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TPS25921A, TPS25921L
SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
TPS25921x 4.5V - 18V eFuse with Precise Current Limit and Over Voltage Protection
1 Features
3 Description
•
•
•
•
•
•
•
The TPS25921 is a compact, feature rich eFuse with
a full suite of protection functions. The wide operating
voltage allows control of many popular DC buses.
The precise ±2% current limit, at room temperature,
provides excellent accuracy making the TPS25921
well suited for many system protection applications.
1
•
•
•
•
4.5 V – 18 V Operating Voltage, 20 V (Max)
90 mΩ RDS(ON) (Typical)
0.4 A to 1.6 A Adjustable Current Limit
±2% Accurate ILIMIT at 1A at 25°C
±3% Overvoltage, Undervoltage Threshold
Programmable dVO/dt Control
Fault Output for Thermal Shutdown, UVLO and
OVP
-40°C to 125°C Junction Temperature Range
Auto-Retry and Latch-Off Versions
UL2367 Recognized - File No. E169910
UL60950 - Safe during Single Point Failure Test
2 Applications
•
•
•
•
•
•
•
White Goods, Appliances
Set Top Boxes, DVD and Gaming Consoles
HDD and SSD drives
Smart Meters, Gas Analyzers
Smart Load Switch
USB Switch
Adapter Power Devices
Load, source and device protection are provided with
multiple programmable features including overcurrent,
overvoltage and undervoltage. 3% threshold accuracy
for UV and OV, ensures tight supervision of bus
voltages, eliminating the need for supervisor circuitry.
Fault flag output (FLT) is provided for system status
monitoring and down stream load control.
For hot-plug-in boards, TPS25921 provides in-rush
current control and programmable output ramp-rate.
Output ramp rate is programmable using a capacitor
at soft-start (SS) pin, for maximum design flexibility.
Device Information(1)
PART NUMBER
TPS25921A
TPS25921L
PACKAGE
BODY SIZE (NOM)
SOIC
4.90mm x 3.91mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
4 Application Schematic
V(IN)
4.5 to 18 V
IN
OUT
Load
12V Short Circuit Response
90mO
10 V/div
FLTb
ENUV
SS
ILIM
1 A/div
TPS25921x
10 V/div 5 V/div
FLT
OVP
GND
V(OUT)
V(IN)
I_IN
TIME = 20 ms/div
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
TPS25921A, TPS25921L
SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
9
Features ..................................................................
Applications ...........................................................
Description .............................................................
Application Schematic ..........................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
1
2
3
3
7.1
7.2
7.3
7.4
7.5
7.6
7.7
3
3
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings ............................................................
Recommended Operating Conditions.......................
Thermal Characteristics ...........................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Parametric Measurement Information ............... 11
Detailed Description ............................................ 12
9.1 Overview ................................................................. 12
9.2 Functional Block Diagram ....................................... 12
9.3 Feature Description................................................. 13
9.4 Device Functional Modes........................................ 17
10 Applications and Implementation...................... 18
10.1 Application Information.......................................... 18
10.2 Typical Application ................................................ 18
10.3 System Examples ................................................. 25
11 Power Supply Recommendations ..................... 28
11.1 Transient Protection .............................................. 28
11.2 Output Short-Circuit Measurements ..................... 29
12 Layout................................................................... 30
12.1 Layout Guidelines ................................................. 30
12.2 Layout Example .................................................... 30
13 Device and Documentation Support ................. 31
13.1
13.2
13.3
13.4
13.5
Related Links ........................................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
31
31
31
31
31
14 Mechanical, Packaging, and Orderable
Information ........................................................... 31
5 Revision History
Changes from Revision B (August 2015) to Revision C
Page
•
Changed Equation 2 From: 0.07 To: 70 pF, and added text "where C(ss) is in Farad" ....................................................... 14
•
Changed Equation 21 From: (1 + 0.07) To: (1 x10-9 + 70 x 10-12) ....................................................................................... 22
•
Changed Equation 26 From: (4.7 + 0.07) To: (4.7 x10-9 + 70 x 10-12) ................................................................................. 22
Changes from Revision A (March 2015) to Revision B
•
Page
Changed tss in Timing Requirements From: V(OUT) = 11.7 V To V(OUT) = 11 V and C(SS) = 1 nF To: C(SS) = 1.2 nF .............. 6
Changes from Original (August 2014) to Revision A
Page
•
Changed Features From: UL2367 Recognition Pending To: UL2367 Recognized - File No. E169910 ............................... 1
•
Moved the Storage temperature range From: Handling Ratingstable To : Absolute Maximum Ratings .............................. 3
•
Changed the Handling Ratings table To: ESD Ratings ......................................................................................................... 3
•
Changed Equation 31 From: V(IN) x I(LOAD) To: V(IN) + I(LOAD). ............................................................................................... 28
2
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Product Folder Links: TPS25921A TPS25921L
TPS25921A, TPS25921L
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
6 Pin Configuration and Functions
D Package
8-Pin SOIC
Top View
GND
1
8
OVP
SS
2
7
ILIM
ENUV
3
6
FLT
IN
4
5
OUT
Pin Functions
NAME
NUMBER
DESCRIPTION
GND
1
Ground.
