MAX5940CESA datasheet(8/15 Pages) MAXIM

8 / 15 page

To adjust the UVLO threshold (MAX5940B/MAX5940D

only), connect an external resistor-divider from GND to

UVLO and from UVLO to VEE. Use the following equations

to calculate R1 and R2 for a desired UVLO threshold:

R1 = 25.5k

Ω - R2

where VIN,EX is the desired UVLO threshold. Since the

resistor-divider replaces the 25.5k

Ω PD detection resis-

tor, ensure that the sum of R1 and R2 equals 25.5k

±1%. When using the external resistor-divider, the

MAX5940B/MAX5940D has an external reference volt-

age hysteresis of 20% (typ). When UVLO is pro-

grammed externally, the turn-off threshold is 80% (typ)

of the new UVLO threshold.

REF UVLO

IN EX

225 5

IEEE 802.3af PD Interface Controller

For Power-Over-Ethernet

_______________________________________________________________________________________

GND

UVLO

GND

(UVLO)

( ) MAX5940B.

GATE

MAX5940B

MAX5940D

CLASSIFICATION

RCLASS

(PGOOD)

6.8V

REF

2.46V

200mV

VEE

VGATE

1.2V, REF

5V, REF

PGOOD

OUT

20%

Figure 2. Block Diagram

UVLO

GND

VEE

VIN = 12V TO 67V

MAX5940B

MAX5940D

Figure 3. Setting Undervoltage Lockout with an External

Resistor-Divider

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