEN 2 Note that generally depending on...

Страница 16: ...se but is then held during the subsequent switch ON portion of the nextcycle ThisactionnaturallyholdstheVC voltagestable duringthecurrentcomparatorsenseaction currentmode switching PCB LAYOUT CONSIDER...

Страница 17: ...nce to discharge to 11V Feedback voltage is fed directly through a resistor divider to the RREF pin The load compensation circuitry is bypassed resulting in 5 load regulation Finally the 12V to 5V Iso...

Страница 18: ...2 F 35V 15 F 35V 3k 15 F 35V 1000pF 0 1 F 130 330pF 9 MBR0540LT1 1425 TA06 BAV21 BAV21 MUR120 LT1425 5k 18 MBR745 10 4 7 8 T1 3 2 1 GND NC RFB VC RREF SYNC SGND GND GND SHDN ROCOMP RCCOMP VIN VSW PGND...

Страница 19: ...rwise noted S Package 16 Lead Plastic Small Outline Narrow 0 150 LTC DWG 05 08 1610 0 016 0 050 0 406 1 270 0 010 0 020 0 254 0 508 45 0 8 TYP 0 008 0 010 0 203 0 254 1 2 3 4 5 6 7 8 0 150 0 157 3 810...

Страница 20: ...Flyback Regulators Uses Ultrasmall Magnetics LT1424 Application Specific Isolated Regulator 8 Pin Fixed Voltage Version of LT1425 220 F 10V 1425 TA05 LT1425 MBRS340T3 2 5 1 4 6 3 10 7 11 8 12 9 GND NC...

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