Linear Technology DC2019A Demo Manual

Description

Demonstration circuit 2019A is a 42V, 4A micropower
synchronous step-down Silent Switcher™ featuring the
LT 8614. The demo board is designed for 5V output
®
from a 5.8V to 42V input. The wide input range allows a
variety of input sources, such as automotive batteries and
industrial supplies. The LT8614 is a compact, ultralow
emission, high efficiency and high speed synchronous
monolithic step-down switching regulator. The integrated
power switches and inclusion of all necessary circuitry
reduce the components count and solution size. Special
Silent Switcher architecture minimizes EMI/EMC emis-
sions. Ultralow 2.5µA quiescent current in Burst Mode
operation achieves high efficiency at very light loads. Fast
minimum on-time of 30ns enables high V
conversion at high frequency.
The LT8614 switching frequency can be programmed either
via oscillator resistor or external clock over a 200kHz to
3MHz range. The SYNC pin on the demo board is grounded
by default for low ripple Burst Mode operation. To syn-
chronize to an external clock, move JP1 to SYNC and
apply the external clock to the SYNC turret. Once JP1 is
on SYNC position, a DC voltage of higher than 3V can be
applied to the SYNC turret for pulse-skipping operation.
Figure 1 shows the efficiency of the circuit at 12V input
Performance summary
SYMBOL PARAMETER
V Input Supply Range
IN
V Output Voltage
OUT
I Maximum Output Current
OUT
f Switching Frequency
SW
E Efficiency at DC
FE
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DEMO MANUAL DC2019A
Synchronous Step-Down
in Burst Mode operation (input from V
the LT8614 temperature rising on DC2019A demo board
under different load conditions. The rated maximum load
current is 4A, while derating is necessary for certain V
and thermal conditions.
The demo board has an EMI filter installed. The EMI perfor-
mance of the board (with EMI filter) is shown in Figure 3.
The red line in Figure 3 is CISPR25 Class 5 peak limit. The
figure shows that the circuit passes the test with a wide
margin. To use the EMI filter, the input should be tied to
V , not V
EMI
®
The LT8614 data sheet gives a complete description of the
part, operation and application information. The data sheet
to low V
IN OUT
must be read in conjunction with this demo manual for
demo circuit 2019A. The LT8614 is assembled in a 3mm
× 4mm plastic QFN package with exposed pads for low
thermal resistance. Proper board layout is essential for both
low EMI operation and maximum thermal performance.
See the data sheet sections, "Low EMI PCB Layout" and
"High Temperature Considerations."
Design files for this circuit board are available at
http://www.linear.com/demo/DC2019A
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and Silent Switcher is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
Specifications are at T
A
CONDITIONS
Derating is Necessary for Certain V
Thermal Conditions
V = 12V, I = 3A
IN OUT
42V, 4A Micropower
Silent Switcher
.
IN
= 25°C
MIN
5.8
4.85
and 4
IN
1.85
LT8614
). Figure 2 shows
IN
IN
TYP MAX UNITS
42 V
5 5.15 V
A
2 2.15 MHz
91.3 %
dc2019afa
1