max5969a Maxim Integrated Products, Inc., max5969a Datasheet - Page 10

• Manufacturer Part Number: max5969a
• Description: Ieee 802.3af/at-compliant, Powered Device Interface Controllers With Integrated Power Mosfet
• Manufacturer: Maxim Integrated Products, Inc.

IEEE 802.3af/at-Compliant, Powered Device Interface
Controllers with
Depending on the input voltage (V
MAX5969A/MAX5969B operate in four different modes:
PD detection, PD classification, mark event, and PD
power. The devices enter PD detection mode when the
input voltage is between 1.4V and 10.1V. The device
enters PD classification mode when the input voltage is
between 12.6V and 20V. The device enters PD power
mode once the input voltage exceeds V
In detection mode, the PSE applies two voltages on V
in the range of 1.4V to 10.1V (1V step minimum) and
then records the current measurements at the two points.
The PSE then computes DV/DI to ensure the presence
of the 24.9kω signature resistor. Connect the signature
resistor (R
detection. The MAX5969A/MAX5969B pull DET low in
detection mode. DET goes high impedance when the
input voltage exceeds 12.5V. In detection mode, most of
the MAX5969A/MAX5969B internal circuitry is off and the
offset current is less than 10µA.
If the voltage applied to the PD is reversed, install pro-
tection diodes at the input terminal to prevent internal
damage to the MAX5969A/MAX5969B (see the Typical
Application Circuit). Since the PSE uses a slope tech-
nique (DV/DI) to calculate the signature resistance, the
DC offset due to the protection diodes is subtracted and
does not affect the detection process.
Table 1. Setting Classification Current
*V
10
CLASS
IN
is measured across the MAX5969A/MAX5969B input V
0
1
2
3
4
5
_____________________________________________________________________________________
DET
POWER USED
0.44 to 12.95
6.49 to 12.95
12.95 to 25.5
) from V
0.44 to 3.94
3.84 to 6.49
MAXIMUM
BY PD
> 25.5
(W)
Detection Mode (1.4V ≤ V
Detailed Description
DD
to DET for proper signature
R
66.5
43.7
30.9
21.3
615
117
(I)
CLS
Operating Modes
IN
Integrated Power MOSFET
= V
ON
DD
12.6 to 20
12.6 to 20
12.6 to 20
12.6 to 20
12.6 to 20
12.6 to 20
.
V
(V)
IN
- V
IN
*
≤ 10.1V)
SS
), the
DD
IN
CLASS CURRENT SEEN AT
to V
MIN
17
26
36
54
SS
0
9
In the classification mode, the PSE classifies the PD
based on the power consumption required by the PD. This
allows the PSE to efficiently manage power distribution.
Class 0 to 5 is defined as shown in Table 1. (The IEEE
802.3af/at standard defines only Class 0 to 4 and Class 5
for any special requirement.) An external resistor (R
connected from CLS to V
The PSE determines the class of a PD by applying a volt-
age at the PD input and measuring the current sourced
out of the PSE. When the PSE applies a voltage between
12.6V and 20V, the MAX5969A/MAX5969B exhibit a cur-
rent characteristic with a value shown in Table 1. The
PSE uses the classification current information to classify
the power requirement of the PD. The classification cur-
rent includes the current drawn by R
current of the MAX5969A/MAX5969B so the total current
drawn by the PD is within the IEEE 802.3af/at standard
figures. The classification current is turned off whenever
the device is in power mode.
During 2-event classification, a Type 2 PSE probes PD
for classification twice. In the first classification event,
the PSE presents an input voltage between 12.6V and
20.5V and the MAX5969A/MAX5969B present the pro-
grammed load I
voltage below the mark event threshold of 10.1V and
the MAX5969A/MAX5969B present the mark current
(I
.
MARK
V
IN
). This sequence is repeated one more time.
(mA)
MAX
Classification Mode (12.6V ≤ V
12
20
30
44
64
4
CLASS
2-Event Classification and Detection
. The PSE then drops the probing
SS
CLASSIFICATION CURRENT
sets the classification current.
SPECIFICATION (mA)
MIN
16
25
35
—
0
8
IEEE 802.3at PSE
CLS
and the supply
MAX
IN
13
21
31
45
—
5
≤ 20V)
CLS
)