DC1695B - Demo Board

DEMO CIRCUIT 1695
QUICK START GUIDE
LOW QUIESCENT CURRENT, HIGH VOLTAGE STEP-DOWN
CONVERTER
DESCRIPTION
Demonstration circuit 1695 is a Low Quiescent
Current, Synchronous Buck Converter featuring
the LTC3891EFE. DC1695 converts a 4.5V-60V
voltage source to 3.3V at 5.0A.
The main features of the board include an internal
LDO for power gate driver from VIN or EXTVCC,
RUN and PGOOD pins and a Mode selector that
allows converter to run in CCM, Pulse Skipping or
Burst Mode operation, selectable current limit.
DC1695 supports also adjustable output voltage,
Soft-Start and Tracking. Synchronization to an external clock is possible as well. The wide input voltage range of 4.5V to 60V is suitable for automotive
or other battery fed application and Distributed DC
Power Systems where low quiescent current is
important.
The LTC3891EFE datasheet gives a complete description of this part, operation and application information. The datasheets must be read in conjunction with this quick start guide for demo circuit
1695.
The 60V avalanche rated MOSFETs, which are
used on DC1695, can be operated at their rated
voltage. However, if application derating requirements are stricter, MOSFETs with higher voltage
PARAMETER
Minimum Input Supply Voltage
Maximum Input Supply Voltage
Output Voltage Range
Typical switching frequency
Typical Output Ripple (VOUT, 3.3V)
Efficiency Typical (VOUT, 3.3V)
Supply Quiescent Current
Supply Shutdown Current
rating can be used. Please note, MOSFETs with
higher voltage ratings may affect the efficiency. If
60V MOSFETs are used, keep in mind that 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.
DC1695 supports following MOSFET packages:
LFPAK, PowerPAK SO-8 and PowerPAK 1212-8.
Subsequent logic level MOSFETs can be used
with DC1695
Si7850DP
Vishay
RJK0651DPB
Renesas
HAT2266H
Renesas
BSC100N06LS3 G
Infineon
Si7120DN
Vishay
Design files for this circuit board are available.
Call the LTC factory.
L, LTC, LTM, LT are registered trademarks of Linear Technology Corporation.
CONDITIONS
VIN = 4.5V to 60V, IOUT1 = 0A to 5A
ILOAD = 5.0A
Vin=24V; VOUT=3.3V, Io=0A, Burst mode
Vin=24V
VALUE
4.5
60
3.3±2%
225
40
92
50.8
14.7
UNITS
V
V
V
kHz
mV
%
µA
µA
1
QUICK START PROCEDURE
Demonstration circuit 1695 is easy to set up to
evaluate the performance of the LTC3891EFE.
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 VIN or VOUT and GND terminals. See
Figure 2 for proper scope probe technique.
2. With power off, connect the input power supply to VIN and GND.
3. Turn on the power at the input. Check for the
proper output voltages
VOUT1=3.234V to 3.366V,
NOTE. If there is no output, temporarily disconnect the load to
make sure that the load is not set too high.
4. 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.
1. Place jumper JP1 in the ON position:
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Measuring Input or output Ripple
2
Efficiency vs Load Curret
100
90
80
70
%
60
50
40
30
20
10
0
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
A
Figure 3. 3.3V Output, Efficiency vs. Load, Burst Mode, Vin 12V
3
4
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