Linear Technology 1956A Demo Manual

Description

Demonstration circuit 1956A features the
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.
performance summary
SYMBOL PARAMETER
V Input Supply Range
IN
V Output Voltage Range
OUT
f Switching Frequency
SW
I Loss-of-Signal APD Current
LOS
I APD Current Limit
LIM
V /I MON Voltage to APD Current Ratio
MON APD
DEMO MANUAL DC1956A
Boost DC/DC Converter with
LT 3905, a boost 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
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.
Specifications are at T
CONDITIONS
V = 3.3V, I = 1mA
IN APD
JP2: 1MHz
R10 = 1MΩ
R8 = 12.4kΩ
R11 = 4.99kΩ
APD Current Monitor
100
V = 50V
APD
80
60
40
20
0
0 0.5 1
I (mA)
APD
Figure 1. DC1956A Input Current vs APD Current
= 25°C
A
MIN
2.7
48
0.9
12.5
LT3905
V = 3.3V
IN
V = 5V
IN
1.5 2
DC1956A F01
TYP MAX UNITS
12 V
50 52 V
1 1.1 MHz
µA
2 mA
1 mV/µA
dc1956afa
1