DEMO MANUAL
DC1997A-A/DC1997A-B
LTC3838EUHF-1/
LTC3838EUHF-2
High Current, Dual Output
Synchronous Buck Converter
DESCRIPTION
Demonstration circuits
DC1997A-A/DC1997A-B
are
dual output synchronous buck converters featuring the
LTC
®
3838EUHF-1/LTC3838EUHF-2.
Both assemblies
provide two outputs of 1.5V/20A and 1.2V/20A over an
input voltage range of 4.5V to 14V at a switching frequency
of 300kHz.
Applications requiring the output to be adjusted with an
external reference can be implemented with the DC1997A-B
assembly. Such applications include adaptive voltage scal-
ing optimization (AVSO) where the processor voltage is
adjusted to achieve optimal efficiency, wide output voltage
applications controlled by a DAC, or margining. The 2nd
channel of the DC1997A-B assembly is regulated to an
onboard 1.2V reference in the default setup. The same
reference can be set from 0.8V to 1.5V with a potentiometer
or the 2nd channel can regulate to a source external to the
board. The 1st channel on the DC1997A-B assembly and
both channels on the DC1997A-A version are regulated
to the internal reference.
The entire converter, excluding the bulk input and output
capacitors, fits within a 1.5in
2
area on the board. The high
density is a result of the compact, 2-sided drop-in layout
and the use of dual channel FETs.
Additional features of this demo board include:
• Remote sensing for each output.
• PLLIN and CLKOUT pins.
• PGOOD, RUN and TRK/SS pins for each output.
• Optional resistors to tie the two outputs together.
• Optional footprint for discrete single channel FETs for
higher output current.
• Optional footprints to implement DTR (detect transient)
to reduce overshoot following a load release.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
OUT1
Output Voltage V
OUT2
V
OUT1
Maximum Output Current, I
OUT1
V
OUT2
Maximum Output Current, I
OUT2
Nominal Switching Frequency
Efficiency (Measured on DC1997A-B Assembly)
See Figure 2
Specifications are at T
A
= 25°C, No Airflow
VALUE
4.5V
14V
CONDITION
I
OUT1
= 0A to 20A, V
IN
= 4.5V to 14V
I
OUT2
= 0A to 20A, V
IN
= 4.5V to 14V
V
IN
= 4.5V to 14V, V
OUT1
= 1.5V
V
IN
= 4.5V to 14V, V
OUT2
= 1.2V
V
OUT1
= 1.5V, I
OUT1
= 20A, V
IN
= 12V
V
OUT2
= 1.2V, I
OUT2
= 20A, V
IN
= 12V
1.5V ± 2%
1.2V ± 2%
20A
20A
300kHz
90.4% Typical
88.8% Typical
dc1997a-af
1
DEMO MANUAL
DC1997A-A/DC1997A-B
QUICK START PROCEDURE
Demonstration circuit DC1997A-A/DC1997A-B is easy to
set up to evaluate the performance of the LTC3838EUHF-1/
LTC3838EUHF-2. Please refer to Figure 1 for proper mea-
surement equipment setup and follow the procedure below.
1. With power off, connect the input supply, load and
meters as shown in Figure 1. Preset the load to 0A
and VIN supply to be 0V. For both assemblies, place
the jumpers in the following positions:
JP4
JP1
JP2
RUN1
RUN2
MODE
ON
ON
FCM
Adjusting the Onboard Reference:
1. Remove power from the input of the board.
2. Place these jumpers in the following positions:
JP5
JP6
ON BD REF
REF
ADJ
ON BD
3. Apply power to the input of the board.
4. Adjust reference with potentiometer at R52.
Connecting a Reference External to the Board:
1. Remove power from the input of the board.
2. Place JP6 in the EXT position.
3. Connect the external reference between the EXTREF2+
and EXTREF2- turrets.
4. Apply power to the input of the board.
5. Turn-on the external reference.
Note 3: For accurate efficiency measurements in DCM at
light load at V
IN
greater than 5V, remove R51 and apply
an external reference to the board as mentioned above.
Single Output/Dual Phase Operation
A single output/dual phase converter may be preferred
for higher output current applications. The optional com-
ponents required to tie the phases together are found on
the top middle of the first sheet. To tie the two outputs
together, make the following modifications:
1. Tie the two VOUT shapes together with a piece of copper
at the edge of the board where the copper is exposed.
