DC1155A - Demo Manual

DEMO CIRCUIT
1155A
155A
LTC3780EUH
LTC3 780EUH
SMALL SIZE HIGH EFFICIENCY
BUCKBUCK- BOOST DC/DC CONVERTER
DESCRIPTION
Demonstration circuit 1155A is a compact high efficiency synchronous buck-boost DC/DC converter
with 6V to 32V input range. It can supply 2A maximum load current at 12V output. The demo board
features the LTC®3780EUH controller. The constant
frequency current mode architecture allows a phaselockable frequency of up to 400kHz. With a wide input range, output range and seamless transfers between operation modes, the LTC3780 is ideal for
automotive, telecom and battery-powered systems.
This board has a compact solution size with dual So8 MOSFETs, small inductor and capacitor footprints.
The package of LTC3780EUH is a small, low thermal
impedance 5mm x 5mm 32-Lead QFN.
The operation mode of the converter is determined
with the FCB pin. Use JP2 jumper to select burst
mode, discontinuous mode or forced continuous
mode operation. Switching frequency is pre-set at
about 270kHz. This frequency can be easily modified
from 200kHz to 400kHz by changing PLLFLTR pin
DC voltage level (through R20 and R23). The converter can also be externally synchronized from
200kHz to 400kHz through PLLIN pin (SYNC terminal on the board). To shut down the converter, one
simple way is to force the RUN pin below 1.5V (JP1:
OFF). The power good output (PGOOD terminal) is
low when the output is not within +/-7.5% of its designed set point.
Design files for this circuit board are available. Call
the LTC factory.
Table 1.
Performance Summary (TA = 25°C)
PARAMETER
CONDITION
Input Voltage Range
VALUE
6V to 32V
Output Voltage, VOUT
VIN = 6-32V, IOUT = 0A to 2A
12V ±2%
Maximum Output Current, IOUT
VIN = 6-32V, VOUT = 12V
2A
Typical Efficiency
VIN = 18V, VOUT = 12V, IOUT = 2A
96.1%
Typical Switching Frequency
270kHz
1
LTC3780EUH
QUICK START PROCEDURE
Demonstration circuit 1155A is easy to set up to
evaluate the performance of the LTC3780EUH. Refer
to Figure 1 for the proper measurement equipment
setup and follow the procedure below:
1. With power off, connect the input power supply to Vin (6V-32V) and GND (input return).
2. Connect the 12V output load between Vout and
GND (Initial load: no load).
3. Connect the DVMs to the input and outputs.
4. Turn on the input power supply and check for
the proper output voltages. Vout should be
12V+/-2%.
5. Once the proper output voltages are established, adjust the loads within the operating
range and observe the output voltage regulation, ripple voltage and other parameters.
Note: When measuring the output or input voltage
ripple, do not use the long ground lead on the oscilloscope probe. See Figure 2 for the proper scope probe
technique. Short, stiff leads need to be soldered to the
(+) and (-) terminals of an output capacitor. The
probe’s ground ring needs to touch the (-) lead and
the probe tip needs to touch the (+) lead.
2
LTC3780EUH
Figure 1. Proper Measurement Equipment Setup
+
COUT
VOUT
-
GND
Figure 2. Measuring Output Voltage Ripple
3
LTC3780EUH
100
Efficiency (%)
95
90
6Vin
18Vin
32Vin
85
80
75
70
0
0.4
0.8
1.2
1.6
2
Load current (A)
Figure 3. Efficiency vs load current (JP2: Burst)
4
LTC3780EUH
5
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