MAX6885 データシートの表示（PDF） - Maxim Integrated

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MAX6885

EEPROM-Programmable, Hex Power-Supply Supervisory Circuits

Maxim Integrated 

EEPROM-Programmable, Hex

Power-Supply Supervisory Circuits

Powering the MAX6884/MAX6885

The MAX6884/MAX6885 derive power from the voltage-

detector inputs: IN1–IN4 or through an externally sup-

plied VCC. A virtual diode-ORing scheme selects the

positive input that supplies power to the device (see the

Functional Diagram). The highest input voltage on

IN1–IN4 supplies power to the device. One of VIN1–VIN4

must be at least 2.7V to ensure proper operation.

Internal hysteresis ensures that the supply input that initially

powered the device continues to power the device when

multiple input voltages are within 50mV of each other.

VCC powers the analog circuitry and is the bypass con-

nection for the MAX6884/MAX6885 internal supply.

Bypass VCC to GND with a 1µF ceramic capacitor

installed as close to the device as possible. The internal

supply voltage, measured at VCC, equals the maximum

of IN1–IN4. If VCC is externally supplied, VCC must be at

least 200mV higher than any voltage applied to IN–IN4

and VCC must be brought up first. VCC always powers

the device when all IN_ are factory set as “ADJ.” Do not

use the internally generated VCC to provide power to

external circuitry. Externally supply power through VCC.

To externally supply power through VCC:

1) Apply a voltage to only one of VCC (2.7V to 5.5V) or

IN1–IN4 (2.7V to 5.8V).

2) Program the internal/external VCC Power EEPROM at

96h, Bit[5] = 1 (see Table 2).

3) Power down the device.

Subsequent power-ups and software reboots require an

externally supplied VCC to ensure the device is fully

operational.

Table 2. Internal/External VCC

REGISTER

ADDRESS

EEPROM

MEMORY

ADDRESS

BIT

RANGE

DESCRIPTION

1 = VCC Powered

[5] 0 = IN1–IN4 or VCC

Powered

16h

96h

[2] Not Used

[4] Not Used

[6] Not Used

The MAX6884/MAX6885 also generate a digital supply

voltage (DBP) for the internal logic circuitry and the

EEPROM. Bypass DBP to GND with a 1µF ceramic

capacitor installed as close to the device as possible.

The nominal DBP output voltage is 2.55V. Do not use

DBP to provide power to external circuitry.

ADC (MAX6884 Only)

An internal 10-bit ADC (MAX6884 only) converts volt-

ages at IN1–IN4, AUXIN, and VCC through a multiplexer

that automatically sequences through all inputs every

200ms. Registers 18h to 27h store the ADC data (see

Table 3). Read the ADC data from the MAX6884 with

the serial interface. The ADC has no effect on program-

mable outputs RESET, UV/OV, or WDO.

Inputs

The MAX6884/MAX6885 offer the following inputs: volt-

age-detector inputs IN1–IN4, auxiliary input AUXIN

(MAX6884 only), manual reset input MR, margin input

MARGIN, and reference input REFIN (MAX6884 only).

IN1–IN6

The MAX6884/MAX6885 offer six voltage-detector inputs:

IN1–IN6. Each voltage-detector input offers a program-

mable primary undervoltage threshold and a secondary

undervoltage/overvoltage threshold. Program thresholds

from 0.5V to 3.05V in 10mV increments, 1.0V to 5.8V in

20mV increments, or from 0.1667V to 1.0167V in 3.3mV

increments. Use the following equations to program

thresholds in the appropriate registers:

X = VTH − 1V

0.02V

for 1V to 5.8V range in 20mV increments (program bits

R0Fh[5:0]).

X = VTH − 0.5V

0.01V

for 0.5V to 3.05V range in 10mV increments (program

bits R0Fh[5:0]).

X = VTH − 0.1667V

0.0033V

for 0.1667V to 1.0167V in 3.3mV increments (see the

External Voltage-Divider section).

where VTH is the desired threshold voltage and X is the

decimal code for the desired threshold (see Table 4). To

set a threshold for the 1V to 5.8V range, X must equal 240

or less. Set the secondary threshold for an undervoltage

or overvoltage threshold by programming bits R0Eh[5:0].

To achieve thresholds in between the 10mV and 20mV

steps or to monitor voltages higher than 5.8V, program a

voltage-detector input for high impedance through bits

R10h[5:0] and add a resister voltage-divider (see the

External Voltage-Divider section).

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