3.6.9 MPDDRC DDR3 Calibration Register

This register can only be written if the WPEN bit is cleared in the MPDDRC Write Protection Mode Register.

Name: MPDDRC_DDR3_CAL
Offset: 0x2C
Reset: 0x00000000
Property: Read/Write

Bit 3130292827262524 
          
Access  
Reset  
Bit 2322212019181716 
          
Access  
Reset  
Bit 15141312111098 
 COUNT_CAL[15:8] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 
Bit 76543210 
 COUNT_CAL[7:0] 
Access R/WR/WR/WR/WR/WR/WR/WR/W 
Reset 00000000 

Bits 15:0 – COUNT_CAL[15:0]  DDR3 Calibration Timer Count

This 16-bit field is loaded into a timer which generates the calibration pulse. Each time the calibration pulse is generated, a ZQCS calibration sequence is initiated. The ZQCS Calibration command is used to calibrate DRAM Ron values over PVT. One ZQCS command can effectively correct at least 1.5% of output impedance errors within Tzqcs.

One method for calculating the interval between ZQCS commands gives the temperature (Tdriftrate) and voltage (Vdriftrate) drift rates to which the SDRAM is subject in the application. The interval could be defined by the following formula:
  • ZQCorrection/((TSens x Tdriftrate) + (VSens x Vdriftrate))

where TSens = max(dRONdTM) and VSens = max(dRONdVM) define the SDRAM temperature and voltage sensitivities.

For example, if TSens = 0.75%/C, VSens = 0.2%/mV, Tdriftrate = 1C/sec and Vdriftrate = 15 mV/s, then the interval between ZQCS commands is calculated as:
  • 1.5/((0.75 x 1) + (0.2 x 15)) = 0.4s

In this example, the devices require a calibration every 0.4s. The value to be loaded depends on the average time between the REFRESH commands, tREF. For example, for a device with the time between refresh of 7.8 μs, the value of the COUNT_CAL field is programmed as follows: (0.4/7.8 x 10-6) = 0xC852.

TSens and VSens are provided by the manufacturer (Output Driver Sensitivity definition). Tdriftrate and Vdriftrate are defined by the end user.