DEMO BOARD QUICK START GUIDE DC342
LOW NOISE, CONSTANT FREQUENCY, STEP-DOWN CHARGE PUMP
LTC1911
DESCRIPTION
Demo board DC342 features the LTC1911
Low Noise, Constant Frequency, Step-
Down Charge Pump.
QUICK START PROCEDURE
Refer to Figure 1 for the connection
diagram and follow the procedure be-
low:
1. Before turning on the power supply
connect a 3.3V, 500mA bench supply
to the VIN and GND terminals.
2. Set jumper JP1 to the ON (lower)
position.
3. Turn on the input supply and ob-
serve the output voltage with a
voltmeter. The output voltage
should be 1.8V±4% for the DC342A-A
version, and 1.5V±4% for the
DC342A-B version. A load (I
OUT
<
250mA) may be attached from VOUT
to GND. The load current must flow
from VOUT to GND because the
LTC1911 is only designed to source
current and cannot sink current.
4. To shutdown the LTC1911 (V
OUT
= 0V)
set JP1 to the OFF (upper) posi-
tion.
SOFT-START OPERATION
To observe soft-start operation refer
to Figure 2 proper equipment setup
and follow the procedure outlined be-
low.
1. Before turning on the power supply
connect a 3.3V, 500mA bench supply
to the VIN and GND terminals.
2. Set jumper JP1 to the ON (lower)
position.
3. Connect a 50Ω load from VOUT to
GND. Connect a scope probe to
VOUT, and clip the scope probe
ground lead to GND.
4. Use a low leakage NMOS FET (<1µA
when off) such as a 2N7002, to
short SS/SD to GND. Connect the
Source to GND, the Drain to SS/SD
and drive the Gate with a 50Hz 5V
square wave.
5. Turn on the input power supply and
observe the output trace on the
scope.
RIPPLE MEASUREMENTS
To observe the voltage ripple at VIN
or VOUT refer to Figure 3 and Figure
4 for proper equipment setup and fol-
low the procedure outlined below.
1. Before turning on the power supply
connect a 3.3V, 500mA bench supply
to the VIN and GND terminals.
2. Set jumper JP1 to the ON (lower)
position.
3. Turn on the input. Attach desired
load (I
OUT
< 250mA) from VOUT to
GND. The load current must flow
from VOUT to GND as stated previ-
ously.
1
DEMO BOARD QUICK START GUIDE DC342
LOW NOISE, CONSTANT FREQUENCY, STEP-DOWN CHARGE PUMP
4. When measuring the input or output
voltage ripple, avoid a long
ground return for the oscilloscope
probe by using the following pro-
cedure:
a. Remove the grabber and outer
plastic sleeve from the scope
probe.
b. Measure the input ripple by
touching the probe between VIN
and GND as shown in Figure 3.
c. Measure the output ripple by
touching the probe between VOUT
and GND as shown in Figure 4.
+
–
+
–
LOAD
+
–
+
–
Figure 1. Proper Measurement Equipment Setup
50Ω
+
–
'SCOPE
5V
0V
2N7002
FUNCTION
GENERATOR
Figure 2. Observing Soft Start Operation
VIN
GND
Figure 3. Proper Ripple Measurement Technique for Input
2
DEMO BOARD QUICK START GUIDE DC342
LOW NOISE, CONSTANT FREQUENCY, STEP-DOWN CHARGE PUMP
VOUT
GND
Figure 4. Proper Ripple Measurement Technique for Output
3
