Linear Technology LT3740EDHC Manuale utente

LT3740EDHC

DESCRIPTION

Demonstration circuit 947 is a Wide Operating

Range, Valley Mode, No R

SENSE

™ Synchronous

Step-Down Controller featuring the LT3740EDHC.

It produces 1.8VDC for loads up to 10A from an

input range of 3-15VDC, switching at a fixed fre-

quency of 300KHz.

In order to operate from an input voltage as low as

3V, the circuit must provide adequate voltage to

drive the external power MOSFETs. To this end,

the LT3740 includes an on-chip step-up converter

to provide a bias about 7V above the input voltage

to power the top MOSFET gate driver. The stock

configuration of DC947 also uses this bias to

power the bottom gate drive circuit, but pads have

been added to the circuit board to power the bot-

tom gate drive from another source.

The LT3740 is equipped with an external reference

input that allows the user to override the 0.8V in-

ternal reference with any lower value, allowing full

control of the output voltage during operation, out-

put voltage tracking or soft-start.

In addition, the LT3740 has three current limit lev-

els that can be chosen by connecting the RANGE

pin to ground, leaving it open circuit, or tying to the

input.

DC947 is equipped with jumpers that allow the

user to select among soft-start options and refer-

ence voltage sources. Unpopulated pads have

been added to DC947 in order to facilitate input

voltages higher than 15V and No R

SENSE

™ opera-

tion.

Design files for this circuit board are available.

Call the LTC factory.

and LT are registered trademarks of Linear Technology Corporation. No RSENSE

is a trademark of Linear Technology Corporation. Other product names may be

trademarks of the companies that manufacture the products.

PERFORMANCE SUMMARY

Specifications are at TA = 25°C

SYMBOL

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Supply Range

3.0 15.0

OUT

Output Voltage Range V

= 3.0 – 15.0V, I

LOAD

= 0-10A 1.76 1.84

OUT

Output current V

= 3.0 – 15.0V, V

OUT

= 1.8V

0 10.0 A

RIPPLE

Output Ripple V

= 3.0 – 15.0V, I

LOAD

= 0-10A 20

QUICK START PROCEDURE

Demonstration circuit 947 is easy to set up to

evaluate the performance of the LT3740EDHC. Refer to Figure 1 for proper measurement equip-

ment setup and follow the procedure below:

DEMO CIRCUIT

947

QUICK START GUIDE

LT3740EDHC

Wide Operating Range, Valley Mode,

No R

NSE

™ Synchronous Step-

Down Controller

LT3740EDHC

NOTE.

When measuring the output voltage ripple, care must be

taken to avoid a long ground lead on the oscilloscope probe.

Measure the input or output voltage ripple by touching the probe tip

directly across the Vin or Vout and GND terminals. See Figure 2 for

proper scope probe technique.

Place jumpers in the following positions:

Up (Internal Reference)

Up (Voltage_SS ON)

Down (Current_SS ON)

With power off, connect the input power supply

to Vin and GND.

Connect the 0-10A load.

Turn on the power at the input. Make sure that

the input voltage is between 3 and 15V.

NOTE.

Make sure that the input voltage does not exceed 15V.

Check for the proper output voltages. Vout

should be 1.8V, nominal. If there is no output,

temporarily disconnect the load to make sure

that the load is not set too high.

Once the proper output voltages are estab-

lished, adjust the loads within the operating

range and observe the output voltage regula-

tion, ripple voltage, efficiency and other parame-

ters.

Figure 1. Proper Measurement Equipment Setup

JP1

JP2

JP3

LT3740EDHC

VIN

GND

Figure 2. Measuring Input/Output Ripple

OPERATION

The LT3740 is a current-mode synchronous buck

controller that can accept input voltages as low as

2.2V, and as high as 22V, but still provides at least

7V for the MOSFET gate drives through an internal

boost regulator. It is equipped for No Rsense

operation to maximize efficiency and features

three user selectable current limit ranges and a

flexible soft-start system capable of output track-

ing.

To close the current loop, the LT3740 reads the

switching current through the bottom MOSFET

“on” resistance. The chip features three user se-

lectable current limit thresholds to optimize effi-

ciency: 45mV, 75mV and 105mV. DC947 uses the

middle setting, but unpopulated pads are available

for selecting the other two settings.

In the interest of making the board able to handle a

wide variety of input and output voltage combina-

tions, DC947 does not use the No Rsense

fea-

ture, but has been configured so that it is easy to

do so. This is accomplished by shorting out the

R1 sense resistor and moving the zero ohm resis-

tor at location R14 to location R13. Change R28

to 1 ohm. Other component changes unique to

the desired output voltage, input voltage range and

frequency compensation may be necessary.

DC947 is configured such that the bottom gate

drive power (BGDP) pin is connected directly to

the output of the on-chip boost regulator (BIAS)

through R32. This is what allows the circuit to pro-

vide sufficient power MOSFET gate drive when the

input is as low as 3V.

If the design is not required to operate at input

voltages below 7V, the BGDP pin can be tied to

Vin to reduce the loading on the boost converter

and thus save power. To do this, move the zero

ohm resistor at location R32 to R31 and add a 1uF

ceramic capacitor at location C25. Also, imple-

ment the UVLO circuit by removing R30 and popu-

lating the circuitry made up of D3, Q3, and R29.

