DEMO MANUAL DC2006A-B
LTC3862-2
High Power, High Voltage
Step-Up Converter
Description
Demonstration circuit 2006A-B is a multiphase high power,
high voltage step-up DC/DC converter featuring two the
LTC
®
3862-2
boost controllers. This demo board converts
a 6V to 36V input voltage to a 120V output at up to 2.0A
with two stages. The first stage converts the input voltage
to 50V. The second stage converts the 50V to 120V and
each stage uses one LTC3862-2.
The DC2006A-B supports three ways of biasing the
LTC3862-2 controllers IC’s by directly from the input
voltage, or from a low power switching power supply or
from an LDO regulator.
An onboard SEPIC power supply can provide a stable 10V
bias voltage for both LTC3862-2 controllers over the wide
varying input voltage. This allows the use of either logic
level or standard level MOSFETs, even when the input
voltage drops below the 10V set-point, which is useful in
wide varying input applications.
An onboard LDO regulator can be selected for biasing the
LTC3862-2 controllers which simplifies the design and is
useful in applications where the input voltage is always
higher than the required gate drive voltage.
The LTC3862-2 is a multiphase step-up (boost) DC/DC
controller that delivers high output power in a compact
footprint. Up to 12 power stages can be paralleled and
clocked out-of-phase to minimize input and output filtering
requirements. It has a 5.5V to 36V input voltage range and
an output voltage range that is dependent on the choice
of external components.
The LTC3862-2 utilizes peak current mode architecture for
easy loop compensation and multiphase operation with
very accurate phase-to-phase current matching. The fixed
operating frequency can be set with a single resistor over
a 75kHz to 500kHz range or can be synchronized to an
external clock over a 50kHz to 600kHz frequency range.
A current sense resistor is used in each phase to provide
a precise cycle-by-cycle current limit. The powerful on-
board gate drivers minimize switching losses and allow
the use of multiple MOSFETs in parallel for very high
current applications.
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 Supply Voltage
Maximum Input Supply Voltage
Output Voltage Range
Typical switching frequency
Typical Output Ripple (V
OUT
, 120V)
Efficiency Typical (V
OUT
, 120V, V
IN
14V)
I
LOAD
= 1.0A
See Figure 3
V
IN
= 6V to 36V, I
OUT1
= 0A to 2.0A
CONDITIONS
VALUE
6
36
120 ±2%
200
150
93
UNITS
V
V
V
kHz
mV
%
dc2006abfa
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DEMO MANUAL DC2006A-B
Quick start proceDure
Demonstration circuit 2006 is easy to set up to evaluate
the performance of the LTC3862-2 controllers. Refer to
Figure 1 for proper measurement equipment setup and
follow the 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 V
IN
or
V
OUT
and GND terminals. See Figure 2 for proper scope
probe technique.
1. Place jumper RUN1 (JP11) in the ON position. Place
jumper RUN2 (JP10) in ON position also.
2. Place jumper BIAS (JP12) to the V
IN
position.
3. With power off, connect the input power supply to V
IN
and GND.
Turn the input power source on and slowly increase the
input voltage. Be careful not to exceed 36V.
NOTE: Make sure that the input voltage V
IN
does not ex-
ceed 36V. If higher operating voltage is required, power
components with higher voltage ratings should be used.
4. Check for the proper output voltage of 120V. If there is
no output, temporarily disconnect the load to make sure
that the load is not set too high. Take all the precautions
needed to work with high 120V output voltage.
5. Once the proper output voltages are established, adjust
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
LTC3862-2 BIAS CIRCUITS
The demo board DC2006A supports three ways of biasing
LTC3862-2 controllers. Place jumper BIAS (JP12) to the
V
IN
position for input voltage above 10V, but below 36V.
In this case bias pins of LTC3862-2 controllers will be
connected directly to the input voltage.
Place jumper BIAS (JP12) to the AUX position for input volt-
age that can drop below 10V. The bias pins of LTC3862-2
controllers will be connected directly to the low power
SEPIC converter, which provides regulated 10V.
The demo board DC2006A can be used for higher than 36V
input voltages. In that case, the bias power for LTC3862-2
has to be limited under 36V. An external power source can
be used to accomplish this or the optional bias regulator
can be used. Remove R44 and R47 resistors and install
0Ω resistors R44 and R42.
Place jumper BIAS (JP12) to the AUX position. Since the
power dissipation in linear regulator Q17 depends on the
size of MOSFETs, switching frequency and voltage differ-
ence across Q17, all of the factors need to be considered
when selecting the appropriate device for Q17. Please
refer to LTC3862-2 data sheet.
CONVERTER EffICIENCy
DC2006A-B efficiency reaches 92% at 12V input voltage
generating 120V at 2.0A and 93% at 14V input voltage,
see Figure 3. However, output current should be decreased
at input voltages below 11V to reduce thermal stress on
the converter. Figure 4 demonstrates maximum output
current, as function of input voltage, assuming 120V
output voltage.
All measurements were conducted at room temperature,
natural convection cooling with no air flow.
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dc2006abfa
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