DEMO MANUAL DC1953A
LTC3374EUHF
8-Channel Parallelable
1A Buck DC/DC
Description
Demonstration circuit 1953A is an 8-output power supply
featuring the
LTC
®
3374.
The LTC3374 has eight synchro-
nous buck regulators each with an independent V
IN
supply.
Up to four buck regulators may be paralleled together to
create a higher power buck regulator with a single induc-
tor. The input range of the LTC3374 is ideal for single cell
Li-Ion/Polymer battery applications.
The buck regulators can be enabled via external preci-
sion threshold enable pins to allow hardwired power up
sequences.
The LTC3374 has a default operating frequency of 2MHz
or it can be set between 1MHz and 3MHz using an external
resistor. The LTC3374 also has a SYNC pin which allows
the internal oscillator to synchronize to an external clock
from 1MHz to 3MHz.
Refer to the LTC3374 data sheet for more details on the
electrical and timing specifications.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1953A
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
Input Supply Range (V
IN1-8
)
V
CC
V
OUT1
V
OUT2
V
OUT3
V
OUT4
V
OUT5
V
OUT6
V
OUT7
V
OUT8
Specifications are at T
A
= 25°C
MIN
2.25
2.7
TYP
MAX
5.5
5.5
3.3
3.0
2.5
2.0
1.8
1.5
1.2
1.0
UNITS
V
V
V
V
V
V
V
V
V
V
CONDITIONS
V
IN1
> 3.3V, I
VOUT1
0A to 1A
V
IN2
> 3.0V, I
VOUT2
0A to 1A
V
IN3
> 2.5V, I
VOUT3
0A to 1A
I
VOUT4
0A to 1A
I
VOUT5
0A to 1A
I
VOUT6
0A to 1A
I
VOUT7
0A to 1A
I
VOUT8
0A to 1A
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DEMO MANUAL DC1953A
Quick start proceDure
The DC1953A is easy to set up to evaluate the performance
of the LTC3374. Refer to Figure 1 and Figure 2 for proper
measurement equipment setup and follow the evaluation
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 output voltage
ripple by touching the probe tip directly across the VIN or
VOUT and GND terminals. See Figure 2 for proper scope
probe technique.
1.
2.
3.
Set the JP1-JP8 jumpers on the DC1953A board to
the OFF position.
Set the MODE jumper, JP9, to the BURST position.
With power off, connect a 0V to 6V, 100mA power
supply to VCC and GND with a voltmeter as shown
in Figure 1.
With power off, connect a 0V to 6V, 3A power supply
to each VIN and GND with a series ammeter and a
voltmeter as shown in Figure 1. A single 0V to 6V, 10A
supply can be used instead to supply all VIN inputs
simultaneously.
Turn on and set the VCC input power supply to 3.3V
and turn on and set the VIN1 supply to 5V.
9.
Note:
Make sure that the input voltages do not exceed 6V.
6.
Set the JP1 jumper, EN1, to the ON position and
observe the VOUT1 regulator turns on and the
PGOOD_ALL LED extinguishes.
Note:
All regulators not powered or set up as a slave must
have their EN pins tied to GND to allow the PGOOD_ALL
LED to extinguish.
7.
With power off, connect a 0V to 3A load to each VOUT
and GND with a series ammeter and a voltmeter as
shown in Figure 1.
Slowly increase LOAD1 from 0A to 1A and observe
the output voltage. The output ripple may also be
observed using an oscilloscope with the probe con-
nected as shown in Figure 2.
When done evaluating VOUT1, repeat steps 5 through
8 for each regulator.
8.
4.
10. Refer to the LTC3374 data sheet for more details on
how the LTC3374 operates.
11. When done, turn off all loads and power supplies.
5.
