DS1035 Datasheet, PDF (37/106 Pages) Dallas Semiconductor – 3-in-1 High.Speed Silicon Delay Line

Architecture
MachXO2 Family Data Sheet
Table 2-18. MachXO2 Power Saving Features Description
Device Subsystem
Bandgap
Power-On-Reset (POR)
On-Chip Oscillator
PLL
I/O Bank Controller
Dynamic Clock Enable for Primary
Clock Nets
Power Guard
Feature Description
The bandgap can be turned off in standby mode. When the Bandgap is turned off, ana-
log circuitry such as the POR, PLLs, on-chip oscillator, and referenced and differential 
I/O buffers are also turned off. Bandgap can only be turned off for 1.2V devices.
The POR can be turned off in standby mode. This monitors VCC levels. In the event of
unsafe V_CC drops, this circuit reconfigures the device. When the POR circuitry is turned
off, limited power detector circuitry is still active. This option is only recommended for ap-
plications in which the power supply rails are reliable.
The on-chip oscillator has two power saving features. It may be switched off if it is not
needed in your design. It can also be turned off in Standby mode.
Similar to the on-chip oscillator, the PLL also has two power saving features. It can be
statically switched off if it is not needed in a design. It can also be turned off in Standby
mode. The PLL will wait until all output clocks from the PLL are driven low before power-
ing off.
Referenced and differential I/O buffers (used to implement standards such as HSTL,
SSTL and LVDS) consume more than ratioed single-ended I/Os such as LVCMOS and
LVTTL. The I/O bank controller allows the user to turn these I/Os off dynamically on a
per bank selection.
Each primary clock net can be dynamically disabled to save power.
Power Guard is a feature implemented in input buffers. This feature allows users to
switch off the input buffer when it is not needed. This feature can be used in both clock
and data paths. Its biggest impact is that in the standby mode it can be used to switch off
clock inputs that are distributed using general routing resources.
For more details on the standby mode refer to TN1198, Power Estimation and Management for MachXO2 Devices.
Power On Reset
MachXO2 devices have power-on reset circuitry to monitor V_CCINT and V_CCIO voltage levels during power-up and
operation. At power-up, the POR circuitry monitors V_CCINT and V_CCIO0 (controls configuration) voltage levels. It
then triggers download from the on-chip configuration Flash memory after reaching the V_PORUP level specified in
the Power-On-Reset Voltage table in the DC and Switching Characteristics section of this data sheet. For devices
without voltage regulators (ZE and HE devices), V_CCINT is the same as the V_CC supply voltage. For devices with
voltage regulators (HC devices), V_CCINT is regulated from the V_CC supply voltage. From this voltage reference, the
time taken for configuration and entry into user mode is specified as Flash Download Time (t_REFRESH) in the DC
and Switching Characteristics section of this data sheet. Before and during configuration, the I/Os are held in tri-
state. I/Os are released to user functionality once the device has finished configuration. Note that for HC devices, a
separate POR circuit monitors external V_CC voltage in addition to the POR circuit that monitors the internal post-
regulated power supply voltage level.
Once the device enters into user mode, the POR circuitry can optionally continue to monitor V_CCINT levels. If
V_CCINT drops below V_PORDNBG level (with the bandgap circuitry switched on) or below V_PORDNSRAM level (with the
bandgap circuitry switched off to conserve power) device functionality cannot be guaranteed. In such a situation
the POR issues a reset and begins monitoring the V_CCINT and V_CCIO voltage levels. V_PORDNBG and V_PORDNSRAM
are both specified in the Power-On-Reset Voltage table in the DC and Switching Characteristics section of this data
sheet.
Note that once a ZE or HE device enters user mode, users can switch off the bandgap to conserve power. When
the bandgap circuitry is switched off, the POR circuitry also shuts down. The device is designed such that a mini-
mal, low power POR circuit is still operational (this corresponds to the V_PORDNSRAM reset point described in the
paragraph above). However this circuit is not as accurate as the one that operates when the bandgap is switched
on. The low power POR circuit emulates an SRAM cell and is biased to trip before the vast majority of SRAM cells
flip. If users are concerned about the V_CC supply dropping below V_CC (min) they should not shut down the bandgap
or POR circuit.
2-33