Linear Technology 1602A Demo Manual

Description
Demonstration circuit 1602A is a high power constant
current, constant voltage synchronous buck controller
featuring the LT 3741. The demo board is optimized for
®
20A output from a 12V input. Being an LED driver, the
output current is being regulated until the output voltage
reaches a programmed voltage limit. The voltage limit on
this demo board is set to around 6V by R11 and R14. The
6V is chosen because of the 10V voltage rating of the output
capacitors. Higher output voltage can be easily achieved
with higher voltage rated output capacitors. The ideal load
to be used with this demo board is a single LED, such as
PT120 from Luminus Devices. Smaller LEDs may not be
able to handle the high current, even for a short period of
time. At 20A, the demo circuit can operate continuously.
However, it is necessary to mount the LED load on a proper
heat sink and possibly with a fan to avoid exceeding its
maximum temperate rating.
The input voltage range of the LT3741 itself is 6V to 36V.
However, the demo board utilizes 30V MOSFETs to demon-
strate best efficiency, so the maximum recommended input
voltage is 24V for the demo board. The typical efficiency
of the demo board is 94% from a 12V input to 5V, 20A
load. The lower the input voltage, the higher the efficiency
tends to be with a given load. At output power level of
performance summary
SYMBOL PARAMETER
PV * Input Supply Range. PV
IN
V * Output Voltage
OUT
I Output Current
OUT
V Output Voltage
OUT
F Switching Frequency
SW
EFE Efficiency at DC
* PV and V of the demo circuit are limited to 24V typical by the selection of MOSFETs. The LT3741 input range is 6V to 36V. V
IN IN
demo circuit is limited to 6V due to the selection of the output capacitors.
High Power Constant Current, Constant
Voltage Synchronous Buck Controller
Specifications are at T
CONDITIONS
= V L1 is Optimized for 12V.
IN IN
With ONE PT120 LED. 6V Is the Overvoltage
Limit
In Current Mode
In Voltage Mode
R3 = 100k
V = 12V, V
IN
DEMO MANUAL DC1602A
100W, a couple of percent of efficiency improvement is
a huge advantage in minimizing temperature rise. If an
efficiency measurement is needed in an application, the
output voltage must be measured at the output capacitors
instead of at the LED load. This prevents cable loss from
being counted as a loss of the board. Output current can
be adjusted by varying the CTRL1 voltage.
R16 can be used to slow down the gate drive. Slower gate
drive helps to reduce ringing on the SW node without
noticeable effect on the efficiency. A 10Ω is usually more
than enough to completely damp any ringing.
R10, R13 and C14 help filtering out voltage spikes seen
+
on the SENSE or SENSE
components on a board.
The LT3741 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 1602A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1602A.
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.
= 25°C
A
= 5V, I = 20A
OUT OUT
LT3741
–
pin. It is critical to have those
MIN TYP MAX
12 24
4.5 6
18.8 20 21.2
5.88 6 6.12
380 420 460
94
maximum of the
OUT
UNITS
V
V
A
V
kHz
%
dc1602af
1