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Texas Instruments Protecting the TPS25810 from High Voltage DFPs Application notes
Application Report
SLVA751 – November 2015
Protecting the TPS25810 from High Voltage DFPs
Nick Smith .................................................................................................................. Power Interface
ABSTRACT
The TPS25810 is a USB Type-C Downstream Facing Port (DFP) controller that monitors the Type-C
Configuration Channel (CC) lines to determine when a USB device is attached. If an Upstream Facing
Port (UFP) device is attached, the TPS25810 applies power to VBUS. One concern in USB Type-C
applications is that a non-compliant DFP device that disregards the USB Type-C specification can be
connected to the port controlled by the TPS25810. Such a device may apply a voltage above the absolute
maximum rating of the TPS25810 which could damage the part. This application note presents three
design solutions which can be used to protect USB Type-C DFP systems against such scenarios.
1
2
3
4
5
6
Contents
Introduction and Related Material .........................................................................................
High Voltage Protection with a PFET .....................................................................................
High Voltage Protection with an NFET....................................................................................
High Voltage Protection with an OVP Switch ............................................................................
Conclusion ....................................................................................................................
References ...................................................................................................................
2
3
5
7
9
9
List of Figures
1
PFET Protection Scheme ................................................................................................... 3
2
Plug in of a Compliant USB Type-C UFP Device with PFET Solution in Place ..................................... 4
3
Unplug of a Compliant USB Type-C UFP Device with PFET Solution in Place ..................................... 4
4
Hot plug of Non-compliant DFP Device with PFET Solution in Place
5
Hot unplug of Non-compliant DFP Device with PFET Solution in Place ............................................. 4
6
Hot Plug of Non-compliant DFP Device with TPS25810 Powered off and PFET Solution in Place .............. 4
7
Hot Unplug of Non-compliant DFP Device with TPS25810 Powered off and PFET Solution in Place ........... 4
8
NFET Protection Scheme................................................................................................... 5
9
Plug in of Compliant USB Type-C UFP Device with NFET Solution in Place ....................................... 6
10
Unplug of Compliant USB Type-C UFP Device with NFET Solution in Place ....................................... 6
11
Hot plug of a Non-compliant DFP Device with NFET Solution in Place .............................................. 6
12
Hot unplug of a Non-compliant DFP Device with NFET Solution in Place ........................................... 6
13
Hot plug of Non-compliant DFP Device with TPS25810 Powered off and NFET Solution in Place .............. 6
14
Hot Unplug of Non-compliant DFP Device with TPS25810 Powered off and NFET Solution in Place........... 6
15
OVP Switch Protection Scheme ........................................................................................... 7
16
Plug in of Compliant USB Type-C UFP Device with OVP Switch Solution in Place ................................ 8
17
Unplug of Compliant USB Type-C UFP Device with OVP Switch Solution in Place................................ 8
18
Hot Plug of a Non-compliant DFP Device with OVP Switch Solution in Place ...................................... 8
19
Hot Unplug of a Non-compliant DFP Device with OVP Switch Solution in Place ................................... 8
20
Hot Plug of Non-compliant DFP Device with TPS25810 Powered off and OVP Switch Solution in Place
21
...............................................
......
Hot Unplug of Non-compliant DFP Device with TPS25810 Powered off and OVP Switch Solution in Place ...
4
8
8
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Copyright © 2015, Texas Instruments Incorporated
1
Introduction and Related Material
1
www.ti.com
Introduction and Related Material
The focus of this application note is to present design solutions for the TPS25810 to protect against the
case of a non-compliant USB Type-C DFP adapter which ignores the USB Type-C power negotiation
specification and puts a high voltage on the VBUS line by default. USB Type-C is capable of power
delivery, so voltage levels from 5 V to 20 V are expected; however, there is a strict power negotiation
protocol in order to achieve the delivery of these different voltage levels. Some non-compliant USB TypeC DFP adapters may ignore this negotiation and apply a high voltage on VBUS which is dangerous for a
USB Type-C DFP system. The pins of the TPS25810, such as the OUT pin which connects to VBUS, are
rated up to 7V, so being exposed to a high voltage would damage the TPS25810. There are simple,
efficient solutions that can solve this problem, and the performance of three of these possible solutions is
explored in this application note.
The first two solutions have similar architectures and use the UFP pin of the TPS25810 to turn on and off
an external blocking MOSFET. This FET must be rated at 30 V (VDS/VSD ABS MAX) in order to handle
the high voltage of non-compliant devices. The external blocking MOSFET remains off by default and
blocks any high voltage on VBUS in the event of a non-compliant DFP device. The MOSFET will only turn
on, connecting the OUT pin of the TPS25810 to the VBUS pin of the Type-C connector, if the device is
Type-C UFP compliant.
Note that the solutions presented in Section 2 and Section 3 using an external blocking FET are only
viable if UFP remains high when a DFP is plugged in. The third solution presented is a single chip solution
using the TPD1S414, a USB OVP switch, and does not rely on the UFP pin of the TPS25810. This is the
simplest solution to implement and provides the most robust protection; however, the higher RDS(ON) and
BOM cost may be a concern.
