Datasheet

MAX5940A/MAX5940B/MAX5940C/MAX5940D
To adjust the UVLO threshold (MAX5940B/MAX5940D
only), connect an external resistor-divider from GND to
UVLO and from UVLO to V
EE
. Use the following equations
to calculate R1 and R2 for a desired UVLO threshold:
R1 = 25.5kΩ - R2
where V
IN,EX
is the desired UVLO threshold. Since the
resistor-divider replaces the 25.5kΩ PD detection resis-
tor, ensure that the sum of R1 and R2 equals 25.5kΩ
±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.
Rkx
V
V
REF UVLO
IN EX
2255= .
,
,
Ω
IEEE 802.3af PD Interface Controller
For Power-Over-Ethernet
8 _______________________________________________________________________________________
R1
GND
UVLO
GND
(UVLO)
( ) MAX5940B.
GATE
R2
R3
MAX5940B
MAX5940D
CLASSIFICATION
RCLASS
(PGOOD)
6.8V
EN
REF
2.46V
200mV
V
EE
V
GATE
1.2V, REF
5V, REF
Q4
PGOOD
OUT
Q3
Q1
Q2
EN
20%
Figure 2. Block Diagram
R1
UVLO
GND
V
EE
R2
V
IN
= 12V TO 67V
MAX5940B
MAX5940D
Figure 3. Setting Undervoltage Lockout with an External
Resistor-Divider