Rainbow Electronics MAX6871 - Manual (Page 19)

REFIN
The MAX6870/MAX6871 feature an internal +1.25V volt-
age reference. The voltage reference sets the threshold
of the voltage detectors and provides a reference volt-
age for the internal ADC. Program register 44h to use
the internal reference or an external reference (Table
9). Leave REFIN unconnected when using the internal
reference. REFIN accepts an external reference in the
+1.225V to +1.275V range.
Programmable Outputs
The MAX6870 features eight programmable outputs,
while the MAX6871 features five programmable outputs.
Selectable output-stage configurations include: active low
or active high, open drain, weak pullup, push-pull, or
charge pump. During power-up, the programmable out-
puts pull to GND with an internal 10µA current sink for 1V
< V
ABP < V UVLO . The programmable outputs remain in
their active states until PO_ timeout period expires, and
all of the programmed conditions are met for each output.
Any output programmed to depend on no condition
always remains in its active state (Table 22). An active-
high configured output is considered asserted when that
output is logic-high. No output can depend solely on MR.
The positive voltage monitors generate fault signals
(logical 0) to the MAX6870/MAX6871’s logic array when
an input voltage is below the programmed undervolt-
age threshold, or when that voltage is above the over-
voltage threshold. The negative voltage monitor (IN2)
generates a fault signal to the logic array when the
input voltage is less negative than the undervoltage
threshold, or when that voltage is more negative than
the overvoltage threshold.
Registers 0Eh through 3Ah and 40h configure each of
the programmable outputs. Programmable timing
blocks set the PO_ timeout period from 25µs to 1600ms
for each programmable output. See register 3Ah (Table
22) to set the active state (active-high or active-low) for
each programmable output and registers 11h, 15h,
1Ch, 23h, 2Ah, 31h, 35h, and 39h to select the output
stage types (Tables 23 and 24), and PO_ timeout peri-
ods (Table 25) for each output.
Control selected programmable outputs with a sum of
products (Tables 10–21). Each product allows a differ-
ent set of conditions to assert each output. Outputs
PO3 (MAX6870)/PO1 (MAX6871) and PO6 (MAX6870)/
PO4 (MAX6871) allow two sets of different conditions to
assert each output. Outputs PO1 and PO2 (MAX6870
only), PO7 (MAX6870)/PO5 (MAX6871), and PO8
(MAX6870 only) allow only one set of conditions to
assert each output.
For example, Product 1 of the PO3 (MAX6870—Table
12) programmable output may depend on the IN1 pri-
mary undervoltage threshold, and the states of GPI1,
PO1, and PO2. Write a one to R16h[0], R17h[6], and
R18h[3:2] to configure Product 1 as indicated. IN1
must be above the primary undervoltage threshold
(Table 2), GPI1 must be inactive (Table 6), and PO1
(Tables 10 and 22) and PO2 (Tables 12 and 23) must
be in their deasserted states for Product 1 to be a logi-
cal 1. Product 1 is equivalent to the logic statement:
V1A
• GPI1 • PO1 • PO2.
Product 2 of PO3 (MAX6870, Table 13) may depend on
an entirely different set of conditions, or the same condi-
tions, depending on the system requirements. For
example, Product 2 may depend on the IN1 undervolt-
age threshold, and the states of GPI2 and WDI1. Write
ones to R19h[6, 0] and R1Ah[7] to configure Product 2
as indicated. IN1 must be above the primary undervolt-
age threshold (Table 2), GPI2 must be inactive (Table
6), and the WDI1 timer must not have expired (Tables
27 and 28) for Product 2 to be a logical 1. Product 2 is
equivalent to the logic statement: V1A
• GPI2 • WDI1.
PO3 deasserts if either Product 1 or Product 2 is a logi-
cal 1. The logical statement: Product 1 + Product 2
determines the state of PO3.
MAX6870/MAX6871
EEPROM-Programmable Hex/Quad
Power-Supply Sequencers/Supervisors with ADC
______________________________________________________________________________________ 19
Table 9. Reference Register
REGISTER
ADDRESS
EEPROM
MEMORY
ADDRESS
BIT
RANGE
DESCRIPTION
[0]
0 = internal reference.
1 = external reference.
44h 8044h
[7:1] Not used.