Belkin XM Commander Especificações descarregar pdf (Página 46)

REF: BB_SRM_xM BeagleBoard-xM System

Reference Manual

Revision A2

Page 46 of 164

8.2.1 Detection

The detection is handled by a TPS3803G15 voltage detector which has a fixed-sense

threshold voltage of 1.4V set by an internal voltage divider, There is a another version of

this devices, the TPS3803−01 has an adjustable SENSE input that can be configured by

two external resistors. The design does allow for this, but the resistors are not populated

and the TPS3803G15 device is used in the design. RESET is asserted in the case where

the VDD drops below the 1.4V level.

In this design we use the device in reverse. If the voltage exceeds 1.4 volts, the RESET is

released which results in an error condition. The voltage divider made of R168 and R169

is set to where if the voltage coming in is over 5.3V a level in excess of the 1.4V is

presented to the TPS3803G15. If detected, a release of the RESET signal, which is open

drain, will result in the signal going high via the pullup R158.

8.2.2 Indication

When the error condition occurs, a red LED, D16, will turn on. This is driven by ½ of

Q3. This indicates to the user that the voltage is too high and that another power supply

should be used. The LED will remain on until the overvoltage condition has been

removed.

8.2.3 Shutdown

The error condition also results in ½ of Q3 being activated which takes the VOLTERR

signal low. This will prevent the two FDC6330L load switches from turning on.

One load switch, U35, removes the power form the main board regulator that provides

power to the board, preventing anything from receiving power. Until the overvoltage

condition has been resolved, the board will not power up.

The other load switch, U34, removes the power from the DC_5V_USB rail which

provides the power to the USB devices. This helps prevent damage to any USB device

that may be plugged in at the time of power up. Until the overvoltage condition has been

resolved, the board will not power up.

If there is no overvoltage condition or if the previous one has been removed, the pullup,

R160, will turn on the two load switches connecting the power. Each of these switches

can handle in excess of 2A in normal operation.

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Belkin XM Commander Especificações Página 46