DESCRIPTION
DEMO MANUAL DC1940A
Low Quiescent Current,
High Voltage Step-Down
Converter
Demonstration circuit 1940A is a low quiescent current,
®
synchronous buck converter featuring the LTC
3891EUDC.
This demo board converts a 16V to 60V voltage to a 12V
at 15A output.
The main features of this board include an internal LDO
for gate drive power from V
or EXTVCC, RUN and
IN
PGOOD pins, a mode selector that allows the converter
to run in constant current mode (CCM), pulse-skipping or
®
Burst Mode
operation, and selectable current limit. The
DC1940A supports an adjustable output voltage, soft-start
and tracking. The wide input voltage range of 16V to 60V is
suitable for double battery automotive and distributed DC
power systems where low quiescent current is important.
The LTC3891 data sheet gives a complete description of
this part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1940A.
The 60V avalanche rated MOSFETs, which are used
on DC1940A, can be operated at their rated voltage.
However, if application derating requirements are
stricter, MOSFETs with higher voltage rating can be used.
Please note, MOSFETs with higher voltage ratings may affect the efficiency. If 60V MOSFETs are used, the MOSFET
avalanche rating and testing is typically done with 30%
over voltage margin (78V for 60V rated MOSFET). Please
check with particular MOSFET manufacturer to ensure the
avalanche voltage rating.
The DC1940A supports the following MOSFET packages:
LFPAK, PowerPAK SO-8 and Power 56. The subsequent
logic level (SV gate) MOSFETs can be used with DC1940A.
Si7850DP Vishay
RJK0651DPB Renesas
HAT2266H Renesas
BSC100N06LS3 G Infineon
FDMS86520L Fairchild
For synchronization to an external clock, remove jumper
JP2 and apply sync signal on terminal SYNC.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Burst Mode, 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 CONDITIONS VALUE UNITS
Minimum Input Supply Voltage 16 V
Maximum Input Supply Voltage 60 V
Output Voltage Range V
Typical Switching Frequency 125 kHz
Typical Output Ripple (V
Efficiency Typical (V
Supply Quiescent Current V
Supply Shutdown Current V
, 12V) I
OUT
, 12V) 97 %
OUT
(TA = 25°C)
= 16V to 60V, I
IN
= 15A 80 mV
LOAD
= 24V; V
IN
= 24V 14.7 μA
IN
OUT
= 0A to 5A 12 ± 2% V
OUT1
= 12V, IO = 0A, Burst Mode Operation 50.8 μA
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1
DEMO MANUAL DC1940A
QUICK START PROCEDURE
Demonstration circuit 1940A is easy to set up to evaluate
the performance of the LTC3891EUDC. 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
and GND terminals. See Figure 2 for proper scope
V
OUT
probe technique.
1. Place jumper JP1 in the ON position.
2. With power off, connect the input power supply to V
and GND.
IN
or
IN
3. Turn on the power at the input. Check for the proper
output voltages:
V
NOTE: If there is no output, temporarily disconnect the
4. Once the proper output voltages are established, adjust
= 11.9V to 12.4V
OUT1
load to make sure that the load is not set too high.
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
2
DC1940a F01
Figure 1. Proper Measurement Equipment Setup
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