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LT1681I

Dual Transistor Synchronous Forward Controller

Linear Technology 

LT1681

ELECTRICAL CHARACTERISTICS

The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.

VCC = VBST = 12V, VBSTREF = 0V, VVC = 2V, VFB = VREF = 1.25V, CTG = CBG = CSG = 1000pF.

SYMBOL PARAMETER

CONDITIONS

MIN TYP MAX

5V External Reference

V5VREF 5V Reference Voltage

0 ≤ (I5VREF – IVC) < 20mA

4.85

5

5.10

q

4.80

5.15

I5VREFSC Short-Circuit Current

R5VREF Output Impedance

Error Amp

Source, IVC = 0

0 ≤ (I5VREF – IVC) < 20mA

q

20

45

1

VFB

Error Amplifier Reference Voltage

Measured at Feedback Pin

1.242 1.250 1.258

q 1.225

1.265

IFB

Feedback Input Current

AV

Error Amplifier Voltage Gain

IVC

Error Amplifier Current Limit

VFB = VREF

Source

Sink

– 50

72

q

10

25

q

0.5

1

VVC

Zero Current Output Voltage

1.4

Maximum Output Voltage

3.2

GBW Gain Bandwidth Product

(Note 3)

1

Current Sense and Blanking

AV

ISENSE

VSENSE

Amplifier DC Gain

Input Bias Current

Current Limit Threshold

Measured at SENSE Pin

12

– 275

135 150 165

q

130

170

tD

Current Sense to Switch Delay

VBLKSENS Blanking Input Threshold

IBLKSENS Blanking Input Bias Current

tMIN

Switch Minimum On Time

IMAX Sense

IIMAX

Input Bias Current

VIMAX

IMAX Threshold (Rising Edge)

IMAX Threshold Hysteresis

tP

IMAX Output Switch Disable Delay

THERM and OVLO Fault Detectors

q

VBLKSENS = VBG, Measured at BG Output

175

4.5

5

5.5

–2

250

Measured at IMAX Input

Measured at IMAX Input

Measured at BG Output

– 250

q

320 360 400

140

130

VTHERM/ Threshold (Rising Edge)

VOVLO Threshold Hysteresis

tP

Fault Delay to Output Disable

Oscillator and Synchronization Decoder

50mV Overdrive

q

1.2

1.25

1.3

q

20

40

60

650

fOSC

IFSET

VSYNC

Oscillator Frequency, Free Run

Frequency Programming Error, Free Run

FSET Input Bias Current

SYNC Logic High Input Threshold

SYNC Logic Low Input Threshold

Measured at FSET Pin

fOSC ≤ 500kHz (Note 3)

FSET Charging, VFSET = 2V

Positive-Going Edge

Negative-Going Edge

700

q

–10

5

50

q

1.4

2

q

0.8

1.4

fSYNC

tH, L

SYNC Frequency

Maximum SYNC Pulse Width

(Logic High or Logic Low)

fOSC = Oscillator Free-Run Frequency

q

fOSC/2

350

1/fOSC

UNITS

V

V

mA

Ω

V

V

nA

dB

mA

mA

V

V

MHz

V/V

µA

mV

mV

ns

V

µA

ns

µA

mV

mV

ns

V

mV

ns

kHz

%

nA

V

V

kHz

s

1681f

3

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