Linear Technology DC1317A-B Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

LT1 52

DESCRIPTION

DESCRIPTIONDESCRIPTION

DESCRIPTION

Demonstration circuit 1317A-A is isolated input to

high current output 1/8th Brick footprint

1/8th Brick footprint1/8th Brick footprint

1/8th Brick footprint converter

featuring the LT®1952 switching controller with Ac-

tive Reset circuit. The Active Reset circuit can im-

prove the efficiency in wide input voltage applica-

tions. Also, the Active Reset allows the implementa-

tion of self-driven synchronous secondary rectifiers

in some applications.

The DC1317A-A converts isolated 34V to 75V input to

3.3V output and provides over 30A of output current.

The converter operates at 300kHz with the peak effi-

ciency greater than 93%. The DC1317 can be easily

modified to generate output voltages in the range

from 0.6V to 48V. The output currents are limited by

total output power of up to 150W.

The other available versions of DC1317A are:

DC1317A-B, 18-72Vin to 5V, 25A

DC1317A-C, 18-72Vin to 12V, 10A

DC1317A-D, 18-72Vin to 24V, 5A

DC1317A-E, 36-72Vin to 5V, 12A

DC1317A-F, 9-36Vin to 3.3V, 20A

DC1317A-G, 9-36Vin to 12V, 5A

DC1317A-H, 9-36Vin to 48V, 1.5A

The DC1317 circuit features soft-start which prevents

output voltage overshoot on startup or when recover-

ing from overload condition.

The DC1317 has precise over-current protection cir-

cuit that allows for continuous operation under short

circuit conditions. The low power dissipation under

short circuit conditions insures high reliability even

during short circuits.

The LT1952 can be synchronized to an external clock

of up to 400kHz. Please refer to LT1952 data sheet for

design details and applications information.

Design files for this circuit board are avai

Design files for this circuit board are avaiDesign files for this circuit board are avai

Design files for this circuit board are avail

lable.

able.able.

able.

Call the LTC factory.

Call the LTC factory.Call the LTC factory.

Call the LTC factory.

LT is a trademark of Linear Technology Corporation

Table 1.

Table 1.Table 1.

Table 1.

Performance Summary

Performance SummaryPerformance Summary

Performance Summary

PARAMETER

PARAMETERPARAMETER

PARAMETER

CONDITION

CONDITIONCONDITION

CONDITION

VALUE

VALUEVALUE

VALUE

Minimum Input Voltage IOUT = 0A to 30A 34V

Maximum Input Voltage IOUT = 0A to 30A 75V

VOUT VIN = 34V to 75V, IOUT = 0A to 30A 3.3V ±3%

Typical Output Ripple VOUT VIN = 34V to 75V, IOUT = 0A to 30A 50mVP–P

Nominal Switching Frequency 300kHz

QUICK START PROCEDUR

QUICK START PROCEDURQUICK START PROCEDUR

QUICK START PROCEDURE

Demonstration circuit 1317 is easy to set up to evalu-

ate the performance of LT1952 circuit. Refer to Fi

Refer to FiRefer to Fi

Refer to Fig-

g-g-

ure 1 for proper measurement equipment setup

ure 1 for proper measurement equipment setupure 1 for proper measurement equipment setup

ure 1 for proper measurement equipment setup

and follow the procedure below:

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

NOTE:

NOTE:NOTE:

NOTE:

When measuring the input or output voltage

ripple, care must be taken to avoid a long ground lead

on the oscilloscope probe. Measure the input or out-

put voltage ripple by touching the probe tip directly

across the Vin or Vout and GND terminals. See Figure

2. for proper scope probe technique.

1.1.

With power off, connect the input power supply to

Vin and GND. Make sure that the input power sup-

ply has sufficient current rating at minimum input

voltage for the required output load.

2.2.

Turn on the power at the input.

NOTE:

NOTE:NOTE:

NOTE:

Make sure that the input voltage does not

exceed 75V.

3.3.

Check for the proper output voltage.

Vout = 3.3V.

If there is no output, temporarily disconnect the

load to make sure that the load is not set too high.

4.4.

Once the proper output voltage is established, ad-

just the load within the operating range and ob-

serve the output voltage regulation, ripple voltage,

efficiency and other parameters.

5.5.

The DC1317 is equipped with an output capacitor

CSYS (470uF) that approximates typical system

rail capacitance. If system board already has ca-

pacitance of similar value CSYS can be removed.