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DEMO MANUAL DC1953A
Quick start proceDure
Figure 1. Proper Measurement Equipment Setup
VIN
GND
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Figure 2. Measuring Input or Output Ripple
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DEMO MANUAL DC1953A
combining buck regulators with multiple output filters
The LTC3374 has the ability to combine up to 4 consecu-
tively numbered bucks to achieve output currents of 1A,
2A, 3A or 4A. The easiest way to configure the DC1953A
with combined outputs is to use an output inductor and
output capacitor on each switch node. While combining
stages with multiple filters is not ideal for performance or
minimization of components, it does provide the easiest
way to prototype with the desired current levels. Follow
the steps below to make an output a slave to the adjacent
regulator:
1. Remove the desired slave regulator’s associated FB
resistors and feed forward capacitor.
2. Add the associated 0Ω resistor to tie the FB pin to its
VIN pin.
3. Connect the outputs together at the output capacitors.
4. Connect the VIN of the slave regulator to the VIN of the
master regulator.
For example, to make regulator 2 a slave of regulator 1:
1. Remove R6, R7 and C16.
2. Solder a 0Ω resistor to R5.
3. Connect VIN1 to VIN2 at the VIN terminals.
4. Connect VOUT1 to VOUT2 at the output capacitors C12
and C17.
Regulator 3 can also be combined with regulator 1 and
regulator 2 to create a 3A output by:
1. Removing FB3 components, R10, R11 and C19.
2. Solder a 0Ω resistor to R9.
3. Connect VIN3 to VIN2 and VIN1 at the VIN terminals.
4. Connect VOUT3 to VOUT2 and VOUT1 at the output
capacitors.
Regulator 4 can also be added to this combination by
following the same steps with regulator 4’s associated
components.
The higher number regulator is always a slave to the ad-
jacent lower number regulator; therefore regulator 1 can
never be a slave and regulator 8 can never be a master.
combining buck regulators with a single output filter
In most applications it is more practical to use a single
output filter on a combined regulator. To do this the switch
nodes of the combined regulators need to be shorted
together, and the output inductor and capacitor need to
be sized correctly. Please refer to the Combined Buck
Regulator section in the LTC3374 data sheet for more
information on sizing the output capacitor and inductor.
Note:
The DC1953A layout was optimized for eight 1A
outputs. For applications with combined regulators the
layout should be optimized for the components used,
the lowest and equal impedance on the combined switch
nodes, and the shortest AC current paths as possible.
To combine regulators 1 and 2 for a 2A output, perform
the following steps and refer to Figure 3:
1. Remove L2, R6, R7 and C16.
2. Add a 0Ω resistor to R5.
3. Replace L1 with an inductor that can handle the 2A
output at current limit.
4. Replace C12 with at least a 47µF ceramic capacitor.
5. Short SW1 and SW2 together. To reduce the impedance
on the SW node, cut the excess trace from SW2 to L2
close to the short as possible.
6. Short VIN1 and VIN2 together near the VIN terminals.
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DEMO MANUAL DC1953A
combining buck regulators with a single output filter
Figure 3. Combined 2A Output Regulators 1 and 2
To combine regulators 2, 3 and 4 for a 3A output, perform
the following steps and refer to Figure 4:
1. Remove L2, L3 and L4.
2. Add copper foil between the L2 and L3 SW node pads.
Refer to Figure 5 for steps 2 thru 5.
Note:
Copper foil does not provide as low thermal or electri-
cal impedance as PCB copper traces. An optimized layout
should be fabricated to accurately evaluate a 3A output.
3. Add copper foil between VOUT2 and VOUT3 nodes at
the location needed for the inductor pad. The solder
mask may need to be scraped away to do this.
4. Short SW3 and SW4 together.
5. Cut excess SW4 node between short and the L4 pad.
6. Remove R10, R11, R15, R17, C19 and C23.
7. Add 0Ω resistors to R9 and R14.
8. C17 and C20 must have at least 33µF ceramic
capacitors.
9. Connect VIN2, VIN3 and VIN4 together at the VIN
terminals.
Figure 4. Combined 3A Output Regulators 2, 3, 4
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