SS
2
A capacitor from this pin to GND sets the ramp rate of output voltage at device turn-on.
ENUV
3
Input for setting programmable undervoltage lockout threshold. An undervoltage event will open internal FET and
assert FLT to indicate power-failure. When pulled to GND, resets the thermal fault latch in TPS25921L.
IN
4
Power Input and supply voltage of the device.
OUT
5
Power Output of the device.
FLT
6
Fault event indicator, goes low to indicate fault condition due to Undervoltage, Overvoltage, and Thermal shutdown
event. A nuisance fast trip does not trigger fault. It is an open drain output.
ILIM
7
A resistor from this pin to GND will set the overload and short circuit limit.
OVP
8
Input for setting programmable overvoltage protection threshold. An overvoltage event will open the internal FET and
assert FLT to indicate overvoltage.
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
(1)
VALUE (2)
IN, OUT, ENUV, OVP, FLT
Input voltage range
Source current
MAX
–0.3
20
IN (10 ms Transient)
UNIT
V
22
ILIM, SS
Sink current
MIN
–0.3
7
SS
FLT
ILIM, SS, FLT
5
mA
100
mA
Internally Limited
Maximum junction temperature, TJ
Internally Limited
°C
Storage temperature range, Tstg
-65
°C
(1)
(2)
150
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only and functional operation of the device at these or any conditions beyond those indicated under recommended operating conditions
is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
All voltage values, except differential voltages, are with respect to network ground terminal.
7.2 ESD Ratings
VALUE
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001
V(ESD)
(1)
(2)
Electrostatic discharge
(1)
Charged device model (CDM), per JEDEC specification JESD22C101 (2)
UNIT
±2000
±500
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
Copyright © 2014–2015, Texas Instruments Incorporated
Product Folder Links: TPS25921A TPS25921L
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
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7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
IN
Input voltage range
Resistance
External capacitance
TYP
MAX
4.5
18
OUT, OVP, ENUV, FLT
0
18
SS
0
6
ILIM
0
3.3
ILIM
35.7
95.3
OUT
0.1
1
SS
Operating junction temperature range, TJ
–40
158
UNIT
V
kΩ
µF
1
1000
nF
25
125
°C
7.4 Thermal Characteristics (1)
TPS2592xx
THERMAL METRIC
SOIC (8) PINS
RθJA
Junction-to-ambient thermal resistance
120.8
RθJCtop
Junction-to-case (top) thermal resistance
65.5
RθJB
Junction-to-board thermal resistance
51.8
ψJT
Junction-to-top characterization parameter
17.4
ψJB
Junction-to-board characterization parameter
61.2
(1)
4
UNIT
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
7.5 Electrical Characteristics
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, 4.5 V ≤ V(IN) ≤ 18 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3
