Linear Technology DC2435A-A Demo Manual

Description
Demonstration circuit DC2435A is a step-up/down sup-
ply featuring the LTC 7813EUH. The LTC7813 is a high
®
performance dual output (buck and boost) synchronous
DC/DC switching regulator controller. The board has three
different configurations:
DC2435A-A: Regulated output voltage of 24 Volt
DC2435A-B: Narrowed output voltage between 20V and
28V
DC2435A-C: Dual output voltages of 24V (Boost V
channel) and 5V (Buck V
The circuit enables a drop-in layout where the total circuit
area is only 1½" by 1½". The LTC7813EUH is in a 32-lead
exposed pad QFN package.
The main features of the board include rail tracking (buck
channel only), an internal 5V linear regulator for bias,
separate RUN pins for each output and a Mode selector
that allows the converter to run in CCM, pulse-skipping
or Burst Mode operation. Synchronization to an external
clock is also possible.
performance summary
Table 1
SYMBOL PARAMETER
V Input Supply Range
IN
V Output1 Voltage Range
OUT1
V V Voltage Range (-C only)
BUS BUS
f Typical Free Running Switching Frequency Efficiency
SW
See Figures 4, 5, 6 and 7 for
efficiency curves
# I starts to de-rate when V
OUT1 IN
4V to 56V V
channel)
OUT1
Specifications are at T
CONDITIONS
-A V = 4V* – 56V, I
IN
-B
-C
V < 24V
IN
-A V = 14V, V
IN
V = 48V, V
IN
-B V = 14V, V
IN
V = 24V, V
IN
V = 48V, V
IN
-C V = 14V, V
IN
V = 14V, V
IN
V = 48V, V
IN
< 14V. * V needs to be > 8V to start up.
IN
DEMO MANUAL DC2435A-A/
DC2435A-B/DC2435A-C
, Step-Up/Step-Down
IN
The LTC7813 buck input is supplied from the Boost output
for the DC2435A-A and DC2435A-B only. With this boost-
then-buck topology, the buck outputs maintain regulation
over the entire input range of 4V to 56V, making it suitable
for automotive or other battery fed applications where low
quiescent current is important.
The DC2435A-B is designed such that V
regulated between 20V and 28V for higher efficiency
(Figure 5a), reduced power loss, and switching noise.
When V is between 20V and 28V, it operates in pass-
BUS
IN
thru mode with the boost synchronous FET fully on and
the buck in drop-out with >99% duty cycle. When V
below 20V, the boost is activated and when V
28V, the buck is activated as shown in Figure 5b.
The LTC7813 data sheet gives a complete description of
the part, operation and application information and must
be read in conjunction with this quick start guide.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2435A
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
= 0A to 5A#
OUT1
= 24V, I = 5A
OUT1 OUT1
= 24V, I = 5A
OUT1 OUT1
= 20V, I = 5A
OUT1 OUT1
= 24V, I = 5A
OUT1 OUT1
= 28V, I = 5A
OUT1 OUT1
= 24V, I = 3A
BUS BUS
= 5V, I = 8A
OUT1 OUT1
= 5V, I = 8A
OUT1 OUT1
** V follows V when V
OUT1 IN
LTC7813EUH
Power Supply
is partially
OUT
IN
MIN TYP MAX
4 56
23.5 24 24.5
19 28.6
4.9 5** 5.1
23.5 24 24.5
200 kHz
94.6
96.9
96.3
98.5
97.3
97.1
92.8
88.9
< 5V.
IN
is
IN
is above
UNITS
V
V
V
V
V
%
%
%
%
%
%
%
%
dc2435af
1