Rainbow Electronics MAX5965B User Manual

Page 22

MAX5965A/MAX5965B

High-Power, Quad, Monolithic, PSE Controllers
for Power over Ethernet

______________________________________________________________________________________

Digital Logic

supplies power for the internal logic circuitry. V

ranges from +3.0V to +5.5V and determines the logic
thresholds for the CMOS connections (SDAIN, SDAOUT,
SCL, AUTO, SHD_, A_). This voltage range enables the
MAX5965A/MAX5965B to interface with a nonisolated
low-voltage microcontroller. The MAX5965A/MAX5965B
check the digital supply for compatibility with the internal
logic. The MAX5965A/MAX5965B also feature a V

undervoltage lockout (V

DDUVLO

) of +2.0V. A V

DDUVLO

condition keeps the MAX5965A/MAX5965B in reset and
the ports shut off. Bit 0 in the supply event register shows
the status of V

DDUVLO

(Table 12) after V

has recov-

ered. All logic inputs and outputs reference to DGND.
For AC-disconnected detection, DGND and AGND must
be connected together externally. Connect DGND to
AGND at a single point in the system as close as possi-
ble to the MAX5965A/MAX5965B.

Hardware Shutdown

SHD_ shuts down the respective ports without using the
serial interface. Hardware shutdown offers an emer-
gency turn-off feature that allows a fast disconnect of
the power supply from the port. Pull SHD_ low to
remove power. SHD_ also resets the corresponding
events and status register bits.

Interrupt

The MAX5965A/MAX5965B contain an open-drain logic
output (INT) that goes low when an interrupt condition
exists. R00h and R01h (Tables 6 and 7) contain the defin-
itions of the interrupt registers. The mask register R01h
determines events that trigger an interrupt. As a response
to an interrupt, the controller reads the status of the event
register to determine the cause of the interrupt and takes
subsequent actions. Each interrupt event register also
contains a Clear on Read (CoR) register. Reading
through the CoR register address clears the interrupt. INT
remains low when reading the interrupt through the read-
only addresses. For example, to clear a startup fault on
the port 4 read address 09h (see Table 11). Use the glob-
al pushbutton bit in register 1Ah (bit 7, Table 23) to clear
interrupts, or use a software or hardware reset.

Undervoltage and

Overvoltage Protection

The MAX5965A/MAX5965B contain several undervoltage
and overvoltage protection features. Table 12 in the

section shows a detailed

list of the undervoltage and overvoltage protection fea-
tures. An internal V

undervoltage lockout (V

EEUVLO

) cir-

cuit keeps the MOSFET off and the MAX5965A/
MAX5965B in reset until V

AGND

- V

exceeds 29V for

more than 3ms. An internal V

overvoltage (V

EE_OV

) cir-

cuit shuts down the ports when (V

AGND

- V

) exceeds

60V. The digital supply also contains an undervoltage
lockout (V

DDUVLO

). The MAX5965A/MAX5965B also fea-

ture three other undervoltage and overvoltage interrupts:
V

undervoltage interrupt (V

EEUV

), V

undervoltage

interrupt (V

DDUV

), and V

overvoltage interrupt

DDOV

). A fault latches into the supply events register

(Table 12), but the MAX5965A/MAX5965B does not shut
down the ports with V

EEUV

, V

DDUV

, or V

DDOV

DC Disconnect Monitoring

Setting R13h[DCD_EN_] bits high enables DC load moni-
toring during a normal powered state. If V

(the voltage

across R

) falls below the DC load disconnect threshold,

DCTH

, for more than t

DISC

, the device turns off power

and asserts the LD_DISC_ bit of the corresponding port.

AC Disconnect Monitoring

(MAX5965A/MAX5965B)

The MAX5965A/MAX5965BB feature AC load discon-
nect monitoring. Connect an external sine wave to
OSC. The oscillator requirements are:

1) V

P-P

x Frequency = 200V

P-P

x Hz ±15%

2) Positive peak voltage > +2.2V

3) Frequency > 60Hz

A 100Hz ±10%, 2V

P-P

±5%, with +1.3V offset (V

PEAK

+2.3V typical) is recommended.

The MAX5965A/MAX5965BB buffer and amplify three
times the external oscillator signal and sends the signal
to DET_, where the sine wave is AC-coupled to the out-
put. The MAX5965A/MAX5965BB sense the presence
of the load by monitoring the amplitude of the AC cur-
rent returned to DET_ (see the

Functional Diagram

Setting R13h[ACD_EN_] bits high enable AC load dis-
connect monitoring during a normal powered state. If
the AC current peak at the DET_ input falls below I

ACTH

for more than t

DISC

, the device turns off power and

asserts the LD_DISC_ bit of the corresponding port.
I

ACTH

is programmable using R23h[0-3].

An internal comparator checks for a proper amplitude of
the oscillator input. If the positive peak of the input sinu-
soid falls below a safety value of 2V (typ), OSC_FAIL
sets and the port shuts down. Power cannot be applied
to the ports when ACD_EN is set high and OSC_FAIL is
set high. Leave OSC unconnected or connect it to
DGND when not using AC-disconnect detection.

Thermal Shutdown

If the MAX5965A/MAX5965B die temperature reaches
+150°C, an overtemperature fault generates and the
MAX5965A/MAX5965B shut down. The MOSFETs turn off.
The die temperature of the MAX5965A/MAX5965B must
cool down below +130°C to remove the overtemperature
fault condition. After a thermal shutdown, the part is reset.