Linear Technology DC1345 Quick Start Manual

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.
Table 1. Performance Summary (T
PARAMETER
Minimum Input Voltage
Maximum Input Voltage
Output Voltage V
OUT
Maximum Output Current
Typical Output Voltage Ripple
Nominal Switching Frequency
Efficiency (see Figure 3 for efficiency curves)

QUICK START PROCEDURE

Demonstration circuit 1345 is easy to set up to evalu-
ate the performance of the LTC3879EMSE. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
When measuring the output voltage ripple, care
NOTE:
must be taken to avoid a long ground lead on the oscil-
loscope 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.
NO RSENSE STEP-DOWN DC/DC CONVERTER
The fixed on-time valley current mode architecture of
the LTC3879EMSE provides a very fast load step re-
sponse. 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.
= 25°C)
A
CONDITION
V = 4.5V to 34V, I = 0A to 12A
IN OUT
V = 12V, I = 12A (20MHz BW)
IN OUT
V = 12V, I = 12A
IN OUT
V = 12V, I = 12A
IN OUT
Place jumpers in the following positions:
1.
RUN
MODE
With power off, connect the input power supply to
2.
Vin and GND.
Turn on the power at the input.
3.
Check for the proper output voltages.
4.
Vout = 1.176V to 1.224V
Once the proper output voltages are established,
5.
adjust the loads within the operating range and ob-
serve the output voltage regulation, ripple voltage,
efficiency and other parameters.
DEMO CIRCUIT 1345
Quick Start Guide
WIDE INPUT VOLTAGE RANGE
LTC3879EMSE
VALUE
4.5V
34V
1.2V ±2%
12A
20mV
P–P
300kHz
90% Typical
ON
CCM
1