The LT3740 has an active high, open collector

power good signal. On the demo board, it is pulled

up to the 1.8V output through a 100K resistor, and

can be conveniently read at TP6. Note that this

pull-up voltage may not be compatible with all volt-

age systems. Please refer to the data sheet for a

detailed description of the PGOOD signal.

A 0-0.8V external reference may be applied to the

LT3740 at TP5. This is used to over-ride the inter-

nal 0.8V reference, giving control of the DC947

output voltage to an external signal source. Use of

this function must first be enabled by setting JP1

(REFERENCE) to the EXTERNAL position. For

further details about the external reference func-

tion, please refer to the XREF function described

in the LT3740 data sheet.

JP2 (VOLTAGE_SS) and JP3 (CURRENT_SS)

must both be set to their respective ON positions

in order for the DC947 output to power up. If ei-

ther of these jumpers is set to the OFF position,

the output will not turn on. JP2 (VOLTAGE_SS) is

associated with the XREF input, while JP3

(CURRENT_SS) ties into the SHDN input. For

further details about the LT3740 soft-start opera-

tion, please refer to the data sheet.

On the DC947 demo board, the signals applied to

both of the soft-start inputs are generated by sim-

ple RC circuits. The RC time constant of the

CURRENT_SS soft-start is much longer than that

of the VOLTAGE_SS, so the CURRENT_SS will

LT3740EDHC

C23

0.01uF

C21

1uF

R16

100K

VOUT

1.8V @ 10AR18

100K

R20

12K

C16

C18

R33

100K

C12

22pF

C13

2200pF

LT3740EDHC

SN-

PGND

BGATE

BGDP

SN+

TGATE

BIAS

SWB

VIN

RANGE

PGOOD

XREF

SHDN

GND

R17

80.6K

PH8230E

C10

10uF each

C22

10uF

C19

R22

15K

PH3830L D1

B320A

0.007

L1 0.9uH

C20

1uF

R19

VIN

3-15V

22uH

C14

100pF

C17

100uF each

150uF

dominate the behavior of the demo board output.

To observe the behavior of the output when under

VOLTAGE_SS control, simply change the RC time

constant of R18 and C15 to make it longer than

that of R22 and C20. Make sure that JP1 is set to

INTERNAL.

DC947A is equipped with many optional compo-

nents to facilitate the implementation of many op-

tional functions. A simplified schematic of essen-

tial components is shown in figure 3, while a full

schematic of the board is given in at the end of this

document.

Figure 3. Simplified Schematic showing only essential components.

LT3740EDHC

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:

DC947A

Indice

Altri manuali Linear Technology Hardware per computer

Linear Technology

Linear Technology 1791A Manuale utente

Linear Technology

Linear Technology 1464 Manuale utente

Linear Technology

Linear Technology LTC4227-1 Guida rapida alla configurazione

Linear Technology

Linear Technology DC1920A Guida rapida alla configurazione

Linear Technology

Linear Technology DC2430A Guida rapida alla configurazione

Linear Technology

Linear Technology LTC2175-12 Manuale utente

Linear Technology

Linear Technology LTC2172-12 Manuale utente

Linear Technology

Linear Technology DC2012A Guida rapida alla configurazione

Linear Technology

Linear Technology LTC1592 Manuale utente

Linear Technology

Linear Technology DC1791A Guida rapida alla configurazione

Linear Technology

Linear Technology DC1307A Guida rapida alla configurazione

Linear Technology

Linear Technology 630 Manuale utente

Linear Technology

Linear Technology LTC2377-20 Manuale utente

Linear Technology

Linear Technology 968A-D Manuale utente

Linear Technology

Linear Technology DC1007C Manuale utente

Linear Technology

Linear Technology DC1057 Manuale utente

Linear Technology

Linear Technology DC2455A-C Guida rapida alla configurazione

Linear Technology

Linear Technology DC1805A Series Manuale utente

Linear Technology

Linear Technology LT6411 Manuale utente

Linear Technology

Linear Technology LTC3588-1 Guida alla risoluzione dei problemi

Linear Technology

Linear Technology LTC6930 Series Manuale utente

Linear Technology

Linear Technology DC1304A-A Manuale utente

Linear Technology

Linear Technology DC890B Manuale utente

Linear Technology

Linear Technology DC2355A Manuale utente

Manuali Hardware per computer popolari di altre marche

EMC2

EMC2 VNX Series Manuale del proprietario

Panasonic

Panasonic DV0PM20105 Manuale utente

Mitsubishi Electric

Mitsubishi Electric Q81BD-J61BT11 Manuale utente

Gigabyte

Gigabyte B660M DS3H AX DDR4 Manuale utente

Raidon

Raidon iT2300 Manuale utente

National Instruments

National Instruments PXI-8186 Manuale utente

Hauppauge

Hauppauge WinTV-HVR-2250 Manuale utente

Kontron

Kontron CP6002 Manuale utente

Manhattan

Manhattan 702843 Manuale utente

Aphex

Aphex 230 Manuale utente

AMD

AMD Phenom II Manuale operativo

Intel

Intel NUC 12 Pro Manuale utente

dbx

dbx Zone Pro 1260 Manuale utente

Galaxy

Galaxy GHDX2-2430S-24F4D Manuale utente

Intel

Intel AXXRMFBU4 Manuale utente

Kontron

Kontron DIMM-PC/MD Manuale utente

ST X-NUCLEO-SAFEA1B Istruzioni operative

STEINWAY LYNGDORF

STEINWAY LYNGDORF SP-1 Manuale utente