kΩ, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages are referenced to GND (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SUPPLY VOLTAGE AND INTERNAL UNDERVOLTAGE LOCKOUT
V(IN)
Operating Input Voltage
4.5
V(UVR)
UVLO Threshold, Rising
4.10
4.26
4.40
18
V
V
V(UVHys)
UVLO Hysteresis
168
224
279
mV
IQ( ON)
Supply Current, Enabled
V(ENUV) = 2 V, V(IN) = 12 V
0.22
0.41
0.58
mA
IQ( OFF)
Supply Current, Disabled
V(ENUV) = 0 V, V(IN) = 12 V
0.08
0.132
0.20
mA
OVERVOLTAGE PROTECTION (OVP) INPUT
V(OVPR)
Overvoltage Threshold Voltage,
Rising
1.35
1.39
1.43
V
V(OVPF)
Overvoltage Threshold Voltage,
Falling
1.30
1.34
1.37
V
I(OVP)
OVP Input Leakage Current
–100
0
100
nA
0V ≤ V(OVP) ≤ 18 V
ENABLE AND UNDERVOLTAGE LOCKOUT (ENUV) INPUT
V(ENR)
ENUV Threshold voltage, rising
1.36
1.39
1.42
V
V(ENF)
ENUV Threshold voltage, falling
1.30
1.34
1.37
V
V(ENF_RST)
ENUV Threshold voltage to reset
thermal fault, falling
0.5
0.61
0.8
V
IEN
EN Input leakage current
–100
0
100
nA
0 ≤ V(ENUV) ≤ 18 V
SOFT START: OUTPUT RAMP CONTROL (SS)
I(SS)
SS charging current
V(SS) = 0 V
0.9
1.04
1.2
µA
R(SS)
SS discharging resistance
V(ENUV) = 0 V, I(SS) = 10 mA sinking
60
70
85
Ω
V(SSmax)
SS maximum capacitor voltage
GAIN(SS)
SS to OUT gain
5.5
ΔV(OUT)/ΔV(SS)
4.81
4.86
V
4.92
V/V
µA
CURRENT LIMIT PROGRAMMING (ILIM)
I(ILIM)
ILIM Bias current
Current Limit (1)
ILIMIT
Short-circuit current limit (1)
IOS
6
10
16
R(ILIM) = 35.7 kΩ, (V(IN) - V(OUT)) = 1 V
0.284
0.368
0.452
R(ILIM) = 45.3 kΩ, (V(IN) - V(OUT)) = 1 V
0.547
0.394
0.471
R(ILIM) = 95.3 kΩ, (V(IN) - V(OUT)) = 1 V, TA = TJ= 25°C
0.98
1.0
1.02
R(ILIM) = 95.3 kΩ, (V(IN) - V(OUT)) = 1 V
0.93
1.0
1.062
R(ILIM) = 150 kΩ, (V(IN) - V(OUT)) = 1 V
1.43
1.57
1.7
R(ILIM) = SHORT, Shorted resistor current limit
R(ILIM) = OPEN, Open resistor current limit
(Single Point Failure Test: UL60950)
0.12
0.257
0.406
R(ILIM) = 35.7 kΩ, (V(IN) - V(OUT)) = 12 V
0.275
0.356
0.438
R(ILIM) = 45.3 kΩ, (V(IN) - V(OUT)) = 12 V
0.376
0.45
0.522
R(ILIM) = 95.3 kΩ, (V(IN) - V(OUT)) = 12 V
0.837
0.9
0.964
R(ILIM) = 150 kΩ, (V(IN) - V(OUT)) = 12 V
1.219
1.34
1.46
I(FASTRIP)
Fast-Trip comparator threshold
R(ILIM) in kΩ
V(ILIMopen)
ILIM Open resistor detect threshold
V(ILIM) Rising, R(ILIM) = OPEN
0.0142 x
R(ILIM) +
0.36
A
A
A
2.81
3.0
3.25
–40°C ≤ TJ ≤ 85°C
55
87
120
–40°C ≤ TJ ≤ 125°C
55
87
135
V(ENUV) = 0 V, V(OUT) = 0 V (Sourcing)
–2
0
1
5
7
10
V
MOSFET – POWER SWITCH
RDS(on)
FET ON resistance (2)
mΩ
PASS FET OUTPUT (OUT)
Ilkg(OUT)
Isink(OUT)
(1)
(2)
OUT Bias current in off state
V(ENUV) = 0V, V(OUT) = 300 mV (Sinking)
µA
Pulse-testing techniques maintain junction temperature close to ambient temperature. Thermal effects must be taken into account
separately.
The limits for these parameters are specified based on design and characterization data, and are not tested during production.
