LT3435(RevA) Просмотр технического описания (PDF) - Linear Technology

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LT3435
(Rev.:RevA)

High Voltage 3A, 500kHz Step-Down Switching Regulator with 100µA Quiescent Current

Linear Technology 

LT3435

TYPICAL PERFOR A CE CHARACTERISTICS

Dropout Operation

4.0 VOUT = 3.3V

3.5 BOOST DIODE = DIODES INC DFLS160

3.0

2.5

2.0

1.5

LOAD CURRENT = 2.5A

1.0

LOAD CURRENT = 250mA

0.5

0

2 2.5 3 3.5 4 4.5 5 5.5 6

INPUT VOLTAGE (V)

3435 G19

Burst Mode Operation

Dropout Operation

6

VOUT = 5V

BOOST DIODE = DIODES INC DFLS160

5

4

Burst Mode Operation

VOUT

50mV/DIV

AC-COUPLED

3

ISW

500mA/DIV

LOAD CURRENT = 2.5A

2

1

LOAD CURRENT = 250mA

VIN = 12V

VOUT = 3.3V

10ms/DIV

0

2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5

INPUT VOLTAGE (V)

3435 G20

No Load 2A Step Response

Step Response

VOUT

50mV/DIV

AC-COUPLED

VOUT

200mV/DIV

AC-COUPLED

VOUT

200mV/DIV

AC-COUPLED

ISW

500mA/DIV

VIN = 12V

VOUT = 3.3V

10µs/DIV

3435 G22

IOUT

1A/DIV

VIN = 12V

VOUT = 3.3V

COUT = 100µF

500µs/DIV

IOUT

1A/DIV

3435 G23

VIN = 12V

500µs/DIV

VOUT = 3.3V

COUT = 100µF

ILOAD(DC) = 500mA

3435 G21

3435 G24

PI FU CTIO S

NC (Pin 1): No Connection.

SW (Pins 2, 5): The SW pin is the emitter of the on-chip

power NPN switch. This pin is driven up to the input pin

voltage during switch on time. Inductor current drives the

SW pin negative during switch off time. Negative voltage

is clamped with the external catch diode. Maximum nega-

tive switch voltage allowed is –0.8V.

VIN (Pins 3, 4): This is the collector of the on-chip power

NPN switch. VIN powers the internal control circuitry when

a voltage on the BIAS pin is not present. High di/dt edges

occur on this pin during switch turn on and off. Keep the

path short from the VIN pin through the input bypass

capacitor, through the catch diode back to SW. All trace

6

inductance on this path will create a voltage spike at switch

off, adding to the VCE voltage across the internal NPN.

BOOST (Pin 6): The BOOST pin is used to provide a drive

voltage, higher than the input voltage, to the internal

bipolar NPN power switch. Without this added voltage, the

typical switch voltage loss would be about 1.5V. The

additional BOOST voltage allows the switch to saturate

and its voltage loss approximates that of a 0.1Ω FET

structure.

CT (Pin 7): A capacitor on the CT pin determines the amount

of delay time between the PGFB pin exceeding its thresh-

old (VPGFB) and the PG pin set to a high impedance state.

3435fa

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