Question :
As seeing Reference schematic for all the MSMs which are supporting HS-USB by using internal HS-USB PHY circuit, TCXO_EN signal is used for enable signal of NAND gate for USB clock. But USB clock is usually not required when USB block is not operating without USB cable inserted.
So to reduce leakage current on this NAND gate and control USB clock properly at this case, can any GPIO instead of TCXO_EN be used for enable signal of this NAND gate?
Answer :
No. TCXO_EN should be used for this. Basically, USB clock should be supplied during normal operation even when USB is not operating including suspend mode, in order to meet USB 2.0 specification requirement for HS-USB enumeration time.
In addition, in case of using normal GPIO, sleep current actually increases to more than 1mA from both VREG_MSMC & VREG_MSMA due to feedback nature of the external NAND circuit when TCXO was no longer supplied.
No comments:
Post a Comment