Throughout this application note, “compliant” and “non-compliant” are used to describe USB Type-C
devices. A compliant UFP device is one that uses the CC line properly as defined in the Type-C and USB
PD specification. A non-compliant DFP device is one that applies >5 V without going through the proper
power negotiation as defined in the Type-C and USB PD specification.
The TPS2810 datasheet (SLVSCR1), the TPD1S414 datasheet (SLLSEH9), and the USB Type-C
documentation (http://www.usb.org/developers/usbtypec/) are good resources to have a general
understanding of before reading this application note
2
Protecting the TPS25810 from High Voltage DFPs
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High Voltage Protection with a PFET
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2
High Voltage Protection with a PFET
Q1 Si7491
VBUS
C3 0.1u
VAUX
R3 1M
5V
C2 220n
C1 10u
R2 100K
OUT
IN1
D1 1N4148
TPS25810
C4 10n
___
UFP
R1 100K
Q2 2N7000
Figure 1. PFET Protection Scheme
2.1
Circuit Operation
The operation of the non-compliant DFP device blocking circuit presented in Figure 1 depends on turning
on and off the PFET (Q1) using the UFP signal from the TPS25810. When a compliant UFP device is
plugged in, the UFP pin on the TPS25810 pulls low which turns on the PFET. However, if a non-compliant
DFP device is plugged in that offers >5 V without first going through the proper power negotiation, UFP
stays high-z. Thus, the PFET does not get turned on and the high voltage on the VBUS is not transferred
to the OUT pin of the TPS25810.
Q2 serves as a cascade device and protects the UFP pin from going above 5 V. This is important because
the gate of Q1 is 20 V when 20 V is applied to VBUS, and the absolute maximum of the TPS25810 pins is
7 V.
The 1N4148 diode, D1, is used to limit leakage current through Q2 that could result in unwanted voltage
on VBUS or the OUT pin.
R3 is used to discharge the voltage on the VBUS line when a device is disconnected. This must be done
in order to comply with the USB Type-C specification that the voltage must discharge to 0.8 V within 650
ms.
C2 is used to prevent the parasitic turn on of the PFET during a hot plug event.
C4 is used to suppress transients on the UFP pin of the TPS25810.
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3
High Voltage Protection with a PFET
2.2
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Testing
VIN
VIN
OUT
5 V/div
5 V/div
OUT
VBUS
VBUS
UFP
UFP
Time t 5 ms/div
Time t 1 ms/div
Figure 3. Unplug of a Compliant USB Type-C UFP Device
with PFET Solution in Place
Figure 2. Plug in of a Compliant USB Type-C UFP Device
with PFET Solution in Place
VIN
VIN
VBUS
OUT
5 V/div
5 V/div
OUT
UFP
UFP
VBUS
Time t 100 ms/div
Time t 50 Ps/div
Figure 5. Hot unplug of Non-compliant DFP Device with
PFET Solution in Place
Figure 4. Hot plug of Non-compliant DFP Device with
PFET Solution in Place
VIN
VIN
OUT
5 V/div
5 V/div
OUT
VBUS
UFP
UFP
VBUS
Time t 50 Ps/div
Time t 100 ms/div
Figure 6. Hot Plug of Non-compliant DFP Device with
TPS25810 Powered off and PFET Solution in Place
4
Figure 7. Hot Unplug of Non-compliant DFP Device with
TPS25810 Powered off and PFET Solution in Place
Protecting the TPS25810 from High Voltage DFPs
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High Voltage Protection with an NFET
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3
High Voltage Protection with an NFET
Q1 CSD17553
VBUS
5V
VAUX
C2 0.1u
C1 10u
R3 1M
OUT
IN1
R2 100K
12V
TPS25810
___
UFP
R1 100K
Q2 2N7000
Figure 8. NFET Protection Scheme
3.1
Circuit Operation
The operation of the non-compliant DFP device blocking circuit presented in Figure 8 depends on turning
on and off Q1 using the UFP signal from the TPS25810. Because an NFET is used, an external 12 V rail
is required for this solution in order to provide gate drive voltage above the 5 V output. When a compliant
UFP is plugged in, the UFP pin on the TPS25810 asserts low and the 12 V rail turns on Q1. However, if a
non-compliant DFP device is plugged in that offers >5 V without first going through the proper power
negotiation, UFP stays high-z. Thus, Q1 does not get turned on, and the high voltage on the VBUS is not
transferred to the OUT pin of the TPS25810.
The gate of Q2 is driven by the UFP pin from the TPS25810. When the UFP pin is pulled high, Q2 is on
and pulls the gate of Q1 low. When the UFP pin is asserted low Q2 is off and the 12 V rail turns on Q1.
R3 is used to discharge the voltage on the VBUS line when a device is disconnected in order to comply
with the USB Type-C specification that the voltage must discharge to 0.8 V within 650 ms.
