DC1244A - Demo Manual

DEMO CIRCUIT 1244
QUICK START GUIDE
LOW QUIESCENT CURRENT, DUAL OUTPUT HIGH VOLTAGE STEPDOWN CONVERTER
DESCRIPTION
Demonstration circuit 1244 is a Low Quiescent Current,
Dual Output Synchronous Buck Converter featuring the
LTC3890EGN-1. DC1244 converts a 4.5V-60V voltage
source to 3.3V at 5.0A and 8.5V at 3.0A. When the input
voltage is close or below 9V, 8.5V output enters into
dropout mode.
The main features of the board include an external 5V
linear regulator for bias, RUN1, RUN2, PGOOD1 pins
and a Mode selector that allows converter to run in CCM
or Burst Mode operation. DC1244 supports also Pulse
Skipping Mode, 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 LTC3890EGN-1 datasheet gives a complete description of these parts, operation and application informa-
PARAMETER
Minimum Input Supply Voltage
Maximum Input Supply Voltage
Output Voltage Range (VOUT1)
Output Voltage Range (VOUT2)
Typical switching frequency
Typical Output Ripple (VOUT1, 3.3V)
Typical Output Ripple (VOUT2, 8.5V)
Efficiency Typical (VOUT1, 3.3V)
Efficiency Typical (VOUT2, 8.5V)
tion. The datasheets must be read in conjunction with
this quick start guide for demo circuit 1244.
The 60V avalanche rated MOSFETs, which are used on
DC1244, 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, 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.
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
VIN = 9V to 60V, IOUT2 = 0A to 3A
ILOAD = 5.0A
ILOAD = 3.0A
VOUT1 is ON, VOUT2 is OFF
VOUT1 is OFF, VOUT2 is ON
VALUE
4.5
60
3.3±2%
8.5±2%
225
40
60
92
96
UNITS
V
V
V
V
kHz
mV
mV
%
%
1
QUICK START PROCEDURE
Demonstration circuit 1244 is easy to set up to evaluate
the performance of the LTC3890EGN-1. 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=3.23V to 3.37V,
VOUT2 = 8.33V to 8.67V
NOTE. If there is no output, temporarily disconnect the load to make sure
that the load is not set too high.
1. Place jumpers in the following positions:
4. Once the proper output voltages are established,
adjust the loads within the operating range and observe the output voltage regulation, ripple voltage,
efficiency and other parameters.
JP4 RUN1 ON,
JP3 RUN2 ON,
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or output Ripple
2
DC1244, LTC3890EGN-1, VIN 10V to 60V
100
95
90
%
85
10V
80
30V
60V
75
70
65
60
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
A
Figure 3. 3.3V Output, Efficiency vs. Load
DC1244, LTC3890EGN-1, VIN 10V to 60V
100
98
96
%
94
10V
92
30V
90
60V
88
86
84
82
0.5
1
1.5
2
2.5
3
A
Figure 4. 8.5V Output, Efficiency vs. Load
3
4
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