MAX820(1998) 데이터 시트보기 (PDF) - Maxim Integrated

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MAX820
(Rev.:1998)

Microprocessor and Nonvolatile Memory Supervisory Circuits

Maxim Integrated 

Microprocessor and Non-Volatile

Memory Supervisory Circuits

REGULATOR

R3

VCC

RESET IN/INT

RESET 2

TO µP

R1

R4

MAX792

MAX820

LLIN/REFOUT

RESET 1

TO µP

R2

( ) VLOW LINE = 1.3 R1 + R2

R2

( ) VRESET = 1.3 R3 + R4

R4

LOW LINE 10

GND

TO µP NMI

Figure 4c. Alternative Connection for External Programming Mode

Reset Outputs (RESET and RESET)

The RESET output is active low and typically sinks 1.6mA

at 0.1V. When deasserted, RESET sources 1.6mA at typi-

cally VCC - 1.5V. The RESET output is the inverse of

RESET. RESET is guaranteed to be valid down to VCC = 1V,

and an external 10kΩ pull-down resistor on RESET

ensures that it will be valid with VCC down to GND

(Figure 5). As VCC goes below 1V, the gate drive to the

RESET output switch reduces accordingly, increasing the

rDS(ON) and the saturation voltage. The 10kΩ pull-down

resistor ensures that the parallel combination of switch

plus resistor will be around 10kΩ and the saturation

voltage will be below 0.4V while sinking 40µA. When

using an external pull-down resistor of 10kΩ, the high

state for the RESET output with VCC = 4.75V is typically

4.60V.

Overvoltage Comparator

The overvoltage comparator is an uncommitted com-

parator that has no effect on the operation of other chip

functions. Use this input to provide overvoltage indica-

tion by connecting a voltage divider from the input sup-

ply, as in Figure 6.

Connect OVI to ground if the overvoltage function is not

used. OVO goes low when OVI goes above 1.30V. With

OVI below 1.30V, OVO is actively pulled to VCC and can

source1µA.

1

RESET

MAX792

MAX820

TO µP RESET

10k

Figure 5. Adding an external pull-down resistor ensures RESET

is valid with VCC down to GND.

VOLTAGE REGULATOR

3

VCC

7 OVI

MAX792

MAX820

OVO 6

OVERVOLTAGE

1.30V

GND

12

Figure 6. Detecting an Overvoltage Condition

Watchdog Function

The watchdog monitors µP activity via the watchdog

input (WDI). If the µP becomes inactive, WDO and WDPO

are asserted. To use the watchdog function, connect

WDI to a µP bus line or I/O line. If WDI remains high or

low for longer than the watchdog timeout period

(1.6sec nominal), WDPO and WDO are asserted, indicat-

ing a software fault condition (see Watchdog-Pulse

Output and Watchdog Output sections).

Watchdog Input

If the watchdog function is unused, connect WDI to VCC

or GND. A change of state (high-to-low, low-to-high, or

a minimum 100ns pulse) at WDI during the watchdog

period resets the watchdog timer. The watchdog timer

______________________________________________________________________________________ 11

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