DC1185A-A Datasheet DC1185A-A | P1-P3

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1185

DUAL PHASE/DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER

LTC3850EUF

DESCRIPTION

Demonstration circuit 1185 is a dual phase/dual output

synchronous buck converter featuring the LTC3850EUF.

The demo board comes in two versions. The output

voltages for version -A are 2.0V/10A and 1.8V/10A and

the output voltages for version -B are 1.5V/15A and

1.2V/15A. The input voltage range is 6.5V to 14V for

both versions. For applications that have a 5V +/- 0.5V

input, the board has an optional resistor to tie the

INTVCC pin to the VIN pin.

The demo board uses a high density, two sided drop-in

layout. The power components, excluding the bulk out-

put and input capacitors, fit within a 1.35” X 0.75” area

on the top layer. The control circuit resides in a 0.60” X

0.75” area on the bottom layer. The package style for the

LTC3850EUF is a 4mm X 4mm 28-lead QFN with an ex-

posed ground pad.

The main features of the board include an internal 5V

linear regulator for bias, RUN pins for each output, an

EXTVCC pin and a PGOOD signal. The board can be con-

figured for either CCM (original setting), Burst Mode, or

pulse skip operation with the MODE jumper. The board

also has optional resistors for single output / dual phase

operation, rail tracking, DCR sensing and synchroniza-

tion to an external clock.

Design files for this circuit board are available. Call

the LTC factory.

Table 1.

Performance Summary (T

= 25°C)

PARAMETER CONDITION VALUE

Minimum Input Voltage 6.5V

Maximum Input Voltage 14V

Version -A

Output Voltage V

OUT1

= 0A to 10A 2.0V ±2%

Output Voltage V

OUT2

= 0A to 10A 1.8V ±2%

Nominal Switching Frequency 500kHz

OUT1

= 2.0V, I

OUT1

= 10A , V

= 12V 88.0% Full Load Efficiency

(see Figure 3 for efficiency curves)

OUT2

= 1.8V, I

OUT2

= 10A , V

= 12V 87.0%

Version -B

Output Voltage V

OUT1

= 0A to 15A 1.5V ±2%

Output Voltage V

OUT2

= 0A to 15A 1.2V ±2%

Nominal Switching Frequency 400kHz

OUT1

= 1.5V, I

OUT1

= 15A , V

= 12V 87.4% Full Load Efficiency

(see Figure 4 for efficiency curves)

OUT2

= 1.2V, I

OUT2

= 15A , V

= 12V 85.3%

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1185

DUAL PHASE/DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER

QUICK START PROCEDURE

Demonstration circuit 1185 is easy to set up to evaluate

the performance of the LTC3850EUF. Refer to Figure 1

for the proper measurement equipment setup and follow

the procedure below:

NOTE:

When measuring the output or input voltage rip-

ple, care must be taken to avoid a long ground lead on

the oscilloscope probe. See Figure 2 for the proper

scope probe technique. Short, stiff leads need to be sol-

dered to the (+) and (-) terminals of an output capacitor.

The probe’s ground ring needs to touch the (-) lead and

the probe tip needs to touch the (+) lead.

Place jumpers in the following positions:

JP1 RUN1 ON

JP2 RUN2 ON

JP3 MODE CCM

With power off, connect the input power supply to VIN

and GND.

Turn on the power at the input.

NOTE:

Make sure that the input voltage does not exceed

15V.

Check for the proper output voltages.

Version –A:

Vout1 = 1.960V to 2.040V

Vout2 = 1.764V to 1.836V

Version –B:

Vout1 = 1.470V to 1.530V

Vout2 = 1.176V to 1.224V

Once the proper output voltages are established, adjust

the loads within the operating range and observe the

output voltage regulation, ripple voltage, efficiency and

other parameters.

NOTE:

Do not apply load across the VOSn+ and VOSn-

turrets. These turrets are only intended to Kelvin sense

the output voltage across COUT1 and COUT4. Heavy

load currents may damage the output voltage sense

traces.

SINGLE OUTPUT / DUAL PHASE OPERATION

A single output / dual phase converter may be preferred

for high output current applications. The benefits of sin-

gle output / dual phase operation is lower ripple current

through the input and output capacitors, improved load

step response and simplified thermal design. To imple-

ment single output / dual phase operation, make the fol-

lowing modifications:

Tie VOUT1 to VOUT2 by tying together the ex-

posed copper pads near J3 and J5 at the edge of

the board. Use a piece of heavy copper foil.

2. Tie ITH1 to ITH2 by stuffing 0

Ω

at R49.

3. Tie VFB1 to VFB2 by stuffing 0

Ω

at R50.

4. Tie TRK/SS1 to TRK/SS2 by stuffing 0

Ω

R52.

5. Tie RUN1 to RUN2 by stuffing 0

Ω

at R55.

Remove the redundant ITH compensation

network and VFB divider.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1185

DUAL PHASE/DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER

RAIL TRACKING

Demonstration circuit 1185 is setup for independent

turn-on of VOUT1 and VOUT2. The ramp-rate for VOUT1

is determined by the TRK/SS1 cap at C2 and the ramp-

rate for VOUT2 is determined by the TRK/SS2 cap at

C47. The turn-on of one rail will not affect the other for

the original demo board.

This board can be modified on the bench to allow

VOUT1 to track an external signal. It can also be modi-

fied to allow VOUT2 to track VOUT1 or to allow VOUT2

to track an external signal. Tables 2 and 3 cover the rail

tracking options for each rail, with the –B version used

as an example.

Table 1.

OUT1

Tracking Options for a 1.5V Output.

TRACK1 DIVIDER TRK/SS1 CAP

CONFIGURATION R3 R2 C2

Soft Start Without Tracking (original board) 0

Ω

Not stuffed 0.1uF

External Coincident Tracking

17.8k

Ω

20.0k

Ω

Not Stuffed

Table 2.

OUT2

Tracking Options for a 1.2V Output.

TRACK2 DIVIDER TRK/SS2 CAP

CONFIGURATION R36 R34 R37 C47

Soft Start Without Tracking (original board) 0

Ω

Not stuffed Not stuffed

0.1uF

Coincident Tracking to V

OUT1

(1.5V) 0

Ω

10.0k

Ω

20.0k

Ω

Not Stuffed

External Coincident Tracking 10.0k

Ω

Not stuffed 20.0k

Ω

Not Stuffed

INDUCTOR DCR SENSING

Demonstration circuit 1185 provides an optional circuit

for DCR sensing. DCR sensing uses the DCR of the in-

ductor to sense the inductor current instead of discrete

sense resistors. The advantages of DCR sensing are

lower cost, reduced board space and higher efficiency,

but the disadvantage is a less accurate current limit. If

DCR sensing is used, be sure to select an inductor cur-

rent with a sufficiently high saturation current or use an

iron powder type. Tables 3 and 4 show an example of

how to modify the DC1185 for DCR sensing using these

parameters:

OUT1

= 2.0V / 10A

OUT2

= 1.8V / 10A

= 6.5V to 14V

Fsw

= 500kHz, typical

L1,2

= Toko FDU0650-R56M=P3

(0.56uH,

DCR = 2.45m

Ω

typ, 3.2m

Ω

max

)

ILIM = FLOATING (R42,R44 = OPEN)

P1-P3 P4-P6 P7-P8

DC1185A-A

Mfr. #:

Buy DC1185A-A

Manufacturer:

Analog Devices / Linear Technology

Description:

Power Management IC Development Tools LTC3850EUF Demo Board 4.5V = VIN = 14V; VOUT1: 2V @ 10A, VOUT2: 1.8V @ 10A

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DC1185A-A