DEMO MANUAL DC381A
QUICK START GUIDE
DC381A is used to evaluate the LTC3201 low noise charge pump LED driver.
• Before turning on the power supply, connect a 3.3V, 500mA bench power supply
to the VIN terminal. Connect ground from the power supply to the GND terminal.
• Disconnect jumpers from D0,D1,D2. This sets the DAC output to maximum LED
current. D0,D1,D2 pull high to VIN. Connecting all 3 jumpers puts the part into
shutdown mode. Note that the 300K pull-up resistors connected to D0,D1,D2 will
draw some current.
• Turn on bench power supply. LEDs should light up. Voltage at FB terminal
should measure about 0.62V. VOUT terminal should measure approximately
4.22V (0.62V + 3.6V forward drop of the LED5).
• Change D0,D1,D2 DAC input terminals that and notice LED current change
accordingly. Also note that each LSB change causes an approximate 90mV
change at the FB pin.
• When measuring input/output voltage ripple, care must be taken to avoid a long
ground return for the oscilloscope probe. After removing the grabber and outer
plastic sleeve from the scope probe, measure the input voltage ripple by touching
the probe tip to the VIN terminal and simultaneously touching the probe ground
casing to the GND terminal. VOUT ripple is measured similarly between VOUT
and its adjacent GND.
• When measuring VIN ripple, note the importance of the impedance of the bench
power supply plus the impedance of the connectors from the supply to the part.
The VIN voltage ripple will depend on the ripple current of the LTC3201 times
the total impedance mentioned above. In order to see the true effect of the low
input noise of the LTC3201, the user should connect the actual application
BATTERY. Make sure that the connector between the battery and the DC381A is
very short and made with heavy gauge wire. Measure VIN terminal. This ripple
now represents the input ripple of the LTC3201 times the impedance of the
battery.
