DC1317A-E - ANALOG DEVICES

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

LT1952

DESCRIPTION

Demonstration circuit 1317A-E 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-E converts isolated 36V to 72V input

to 5V output and provides over 12A of output cur-

rent. The converter operates at 260kHz with the peak

efficiency greater than 94% at 8A load. 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-A, 36-72Vin to 3.3V, 30A

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

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

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

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 pre-

vents output voltage overshoot on startup or when

recovering 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 12A 36V

Maximum Input Voltage IOUT = 0A to 12A 72V

VOUT VIN = 36V to 72V, IOUT = 0A to 12A 5V ±3%

Typical Output Ripple VOUT VIN = 36V to 72V, IOUT = 0A to 12A 50mVP–P

Nominal Switching Frequency 260kHz

QUICK START PROCEDURE

Demonstration circuit 1317 is easy to set up to

evaluate the performance of LT1952 circuit. Refer

to Figure 1 for proper measurement equipment

setup and follow the procedure below:

NOTE:

When measuring the input or output volt-

age 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 di-

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

rectly 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

supply 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 72V.

Check for the proper output voltage.

Vout = 5V.

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 (470uF) 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

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

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

PRIMARY MOSFET DRIVER LTC4440

The DC1317 has an optional LTC4440 MOSFET

driver U2. The LTC4440 can be used if much big-

ger MOSFETs are used. Please contact LT factory

for assistance.

ACTIVE RESET CIRCUIT

The DC1317 is equipped with an active reset cir-

cuit that consists of Q13 and C25. The capacitor

C25 charges to the appropriate transformer reset

voltage. The MOSFET Q13 applies the C25 reset

voltage across the primary of transformer T1. The

C25 reset voltage varies with the duty cycle and

automatically adjusts to provide volt-second bal-

ance for transformer magnetizing current.

LT1952 Efficiency (DC1317A-E) Self Driven SR,

5V output

86%

87%

88%

89%

90%

91%

92%

93%

94%

95%

0 2 4 6 8 10 12 14

Iout [A]

Efficiency

Figure 3. High efficiency of DC1317A-E allows

the board to be used in thermally demanding

applications

OUTPUT LOAD STEP RESPONSE

The load step response of DC1317A-E is very fast

even though relatively small amount of output ca-

pacitance is present (100uF ceramic and 470uF

electrolytic). This is thanks to fast error amplifier

of LT4430, optimal amount of current slope com-

pensation 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 4.

Figure 4. Fast transient response of DC1317A-E

is superior to many competing power modules

without 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 5. The rise time

of output voltage is controlled by capacitor C19

that is connected to OC (overshoot control) pin of

LT4430.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

Figure 5. 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

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 feedback circuit

LT4430 diode OR a 10V, 100mA power source

into collector of Q9.

Once the primary and secondary controllers are

running the MOSFET gate timing can be checked.

If the MOSFET gate timing is correct the main

power input can be applied to +Vin. By slowly in-

creasing the +Vin from 0V to 48V the output volt-

age and input current can be monitored. The input

current should not exceeded 100mA without the

output load. If one of the MOSFETs is damaged,

the input current will exceed 100mA.

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

components that can be removed. Also, the PCB lay-

out has a common schematic that is used just for the

layout. The actual circuit schematic shows compo-

nent values. In some cases, a resistor is used inplace

holder for a capacitor as in 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-

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

use the same guidelines as 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-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

Rcs1

0.025R

Cin1

+Vin

R29

22K

Cu1

4.7u

R23 910

R24

39K

Vu1

R15 115k

R20

75k

C10

0.1u

C15

2.2nF, 2kV

R28

442k

R22

13.3k

Si7818

PA2720

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

R33

158k C13

.47u

R26

220R

R30

1.2k

R14

33K

C23

1uF

Vfb

Vfb R13

22K

R42 0R

Co1

100uF, X7R

+Vo1

R27

270R

R38

18.2K

R35

137k

R34

5.36k

C19

0.33u

C16

.22u, 10V

C17

10n

+Vo1SS

Vcc

FB 4

Opto 6

GND

2Comp 5

LT4430

Cin3

2.2uF, 100V

+Vin

PDZ10B

Vu1

BAS516

R11

82k

-Vin

+Vin

36V to 72V

2.2R

R32

332k

3.1uH

FDMC8854

BAS516

100R

Q12 BC856T

BAS516

Q10

PBSS8110

+Vb

1.5mH

PS2801-1

D11

BAS516

GND

+Vout

DC1317A-E schematic

Csys

470uF, 6.3V

C24

47p

100p

C25

33n, 200V, 1206

Q13

Si2325

D14

BAS516

R45

10k

+Vr2

R50

3.3R

D17

BAS516

R53

200

6, 7

9, 10

C33

0.1u

NOTE:

This schematic shows only the components required for operation of -E 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-E schematic to decide if any of the optional components should be included in your design.

5V, 12A

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E

ACTIVE RESET ISOLATED DC/DC POWER CONVERTER