LT1371 데이터 시트보기 (PDF) - Linear Technology

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LT1371

500kHz High Efficiency 3A Switching Regulator

Linear Technology 

TYPICAL PERFORMANCE CHARACTERISTICS

VC Pin Threshold and High

Clamp Voltage vs Temperature

2.4

2.2

2.0

VC HIGH CLAMP

1.8

1.6

1.4

1.2

VC THRESHOLD

1.0

0.8

0.6

0.4

–50 –25 0 25 50 75 100 125 150

TEMPERATURE (°C)

LT1371 • G10

Feedback Input Current

vs Temperature

800

700 VFB =VREF

600

500

400

300

200

100

0

–50 –25

0 25 50 75 100 125 150

TEMPERATURE (°C)

LT1371 • G11

LT1371

Negative Feedback Input Current

vs Temperature

0

VNFB =VNFR

–10

–20

–30

–40

–50

–50 –25

0 25 50 75 100 125 150

TEMPERATURE (°C)

LT1371 • G12

PIN FUNCTIONS

VC: The Compensation pin is used for frequency compen-

sation, current limiting and soft start. It is the output of the

error amplifier and the input of the current comparator.

Loop frequency compensation can be performed with an

RC network connected from the VC pin to ground.

FB: The Feedback pin is used for positive output voltage

sensing and oscillator frequency shifting. It is the invert-

ing input to the error amplifier. The noninverting input of

this amplifier is internally tied to a 1.245V reference. Load

on the FB pin should not exceed 250µA when NFB pin is

used. See Applications Information.

NFB: The Negative Feedback pin is used for negative

output voltage sensing. It is connected to the inverting

input of the negative feedback amplifier through a 100k

source resistor.

S/S (R and T7 Packages Only): Shutdown and Synchroni-

zation Pin. The S/S pin is logic level compatible. Shutdown

is active low and the shutdown threshold is typically 1.3V.

For normal operation, pull the S/S pin high, tie it to VIN or

leave it floating. To synchronize switching, drive the S/S

pin between 600kHz and 800kHz.

SHDN: (SW Package Only): The Shutdown pin is active

low and the shutdown threshold is typically 1.3V. For

normal operation, pull the SHDN pin high, tie it to VIN or

leave it floating.

SYNC (SW Package Only): To synchronize switching,

drive the SYNC pin between 600kHz and 800kHz. If not

used, the SYNC pin can be tied high, low or left floating.

VIN: Bypass Input Supply pin with a low ESR capacitor,

10µF or more. The regulator goes into undervoltage lock-

out when VIN drops below 2.5V. Undervoltage lockout

stops switching and pulls the VC pin low.

VSW: The Switch pin is the collector of the power switch

and has large currents flowing through it. Keep the traces

to the switching components as short as possible to

minimize radiation and voltage spikes.

GND: Tie all Ground pins to a good quality ground plane.

5

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