35.7.9 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	31	30	29	28	27	26	25	24

Access
Reset


Bit	23	22	21	20	19	18	17	16

Access
Reset


Bit	15	14	13	12	11	10	9	8
	COUNT_CAL[15:8]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	7	6	5	4	3	2	1	0
	COUNT_CAL[7:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0

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 T_zqcs.

One method for calculating the interval between ZQCS commands gives the temperature (T_driftrate) and voltage (V_driftrate) drift rates to which the SDRAM is subject in the application. The interval could be defined by the following formula:

ZQCorrection/((T_Sens x T_driftrate) + (V_Sens x V_driftrate))

where T_Sens = max(dRONdTM) and V_Sens = max(dRONdVM) define the SDRAM temperature and voltage sensitivities.

For example, if T_Sens = 0.75%/C, V_Sens = 0.2%/mV, T_driftrate = 1C/sec and V_driftrate = 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, t_REF. 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.

T_Sens and V_Sens are provided by the manufacturer (Output Driver Sensitivity definition). T_driftrate and V_driftrate are defined by the end user.