Rainbow Electronics MAX6871 - Manual (Page 13)

MAX6870/MAX6871
EEPROM-Programmable Hex/Quad
Power-Supply Sequencers/Supervisors with ADC
______________________________________________________________________________________ 13
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
V
IN1
≥ +6.5V, in which case IN1 supplies power to the
device. For +4V < V
IN1
< +6.5V and one of V
IN3
through
V 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