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
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Electrical Characteristics (continued)
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, 4.5 V ≤ V(IN) ≤ 18 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3
kΩ, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages are referenced to GND (unless otherwise noted).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
22
26
32
Ω
–0.5
0
0.5
µA
FAULT FLAG (FLT): ACTIVE LOW
R(FLT)
FLT Pull down Resistance
Device in fault condition, V(ENUV) = 0V, I(FLT) = 100mA
I(FLT)
FLT Input Leakage Current
Device not in fault condition, V(FLT) = 0V, 18V
THERMAL SHUT DOWN (TSD)
T(TSD)
TSD Threshold, rising (2)
T(TSDhys)
TSD Hysteresis (2)
Thermal fault: Latched or Auto Retry
155
°C
20
°C
TPS25921L
LATCHED
TPS25921A
AUTORETRY
7.6 Timing Requirements
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, V(IN)= 12 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3 kΩ, CSS =
OPEN, FLT = OPEN. Positive current into terminals. All voltages are referenced to GND (unless otherwise noted). Refer to
Figure 26 for the timing diagrams
MIN
TYP
MAX
UNIT
ENABLE AND UNDERVOLTAGE LOCKOUT (ENUV) INPUT
tOFF(dly)
ENUV ↓ to V(OUT)↓
Turn Off delay
tON(dly)
8
ENUV ↑ to V(OUT) = 1V,
C(SS) = OPEN
Turn-On delay
µs
96
ENUV ↑ to V(OUT) = 1V,
C(SS) > 0.39nF, [C(dVdT) in nF]
µs
14.5 + 0.5 x
(70p + C(SS))
OVERVOLTAGE PROTECTION (OVP) INPUT
tOVP(dly)
OVP Disable delay
OVP↑ to V(OUT)↓
8
µs
SOFT START: OUTPUT RAMP CONTROL (SS)
tSS
Output ramp time
ENUV ↑ to V(OUT) = 11 V, with C(SS) = open,
C(OUT) = 2.2 µF
0.2
0.26
0.33
ENUV ↑ to V(OUT) = 11 V, with C(SS) = 1.2 nF,
C(OUT) = 2.2 µF
2.1
3
3.6
ms
CURRENT LIMIT PROGRAMMING (ILIM)
tFASTRIP(dly)
Fast-Trip comparator delay
I(OUT) > I(FASTRIP)
3
µs
TPS25921A Only, V(IN) = 12 V
150
ms
TPS25921A Only, V(IN) = 4.5 V
100
ms
THERMAL SHUT DOWN (TSD)
tTSD(dly)
6
Retry Delay after TSD
recovery, TJ < [T(TSD) - 20oC]
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
7.7 Typical Characteristics
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, V(IN)= 12 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3 kΩ, C(OUT)
= 2.2 μF, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages referenced to GND (unless otherwise
noted). For all oscilloscope waveforms TA = 25°C.
0.6
V(UVR)
V(UVF)
4.3
Supply Current I Q(ON) (mA)
Internal UVLO Threshold Voltage (V)
4.4
4.2
4.1
4
0.3
0.2
TA = -40qC
TA = 25qC
TA = 85qC
TA = 125qC
0
-25
0
25
50
75
Temperature (qC)
100
125
150
4
6
8
D001
Figure 1. UVLO Threshold Voltage vs Temperature
10
12
Input Voltage (V)
14
16
18
D002
Figure 2. Input Supply Current vs Supply Voltage During
Normal Operation
250
ENUV and OVP Threshold Voltage (V)
1.4
200
Supply Current (PA)
0.4
0.1
3.9
-50
150
100
50
TA = 25qC
TA = 125qC
0
0
5
10
Input Voltage (V)
15
1.38
1.36
1.34
1.32
V(ENR), V(OVPR)
V(ENF), V(OVPF)
1.3
-50
20
-25
0
D003
Figure 3. Input Supply Current vs Supply Voltage at
Shutdown
25
50
75
Temperature (qC)
100
125
150
D004
Figure 4. ENUV and OVP Threshold Voltage vs Temperature
1.2
0.8
1.15
SS Charging Current (PA)
EN Threshold Voltage to Reset Fault Latch (V)
0.5
0.7
0.6
0.5
1.1
1.05
1
0.95
0.4
-50
-25
0
25
50
75
Temperature (qC)
100
125
150
0.9
-50
-25
D006
Figure 5. EN Threshold Voltage to Reset Fault Latch vs
Temperature
0
25
50
75
Temperature (qC)
100
125
150
D007
Figure 6. SS Pin Charging Current vs Temperature
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Typical Characteristics (continued)
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, V(IN)= 12 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3 kΩ, C(OUT)
= 2.2 μF, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages referenced to GND (unless otherwise
noted). For all oscilloscope waveforms TA = 25°C.
