STHS4257A, STHS4257A1
STHS4257L, STHS4257L1
IEEE 802.3af PoE Powered Device (PD)
interface controller with integrated signature resistor
Features
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■
■
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■
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IEEE 802.3af-compliant interface for Powered
Devices (PDs)
Integrated 100V, 450mA power MOSFET low
side switch
Inrush current limit
Normal operation current limit
Integrated 25kΩ signature resistor
Signature disable (STHS4257A1/L1)
Resistor-programmable classification current
(Class 0-4)
Power Good output, open drain
Undervoltage Lockout (UVLO)
Thermal overload protection (two-step for the
STHS4257A/L)
Latch (L) or auto-retry (A) after repetitive
thermal overload
Industrial temperature range: –40 to +85°C
SO8 and DFN8 (3mm x 3mm) packages
RoHS compliant
8
1
SO8 (M)
DFN8 3mm x 3mm (DB)
Applications
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Voice over IP (VoIP) phones
Web cameras
Table 1.
Device options
Signature
disable
Order code
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STHS4257A
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39.2
36.0
39.2
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■
■
■
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WLAN access points
Internet appliances
POS terminals
RFID readers
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UVLO
threshold,
rising (V)
UVLO
threshold,
falling (V)
30.5
30.5
30.5
30.5
Protection
mode
Thermal
overload
protection
2 steps
1 step
2 steps
1 step
Inrush
current limit
(mA, typ)
Normal
operation
current limit
(mA, typ)
Auto
Auto
Latch
Latch
350/188
(1)
140
350/188
(1)
140
375
375
STHS4257A1
STHS4257L
STHS4257L1
✔
36.0
1. Current limit is common for both modes and gets reduced only in case of thermal overload. See
Table 5: Electrical parameters.
July 2007
Rev 4
1/18
www.st.com
1
Contents
STHS4257A, STHS4257A1, STHS4257L, STHS4257L1
Contents
1
Summary description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1.1
1.1.2
1.1.3
1.1.4
1.1.5
1.1.6
Classification (R
CLASS
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
V
IN
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Power supply (GND) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Signature disable input (SIGDISA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Power Good output (PWRGD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Negative power output (V
OUT
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2
IEEE802.3af PD power classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2
3
4
5
6
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
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Package mechanical data . . . . . . . . . . . . . . . . . . . . . . .
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Part numbering . . . . . . . . . . . . . . . . . . . . . . . .
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. . . . . . . . . . . . . . . . . 16
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. . . . . . . . . . . . . . . . . . . . . . . . 17
Revision history . . . . . . . . . . . . . .
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Electrical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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STHS4257A, STHS4257A1, STHS4257L, STHS4257L1
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Device options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
IEEE802.3af PD power classes and corresponding R
CLASS
values. . . . . . . . . . . . . . . . . . . 7
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Electrical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
SO8 – 8-lead plastic small outline, 150mils width, mechanical data. . . . . . . . . . . . . . . . . . 14
DFN8 – 8-lead dual flat no-lead outline, package mechanical data . . . . . . . . . . . . . . . . . . 15
Ordering information scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
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List of figures
STHS4257A, STHS4257A1, STHS4257L, STHS4257L1
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Pin connections (STHS4257A/L, top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Pin connections (STHS4257A1/L1, top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Application circuit overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Block diagram (STHS4257A/L). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Typical application circuit (STHS4257A/L) with a DC/DC converter. . . . . . . . . . . . . . . . . . . 9
Block diagram (STHS4257A1/L1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Typical application circuit (STHS4257A1/L1) with a DC/DC converter. . . . . . . . . . . . . . . . 10
SO8 – 8-lead plastic small outline, 150mils width, mechanical drawing . . . . . . . . . . . . . . . 14
DFN8 – 8-lead dual flat no-lead outline, package mechanical drawing . . . . . . . . . . . . . . . 15
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STHS4257A, STHS4257A1, STHS4257L, STHS4257L1
Summary description
1
Summary description
The STHS4257 is an IEEE802.3af-compliant family of interface controllers for Power over
Ethernet (PoE) Powered Device (PD) applications. The devices consist of two main
sections:
●
●
The IEEE802.3af interface to the PoE powered RJ-45 wall socket, and
the Hot Swap Controller (HSC) functions required to protect the PD during insertion,
operation, and withdrawal from the RJ-45 socket.
These devices have an integrated high voltage power MOSFET (low-side switch) with low
R
ON
and the capability to accept transients as high as 100V. Since the pins (such as GND
and V
IN
) which interface to the RJ-45 socket can routinely see high peak voltages in excess
of 100V, it is strongly recommended that board designers protect the PD device with a
transient voltage suppressor, such as the SMAJ58A (available from STMicroelectronics),
connected between the GND and V
IN
pins (see
Figure 4 on page 8).
The IEEE802.3af-compliant interface includes the basic PD detection and Classification
functions, whereas the ‘Hot Swap’ functions include other basic features, such as Inrush
Current Limiting, Undervoltage Lockout (UVLO), and Thermal Overload Protection. All of the
devices include an open drain Power Good (PWRGD) signal to indicate normal steady
operation (see
Figure 1 on page 6
and
Table 2 on page 6).
The STHS4257 family also
incorporates a 1.5V voltage offset (two series diodes) to accommodate the input diode
bridge used to make the PD polarity insensitive.
The STHS4257A1/L1 includes a dual level current limit circuit. This allows the
STHS4257A1/L1 to interface with legacy Power over Ethernet (LAN) systems while
maintaining compatibility with the current IEEE 802.3af specification.
Each of the two basic part types, the STHS4257A/L and the STHS4257A1/L1, is available
either with Latched Operation (L) Mode or with Automatic Retry (A) Mode after fault
conditions. For product options overview see
Table 1 on page 1.
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