Im currently designing a carrier board for TX1/TX2. My design will use auto-power on instead of waiting for a button press. I have couple of questions regarding the power pins. Same supervisor IC circuitry as suggested in OEM design guide will be used.
CARRIER_PWR_ON: This pin is indicated as 3.3V open collector. However i dont see any pull up resistors on the demoboard. The pull up resistor on the demoboard is NO STUFF.I will use this signal to enable the beginning of the power supply chain of the carrier board. Do i need to use a pull up resistor on the carrier board?
CHARGER_PRSNT#: As mentioned above auto-power on instead of button press will be used. It is indicated that pin has 100k pull up to VDD_5V0_SYS on the module. The problem is that the pull up voltage should be the input supply instead of VDD_5V0_SYS, because VDD_5V0_SYS is not generated until CHARGER_PRSNT# initiates the power generation on the module and since VDD_5V0_SYS is not present, CHARGER_PRSNT# signal will not be able to be logic high before supervisor IC asserts its ouput and drives CHARGER_PRSNT# logic low. Can you clarify this issue?
According to the power up sequence, first the system power supplies including 1.8V on the module is brought up and then Carrier_pwr_on signal is driven by the module. The carrier_pwr_on signal enables the carrier power supplies and until the time carrier supplies are stable, reset_out# should be kept zero. In both the nvidia’s tx1/tx2 demoboard and my carrier board, reset_out# signal will be driven by the 1.8V power supply’s power good signal. In the demoboard, Carrier_pwr_on enables VCC_5V, VCC_5V_POWER_GOOD enables VCC_3V3 generation and VCC_3V3_POWER_GOOD enables VCC_1V8 generation. Therefore, until the there is an input on the VCC_1V8 generation circuitry, 1V8_power_good signal wont be guaranteed to be driven logic 0. And reset_out# wont be kept 0 all the time. Correct me if im wrong but, the situation in the demoboard is like that. Can you tell me how reset_out# is assured to be kept 0 until a certain time in the nvidia’s demoboard? Furthermore, reset_out# has a pull up resistor to 1.8V on the module, do i need to put any other pull up resistors on the carrier board?
VIN_PWR_BAD#: This signal has 10k ohm pull up to 5V on the module. The demoboard has a circuitry to keep this signal 0 until the Input supply to the module has risen up and becomes stable. After this, this pin is left floating by the carrier board open drain circuitry. Since the module just gets the Input supply and cant generate the 5V voltage, how will the pull up on VIN_PWR_BAD# pull this signal to high when left floating by the open drain circuitry on the demoboard? Shouldnt the pull up voltage be the input supply instead of 5V?