One very important consideration when implementing this circuit is that VIN must come up before the 12 V
rail. If the 12 V rail comes up first, Q1 is turned on, and if a non-compliant DFP is plugged in, the
TPS25810 pins are exposed to high voltage which damages the part.
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5
High Voltage Protection with an NFET
3.2
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Testing
VIN
VIN
OUT
5 V/div
5 V/div
OUT
VBUS
VBUS
UFP
UFP
Time t 1 ms/div
Time t 100 ms/div
Figure 9. Plug in of Compliant USB Type-C UFP Device
with NFET Solution in Place
Figure 10. Unplug of Compliant USB Type-C UFP Device
with NFET Solution in Place
VIN
5 V/div
VIN
5 V/div
OUT
OUT
UFP
UFP
VBUS
VBUS
Time t 100 ms/div
Time t 50 Ps/div
Figure 12. Hot unplug of a Non-compliant DFP Device with
NFET Solution in Place
Figure 11. Hot plug of a Non-compliant DFP Device with
NFET Solution in Place
VIN
VIN
OUT
5 V/div
5 V/div
OUT
VBUS
UFP
UFP
VBUS
Time t 100 ms/div
Time t 50 Ps/div
Figure 13. Hot plug of Non-compliant DFP Device with
TPS25810 Powered off and NFET Solution in Place
6
Figure 14. Hot Unplug of Non-compliant DFP Device with
TPS25810 Powered off and NFET Solution in Place
Protecting the TPS25810 from High Voltage DFPs
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High Voltage Protection with an OVP Switch
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4
High Voltage Protection with an OVP Switch
Figure 15. OVP Switch Protection Scheme
4.1
Circuit Operation
This solution uses the TPD1S414 USB Charger OVP Switch. The TPD1S414 is a single chip solution
used to protect the VBUS line of a USB connector. The NFET switch internal to the TPD1S414 ensures
safe current flow in host mode while protecting the internal system circuits from any overvoltage conditions
at the VBUS_CON pin. This device can handle overvoltage protection up to 30 V.
The device protects the pins of the TPS25810 from being exposed to a voltage higher than 6.4 V as
specified in the TPD1S414 datasheet (SLLSEH9). The enable pin of the TPD1S414 is tied low so that
whenever the TPD1S414 is powered via VCC it will be enabled by default.
In the system shown in Figure 15, the VCC of the TPD1S414 is tied to the OUT pin of the TPS25810
meaning that whenever a compliant UFP device is detected, the OUT pin of the TPS25810, which is at a
voltage below 6.4 V, powers the TPD1S414 and the switch opens allowing the system to function
normally. When the TPS25810 does not detect a device, the OUT pin is at 0 V and the TPD1S414 is off
which saves system power.
If a non-compliant DFP applies a high voltage to the VBUS_CON pin of the TPD1S414, because the
TPS25810 OUT pin is at 0 V and the TPD1S414 is off, the switch remains closed and the high voltage is
blocked. With the TPD1S4141 on, regardless of the state of the UFP pin on the TPS25810, if a high
voltage is applied at VBUS the TPD1S414 detects the high voltage and the switch is turned off protecting
the USB Type-C system.
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High Voltage Protection with an OVP Switch
4.2
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Testing
VIN
VIN
5 V/div
5 V/div
OUT
OUT
VBUS
VBUS
Time t 10 ms/div
Time t 20 ms/div
Figure 16. Plug in of Compliant USB Type-C UFP Device
with OVP Switch Solution in Place
Figure 17. Unplug of Compliant USB Type-C UFP Device
with OVP Switch Solution in Place
VIN
VIN
VBUS
5 V/div
5 V/div
VBUS
OUT
OUT
Time t 100 Ps/div
Time t 20 ms/div
Figure 18. Hot Plug of a Non-compliant DFP Device with
OVP Switch Solution in Place
Figure 19. Hot Unplug of a Non-compliant DFP Device
with OVP Switch Solution in Place
VIN
VIN
VBUS
5 V/div
5 V/div
VBUS
OUT
OUT
Time t 100 Ps/div
Time t 20 ms/div
Figure 20. Hot Plug of Non-compliant DFP Device with
TPS25810 Powered off and OVP Switch Solution in Place
8
Figure 21. Hot Unplug of Non-compliant DFP Device with
TPS25810 Powered off and OVP Switch Solution in Place
Protecting the TPS25810 from High Voltage DFPs
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Conclusion
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5
Conclusion
There are many solutions to blocking non-compliant DFP adapters being used with USB Type-C systems
that employ the TPS25810. This application note presented three tested solutions for protecting USB
Type-C DFP systems from the negative effects of non-compliant DFP adapters.
6
References
•
•
•
USB Type-C DFP Controller and Power Switch with Load Detection, SLVSCR1
USB Charger OVP Switch with ESD for VBUS_CON Pin, SLLSEH9
USB Type-C Documentation, http://www.usb.org/developers/usbtypec/
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