SPNS174
–
SEPTEMBER 2011
4.2
Voltage Monitor Characteristics
A voltage monitor is implemented on this device. The purpose of this voltage monitor is to eliminate the
requirement for a specific sequence when powering up the core and I/O voltage supplies.
4.2.1
•
•
Important Considerations
The voltage monitor does not eliminate the need of a voltage supervisor circuit to guarantee that the
device is held in reset when the voltage supplies are out of range.
The voltage monitor only monitors the core supply (VCC) and the I/O supply (VCCIO). The other
supplies are not monitored by the VMON. For example, if the VCCAD or VCCP are supplied from a
source different from that for VCCIO, then there is no internal voltage monitor for the VCCAD and
VCCP supplies.
4.2.2
Voltage Monitor Operation
The voltage monitor generates the Power Good MCU signal (PGMCU) as well as the I/Os Power Good IO
signal (PGIO) on the device. During power-up or power-down, the PGMCU and PGIO are driven low when
the core or I/O supplies are lower than the specified minimum monitoring thresholds. The PGIO and
PGMCU being low isolates the core logic as well as the I/O controls during the power-up or power-down
of the supplies. This allows the core and I/O supplies to be powered up or down in any order.
PRODUCT PREVIEW
When the voltage monitor detects a low voltage on the I/O supply, it will assert a power-on reset. When
the voltage monitor detects an out-of-range voltage on the core supply, it asynchronously makes all output
pins high impedance, and asserts a power-on reset. The voltage monitor is disabled when the device
enters a low power mode.
The VMON also incorporates a glitch filter for the nPORRST input. Refer to
for the timing
information on this glitch filter.
Table 4-1. Voltage Monitoring Specifications
PARAMETER
VCC low - VCC level below this
threshold is detected as too low.
V
MON
Voltage monitoring
thresholds
VCC high - VCC level above this
threshold is detected as too high.
VCCIO low - VCCIO level below this
threshold is detected as too low.
MIN
0.8
1.40
1.9
TYP
0.9
1.7
2.4
MAX
1.0
2.1
2.9
UNIT
V
4.2.3
Supply Filtering
The VMON has the capability to filter glitches on the VCC and VCCIO supplies.
The following table shows the characteristics of the supply filtering. Glitches in the supply larger than the
maximum specification cannot be filtered.
Table 4-2. VMON Supply Glitch Filtering Capability
Parameter
MIN
250ns
250ns
MAX
1us
1us
Width of glitch on VCC that can be filtered
Width of glitch on VCCIO that can be filtered
52
System Information and Electrical Specifications
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