UM0442 datasheet(6/33 Pages) STMICROELECTRONICS

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Hardware configuration and functionality

UM0442

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The configuration of the power source selector as appears in the silkscreen (consider the

following abbreviations as a legend for the picture below) is as follows:

●

BAT: the battery pack is selected as power source. To do this, close the related jumper

and connect the battery pack by plugging in its connector as appropriate (see

Section 4.2: Battery pack power source).

●

EXT: the external 5 V power source is selected as power source.

●

USB: plug in this jumper once the board is connected to a computer through the

mini-USB connector in the upper side of the board.

●

PWR: the standard 9 Vdc power connector is chosen and a voltage regulator

(L7805AB) provides the 5 V supply to all the components in the board.

Figure 3.

Power source selector and jumper legend

It is strongly recommended to not select more than one power source at a time. This is to

prevent possible power source failures, with the consequence to propagate these failures to

the board components.

4.2

Battery pack power source

The battery pack is selected by closing the appropriate jumper as shown in the previous

section.

In order to supply the STR750-MAP the following two steps are required:

●

Plug the battery pack connector onto the STR750-MAP, using the 2-pin connector

named BATTERY in the board silkscreen.

●

Configure the 3-pin strip-line selector S7 as follows: close the middle point of the S7

selector with the point 3 (left side of the S7). In this way, the battery pack is linked to

the L6920D step-up converter in order to furnish the right voltage to all the components

(see Figure 4).

Figure 4.

The selector S7 allows the STR750-MAP to be supplied from the battery

pack

As an alert feature, an LED is placed to give a warning if a low battery level occurs (LED

D10).

The two types of batteries that can be connected to the board to allow all features are the

graphite anode single cell Li-Ion or Li-Polymer. The low threshold voltage detector is fixed at

2.7 V (considering the use of a battery pack at typically 3.7 V/1360 mAh).

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