LT3971IDD View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LT3971IDD

38V, 1.2A, 2MHz Step-Down Regulator with 2.8µA Quiescent Current

Linear Technology 

LT3971/LT3971-3.3/LT3971-5

TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.

5V Start-Up and Dropout

VIN

Feedback Regulation Voltage

1.6

1.2

Minimum Input Voltage to Switch

5

4

0.8

3

VOUT

0.4

2

800kHz

10Ω LOAD

0.5s/DIV

3971 G34

0

2 2.5 3 3.5 4 4.5 5

INPUT VOLTAGE (V)

3971 G35

1

–55 –25

5 35 65 95

TEMPERATURE (°C)

125 155

3971 G36

PIN FUNCTIONS (DFN, MSE10/MSE16)

BD (Pin 1/Pin 1): This pin connects to the anode of the

boost diode. The BD pin is normally connected to the output.

BOOST (Pin 2/Pin 3): This pin is used to provide a drive

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

NPN power switch.

SW (Pin 3/Pin 5): The SW pin is the output of an internal

power switch. Connect this pin to the inductor, catch diode,

and boost capacitor.

VIN (Pin 4/Pin 7): The VIN pin supplies current to the

LT3971’s internal circuitry and to the internal power switch.

This pin must be locally bypassed.

EN (Pin 5/Pin 8): The part is in shutdown when this pin

is low and active when this pin is high. The hysteretic

threshold voltage is 1.005V going up and 0.975V going

down. The EN threshold is only accurate when VIN is above

4.3V. If VIN is lower than 4.2V, ground EN to place the part

in shutdown. Tie to VIN if shutdown feature is not used.

FB (Pin 6, LT3971 Only/Pins 9, 10): The LT3971 regulates

the FB pin to 1.19V. Connect the feedback resistor divider

tap to this pin. Also, connect a phase lead capacitor between

FB and VOUT. Typically this capacitor is 10pF.

VOUT (Pin 6, LT3971-3.3 and LT3971-5 Only): The

LT3971‑3.3 and LT3971-5 regulate the VOUT pin to 3.3V and

5V respectively. This pin connects to the internal 10MΩ

feedback divider that programs the fixed output voltage.

8

SS (Pin 7/Pin 12): A capacitor is tied between SS and

ground to slowly ramp up the peak current limit of the

LT3971 on start-up. The soft-start capacitor is only actively

discharged when EN is low. The SS pin is released when

the EN pin goes high. Float this pin to disable soft-start.

For applications with input voltages above 25V, add a 100k

resistor in series with the soft-start capacitor.

RT (Pin 8/Pin 13): A resistor is tied between RT and ground

to set the switching frequency.

PG (Pin 9/Pin 14): The PG pin is the open-drain output of

an internal comparator. PGOOD remains low until the FB

pin is within 9% of the final regulation voltage. PGOOD is

valid when the LT3971 is enabled and VIN is above 4.3V.

SYNC (Pin 10/Pin 15): This is the external clock synchro-

nization input. Ground this pin for low ripple Burst Mode

operation at low output loads. Tie to a clock source for

synchronization, which will include pulse-skipping at low

output loads. When in pulse-skipping mode, quiescent

current increases to 1.5mA.

GND (Exposed Pad Pin 11/Pin 16, Exposed Pad Pin 17):

Ground. The exposed pad must be soldered to PCB.

NC (None/Pins 2, 4, 6, 11): No Connect. These pins

are not connected to internal circuitry. Float these pins

to achieve FMEA fault tolerance. (See Fault Tolerance of

MS16E Package section.)

3971fd

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