DC353A DEMO BOARD QUICK START GUIDE
DESCRIPTION
Demonstration circuit DC353A demonstrates the capabilities of the LTC1928-5 doubler
charge pump and linear regulator. The board contains the following:
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LTC1928-5 doubler charge pump with low noise linear regulator.
4.7µF ceramic capacitor on V
OUT
4.7µF ceramic capacitor on CPO
4.7µF ceramic capacitor on V
IN
0.47µF ceramic capacitor between CP and CN/SHDNB
N-channel FET type 2N7002 to supply an open-drain pulldown during shutdown
50Ω termination resistor at the gate of the 2N7002 FET
A 100Ω current-limit resistor between the drain of the 2N7002 FET and the
CN/SHDNB pin
The LTC1928-5 generates a low noise regulated 5V output from a DC input supply
voltage connected to the V
IN
terminal. The DC supply voltage range is 2.7V to 4.4V. The
small SOT-23 package and small ceramic capacitors minimize board space requirements.
A power supply connected to V
IN
is the only requirement for basic operation of the demo
board. The termination resistor at the gate of the 2N7002 keeps this FET off and the
LTC1928-5 out of shutdown (enabled).
EXTERNAL CONNECTIONS
Refer to Figure 1 for proper power supply and test equipment setup.
Connect a 2.7V to 4.4V DC voltage supply to the V
IN
terminal.
Connect the DC supply ground to the GND terminal.
Connect a pulse generator switching from 0V to 5V to the SHDN terminal (optional).
The part will be enabled when the pulse generator signal is low and disabled when the
pulse generator signal is high. If the pulse generator is not connected the part will be
enabled.
Connect the load between the V
OUT
and GND terminals directly at the board if noise
measurements are being performed.sdfsdfasdf
LTC1928S6-5
+
+
–
–
+
–
GND
VOUT
VIN
DEMO CIRCUIT 353A
LOW NOISE BOOST
DC/DC CONVERTER
SHDN
–
–
–
+
LOAD
+
+
–
+
Figure 1. DC353 Test and Measurement Setup
OPERATING MODES
DC353A is designed to demonstrate the low noise performance of the LTC1928-5 as well
as its shutdown and current-drive capabilities.
Enable Mode
The device is enabled when the SHDN signal is at 0V. V
OUT
will be between 4.9V and
5.1V. Noise measurements can be performed as outlined in the LTC1928-5 data sheet.
Loads should be applied between the V
OUT
and the GND terminals on the demo board to
avoid ground loops. Ground loops could result in excessive noise generation. A variable
resistor or current source can be applied to the V
OUT
terminal to characterize the output
current drive capabilities.
Shutdown Mode
The 2N7002 FET is required to place the LTC1928-5 in shutdown. Shutdown is achieved
by applying five volts to the SHDN terminal which turns the 2N7002 on. The 50Ω
termination resistor at the SHDN terminal minimizes ringing when the user controls
shutdown using a pulse generator. The pulse generator can be set to switch between 0V
and 5V. The enable and disable characteristics can be determined by obserV
IN
g the
output voltage at V
OUT
and the input current at V
IN
. The pulse generator frequency will be
in the 100s of Hertz range. When the part is disabled, V
OUT
will be discharged to ground
via an internal pull down transistor. The data sheet contains example waveforms showing
the on and off characteristics of V
OUT
. In actual applications, the 2N7002 can be replaced
with an open-drain transistor associated, for example, with a system controller.
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