STV0681
STV0681 Hardware Interfaces
4.5
Power management and battery type
STV0681 and the SDRAM require a 3.3V supply. When a VV6411 or VV6501 (3.3V) sensor is used,
a single voltage regulator can regulate the supply for all three components from the battery, or the
sensor on-board VReg can be used. These are explained more fully in the reference design.
4.5.1 Power switching to USB
Included in the USB compliance requirements, is the ability of the camera to report to the PC when
connected to the USB bus, whether or not there is a fresh battery in the camera. This means that
power sourcing from USB is required, which also saves on battery life while the camera is used in
USB tethered video mode. In order to allow switching from battery to USB power, some additional
hardware is required.
● The USBDETECT input to STV0681 is used to detect that a USB power supply is connected
● If the USB is detected, additional hardware is used to switch off the battery
● An inrush protection circuit can protect the USB bus from current draw in the case of a low battery/
battery not fitted. This may be necessary to comply with the USB specification.
For precise USB compliance requirements, please consult the USB specification version 1.1.
4.5.2 Switched sensor supply
Dependant on the hardware implementation, the SENSPWR output from STV0681 is used to put
the sensor into suspend mode. This has a significant improvement on battery life.
4.5.3 Battery type
It is possible to use various battery types and configurations. The evaluation kit uses four 1.5V AAA
cells.
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STMICROELECTRONICS [ ST ]
