Low Power Current Draw

[sbhushan2]

Posted on May 08, 2008 at 13:24

Low Power Current Draw

[sbhushan2]

Posted on May 17, 2011 at 09:52

Hi,

I have a question regarding current draw during low power sleep mode. The board sleep current varies everytime it is put to sleep anywhere from 450uA to 2.99mA. Our firmware turns OFF all the on-board peripherals before going to sleep. We have so far isolated the problem to the chip itself. The core draws uAmps in sleep mode, while the current draw through the 3.3v supply to the chip appears to be changing everytime the processor goes to sleep. An interesting thing is, when the board is powered ON and if it draws 22mA, the sleep current is 450uA and if the initial power ON current draw is 24mA, the sleep current will be 2.5mA. This means whatever is drawing that extra 2mA draws that even when the processor goes to sleep mode. We have 100k pull-ups on all unused I/O pins and they are configured as GP Inputs. Has anybody faced a similar problem? Any suggestions would be really helpful. Regards, sbhushan.

[michael]

Posted on May 17, 2011 at 09:52

hello,

it depends on the silicon revision. the following applies to revision G of the STR91xFA: ''Description of limitation When the STR91xFA enters Sleep mode, the current drawn from the CPU core voltage (VDD) and from the I/O supply voltage (VDDQ) should drop to a very low value. ISLEEP current on VDD pins correctly drops to as low as 50 μA at 25 °C. However ISLEEP current on the VDDQ pins drops to around 500 μA at 25 °C while it should be less than 10 μA. Workaround using revision G A limited workaround may be implemented to save around 120 μA by using firmware to put the USB transceiver into Suspend mode (bit2, LP_MODE in the USB_CNTR register). This allows reducing Sleep mode current on VDDQ pins to around 380 μA. Sleep mode current consumption on VDDQ pins is reduced to less than 10 μA on revision H silicon devices.''

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