DC1345A - Demo Manual

DEMO CIRCUIT 1345
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WIDE INPUT VOLTAGE RANGE
NO RSENSE STEP-DOWN DC/DC CONVERTER
LTC3879EMSE
DESCRIPTION
Demonstration circuit 1345 is a wide input voltage
range, no Rsense step-down dc/dc converter featuring
the LTC3879EMSE. Its output voltage is 1.2V with a
load rating of 12A and the input voltage range is 4.5V
to 34V.
The fixed on-time valley current mode architecture of
the LTC3879EMSE 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
34V
Output Voltage VOUT
VIN = 4.5V to 34V, IOUT = 0A to 12A
1.2V ±2%
Maximum Output Current
12A
Typical Output Voltage Ripple
VIN = 12V, IOUT = 12A (20MHz BW)
20mVP–P
Nominal Switching Frequency
VIN = 12V, IOUT = 12A
300kHz
Efficiency (see Figure 3 for efficiency curves)
VIN = 12V, IOUT = 12A
90% Typical
QUICK START PROCEDURE
Demonstration circuit 1345 is easy to set up to evaluate the performance of the LTC3879EMSE. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
1. Place jumpers in the following positions:
NOTE: When measuring the output voltage ripple, care
2. With power off, connect the input power supply to
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.
RUN
ON
MODE
CCM
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.
1
DEMO CIRCUIT 1345
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Vin
V
A
A
Iin
Iout
Vin
supply
Load
V
Vout
Figure 1. Proper Measurement Equipment Setup
+
COUT
VOUT
-
GND
Figure 2. Measuring Output Voltage Ripple
2
DEMO CIRCUIT 1345
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Fsw = 300kHz, CCM
95
Vin=5V
Vin=12V
90
Vin=24V
Vin=34V
Efficiency
85
80
75
Parameters:
QT = Infineon BSC093N04LSG
QB = Infineon BSC035N04LSG
L = Wurth 744325072
0.72uH, DCR=1.3mΩ +/- 10%
Ron = 576kΩ
70
65
60
0
2
4
6
8
10
12
14
Load current (Amps)
Figure 3. Typical Efficiency Curves
3
DEMO CIRCUIT 1345
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4
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