Linear Technology DC1317A Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

LT1952-1

DESCRIPTION

Demonstration circuit 1317A-G is isolated input to

high current output 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-G (Figure 7) converts isolated 9V to

36V input to 12V output and provides over 8A of out-

put current depending on cooling. When determining

the cooling requirements the actual input voltage

range and continuous maximum output current must

be taken into account. The converter operates at

200kHz with the peak efficiency greater than 94%.

The DC1317 can be easily modified to generate out-

put voltages in the range from 0.6V to 48V. The out-

put currents are limited by total output power of up to

150W.

The available versions of DC1317A are:

DC1317A-A, 34-75Vin to 3.3V, 35A

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

DC1317A-C, 18-72Vin to 12V, 8A-12A

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

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

DC1317A-F, 9-36Vin to 3.3V, 22A

* DC1317A-F5, 9-36Vin to 5V, 20A

DC1317A-G, 9-36Vin to 12V, 8A

* DC1317A-G18, 9-36Vin to 18V, 5A

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

* The DC1317A-G18 is a slightly modified design fea-

turing 18V @6A output. Please contact the LTC fac-

tory for details.

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 available. Call

the LTC factory.

LT is a trademark of Linear Technology Corporation

Table 1. Performance Summary

PARAMETER CONDITION VALUE

Minimum Input Voltage IOUT = 0A to 8A 9V

Maximum Input Voltage IOUT = 0A to 8A 36V

VOUT VIN = 9V to 36V, IOUT = 0A to 8A (27Amax) 12V ±3%

Typical Output Ripple VOUT VIN = 9V to 36V, IOUT = 0A to 8A 50mVP–P

Nominal Switching Frequency 200kHz

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

QUICK START PROCEDURE

Demonstration circuit 1317 is easy to set up to evalu-

ate the performance of LT1952-1 circuit. Refer to Fig-

ure 1 for proper measurement equipment setup and

follow the procedure below:

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.

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.

Turn on the power at the input.

NOTE:

Make sure that the input voltage does not

exceed 36V.

Check for the proper output voltage.

Vout = 12V.

If there is no output, temporarily disconnect the

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

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.

The DC1317 is equipped with an output capacitor

CSYS (220uF) that approximates typical system

rail capacitance. If system board already has ca-

pacitance of similar value CSYS can be removed.

Figure 1. Proper Measurement Equipment Setup

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

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

ACTIVE RESET CIRCUIT

The Active Reset circuit on DC1317A-F 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 results in lower drain

voltages for Q1 and Q2 MOSFETs. The lower

MOSFET drain voltages allow lower voltage and

lower Rdson MOSFETs to be used. The MOSFETs

must be avalanche rated for the peak reset voltage.

If non-avalanche rated MOSFETs are used a proper

drain voltage derating should be used.

The main benefit of active reset circuit in the case of

DC1317A-G demo board is high efficiency (shown

in Figure 3), wide input range, high power density

and small size. To achieve such high efficiency all of

the power components were carefully selected.

Please consult LT factory for assistance if any

changes to the circuit are required.

If PCB space is limited, a smaller 1825R2-3366.006

transformer from Champs engineering can be used.

However, the efficiency will be about 1% lower. For

more information please consult LT factory.

DC1317A-G 12V Output Efficiency

89%

90%

91%

92%

93%

94%

95%

0 1 2 3 4 5 6 7 8 9

Iout [A]

Efficiency

12V input

24V input

Figure 3. High efficiency of DC1317A-G allows the

board to be used in thermally critical applications

18V OUTPUT CIRCUIT

The DC1317A-G demo board can easily be modified

for 18V output. Only few minor component changes

are required and are shown in the schematic in Figure

The efficiency of 18V Output version of DC1317A-G is

shown in the Figure 4. The efficiency is slightly lower

than the efficiency of 12V version due to higher DC

resistance of transformer and output MOSFETs.

Also, the 18V output can be further increased to

19.5V

just by changing the voltage divider on the FB pin of

LT4430 circuit. The 19.5V version is suitable for sup-

plying laptop computer power from 12V automotive

power source.

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

DC1317A-G-18V 18V Output Efficiency,

89%

90%

91%

92%

93%

94%

95%

0 1 2 3 4 5 6 7 8

Iout [A]

Efficiency

12V input

24V input

Figure 4. The efficiency of modified DC1317A-G

demo board for 18V output.

OUTPUT LOAD STEP RESPONSE

The load step response of DC1317A-G is very fast

even though relatively small amount of output ca-

pacitance is present (200uF ceramic and 220uF

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

Figure 5. Fast transient response of DC1317A-F is

superior to many competing power modules with-

out the additional output capacitors.

SOFT START FUNCTION

The DC1317 features LT4430 opto coupler driver

that has soft start function which produces mono-

tonic startup ramp shown if Figure 6. 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.

Figure 6. The LT4430 opto coupler driver pro-

duces monotonic output voltage rise at startup

without output voltage overshoot.

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

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

remove the resistor R1 and connect 12V, 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 200mA without the output

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

current will exceed 200mA.

