Linear Technology DC1185B-A, DC1185B-B, LTC3850EUF Demo Manual
DESCRIPTION
DEMO MANUAL
DC1185B-A/-B
LTC3850EUF
Dual Phase/Dual Output
Synchronous Buck Converter
Demonstration circuit 1185 is a dual phase/dual output
synchronous buck converter featuring the LTC3850EUF.
The demo board comes in two versions. The output volt
ages for version DC1185B-A are 2.0V/10A and 1.8V/10A.
The output voltages for version DC1185B-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, 2-sided drop-in layout.
The power components excluding the bulk output and input
capacitors, fit within a 1.35" × 0.75" area on the top layer.
The control circuit resides in a 0.60" × 0.75" area on the
bottom layer. The package style for the LTC3850EUF is a
4mm × 4mm 28-lead QFN with an exposed ground pad.
PERFORMANCE SUMMARY
PARAMETER CONDITION VALUE
Minimum Input Voltage 6.5V
Maximum Input Voltage 14V
Specifications are at TA = 25°C
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 configured
for either CCM (original setting), Burst Mode
skipping operation with the MODE jumper. The board
also has optional resistors for single output/dual phase
operation, rail tracking, DCR sensing and synchronization
to an external clock.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Note: Q1-Q4 MOSFETs changed on September 10, 2013.
See Schematic Diagram.
®
, or pulse-
Version DC1185B-A
Output Voltage V
Output Voltage V
Nominal Switching Frequency 500kHz
Full-Load Efficiency
(See Figure 3 for Efficiency Curves)
Version DC1185B-B
Output Voltage V
Output Voltage V
Nominal Switching Frequency 400kHz
Full-Load Efficiency
(See Figure 4 for Efficiency Curves)
OUT1
OUT2
OUT1
OUT2
I
= 0A to 10A 2.0V ±2%
OUT1
I
= 0A to 10A 1.8V ±2%
OUT2
= 2.0V, I
V
OUT1
V
= 1.8V, I
OUT2
I
= 0A to 15A 1.5V ±2%
OUT1
I
= 0A to 15A 1.2V ±2%
OUT2
= 1.5V, I
V
OUT1
V
= 1.2V, I
OUT2
= 10A, VIN = 12V
OUT1
= 10A, VIN = 12V
OUT2
= 15A, VIN = 12V
OUT1
= 15A, VIN = 12V
OUT2
90.2%
89.5%
88.1%
86.5%
dc1185b-a/-bf
1
DEMO MANUAL
DC1185B-A/-B
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 ripple,
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 soldered
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 DC1158B-A:
V
V
Version DC1158B-B:
V
V
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:
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.
= 1.960V to 2.040V
OUT1
= 1.764V to 1.836V
OUT2
= 1.470V to 1.530V
OUT1
= 1.176V to 1.224V
OUT2
Do not apply load across the VOSn+ and VOSn –
2
Figure 1. Proper Measurement Equipment Setup
dc1185b-a/-bf
DEMO MANUAL
VOUT
GND
COUT
+
-
DC1185B-A/-B
QUICK START PROCEDURE
Figure 2. Measuring Output Voltage Ripple
2.0V/10A and 1.8V/10A Efficiency at VIN = 12V and fSW = 500kHz 1.5V/15A and 1.2V/15A Efficiency at VIN = 12V and fSW = 400kHz
95
90
85
80
EFFICIENCY (%)
QTOP: RJK030DPB
QBOTTOM: RJK0330DPB
75
L: TOKO FDU0650-R56M = P3
0.56µH, DCR = 2.45mΩ, 3.2mΩ MAX
R
70
0
= 3mΩ
SENSE
4 6 8
2
LOAD CURRENT (A)
2.0V
1.8V
10 12
Figure 3. Efficiency Curves for the DC1185B-A Figure 4. Efficiency Curves for the DC1185B-B
SINGLE OUTPUT/DUAL PHASE OPERATION
A single output/dual phase converter may be preferred
for high output current applications. The benefits of
single output/dual phase operation is lower ripple current
through the input and output capacitors, improved load
step response and simplified thermal design. To implement
single output/dual phase operation, make the following
modifications:
1. Tie VOUT1 to VOUT2 by tying together the exposed
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 0Ω at R49.
3. Tie VFB1 to VFB2 by stuffing 0Ω at R50.
4. Tie TRK/SS1 to TRK/SS2 by stuffing 0Ω at R52.
5. Tie RUN1 to RUN2 by stuffing 0Ω at R55.
6. Remove the redundant ITH compensation network and
VFB divider.
95
90
85
80
EFFICIENCY (%)
75
70
0
QTOP: RJK030DPB
QBOTTOM: RJK0330DPB
L: VITEC 59PR9875
0.4µH, DCR = 0.47mΩ ±10%
= 2mΩ
R
SENSE
6 9 12
3
LOAD CURRENT (A)
1.5V
1.2V
15 18
dc1185b-a/-bf
3
DEMO MANUAL
DC1185B-A/-B
RAIL TRACKING
Demonstration circuit 1185 is set up for independent
turn-on of VOUT1 and VOUT2. The ramp-rate for VOUT1 is
determined by the TRK/SS1 capacitor at C2 and the ramprate for VOUT2 is determined by the TRK/SS2 capacitor
at C47. The turn-on of one rail will not affect the other for
the original demo board.
Table 1. VOUT1 Tracking Options for a 1.5V Output
TRACK 1 DIVIDER TRK/SS1 CAPACITOR
CONFIGURATION R3 R2 C2
Soft-Start without Tracking (Original Board) 0Ω Not Stuffed 0.1µF
External Coincident Tracking 17.8kΩ 20.0kΩ Not Stuffed
Table 2. VOUT2 Tracking Options for a 1.2V Output
CONFIGURATION R36 R34 R37 C47
Soft-Start without Tracking (Original Board) 0Ω Not Stuffed Not Stuffed 0.1µF
Coincident Tracking to VOUT1 (1.5V) 0Ω 10.0kΩ 20.0kΩ Not Stuffed
External Coincident Tracking 10.0kΩ Not Stuffed 20.0kΩ Not Stuffed
This board can be modified on the bench to allow VOUT1
to track an external signal. It can also be modified to
allow VOUT
an
external signal. Tables 2 and 3 cover the rail tracking
2 to track VOUT1 or to allow VOUT2 to track
options for each rail, with the DC3850B-B version used
as an example.
TRACK 2 DIVIDER TRK/SS2 CAPACITOR
4
dc1185b-a/-bf
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