Figure 1. Pr

Figure 1. PrFigure 1. Pr

Figure 1. Proper Measurement Equipment Setup

oper Measurement Equipment Setupoper Measurement Equipment Setup

oper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

Figure 2. Scope Probe Placement for Measuring Input or Output Ri

Figure 2. Scope Probe Placement for Measuring Input or Output RiFigure 2. Scope Probe Placement for Measuring Input or Output Ri

Figure 2. Scope Probe Placement for Measuring Input or Output Rip

pple

pleple

ple

OPTIONAL PRIMARY MOS

OPTIONAL PRIMARY MOSOPTIONAL PRIMARY MOS

OPTIONAL PRIMARY MOSFET DRIVER LTC4440

FET DRIVER LTC4440FET DRIVER LTC4440

FET DRIVER LTC4440

The DC1317 has an optional LTC4440 MOSFET

driver U2. The LTC4440 can be used if the efficiency

is important and large MOSFET is used. The effi-

ciency gain is usually in the 0.5%-1% range when

LTC4440 is used. If required, please contact LT fac-

tory for assistance.

ACTIVE RESET CIRCUIT

ACTIVE RESET CIRCUITACTIVE RESET CIRCUIT

ACTIVE RESET CIRCUIT

The Active Reset circuit on DC1317A-A demo board

consists of a small P-Channel MOSFET Q13 and

reset capacitor C25. The MOSFET Q13 is used to

connect the reset capacitor across the transformer

T1 primary winding during the reset period when

Q1 MOSFET is off. The voltage across capacitor

C25 automatically adjusts with the duty cycle to

provide complete transformer reset under all oper-

ating conditions.

Also the active reset circuit shapes the reset voltage

into a square waveform that is suitable for driving

the secondary synchronous MOSFET rectifier Q3.

Beware that the gate voltage of Q3 depends on the

reset circuit Q13 and transformer turns ratio.

The main benefit of active reset circuit in the case of

DC1317A-A demo board is high efficiency (shown

in Figure 3)and small size. To achieve such high

efficiency all of the power components were care-

fully selected. Please consult LT factory for assis-

tance if any changes to the circuit are required.

DC1317A-A (LT1952) 48Vin to 3.3V out

Efficiency

88%

89%

90%

91%

92%

93%

94%

0 10 20 30

Iout [A]

Efficiency

Figure 3. High efficiency of DC1317A

Figure 3. High efficiency of DC1317AFigure 3. High efficiency of DC1317A

Figure 3. High efficiency of DC1317A-

-A a

A aA a

A al

llows

lowslows

lows

the board to be used in thermally critical appl

the board to be used in thermally critical applthe board to be used in thermally critical appl

the board to be used in thermally critical appli-

i-i-

cations

cationscations

cations

OUTPUT LOAD STEP

OUTPUT LOAD STEPOUTPUT LOAD STEP

OUTPUT LOAD STEP RESPONSE

RESPONSERESPONSE

RESPONSE

The load step response of DC1317A-A is very fast

even though relatively small amount of output ca-

pacitance is present (200uF ceramic and 470uF

electrolytic). This is thanks to fast error amplifier of

LT4430, optimal amount of current slope compen-

sation of LT1952, fast opto coupler and fast error

amplifier of LT1952. If higher load steps need to be

handled more output capacitance can be added in

order to keep the voltage transients at the desired

level. The load step transients are shown in Figure

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

Figure 4. Fast transient response of DC1317 is

Figure 4. Fast transient response of DC1317 isFigure 4. Fast transient response of DC1317 is

Figure 4. Fast transient response of DC1317 is

uperior to many competing power modules

perior to many competing power modulesperior to many competing power modules

perior to many competing power modules

without the additional output capac

without the additional output capacwithout the additional output capac

without the additional output capaci

itors.

tors.tors.

tors.

SOFT START FUNCTION

SOFT START FUNCTIONSOFT START FUNCTION

SOFT START FUNCTION

The DC1317 features LT4430 opto coupler driver

that has soft start function which produces mono-

tonic startup ramp shown if Figure 5. The rise time

of output voltage is controlled by capacitor C19 that

is connected to OC (Overshoot Control) pin of

LT4430. Also, the soft-start function will prevent

input current surges even with full load at the out-

put.

FiFi

Figure 5. The LT4430 opto coupler driver pr

gure 5. The LT4430 opto coupler driver prgure 5. The LT4430 opto coupler driver pr

gure 5. The LT4430 opto coupler driver pro-

o-o-

duces monotonic output voltage rise at startup

duces monotonic output voltage rise at startupduces monotonic output voltage rise at startup

duces monotonic output voltage rise at startup

without ou

without ouwithout ou

without out

tput voltage overshoot.

put voltage overshoot.put voltage overshoot.

put voltage overshoot.