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. The schematic in figure 7

is showing the circuit without any optional compo-

nents. Also, the circuit in figure 7 does not show any

zero-ohm resistors. Please consult the schematic on

page 7 to determine if any of the options should be

included in your PCB layout.

Also, the PCB layout has a common schematic that is

used just for the layout. The PCB layout schematic is

not included in this quick start guide but it is included

with PCB design files.

Please note that the actual circuit schematic on page 7

shows the component values. The PCB layout sche-

matic included with design files does not show the

component values.

In some cases, a different component like a diode is

used in a place holder for a capacitor such as in the

case of C6. Please modify the reference designators in

your schematic to reflect the actual component used.

The following simple PCB layout rules should be help-

ful.

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

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.

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

Rcs1

0.005R

+Vin

R54

2.2R

Cu1

4.7u

R23 910R

R24

100k

Vu1

R15 178k

R20

100k

C10

0.1u

Vu1

D10*

100p

C15

2.2nF, 2kV

R28

115k

R22

13.3k

HAT2266

G45R2-0306.006

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

LT1952-1

C13

.47u

R26

220R

R30

1.2k

R14

33K

C23

1uF

Vfb

R13

22K

Co1

33uF, X7R

+Vo1

R27

470R

R38

18.2K

R35

348k

R34

12.1k

C19

1uF

C17

15n

+Vo1

Vcc

FB 4

Opto 6

GND

2Comp 5

LT4430

Cin

3x6.8uF

+Vin

PDZ10B

Vu1

BAS516

R11

10k

-Vin

+Vin

9-36V Input

2.2R

R32

196k

HR-PQA2050-16

HAT2266

HAT2173

FG CG

Q12

BC856T

Q10

PBSS8110

+Vb

1.5mH

PS2801-1

D11

BAS516

GND

+Vout

* Please change the ref designator to reflect the symbol.

Csys

220uF, APXE

C25

33n

Q13

Si7309

D14

BAS516

R45

10k

+Vr2

D17

BAS516

2, 3

4, 5

7, 8

10, 11

C33

0.1u

R29*

PMEG3002

C34

0.33u

R53*

10uH

560k

100p

Demo Board DC1317A-G schematic

NOTE:

This schematic shows only the components required for operation of -G 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-G schematic to decide if any of the optional

components should be included in your design.

R17

560R

T2A

PE-68386

C14

C12

470p

R19

60.4k

CS-

CS+

Vcc

4FG 5

GND 6

Timer 7

Sync 8

LTC3900

R21

10k

R18

10k

R16

33k

0.22u

BCX55

R10

PDZ10B

220p

Out

C6*

BAS521

680uH

10uH

665R

Inp

Vcc

TS 4

Boost 6

GND

2TG 5

LTC4440-5

C21

220p

BAS516

Vu1

Figure 7. DC1317A

schematic.

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

Rcs1

0.005R

+Vin

R54

2.2R

Cu1

4.7u

R23 910R

R24

100k

Vu1

R15 178k

R20

100k

C10

0.1u

Vu1

D10*

100p

C15

2.2nF, 2kV

R28

115k

R22

13.3k

RJK0652

G45R2-0207.005

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

LT1952-1

C13

.47u

R26

220R

R30

1.2k

R14

33K

C23

1uF

Vfb

R13

22K

Co1

33uF, X7R

+Vo1

R27

470R

R38

11K

R35

348k

R34

12.1k

C19

1uF

C17

15n

+Vo1

Vcc

FB 4

Opto 6

GND

2Comp 5

LT4430

Cin

3x6.8uF

+Vin

PDZ10B

Vu1

BAS516

R11

10k

-Vin

+Vin

9-36V Input

2.2R

R32

196k

HR-PQA2050-27

HAT2266

RJK2055

FG CG

Q12

BC856T

Q10

PBSS8110

+Vb

1.5mH

PS2801-1

D11

BAS516

GND

+Vout

* Please change the ref designator to reflect the symbol.

Csys

150uF, 20V, APXE

C25

33n

Q13

Si7309

D14

BAS516

R45

10k

+Vr2

D17

BAS516

2, 3

4, 5

7, 8

10, 11

C33

0.1u

R29*

PMEG3002

C34

0.33u

R53*

10uH

560k

100p

Demo Board DC1317A-G18V schematic

NOTE:

This schematic shows the required modifications of DC1317A-G for 18V @6A output.

The component values and part numbers shown in RED are the only changes required for 18V output.

Please contact LT factory for assistance.

R17

560R

T2A

PE-68386

C14

C12

470p

R19

60.4k

CS-

CS+

Vcc

4FG 5

GND 6

Timer 7

Sync 8

LTC3900

R21

10k

R18

10k

R16

33k

0.22u

BCX55

R10

PDZ10B

220p

Out

C6*

BAS521

1.5mH

10uH

511R

Inp

Vcc

TS 4

Boost 6

GND

2TG 5

LTC4440-5

C21

220p

BAS516

Vu1

18V Output

Figure 8. The 18V @6A

version of DC1317A-G.

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G

ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER

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