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dc1956afa
DEMO MANUAL DC1956A
Description
LT3905
Boost DC/DC Converter with
APD Current Monitor
Demonstration circuit 1956A features the LT
®
3905, a boost
DC/DC Converter with APD current monitor that comes in
a 3mm × 3mm QFN package. This demo board is designed
to convert a 2.7V to 12V input to a 50V output at 2mA. The
LT3905 is equipped with indicators for monitoring APD
current, overload, and loss-of-signal (LOS) conditions,
which can easily be changed with their respective resis
-
tors. In addition, the output voltage can be adjusted via the
CTRL
pin. DC1956A is designed for 1MHz operation but
can also be programmed for 2MHz by moving jumper JP2.
For measuring fast transient response, use the installed
Fast Monitor Response Circuit on the bottom of the demo
board and install 0Ω resistors at R14 and R20. Also, remove
R11 and any other capacitances or probes across the APD
node. The transient response should be measured at the
TIA turret. For further information, read the APD Current
Monitor Transient Response section in the data sheet.
The internal LOS_MON comparator hysteresis is 20mV on
the rising edge of the LOS_MON voltage. For additional
hysteresis, use R6, R7, R15, and R21
as stated in the Loss
of Signal Hysteresis section in the data sheet.
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.
performance summary
The LT3905 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 the DC1956A.
Design files for this circuit board are available at
http://www.
linear.com/demo/DC1956A
Specifications are at T
A
= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Input Supply Range 2.7 12 V
V
OUT
Output Voltage Range V
IN
= 3.3V, I
APD
= 1mA 48 50 52 V
f
SW
Switching Frequency JP2: 1MHz 0.9 1 1.1 MHz
I
LOS
Loss-of-Signal APD Current R10 = 1MΩ 12.5 µA
I
LIM
APD Current Limit R8 = 12.4kΩ 2 mA
V
MON
/I
APD
MON Voltage to APD Current Ratio R11 = 4.99kΩ 1 mV/µA
I
APD
(mA)
0
INPUT CURRENT (mA)
20
60
100
40
80
1
DC1956A F01
20 0.5 1.5
V
APD
= 50V
V
IN
= 3.3V
V
IN
= 5V
Figure 1. DC1956A Input Current vs APD Current
