1
dc2139af
DEMO MANUAL DC2139A
Description
LT8610A
42V, 3.5A Micropower
Synchronous Step-Down Regulator
Demonstration circuit 2139A is a 42V, 3.5A micropower
synchronous step-down regulator featuring the
LT
®
8610A
.
The LT8610A is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 2.5µA of quiescent current when output
is regulated at 5V and is unloaded. The 2139A uses two
input ceramic capacitors in series to improve reliability in
case of an input capacitor short failure. Top and bottom
power switches, compensation components and other
necessary circuits are inside of the LT8610A to minimize
external components and simplify design.
The SYNC pin on the demo board is grounded by default
for low ripple burst mode operation. To synchronize 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 2V or INTV
CC
can be applied
to the SYNC turret for pulse-skipping operation. Figure 1
shows the efficiency of the circuit at 12V input.
Figure 2 shows the thermal performance of the circuit.
When running at input voltage greater than 30V, 3.5A
L
, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
performance summary
output current and 2MHz switching frequency, the tem-
perature rise will be significant. Either reducing the input
voltage, the output current or the switching frequency will
bring the temperature down to acceptable level without
external cooling.
The demo board has an EMI filter installed. The board and
the IC are designed to minimize conducted and radiated
EMI. The radiated EMI performances of the board are
shown in Figure 3 to Figure 5. The limits on those figures
are CISPR25, Class 5 peak limits. The circuit passes the
test with a wide margin.
The LT8610A data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 2139A.
Design files for this circuit board are available at
http://www.linear.com/demo
Specifications are at T
A
= 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
*
Input Supply Range
5.5
42
V
V
OUT
Output Voltage
4.8
5
5.2
V
I
OUT
Maximum Output Current
3.5
A
F
SW
Switching Frequency
1.85
2
2.15
MHz
EFE
Efficiency at DC
I
OUT
= 1A
92
%
*Refer to Figure 2 to determine the maximum input voltage. If IC temperature exceeds target, reduce input voltage, output current or switching frequency.
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