DS1886 datasheet(24/92 Pages) MAXIM

24 / 92 page

DS1886

SFP and PON ONU Controller

with Digital LDD Interface

Maxim Integrated

Figure 7. Low-Voltage Hysteresis Example

circuitry is disabled. When VCC reaches POA, the SEE is

recalled, and the analog circuitry is enabled. While VCC

remains above POA, the device is in its normal operating

state, and it responds based on its nonvolatile configura-

tion. If during operation VCC 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 VCC next

exceeds POA. Figure 7 shows the sequence of events

as the voltage varies.

Any time VCC is above POD, the I2C interface can be

used to determine if VCC 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 VCC is below POA; when VCC 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 VCC exceeds POA, allowing the device

address to be recalled from the EEPROM.

Power-On Analog (POA)

POA holds the DS1886 in reset until VCC is at a suitable

level (VCC > POA) for the device to accurately measure

with its ADC and compare analog signals with its quick-

trip monitors. Because VCC cannot be measured by the

ADC when VCC is less than POA, POA also asserts the

VCC LO alarm, which is cleared by a VCC ADC conver-

sion greater than the customer-programmable VCC 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 VCC

low limit. The POA alarm is nonmaskable. See the Low-

Voltage Operation section for more information.

VPOA

VPOD

VCC

SEE

RECALLED VALUE

PRECHARGED

TO 0

PRECHARGED

TO 0

PRECHARGED TO 0

SEE RECALL

DS1886 Datasheet(PDF) 24 Page - Maxim Integrated Products

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