LT1578CS8 datasheet(3/28 Pages) LINER

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LT1578/LT1578-2.5

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Boost Current (Note 5)

ISW = 0.5A

918

ISW = 1.5A

VIN Supply Current (Note 6)

1.9

2.7

Shutdown Supply Current

VSHDN = 0V, VIN ≤ 15V, VSW = 0V, VC Open

µA

Lockout Threshold

VC Open

2.34

2.42

2.50

Shutdown Thresholds

VC Open Device Shutting Down

0.13

0.37

0.60

Device Starting Up

0.25

0.45

0.7

Synchronization Threshold

1.5

2.2

Synchronizing Range

250

400

kHz

SYNC Pin Input Resistance

Ω

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: Gain is measured with a VC swing equal to 200mV above the

switching threshold level to 200mV below the upper clamp level.

Note 3: Minimum input voltage is not measured directly, but is guaranteed

by other tests. It is defined as the voltage where internal bias lines are still

regulated so that the reference voltage and oscillator frequency remain

constant. Actual minimum input voltage to maintain a regulated output will

depend on output voltage and load current. See Applications Information.

Note 4: This is the minimum voltage across the boost capacitor needed to

guarantee full saturation of the internal power switch.

Note 5: Boost current is the current flowing into the boost pin with the pin

held 5V above input voltage. It flows only during switch on time.

Note 6: Input supply current is the bias current drawn by the input pin

with switching disabled.

Note 7: Switch on resistance is calculated by dividing VIN to VSW voltage

by the forced current (1.5A). See Typical Performance Characteristics for

the graph of switch voltage at other currents.

Note 8: Slope compensation is the current subtracted from the switch

current limit at 80% duty cycle. See Maximum Output Load Current in the

Applications Information section for further details.

Note 9: Minimum on-time is 400ns typical. For a 200kHz operating

frequency this means the minimum duty cycle is 8%. In frequency

foldback mode, the effective duty cycle will be less than 8%.

Note 10: Transconductance and voltage gain refer to the internal amplifier

exclusive of the voltage divider. To calculate gain and transconductance

referred to the sense pin on the fixed voltage parts, divide values shown by

the ratio 2.5/1.21.

TYPICAL PERFORMANCE CHARACTERISTICS

Switch Voltage Drop

JUNCTION TEMPERATURE (

°C)

–50

1.23

1.22

1.21

1.20

1.19

100

1576 G03

–25

125

SWITCH CURRENT (A)

0.5

0.4

0.3

0.2

0.1

0.25

0.50

0.75

1.00

1576 G01

1.25

1.50

125

°C

–20

°C

Feedback Pin Voltage

Switch Peak Current Limit

DUTY CYCLE (%)

2.5

2.0

1.5

1.0

0.5

1576 G02

100

TYPICAL

MINIMUM

The q denotes specifications which apply over the full operating tempera-

ture range, otherwise specifications are at TJ = 25°C. VIN = 5V, VC = 1.5V, Boost = VIN + 5V, switch open, unless otherwise noted.

ELECTRICAL CHARACTERISTICS

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