IMX536 current requirement failure & Power on sequence query

neerajshukla — Fri, 19 Jul 2013 10:36:06 GMT

Hello,

We are designing a board for industrial application with maximum temperature of 85C, based on IMX536 processor in our design with PMIC 34709.

But there is a problem regarding current requirement, VGEN2(2.5V) Rail of PMIC is connected to VDD_REG of IMX53.

The current required by IMX53's VDD_REG rail [it powers VDD_ANA_PLL(1.8V) and VDD_DIG_PLL(1.3V) also] is 325mA and current provided by PMIC's VGEN2 rail 250mA which is less,

How is it possible?

So,we are powering VDD_ANA_PLL(1.8V) and VDD_DIG_PLL(1.3V) externally from VUSB2 LDO(2.5V) of PMIC, is it possible to do so? This has not been implemented any where.

Will it affect USB usage in our case as we are planning to use USB also ?

Is there any power up sequence required for rails "VDD_ANA_PLL(1.8V) and VDD_DIG_PLL(1.3V)" ?

Re: IMX536 current requirement failure & Power on sequence query

reyes — Mon, 12 Aug 2013 20:20:47 GMT

VDD_REG 325mA in Table 9 "Maximal Supply Currents" of the i.MX53 Datasheet (IMX53AEC, Rev. 5, 12/2012) is given for the worst conditions, assuming VDDA and VDDAL1 are driven by the VDD_DIG_PLL (produced from VDD_REG). Please refer to footnote 4 to Table 7 "i.MX53xA Operating Ranges": "VDDA and VDDAL1 can be driven by the VDD_DIG_PLL internal regulator using external connections."

Let me remind, according to section 4.9 (Integrated LDO Voltage Regulators Parameters): "The PLL supplies VDD_DIG_PLL and VDD_ANA_PLL can be powered ON from internal LDO voltage regulator (default case). In this case VDD_REG is used as internal regulator’s power source. The regulator’s output can be used as a supply for other domains such as VDDA and VDDAL1."

So max. VDD_REG 325 mA includes at least VDDA + VDDAL1 max.100mA.

On i.MX53 QSB schematic (with the PMIC 34708) VDDA + VDDAL1 are not connected to VDD_DIG_PLL (and not consumes max.100mA from VDD_REG), they are connected to VGEN1. For such connection VDD_REG max current consumption may be estimated as (325mA - 100mA) = 225mA, sufficient for VGEN2 of PMIC 34708.

Please note that Table 9 "Maximal Supply Currents" gives max. currents for worst conditions, typical values are less. For VDD_REG typical current please refer to application note AN4271 (Rev. 0, 7/2011) "i.MX53 Supply Current Measurements on MCIMX53SMD Board"

< http://www.freescale.com/files/32bit/doc/app_note/AN4270.pdf >

2. Recommended power supply solutions may be found in Chapter 5 (Setup Power Management) of “i.MX53 System Development User’s Guide”. Please pay attention on erratum ERR007080 (LDO: On-chip LDO regulators may not enable or have a delayed output on power up).

< http://cache.freescale.com/files/32bit/doc/errata/IMX53CE.pdf >

VDD_ANA_PLL and VDD_DIG_PLL may be powered externally (with proper voltages).

As for power up sequence please take a look at section 4.2.1 (Power-Up Sequence) of the Datasheet: “If VDD_DIG_PLL and VDD_ANA_PLL are powered on externally, to reduce current leakage during the power-up, it is recommended to activate the VDD_REG before or at the same time with VDD_DIG_PLL and VDD_ANA_PLL. If this sequencing is not possible, make sure that the 2.5 V VDD_REG supply shut-off output impedance is higher than 1 kOhm when it is inactive.”

topic IMX536 current requirement failure & Power on sequence query in i.MX Processors

IMX536 current requirement failure & Power on sequence query

Re: IMX536 current requirement failure & Power on sequence query