Datasheet

RM57L843

SPNS215C –FEBRUARY 2014–REVISED JUNE 2016

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6.2 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.

6.2.1 Important Considerations

• The voltage monitor does not eliminate the need of a voltage supervisor circuit to ensure 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.

6.2.2 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 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.

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 I/O supply must be above the threshold for

monitoring the core supply. 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 Section 6.3.3.1 for the timing

information on this glitch filter.

Table 6-1. Voltage Monitoring Specifications

PARAMETER MIN TYP MAX UNIT

MON

Voltage

monitoring

thresholds

VCC low - VCC level below this threshold is detected as too low. 0.75 0.9 1.13

VVCC high - VCC level above this threshold is detected as too high. 1.40 1.7 2.1

VCCIO low - VCCIO level below this threshold is detected as too low. 1.85 2.4 2.99

6.2.3 Supply Filtering

The VMON has the capability to filter glitches on the VCC and VCCIO supplies.

Table 6-2 lists the characteristics of the supply filtering. Glitches in the supply larger than the maximum

specification cannot be filtered.

Table 6-2. VMON Supply Glitch Filtering Capability

PARAMETER MIN MAX UNIT

Width of glitch on VCC that can be filtered 250 1000 ns

Width of glitch on VCCIO that can be filtered 250 1000 ns