DC1289A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289
NO RSENSE STEP-DOWN DC/DC CONVERTER
LTC3879EUD
DESCRIPTION
Demonstration circuit 1289 is a no rsense step-down
dc/dc converter featuring the LTC3879EUD. Its output
supplies 1.2V @ 15A and its input voltage range is from
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 0.69” area on the top layer. The control
circuit on the bottom layer has a footprint of 0.40” x
0.50”.
The fixed on-time valley current mode architecture of the
LTC3879EUD provides a very fast load step response.
Other features of the board include a RUN pin, a TRACK
pin, a PGOOD pin and a MODE jumper to select either
CCM or DCM operation at light load.
Design files for this circuit board are available. Call
the LTC factory.
Table 1. Performance Summary (TA = 25°C)
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
4.5V
Maximum Input Voltage
14V
Output Voltage VOUT
VIN = 4.5V to 14V, IOUT = 0A to 15A
1.2V ±2%
Maximum Output Current
15A
Typical Output Voltage Ripple
VIN = 12V, IOUT = 15A (20MHz BW)
18mVP–P
Nominal Switching Frequency
100% load
430kHz
Efficiency (see Figure 3 for efficiency curves)
VIN = 12V, 100% load
87.7% Typical
QUICK START PROCEDURE
Demonstration circuit 1289 is easy to set up to evaluate
the performance of the LTC3879EUD. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
1.
NOTE: When
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 output voltages.
Vout = 1.176V to 1.224V
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.
measuring the input or output voltage ripple, 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.
Place jumpers in the following positions:
RUN
ON
MODE
CCM
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289
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 1289
NO RSENSE STEP-DOWN DC/DC CONVERTER
Fsw = 430kHz, CCM
95
Efficiency
90
85
80
Parameters:
Qtop = RJK0305DPB
Qbottom = RJK0330DPB
L = Vishay IHLP4040DZ-01 0.36uH
Ron = 402K
Design optimized for a 12V input
75
70
0
2
4
6
8
10
12
14
16
Load current (Amps)
Vin = 12V
Vin = 5V
Figure 3. Typical Efficiency Curves
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289
NO RSENSE STEP-DOWN DC/DC CONVERTER
4
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