Rainbow-electronics MAX6871 Manual de usuario descargar pdf (Pagina 13)

MAX6870/MAX6871

EEPROM-Programmable Hex/Quad

Power-Supply Sequencers/Supervisors with ADC

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Powering the MAX6870/MAX6871

The MAX6870/MAX6871 derive power from the positive

voltage-detector inputs: IN1, or IN3–IN6. A virtual diode-

ORing scheme selects the positive input that supplies

power to the device (see the Functional Diagram). IN1

must be at least +4V or one of IN3–IN6 (MAX6870)/

IN3/IN4 (MAX6871) must be at least +2.7V to ensure

device operation. An internal LDO regulates IN1 down

to +5.4V.

The highest input voltage on IN3–IN6 (MAX6870)/

IN3/IN4 (MAX6871) supplies power to the device, unless

IN1

≥ +6.5V, in which case IN1 supplies power to the

device. For +4V < V

IN1

< +6.5V and one of V

IN3

through

IN6

> +2.7V, the input power source cannot be deter-

mined due to the dropout voltage of the LDO. Internal

hysteresis ensures that the supply input that initially pow-

ered the device continues to power the device when

multiple input voltages are within 50mV of each other.

ABP powers the analog circuitry; bypass ABP to GND

with a 1µF ceramic capacitor installed as close to the

device as possible. The internal supply voltage, mea-

sured at ABP, equals the maximum of IN3–IN6

(MAX6870)/IN3/IN4 (MAX6871) if V

IN1

= 0, or equals

+5.4V when V

IN1

> +6.5V. Do not use ABP to provide

power to external circuitry.

The MAX6870/MAX6871 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

The MAX6870/MAX6871 feature an internal 10-bit ADC

that monitors the voltage-detector inputs and auxiliary

inputs through an internal multiplexer that sequences

through all input voltages in 200ms. Registers 50h to

5Fh store the ADC data. Read the ADC data from the

MAX6870/MAX6871 with the serial interface. The ADC

strictly monitors input voltages and has no effect on

power-supply sequencing, reset detection, or the pro-

grammable outputs.

Inputs

The MAX6870/MAX6871 contain multiple logic and volt-

age-detector inputs. Each voltage-detector input is

simultaneously monitored for primary and secondary

thresholds. The primary threshold must be an under-

voltage threshold. The secondary threshold may be an

undervoltage or overvoltage threshold. Table 1 summa-

rizes these various inputs.

Table 1. Programmable Features

FEATURE DESCRIPTION

High Voltage Input

(IN1)

• Primary undervoltage threshold

• Secondary overvoltage or undervoltage threshold

• +2.5V to +13.2V threshold in 50mV increments

• +1.25V to +7.625V threshold in 25mV increments

Bipolar Voltage Input

(IN2)

• Primary undervoltage threshold

• Secondary overvoltage or undervoltage threshold

• ±2.5V to ±15.25V threshold in 50mV increments

• ±1.25V to ±7.625V threshold in 25mV increments

Positive Voltage Input

IN3–IN6 (MAX6870)

IN3, IN4 (MAX6871)

• Primary undervoltage threshold

• Secondary overvoltage or undervoltage threshold

• +1V to +5.5V threshold in 20mV increments

• +0.5V to +3.05V threshold in 10mV increments

Programmable Outputs

PO1–PO4 (MAX6870),

PO1, PO2 (MAX6871)

• Active high or active low

• Open-drain, weak pullup, or charge-pump output

• Weak pullup to IN3–IN6 (IN3 or IN4 for MAX6871) or ABP

• Dependent on MR, MARGIN, IN_, GPI1–GPI4 , WDI1 and WDI2, and/or PO_

• Programmable timeout periods of 25µs, 1.5625ms, 6.25ms, 25ms, 50ms, 200ms, 400ms, or 1.6s

Programmable Outputs

PO5–PO8 (MAX6870),

PO3, PO4, PO5

(MAX6871)

• Active high or active low

• Open-drain, weak pullup, or push-pull output

• Weak pullup to IN3–IN6 (IN3 or IN4 for MAX6871) or ABP

• Push-pull to IN3–IN6 (IN3 or IN4 for MAX6871)

• Dependent on MR, MARGIN, IN_, GPI1–GPI4 , WDI1 and WDI2 , and/or IN_

• Programmable timeout periods of 25µs, 1.5625ms, 6.25ms, 25ms, 50ms, 200ms, 400ms, or 1.6s

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 50 51

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