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dc1973af
DEMO MANUAL DC1973A
Description
LT8697
USB 5V 2.5A Output, 42V Input Synchronous
Buck with Cable Drop Compensation
Demonstration circuit 1973A is a USB 5V 2.5A output, 42V
input synchronous buck with cable drop compensation
featuring the
LT
®
8697
. The LT8697 is a compact, high
efficiency, high speed synchronous monolithic step-down
switching regulator designed to power 5V USB applica-
tions. Top and bottom power switches, compensation
components and other necessary circuits are inside of
the LT8697 to minimize external components and simplify
design. A precise output voltage and programmable cable
drop compensation maintain accurate 5V regulation at the
USB socket at the end of a long cable.
The circuit runs at 2MHz to minimize external components
size and to avoid AM band. The demo board has an EMI
filter installed. The conducted EMI performance of the
board is shown on Figure 2. The figure shows the circuit
passes the EN55022 Class B with a wide margin.
When the load current is being drawn from VCABLE, the
load current is limited by the current limit of the LT8697
or by 5.8V limit at VOUT, whichever comes first. The
rated load current of the demonstration circuit is set at
2.1A, enough for all USB applications. If higher voltage or
higher current is needed at VCABLE, refer to application
examples on the data sheet. If VCABLE is not connected
to any load, VOUT can be used to power up a load. VSYS
can also be used to supply a small load.
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.
When probing the board, pay attention to GND and C_GND.
On the demonstration board, they are connected together by
default through R13 so a user can connect the ground clip
of a probe to C_GND. However, if a user wants to evaluate
an actual cable, the cable will replace R4 and R13. The
copper between pads of R13 should be cut open. In this
case, C_GND is no longer the same as GND. A differential
measurement is needed to probe across the point of load.
The demonstration board also includes a USB socket.
With the proper configuration of jumpers X1, X2, X3 and
X4, the USB can be configured for different applications.
See Table 1 for configurations.
A 500mA onboard step load can also be activated to evalu-
ate the load transient response of the circuit. To active the
step load, simply set jumper X5 to V+.
The LT8697 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 1973A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1973A
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