2. Tie the VOUT SENSE1+ pin to INTVCC with a 0Ω jumper
at R8. This will tie ITH1 to ITH2 inside the chip.
3. Tie RUN1 to RUN2 by stuffing a 0Ω jumper at R15.
4. If DTR is implemented, then stuff 0Ω jumper at R9 to
tie the two DTR pins together.
The DC1997A-B assembly has additional jumpers for the
reference circuit. Place these jumpers in the following
positions:
JP5
JP6
ON BD REF
REF
FIXED
ON BD
2. Adjust the input voltage to be between 4.5V and 14V.
V
OUT1
should be 1.5V ± 2%.
V
OUT2
should be 1.2V ± 2%.
3. Next, apply 20A load to each output and re-measure
V
OUT
.
4. Once the DC regulation is confirmed, observe the output
voltage ripple, load step response, efficiency and other
parameters.
Note 1: Use the BNC connectors labeled V
OUT1
or V
OUT2
to measure the output volt-age ripple.
Note 2: Do not connect load from the VO1_SNS+ turret
to the VO1_SNS- turret or from the VO2_SNS+ turret to
the VO2_SNS- turret. This could damage the converter.
Only apply load across the stud connectors on the edge
of the board.
Reference Circuit for Channel 2 of DC1997A-B
Assembly
Channel 2 of the DC1997A-B assembly is configured by
default to regulate to the fixed 1.2V reference generated
by the LT
®
6650 reference circuit. If desired, this reference
can be set with a potentiometer, or an external source such
as a DAC or another source. See the following instructions
to set the board for either:
dc1997a-af
2
DEMO MANUAL
DC1997A-A/DC1997A-B
QUICK START PROCEDURE
Dynamic Load Circuit (Optional)
Demonstration circuit DC1997A-A/DC1997A-B provides
a simple load-step circuit consisting of a MOSFET and
sense resistor for each rail. To apply a load step, follow
the steps below.
1. Pre-set the amplitude of a pulse generator to 0.0V and
the duty cycle to 5% or less.
2. Connect the scope to the VOUT BNC connectors for
the rail under test with a coax cable. To monitor the
load-step current, connect the scope probe across the
ISTEP+/- turrets for that rail.
–
+
3. Connect the output of the pulse generator to the PULSE
turret for the rail under test and connect the return to
the adjacent GND turret.
4. With the converter running, slowly increase the am-
plitude of the pulse generator output to provide the
desired load step pulse height. The scaling for the load
step signal is 5mV/Amp.
V
V
OUT2
*
I
IN
A
I
OUT2
A
V
V
IN
A
I
OUT1
–
V
OUT2
LOAD
+
–
+
V
IN
SUPPLY
+
–
+
V
OUT1
LOAD
–
*MONITOR THE OUTPUT VOLTAGE ACROSS
EITHER COUT2 OR COUT7 FOR ACCURATE
EFFECIENCY MEASUREMENTS
DC1997A F01
–
V
+
V
OUT1
*
Figure 1. Proper Measurement Equipment Setup
dc1997a-af
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DEMO MANUAL
DC1997A-A/DC1997A-B
QUICK START PROCEDURE
LTC3838-2 1.5V/20A and 1.2V/20A Converter
95
FCM, V
IN
= 12V, f
SW
= 300kHz
1.5V
90
1.2V
EFFICIENCY (%)
85
EFFICIENCY (%)
100
LTC3838-2 1.5V/20A and 1.2V/20A Converter
FCM AND DCM
90 V
IN
= 12V
f = 300kHz
80
SW
70
60
50
40