DEBUGGING AND TESTIN

DEBUGGING AND TESTINDEBUGGING AND TESTIN

DEBUGGING AND TESTING

The DC1317 can easily be tested and debugged by

powering the bias circuit separately from the main

power circuit. To place DC1317 into debug mode

remove the resistor R1 and connect 48V, 100mA

power source to +Vb node (right side of R1). By

doing this, the primary PWM controller LT1952 can

be activated without the main primary power being

applied to +Vin.

To activate the secondary side control circuit

LT4430 diode OR a 5V, 100mA power source into

pin 1 of LT4430 controller.

Once the primary and secondary controllers are

running the main power (+Vin) can be applied

slowly while observing the switching waveforms

and output voltage.

The input current supplying the power transformer

T1 should not exceeded 100mA without the output

load. If one of the MOSFETs is damaged, the input

current will exceed 100mA.

PCB LAYOUT

PCB LAYOUTPCB LAYOUT

PCB LAYOUT

The pcb layout should be carefully planned to avoid

potential noise problems. The PCB layout for DC1317A

can be used as a guide. Since demo board DC1317A

has 8 versions the PCB layout has optional compo-

nents that can be removed. Also, the PCB layout has a

common schematic that is used just for the layout.

The actual circuit schematic shows component values.

The PCB layout schematic does not show the compo-

nent values.

In some cases, a resistor is used in a place holder for

a capacitor such as in the case of C4. Please modify

the reference designators in your schematic to reflect

the actual component used. The following simple PCB

layout rules should be helpful.

If possible use solid ground planes on layers 2 and

n-1. The ground planes will prevent the switching

noise from coupling into sensitive lines.

Place sensitive lines on the inner layers that will be

shielded by grounds on layers 2 and n-1.

Keep the loop formed by Q1, RCS1, Cin and T1 tight.

Keep the loop formed by Q2, Q3 and T1 tight.

Keep noise sensitive nodes like SD/VSEC, ROSC, FB,

COMP, ISENSE, BLANK and DELAY as small as posible

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

by placing the associated components close to the

LT1952 and LT4430 chips.

Use local vias for all components that connect to

ground planes.

Do not place any traces on the layers 2 and n-1 to

avoid ground planes from being compromised.

If the PCB layout has to be done on 2 or 4-layer PCB

try to stay close to the guidelines outlined above. Also,

maximize the ground connections between compo-

nents by placing the components tight together.

Please contact LT factory for additional assistance.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

Rcs1

0.015R

+Vin

R29

22K

Cu1

4.7u

R23 1.2k

R24

39K

Vu1

R15 115k

R20

174k

C10

0.1u

D10

BAT760

C15

2.2nF, 2kV

R28

442k

R22

13.3k

Si7430

PA0861.004

GND

MaxDC

FB=1.23V

Comp

Rosc

Vr=2.5V

Blank 9

Delay 12

OC 11

Sync

Isense 10

PGND 13

Out 14

Vin 15

Sout 16 U1

LT1952-1

R33

470k

C13

.47u

R26

220R

R30

1.2k

R14

33K

C23

1uF

Vfb

R13

22K

Co1

2x100uF

R27

470

R38

18.2K

R35

82.5k

R34

4.75k

C19

1uF

C16

0.22uF

C17

10n

Vcc

FB 4

Opto 6

GND

2Comp 5

LT4430

Cin

2x2.2uF

+Vin

PDZ10B

Vu1

BAS516

R11

82k

+Vin

2.2R

R32

332k

PA1671.650

HAT2165

B0540W

2.2R

Q12

BC856T

Q10

PBSS8110

+Vb

1.5mH

PS2801-1

D11

BAS516

GND

+Vout

Csys

470uF, 6.3V

C24

47p

100p

C25

10n

R49

2.2R

Q13

Si2325

D14

BAS516

R45

10k

+Vr2

R50

2.2R

D17

BAS516

R53

200

2, 3

4, 5

7, 8

9, 10, 11

C33

0.1u

C34

0.22uf

R54

4.7

-Vin

Demo Board DC1317A-A schematic

NOTE:

This schematic shows only the components required for operation of -A version

of DC1317A demo board.

All optional components of DC1317A demo board have been removed.

Also, all zero-ohm resistors have been replaced with wires.

Please consult the full DC1317A-A schematic to decide if any of the optional

components should be included in your design.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A

ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER

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