DC250A Quick Start Guide
The DC250A demonstration board contains all of the circuitry needed for evaluation of the
LTC1503CMS8-1.8/2 inductorless switching regulator IC. To begin, simply connect an input
power supply to V
IN
(E3) and GND (E4) (see Figure 1). Connect the load between V
OUT
(E2) and
GND (E4). Once power is applied, the LTC1503CMS-1.8/2 will start up automatically and produce
a regulated 1.8V/2V output voltage.
With an input supply of between 2.4V and 6V, the output will regulate correctly for any load
current up to 100mA. Accidental short circuits from V
OUT
to GND will not damage the
LTC1503CMS8-1.8/2 or DC250A demonstration board.
To place the LTC1503CMS8-1.8/2 in shutdown, simply connect the SHDN/SS pin (E5) to GND
(E4). To re-start the LTC1503CMS8-1.8/2 remove the ground connection from SHDN/SS. The IC
will automatically pull up on the SHDN/SS pin and regulate to the correct voltage at its output.
Inrush current can be controlled by the use of jumper JP1. If JP1 is in place, soft-start capacitor C3
is connected to the SHDN/SS pin. C3 limits the inrush current by limiting the dV/dt of the output
voltage upon start-up. Without JP1, the LTC1503CMS8-1.8/2 will deliver current to C
OUT
, the
output capacitor, as quickly as possible until the regulation voltage is reached.
To evaluate the soft-start feature of the LTC1503CMS8-1.8/2 an open-drain output from a
microcontroller or a discrete transistor can be connected to the SHDN/SS pin (E5). For example,
using a discrete transistor, connect the drain of the device to SHDN/SS (E5) and the source to GND
(E4). The gate can be manipulated to a suitable control voltage or pulsed waveform with a function
generator. To see the soft start characteristics on an oscilloscope, a load resistor will be needed to
discharge the output capacitor. A 33ohm resistor will discharge the 10µF output capacitor in about
1ms.
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