LT3970 데이터 시트보기 (PDF) - Linear Technology

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LT3970

40V, 350mA Step-Down Regulator with 2.5µA Quiescent Current and Integrated Diodes

Linear Technology 

LT3970/LT3970-3.3/LT3970-5

PIN FUNCTIONS

FB (Pin 1, LT3970 Only): The LT3970 Regulates the FB

Pin to 1.21V. Connect the feedback resistor divider tap to

this pin.

VOUT (Pin 1, LT3970-3.3 and LT3970-5 Only): The LT3970-

3.3 and LT3970-5 regulate the VOUT Pin to 3.3V and 5V

respectively. This pin connects to the internal feedback

divider that programs the fixed output voltage.

EN (Pin 2): The part is in shutdown when this pin is low

and active when this pin is high. The hysteretic threshold

voltage is 1V going up and 0.97V going down. Tie to VIN

if shutdown feature is not used. The EN threshold is ac-

curate only when VIN is above 4.2V. If VIN is lower than

4.2V, ground EN to place the part in shutdown.

VIN (Pin 3): The VIN pin supplies current to the LT3970’s

internal circuitry and to the internal power switch. This

pin must be locally bypassed.

GND (Pins 4, 5, Exposed Pad (Pin 11, DFN Only)): Ground.

Must be soldered to PCB.

SW (Pin 6): The SW pin is the output of an internal power

switch. Connect this pin to the inductor.

BOOST (Pin 7): This pin is used to provide a drive volt-

age, higher than the input voltage, to the internal bipolar

NPN power switch.

BD (Pin 8): This pin connects to the anode of the boost

diode. This pin also supplies current to the LT3970’s internal

regulator when BD is above 3.2V.

PG (Pin 9): The PG pin is the open-drain output of an

internal comparator. PG remains low until the FB pin is

within 10% of the final regulation voltage. PG is valid when

VIN is above 4.2V and EN is high.

RT (Pin 10): A resistor is tied between RT and ground to

set the switching frequency.

BLOCK DIAGRAM

VIN

C1

3 VIN

1V +

EN

2

–

INTERNAL 1.21V REF

SHDN

RT

10

RT

PG

9

1.09V

+

ERROR

AMP

–

GND

(4, 5)

LT3970 ONLY

FB

1

R2

R1

*LT3970-3.3: R1 = 12.65M, R2 = 7.35M

LT3970-5: R1 = 15.15M, R2 = 4.85M

–

+

SLOPE COMP

OSCILLATOR

200kHz TO 2.2MHz

VC

Burst Mode

DETECT

R2

R1

LT3970-3.3

LT3970-5

ONLY*

VOUT

1

8

SWITCH LATCH

R

Q

S

BD

8

DBOOST

BOOST

7

DCATCH

SW

6

C3

L1

C2

VOUT

3990 BD

3970fa

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