Linear Technology DC250A User manual

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 VIN (E3) and GND (E4) (see Figure 1). Connect the load between VOUT (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 VOUT 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 COUT, 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.
Some invisible text

E1
E2
E3
E4
SHDN/SS
E5
GND
VOUT
VIN
GND
JP1
OSCILLOSCOPE
33Ω2.4V–
6.0V
2N4531 OR EQUIV.
0V–5V
TYP
INSTALL JP1
FOR SOFT-START
LTC1503CMS8
High Efficiency Inductorless
Step-Down DC/DC Converter
Demo Circuit DC250A
Figure 1. DC250A Hook-Up Diagram