Datasheet

DS1886
SFP and PON ONU Controller
with Digital LDD Interface
24Maxim Integrated
Figure 7. Low-Voltage Hysteresis Example
circuitry is disabled. When V
CC
reaches POA, the SEE is
recalled, and the analog circuitry is enabled. While V
CC
remains above POA, the device is in its normal operating
state, and it responds based on its nonvolatile configura-
tion. If during operation V
CC
falls below POA, but is still
above POD, the SRAM retains the SEE settings from the
first SEE recall, but the device analog is shut down and
the outputs are disabled. If the supply voltage recovers
back above POA, the device immediately resumes nor-
mal operation. If the supply voltage falls below POD, the
device SRAM is placed in its default state and another
SEE recall is required to reload the nonvolatile settings.
The EEPROM recall occurs the next time V
CC
next
exceeds POA. Figure 7 shows the sequence of events
as the voltage varies.
Any time V
CC
is above POD, the I
2
C interface can be
used to determine if V
CC
is below the POA level. This is
accomplished by checking the RDYB bit in the STATUS
byte (A2h Lower Memory, Register 6Eh). RDYB is set
when V
CC
is below POA; when V
CC
rises above POA,
RDYB is timed (within 500Fs) to go to 0, at which point
the part is fully functional.
For all device addresses sourced from EEPROM (A2h
Table 02h, Register 8Ch), the default DEVICE ADDRESS
is A2h until V
CC
exceeds POA, allowing the device
address to be recalled from the EEPROM.
Power-On Analog (POA)
POA holds the DS1886 in reset until V
CC
is at a suitable
level (V
CC
> POA) for the device to accurately measure
with its ADC and compare analog signals with its quick-
trip monitors. Because V
CC
cannot be measured by the
ADC when V
CC
is less than POA, POA also asserts the
VCC LO alarm, which is cleared by a V
CC
ADC conver-
sion greater than the customer-programmable V
CC
low
ADC limit. This allows a programmable limit to ensure
that the head room requirements of the transceiver are
satisfied during a slow power-up. The TXFOUT output
does not latch until there is a conversion above the V
CC
low limit. The POA alarm is nonmaskable. See the Low-
Voltage Operation section for more information.
V
POA
V
POD
V
CC
SEE RECALLED VALUE RECALLED VALUE
PRECHARGED
TO 0
PRECHARGED
TO 0
PRECHARGED TO 0
SEE RECALL
SEE RECALL