DC1292A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292
NO RSENSE STEP-DOWN DC/DC CONVERTER
LTC3878EGN
DESCRIPTION
Demonstration circuit 1292 is a NO RSENSE STEPDOWN DC/DC CONVERTER featuring the LTC3878EGN.
Its output supplies 1.2V @ 18A and its input voltage
range is 4.5V to 14V. The demo board uses a high density, two sided drop-in layout. The power components,
excluding the bulk output capacitors and bulk input capacitors, fit within a 0.94” x 0.63” area on the top layer.
The control circuit on the bottom layer has a footprint of
0.63” x 0.40”.
The fixed on-time valley current mode architecture of the
LTC3878EGN provides a very fast load step response.
Other features of the board include a RUN/SS pin, a
PGOOD pin and jumper to select either CCM or DCM
operation at light load.
Design files for this circuit board are available. Call
the LTC factory.
PowerPath is a trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
4.5V
Maximum Input Voltage
14V
Output Voltage
VIN = 4.5V to 14V, IOUT = 0A to 18A
Maximum Output Current
1.2V ±2%
18A
Typical Output Voltage Ripple
VIN = 12V, IOUT = 18A (20MHz BW)
17mVp-p
Nominal Switching Frequency
100% load, VIN = 12V, IOUT = 18A
340kHz
Efficiency
(see Figure 3 for efficiency curves)
VIN = 12V, 100% load
88.4% Typical
QUICK START PROCEDURE
Demonstration circuit 1292 is easy to set up to evaluate
the performance of the LTC3878EGN. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
NOTE: When measuring the input or output voltage rip-
ple, care must be taken to avoid a long ground lead on
the oscilloscope probe. See Figure 2 for proper scope
probe technique. Short, stiff leads should 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.
1. Place jumpers in the following positions:
JP1 RUN
ON
JP2 MODE
CCM
2. With power off, connect the input power supply
to Vin and GND.
3. Turn on the power at the input.
4. Check for the proper
Vout = 1.176V to 1.224V
output
voltages.
5. 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.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292
NO RSENSE STEP-DOWN DC/DC CONVERTER
Figure 1. Proper Measurement Equipment Setup
+
COUT
VOUT
-
GND
Figure 2. Measuring Output Voltage Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292
NO RSENSE STEP-DOWN DC/DC CONVERTER
Fsw = 340kHz, mode = CCM
95
Efficiency
90
85
80
Parameters:
Qtop = RJK0305DPB
Qbottom = RJK0330DPB
L = Pulse PA0515.471NLT
Ron = 499K
Design optimized for a 12V input
75
70
0
2
4
6
8
10
12
14
16
18
20
Load current (Amps)
Vin = 12V
Vin = 5V
Figure 3. Typical efficiency curves
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1292
NO RSENSE STEP-DOWN DC/DC CONVERTER
4
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