Maxim Integrated MAXQ7666 - Manual (Page 87)

2.5.3 Reset Output
The MAXQ7665/MAXQ7666 assert the RESET signal during power-up and also during reset conditions caused by an internal source
(such as brownout, watchdog, or internal reset). On power-up, once DVDD exceeds 1.2V, RESET is asserted to be logic-low. As DVDD
rises, RESET remains low. When DVDD exceeds the default BOR threshold, RESET is kept low until the internal RC oscillator has com-
pleted 65,536 cycles; after this period, if DVDD remains above the default BOR threshold, RESET goes high. If a brownout reset condi-
tion occurs, RESET is asserted low. Each time a DVDD BOR reset is triggered, it stays low until DVDD exceeds the BOR reset threshold.
Note: The RESET pin is an output and an input. The MAXQ7665/MAXQ7666 is placed into an external reset mode if the RESET pin is
held low for at least four clock cycles. See Section 2.7.2 for more information on external reset.
2.6 Power-Supply Voltage Monitors
The MAXQ7665/MAXQ7666 contain two power-supply voltage monitors that can be used to continually monitor the DVDD and DVDDIO
supply voltages for brownout conditions and initiate interrupt requests if enabled. The DVDD and DVDDIO voltage monitors can be inde-
pendently activated by programming the corresponding enable bits (VDBE and VIBE) in the analog power-enable (APE) register.
2.6.1 Digital Core Supply (DVDD) Monitor
The digital core supply monitor detects a brownout condition on the +3.3V DVDD supply. The DVDD supply monitor can be indepen-
dently activated by programming the corresponding enable bit (VDBE) in the analog power enable (APE) register. A brownout is detect-
ed when the DVDD supply voltage drops below the programmed brownout detection threshold (Figure 2-7). The brownout interrupt
threshold level is user selectable, and can be programmed using the brownout interrupt threshold bits (VDBI[1:0]) in the VMC regis-
ter. The supported threshold levels are listed in Table 2-3. If enabled, a DVDD brownout interrupt can be generated that allows for sav-
ing data and the present state of the MAXQ7665/MAXQ7666. A DVDD brownout interrupt is generated only if the interrupt enable bit
(DVBIE) 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, then the brownout reset threshold is tripped, terminating program operation and holding the
MAXQ7665/MAXQ7666 in the brownout reset state. The MAXQ7665/MAXQ7666 remain in the brownout reset state until the supply rises
above the reset threshold. The DVDD monitor brownout interrupt and reset trip points can differ from device to device within the pro-
grammed threshold range. This tolerance error is caused by the monitor comparator offsets, and threshold setting circuitry. The
brownout interrupt and reset thresholds will track each other to some degree. If the brownout interrupt trip point is trending towards the
lower side of the threshold level, then the brownout reset trip point will also trend towards the lower side of the threshold level. The
brownout reset is always below the brownout interrupt threshold for equivalent settings, ensuring adequate notice of a failing supply
condition.
Table 2-3. DVDD Brownout Interrupt Threshold Range
MAXQ7665/MAXQ7666 User’s Guide
2-15
VDBI[1:0] DVDD (CORE) (V)*
00 (default) 2.77–2.99
01 2.84–3.13
10 2.91–3.20
11 2.99–3.27
* Reconfirm the values provided in this table with those in the latest MAXQ7665 and MAXQ7666 data sheets.
Maxim Integrated