Maxim Integrated MAXQ7667 - Manual (Page 279)

16-13 _________________________________________________________________________________________________________
MAXQ7667 User’s Guide
16.4.1 Reset Output
The MAXQ7667 asserts the RESET signal during power-up. On power-up, once DVDD exceeds 1V RESET is asserted to be logic-low.
As DVDD rises, RESET remains low. When DVDD exceeds the DVDD POR threshold, RESET is kept low until the internal RC oscillator
becomes stable and has completed 65,536 cycles. After this period, if DVDD remains above the DVDD POR threshold, RESET goes
high. If a brownout reset condition occurs, RESET is asserted low. Each time a DVDD BOR reset is triggered, it stays low until DVDD
exceeds the BOR reset threshold.
16.5 Power-Supply Voltage Monitors
The MAXQ7667 contains three power-supply voltage monitors that can be used to continually monitor AVDD, DVDD, and DVDDIO sup-
ply voltages. All three power-supply voltage monitors can be monitored for brownout condition and initiate interrupt requests if enabled.
The voltage monitors can be independently activated by programming the corresponding enable bits in the Analog Power Enable reg-
ister (APE), such as VDBE (digital voltage brownout detection enable) for DVDD, VIBE (I/O voltage brownout detection enable) for
DVDDIO, and VABE (analog voltage brownout detection enable) for AVDD.
16.5.1 Digital Core Supply (DVDD) Monitor
The digital core supply monitor detects a brownout condition on the +2.5V DVDD supply. The DVDD supply monitor can be indepen-
dently activated by programming the corresponding enable bit (VDBE) in the APE register. A brownout is detected when the DVDD
supply voltage drops below the brownout interrupt threshold (Figure 16-7). If enabled, a DVDD brownout interrupt can be generated
that would give the application code ample time to react appropriately. A DVDD brownout interrupt is generated only if the interrupt
enable bit (VDBIE) in the Analog Interrupt Enable (AIE) register is set. Also, global interrupt mask bits IM5 (in the IMR register) and IGE
(in the IC register) must be enabled.
If the DVDD supply falls further, the brownout reset threshold is tripped, terminating program operation and holding the MAXQ7667 to
the power-on reset state. The MAXQ7667 remains in the power-on reset state until the supply rises above the reset threshold. See
Section 16.4 for details.
Figure 16-7. DVDD Brownout Interrupt Threshold Detection
NOMINAL DVDD
(+2.5V)
DVDD INTERRUPT
THRESHOLD
DVDD BROWNOUT
RESET THRESHOLD
DVLVL
BROWNOUT
RESET
BROWNOUT
INTERRUPT
RESET
2.25V TO 2.38V
2.10V TO 2.25V
CRYSTAL
WARMUP
DELAY