MAX6332/MAX6333/MAX6334
3-Pin, Ultra-Low-Voltage, Low-Power
P Reset Circuits
4
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______________Applications Information
Interfacing to Ps with Bidirectional
Reset Pins
Since the RESET output on the MAX6334 is open-drain,
this device interfaces easily with Ps that have bidirec-
tional reset pins, such as the Motorola 68HC11.
Connecting the P supervisor’s RESET output directly
to the microcontroller’s (C’s) RESET pin with a single
pull-up resistor allows either device to assert reset
(Figure 1).
Negative-Going VCC Transients
In addition to issuing a reset to the P during power-up,
power-down, and brownout conditions, these devices are
relatively immune to short-duration, negative-going VCC
transients (glitches). The Typical Operating Characteristics
show the Maximum Transient Duration vs. Reset
Comparator Overdrive graph. The graph shows the maxi-
mum pulse width that a negative-going VCC transient may
typically have without issuing a reset signal. As the ampli-
tude of the transient increases, the maximum allowable
pulse width decreases.
Ensuring a Valid Reset Output
Down to VCC = 0
When VCC falls below 1V and approaches the minimum
operating voltage of 0.7V, push/pull-structured reset
sinking (or sourcing) capabilities decrease drastically.
High-impedance CMOS-logic inputs connected to the
RESET pin can drift to indeterminate voltages. This
does not present a problem in most cases, since most
Ps and circuitry do not operate at VCC below 1V. For
the MAX6333, where RESET must be valid down to 0,
adding a pull-down resistor between RESET and GND
removes stray leakage currents, holding RESET low
(Figure 2a). The pull-down resistor value is not critical;
100k
is large enough not to load RESET and small
enough to pull it low. For the MAX6332, where RESET
must be valid to VCC = 0, a 100k
pull-up resistor
between RESET and VCC will hold RESET high when
VCC falls below 0.7V (Figure 2b).
Since the MAX6334 has an open-drain, active-low out-
put, it typically uses a pull-up resistor. With this device,
RESET will most likely not maintain an active condition,
but will drift to a non-active level due to the pull-up
resistor and the reduced sinking capability of the open-
drain device. Therefore, this device is not recommend-
ed for applications where the RESET pin is required to
be valid down to VCC = 0.
VCC
GND
MAX6334
RESET
VCC
GND
RESET
INPUT
MOTOROLA
68HCXX
P
* Factory-trimmed reset thresholds are available in approximately
100mV increments, with a ±1.8% room-temperature variance.
TA = +25°C
TA = -40°C to +125°C
MIN
TYP
MAX
MIN
MAX
MAX633_UR25D_
2.46 2.50
2.55
2.43
2.58
MAX633_UR24D_
2.36 2.40
2.44
2.33
2.47
MAX633_UR23D_
2.26 2.30
2.34
2.23
2.37
MAX633_UR22D_
2.16 2.20
2.24
2.13
2.27
MAX633_UR21D_
2.06 2.10
2.14
2.04
2.16
MAX633_UR20D_
1.96 2.00
2.04
1.94
2.06
MAX633_UR19D_
1.87 1.90
1.93
1.84
1.96
MAX633_UR18D_
1.77 1.80 1.83
1.75
1.85
MAX633_UR17D_
1.67 1.70 1.73
1.65
1.75
MAX633_UR16D_
1.57 1.60 1.63
1.55
1.65
RESET-
THRESHOLD
SUFFIX
Table 1. Factory-Trimmed Reset
Thresholds*
Figure 1. Interfacing to Ps with Bidirectional Reset Pins
Figure 2. Ensuring Reset Valid Down to VCC = 0
VCC
GND
MAX6333
RESET
100k
(a)
VCC
GND
MAX6332
RESET
100k*
(b)
*ASSUMES HIGH-Z RESET INPUT TO THE
P