30
20
10
0
0.001
0.01
1.5V RAIL FCM
1.2V RAIL FCM
1.5V RAIL DCM
1.2V RAIL DCM
0.1
1
LOAD CURRENT (A)
10
100
DC1997A F03
80
75
BOTH RAILS:
MOSFET = INFINEON BSC0911ND (DUAL)
L = WÜRTH 7443330047
0.47µH, DCR = 0.8m ±10%
R
SENSE
= 1m
0
5
15
10
LOAD CURRENT (A)
20
25
DC1997A F02
BOTH RAILS:
MOSFET = INFINEON
BSC0911ND (DUAL)
L = WÜRTH 7443330047
0.47µH, DCR = 0.8m ±10%
R
SENSE
= 1m
70
Figure 2. Efficiency Curves for the 1.5V Rail and 1.2V
Rail of the DC1997A-B Assembly in FCM at V
IN
= 12V
VOUT2 of the LTC3838-2 Demo Board
Adjusted with External Reference
95
FCM, V
IN
= 12V, f
SW
= 300kHz
1.6V
1.2V
EFFICIENCY (%)
85
0.8V
Figure 3. Efficiency Curves for the 1.5V Rail and 1.2V Rail
of the DC1997A-B Assembly in FCM and DCM at V
IN
= 12V
90
1.5VO(AC)
50mV/DIV
109mV
20A
80
75
BOTH RAILS:
MOSFET = INFINEON BSC0911ND (DUAL)
L = WÜRTH 7443330047
0.47µH, DCR = 0.8m ±10%
R
SENSE
= 1m
0
5
15
10
LOAD CURRENT (A)
20
25
DC1997A F04
LOAD STEP
5A/DIV
10A
DC1997A F05
70
20µs/DIV
C
OUT
= 2× SANYO 2R5TPE330M9, 100µF X5R 1206
L = WÜRTH 7443330047 (0.47µH)
f
SW
= 300kHz
Figure 4. Efficiency Curves for VOUT2 on the DC1997A-B
Assembly at Different Output Voltage Settings
Figure 5. 50% to 100% to 50% Load Step Response
of the 1.5V Rail on the DC1997A-A Assembly
1.2VO(AC)
50mV/DIV
102mV
1.5VO(AC)
50mV/DIV
109mV
20A
LOAD STEP
5A/DIV
LOAD STEP
5A/DIV
20A
10A
DC1997A F06
10A
DC1997A F07
20µs/DIV
C
OUT
= 2× SANYO 2R5TPE330M9, 100µF X5R 1206
L = WÜRTH 7443330047 (0.47µH)
f
SW
= 300kHz
20µs/DIV
C
OUT
= 2× SANYO 2R5TPE330M9, 100µF X5R 1206
L = WÜRTH 7443330047 (0.47µH)
f
SW
= 300kHz
Figure 6. 50% to 100% to 50% Load Step Response
of the 1.2V Rail on the DC1997A-A Assembly
Figure 7. 50% to 100% to 50% Load Step Response
of the 1.5V Rail on the DC1997A-B Assembly
dc1997a-af
4
DEMO MANUAL
DC1997A-A/DC1997A-B
QUICK START PROCEDURE
1.2VO(AC)
50mV/DIV
97mV
RUN1
2V/DIV
20A
LOAD STEP
5A/DIV
V
OUT1
TRACK/SS1
500mV/DIV
DC1997A F08
10A
2ms/DIV
C
SS
= 10nF
V
IN
= 12V, FULL LOAD
DC1997A F09
20µs/DIV
C
OUT
= 2× SANYO 2R5TPE330M9, 100µF X5R 1206
L = WÜRTH 7443330047 (0.47µH)
f
SW
= 300kHz
Figure 8. 50% to 100% to 50% Load Step Response
of the 1.2V Rail on the DC1997A-B Assembly
Figure 9. Turn-On of the 1.5V Rail of the DC1997A-A
Assembly. RUN Pin Released from Ground
RUN2
2V/DIV
RUN1
2V/DIV
V
OUT2
TRACK/SS2
500mV/DIV
2ms/DIV
C
SS
= 10nF
V
IN
= 12V, FULL LOAD
DC1997A F10
V
OUT1
TRACK/SS1
500mV/DIV
2ms/DIV
C
SS
= 10nF
V
IN
= 12V, FULL LOAD
DC1997A F11
Figure 10. Turn-On of the 1.2V Rail of the DC1997A-A
Assembly. RUN Pin Released from Ground
Figure 11. Turn-On of the 1.5V Rail of the DC1997A-B
Assembly. RUN Pin Released from Ground
RUN2
2V/DIV
EXTV
REF
500mV/DIV
V
OUT2
TRACK/SS2
500mV/DIV
2ms/DIV
C
SS
= 4.7nF
V
IN
= 12V, FULL LOAD
DC1997A F12
Figure 12. Turn-On of the 1.2V Rail of the DC1997A-B
Assembly. RUN Pin Released from Ground
dc1997a-af
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