1
dc2422af
DEMO MANUAL DC2422A-A,
DC2422A-B, DC2422A-C
DESCRIPTION
LTC7812EUH
Wide V
IN
, Step-Up + Step-Down
DC/DC Converter
Demonstration circuit DC2422A is a step-up + step-down
DC/DC converter featuring the LT C
®
7812EUH, a high per-
formance dual output (Boost + Buck) synchronous DC/
DC switching regulator controller. This board has three
different configurations:
n
DC2422A-A: Regulated V
OUT
to 12V
n
DC2422A-B: Quasi regulated V
OUT
between 10V and
16V
n
DC2422A-C: Dual outputs: 12V (boost channel)
5V (buck channel)
This circuit enables a drop-in layout where the total circuit
area is only 1½" by 1". The LTC7812EUH 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 skip or
Burst Mode
®
operation. Synchronization to an external
clock is also possible.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
PERFORMANCE SUMMARY
The LTC7812 buck input is supplied from the boost output
for the DC2422A-A and DC2422A-B only. With this boost-
then-buck topology, the buck output maintains regulation
over the entire input range. The wide input voltage range
of 4V to 36V is suitable for automotive or other battery
fed applications where low quiescent current is important.
The DC2422A-B is designed such that V
OUT
is partially
regulated between 10V and 16V for higher efficiency
(Figure 4a), reduced power loss, and switching noise.
When V
IN
is between 10V and 16V, it operates in pass-
thru mode with the boost synchronous FET fully on and
the buck in drop-out with >99% duty cycle. When V
IN
is
below 10V, the boost is activated and when V
IN
is above
16V, the buck is activated as shown in Figure 4b.
The LT7812 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/DC2422A
Specifications are at T
A
= 25°C
SYMBOL PARAMETER CONDITIONS M
IN
TYP MAX UNITS
V
IN
Input Supply Range 4 36 V
V
OUT1
Output1 Voltage Range DC2422A-A: V
IN
= 4V* – 36V, I
OUT1
= 0A to 8A
†
11.7 12 12.3 V
DC2422A-B: V
IN
= 4V* – 36V, I
OUT1
= 0A to 8A
†
9.7 16.3 V
DC2422A-C: V
IN
= 4V* – 36V, I
OUT1
= 0A to 8A
†
4.9 5** 5.1 V
V
BUS
V
BUS
Voltage Range (DC2422A-C only) 11.7 12 12.3 V
f
SW
Typical Free Running Switching Frequency 350 kHz
Efficiency
See Figures 3, 4, 5 and 6 for Efficiency
Curves
DC2422A-A:
V
IN
= 8V, V
OUT1
= 12V, I
OUT1
= 8A
V
IN
= 12V, V
OUT1
= 12V, I
OUT1
= 8A
V
IN
= 36V, V
OUT1
= 12V, I
OUT1
= 8A
93
95.4
95
%
%
%
DC2422A-B: V
IN
= 8V, V
OUT1
= 10V, I
OUT1
= 8A
V
IN
= 12V, V
OUT1
= 12V, I
OUT1
= 8A
V
IN
= 36V, V
OUT1
= 16V, I
OUT1
= 6A
94.8
97.2
95.8
%
%
%
DC2422A-C: V
IN
= 8V, V
BUS
= 12V, Ibus = 8A
V
IN
= 12V, V
OUT1
= 5V, I
OUT1
= 8A
V
IN
= 36V, V
OUT1
= 5V, I
OUT1
= 8A
95.8
94
91.9
%
%
%
†
I
OUT1
starts to derate when V
IN
< 8V, *V
IN
needs to be >4.5V to start up, **V
OUT1
follows V
IN
when V
IN
< 5V.
