Linear Technology DC1893A Demo Manual

DESCRIPTION
Demonstration circuit 1893A is a USB 5V, 2.5A output,
35V input buck with cable drop compensation featuring the
LT 3697. The LT3697 is a step-down switching regulator
®
designed to power 5V USB applications.
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 was designed
to run at 500kHz to avoid the AM band. The demo board
has an EMI filter installed. The radiated EMI performance of
the board is on Figures 3 to 5, showing the circuit passes
CISPR25 Class 5 with a wide margin.
This USB converter was optimized for a maximum V
of 5V at 2.4A, enough for all USB applications. If higher, or
lower load current is needed, please read the Cable Drop
Compensation paragraph in the Applications section of
the data sheet, and adjust all pertinent component values
as needed. Always ensure the converter stays within the
guaranteed switch current and the output voltage never
exceeds 6.1V. If higher V
refer to Applications example on the data sheet. If V
is not connected to any load, V
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
CABLE
Max I
OUT
Efficiency
Switching Frequency
Table 1. Configure X1–X4 for Different USB Applications
X1
DO NOT CARE
OPEN
+
D
Arrow.com.
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voltage is needed, please
CABLE
can be used to power
OUT
Specifications are at T
PARAMETER
Input Supply Range
Output Voltage
Maximum Output Current
X2
DO NOT CARE
OPEN
−
D
DEMO MANUAL DC1893A
USB 5V, 2.5A Output, 35V Input
with Cable Drop Compensation
up a load. V
SYS
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.
CABLE
See Table 1 for configurations. A 500mA onboard step
load can also be activated to evaluate the load transient
response of the circuit. To activate the step load, simply set
jumper X5 to V
description of the part, operation and application informa-
tion. The data sheet must be read in conjunction with this
quick start guide for demo circuit 1893A.
CABLE
Design files for this circuit board are available at
http://www.linear.com/demo/DC1893A
L, LT, LTC, LTM, Linear Technology and tthe Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
= 25°C
A
CONDITIONS
I = 2.4A, Measured at V
OUT OUT
X3
DO NOT CARE
SHORT
OPEN
can also be used to supply a 100mA load.
+
. The LT3697 data sheet gives a complete
MIN TYP MAX
8 35
4.8 5 5.2
2.4
90
500
X4
OPEN NOT IN USE
SET
SET USB APPLE 2.4A
LT3697
UNITS
V
V
A
%
kHz
J3
USB–DCP
dc1893af
1