Linear Technology DC250A Quick Start 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 V

(E2) and

OUT

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

to GND will not damage the

OUT

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.

Some invisible text

OSCILLOSCOPE

LTC1503CMS8

High Efficiency Inductorless

Step-Down DC/DC Converter

OUT

IN

Demo Circuit DC250A

SHDN/SS

JP1

E5

INSTALL JP1
FOR SOFT-START

2N4531 OR EQUIV.

0V–5V
TYP

33Ω

2.4V–

6.0V

E1

GND

E2

V

E3

V

E4

GND

Figure 1. DC250A Hook-Up Diagram