XO1.75 B1 C1 Changes

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These are the changes planned for the XO-1.75 C1 prototype, from the B1 prototypes.

C1 Electrical Fixes

Improved MPPT

The circuit generating the PWR_LIMIT_ON needs to be modified to only assert the signal if power limiting is turned on. On B1, it is asserted whenever the laptop is accepting power from the DC input (power limited or not).

The LV_SET signal should probably change to a EC PWM output, allowing a greater voltage swing than the EC DAC output.

Modify Vcore supply

The Vcore suply voltages should be 1.345V nominal and 1.25V nominal, instead of 1.40V and 1.345V as it is now.

Increase bulk bypassing

Add another 22 uF of capacitor to the +3.3V rail (populate PC54).

Pullups on Accelerometer

Both <trac>11041</trac> or <trac>10882</trac> are caused by a lack of external pullups on the I2C bus. 1.3K pullups to should be added between G_SENSOR_SDA/G_SENSOR_SCL and +1.8V_GPIO. VDD_IO on the Accelerometer (U15) should be tied to +1.8V_GPIO, not +1.8V. Same with U5.

C1 Layout Fixes

Internal SD Select

With the replacement of the full-size internal SD slot with a latching microSD slot, there is no loner a card detect signal generated to automatically switch the boot device.

We need to increase the size of R341/R341 to 0603 or 0805, and label them somehow.