LT1943EFE 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

LT1943EFE

High Current Quad Output Regulator for TFT LCD Panels

Linear Technology 

LT1943

U

OPERATIO

Table 3. Schottky Diodes

Part Number

VR (V)

On Semiconductor

MBRM120E

20

MBRM140

40

Diodes Inc.

B120

20

B130

30

B220

20

B230

30

B240

40

International Rectifier

10BQ030

30

20BQ030

30

IAVE (A) VF at 1A (mV)

1

530

1

550

1

500

1

500

2

2

2

1

420

2

VF at 2A (mV)

595

500

500

500

470

470

Boost Pin Considerations

The minimum operating voltage of an LT1943 application

is limited by the undervoltage lockout ~4V and by the

maximum duty cycle. The boost circuit also limits the

minimum input voltage for proper start-up. If the input

voltage ramps slowly, or the LT1943 turns on when the

output is already in regulation, the boost capacitor may not

be fully charged. Because the boost capacitor charges

with the energy stored in the inductor, the circuit will rely

on some minimum load current to get the boost circuit

running properly. This minimum load will depend on input

and output voltages. The Typical Performance Character-

istics section shows a plot of the minimum load current to

start as a function of input voltage for a 3.3V output. The

minimum load current generally goes to zero once the

circuit has started. Even without an output load current, in

many cases the discharged output capacitor will present

a load to the switcher that will allow it to start.

INVERTER/STEP-UP CONSIDERATIONS

Regulating Positive Output Voltages

The output voltage is programmed with a resistor divider

between the output and the FB pin. Choose the resistors

according to:

R3 = R4(VOUT/1.25 – 1)

R4 should be 10kΩ or less to avoid bias current errors. If

switcher 4 is used to generate a positive output voltage,

NFB4 should be tied to FB4.

VOUT

R3

FB4

R4

NFB4

1943 A1

Regulating Negative Output Voltages

The LT1943 contains an inverting op amp with its non-

inverting terminal tied to ground and its output connected

to the FB4 pin. Use this op amp to generate a voltage at FB4

that is proportional to VOUT4. Choose the resistors accord-

ing to:

R6 = R5• | V0UT |

1.245V

–VOUT

R6

NFB4

C1

R5

10pF

10k FB4

1943 A2

Use 10k for R5. Tie 10pF in parallel with R5.

Duty Cycle Range

The maximum duty cycle (DC) of the LT1943 switching

regulator is 85% for SW2, and 83% for SW3 and SW4. The

duty cycle for a given application using the step-up or

charge pump topology is:

DC = | VOUT | –VIN

| VOUT |

The duty cycle for a given application using the inverter or

SEPIC topology is:

1943fa

14

Share Link: