MAX6333(1998) データシートの表示（PDF） - Maxim Integrated

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MAX6333
(Rev.:1998)

3-Pin, Ultra-Low-Voltage, Low-Power µP Reset Circuits

Maxim Integrated 

3-Pin, Ultra-Low-Voltage, Low-Power

µP Reset Circuits

______________Applications Information

Interfacing to µPs with Bidirectional

Reset Pins

Since the RESET output on the MAX6334 is open-drain,

this device interfaces easily with µPs that have bidirec-

tional reset pins, such as the Motorola 68HC11.

Connecting the µP supervisor’s RESET output directly

to the microcontroller’s (µC’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 µP 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

µPs 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;

100kΩ 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 100kΩ 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

VCC

MAX6334

RESET

GND

VCC

µP

MOTOROLA

68HCXX

RESET

INPUT

GND

Figure 1. Interfacing to µPs with Bidirectional Reset Pins

VCC

VCC

MAX6333

RESET

100k

GND

(a)

MAX6332

RESET

GND

(b)

*ASSUMES HIGH-Z RESET INPUT TO THE µP

Figure 2. Ensuring Reset Valid Down to VCC = 0

100k*

Table 1. Factory-Trimmed Reset

Thresholds*

RESET-

THRESHOLD

SUFFIX

MAX633_UR25D_

TA = +25°C TA = -40°C to +85°C

MIN TYP MAX MIN

MAX

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

* Factory-trimmed reset thresholds are available in approximately

100mV increments, with a ±1.8% room-temperature variance.

4 _______________________________________________________________________________________

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