VCLKSTOP_REQ
VCLKSTOP_ACK
MOD_G_RST
VCLK
CHIP_RST
EMIFB
Memory
Controller
PLL
CLKSTOP_REQ
CLKSTOP_ACK
LRST
EMIFB
PSC
PLL_SYSCLK
Architecture
803
SPRUH91D – March 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
External Memory Interface B (EMIFB)
19.2.9 Power Management
Power dissipation from the EMIFB memory controller may be managed by two methods:
•
Self-refresh mode (see
•
Power-down mode
•
Gating input clocks to the module off.
•
Power management in mobile SDRAM, using partial array self refresh.
Gating input clocks off to the EMIFB memory controller achieves higher power savings when compared to
the power savings of self-refresh or power-down mode. The input clocks are turned off outside of the
EMIFB memory controller through the use of the Power and Sleep Controller (PSC) and the PLL
controller.
shows the connections between the EMIFB memory controller, PSC, and PLL.
Before gating clocks off, the EMIFB memory controller must place the SDR SDRAM memory in self-
refresh mode by clearing the SR_PD bit to 0 and setting the LP_MODE bit to 1 in the SDRAM refresh
control register (SDRFC). If the external memory requires a continuous clock, the EMIFB memory
controller clock provided by PLL must not be turned off because this may result in data corruption. See the
following subsections for the proper procedures to follow when stopping the EMIFB memory controller
clocks.
Figure 19-10. EMIFB Memory Controller Power and Sleep Controller Diagram
Power Management Using Self-Refresh Mode
The EMIFB can be placed into a self-refresh state in order to place the attached SDRAM devices into self-
refresh mode, which consumes less power for most SDRAM devices. In this state, the attached SDRAM
device uses an internal clock to perform its own auto refresh cycles. This maintains the validity of the data
in the SDRAM without the need for any external commands. Refer to
for more details on
placing the EMIFB into the self-refresh state.
Power Management Using Power-Down Mode
In case of power-down, to lower the power consumption, EMIFB drives EMB_SDCKE low. EMB_SDCKE
goes high when there is a need to send refresh (REFR) commands, after which EMB_SDCKE is again
driven low. EMB_SDCKE remains low until any request arrives. Refer to
for more
details on placing EMIFB in power-down mode.