Evaluation board components
UM0529
10/29
application involving
the
USB02E/USB03E, such a voltage converter is not needed as the
USB microcontroller will have the V
IF
ranging from 1.6 V to 3.3 V as required for the
transceiver. Also, we need signal inversion for
the
USBOE and SUS signals of transceiver.
This task is also performed by
the
74LCX139MTR in this board. Hence, 74LCX139MTR
usage is basically microcontroller specific.
3.4 LD2985BM33R
voltage regulator U4
The LD2985BM33R is a 150 mA fixed output voltage regulator. The ultra-low drop voltage
and the low quiescent current make them particularly suitable for low-noise, low-power
applications and in battery-powered systems. In sleep mode, quiescent current is less than
1
µ
A when
the INHIBIT pin is pulled low. Shutdown logic control function is available on pin
3 (TTL compatible).
Note:
LD2985BM33R usage is optional in the board. By configuring jumpers J9,J13,J11, the
external voltage regulator can be switched off. In this case,
the
internal voltage regulator of
the
microcontroller is used to power 74LCX139MTR and STUSB02E/ STUSB03 V
IF
.
When external voltage regulator LD2985BM33R is used for powering 74LCX139MTR and
STUSB02E/ STUSB03 V
IF
, overall current consumption of the board increases.
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