5
1k
Output Ramp Time (ms)
Gain(SS) (V/V)
4.95
4.9
4.85
100
10
TA = -40qC
TA = 25qC
TA = 85qC
TA = 125qC
4.8
4.75
-50
1
-25
0
25
50
75
Temperature (qC)
100
125
150
1
10
Soft Start Capacitor (nF)
D008
Figure 7. GAIN(SS) vs Temperature
D009
Figure 8. Output Ramp Time vs C(SS)
2.5
Current Limit and Fast Trip Threshold (A)
0.275
Output Ramp Time (ms)
100
0.27
0.265
0.26
0.255
0.25
-50
-25
0
25
50
75
Temperature (qC)
100
125
2
1.5
1
0.5
ILIMIT
I(FASTRIP)
0
20
150
40
60
D010
80
100
120
R(ILM) Resistor (k:)
140
160
D011
C(SS) = Open
Figure 10. Current Limit vs Current Limit Resistor
2.4
25
15
10
5
1.6
1.2
0.8
0.4
0
0
0.25
0.5
0.75
1
Current Limit (A)
1.25
1.5
1.75
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0
-50
-25
0
D012
Figure 11. Current Limit Accuracy vs Current Limit
8
35.7 k:
45.3 k:
95.3 k:
150 k:
2
20
Current Limit (A)
Accuracy (%) (Process, Voltage, Temperature)
Figure 9. Output Ramp Time vs Temperature
25
50
75
Temperature (qC)
100
125
150
D013
Figure 12. Current Limit vs Temperature Across R(ILIM)
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SLVSCE1C – AUGUST 2014 – REVISED NOVEMBER 2015
Typical Characteristics (continued)
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, V(IN)= 12 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3 kΩ, C(OUT)
= 2.2 μF, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages referenced to GND (unless otherwise
noted). For all oscilloscope waveforms TA = 25°C.
0.28
0
-5
0.27
Current Limit (A)
Current Limit Normalized (%)
R(ILIM) = Short
R(ILIM) = Open
-10
-15
0.26
0.25
-20
0.24
-60
-25
0
5
10
15
Power Dissipation (W)
20
25
-30
0
D014
30
60
Temperature (qC)
90
120
150
D015
PD = [V(IN)V(OUT)]*ILIMIT
Figure 14. Current Limit for R(ILIM) = Open and Short vs
Temperature
Figure 13. Current Limit Normalized (%) vs Power
Dissipation in the Device PD
100000
Thermal Shutdown Time (ms)
135
RDS(ON) (m:)
120
105
90
75
TA -40C
= -40oC
TA 25C
= 25oC
10000
TA 85C
= 85oC
TA 125C
= 125oC
1000
100
10
1
60
0.1
45
-50
0.1
-25
0
25
50
75
Temperature (qC)
100
125
D016
Figure 15. RDS(ON) vs Temperature
C(SS) = Open
1
150
100
C014
Taken on 1-Layer board, 2oz.(0.08-mm thick) with GND plane
area: 14 cm2 (bottom)
Figure 16. Thermal Shutdown Time vs Power Dissipation
C(OUT) = 4.7 nF
Figure 17. Turn ON with Enable
10
Power Dissipation (W)
C(SS) = 1nF
C(OUT) = 4.7 nF
Figure 18. Turn ON with Enable
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Typical Characteristics (continued)
Conditions (unless otherwise noted) are –40°C ≤ TJ ≤ 125°C, V(IN)= 12 V, V(EN UV) = 2 V, V(OVP) = 0 V, R(ILIM) = 95.3 kΩ, C(OUT)
= 2.2 μF, CSS = OPEN, FLT = OPEN. Positive current into terminals. All voltages referenced to GND (unless otherwise
noted). For all oscilloscope waveforms TA = 25°C.
R(FLT) = 100 kΩ
Figure 19. EN Turn ON Delay : EN ↑ to Output Ramp ↑
RL = 12 Ω
10
R(FLT) = 100 kΩ
Figure 20. EN Turn OFF Delay : EN ↓ to Fault ↓
RL = 12 Ω
R(FLT) = 100 kΩ
R(FLT) = 100 kΩ
Figure 21. OVP Turn OFF delay: OVP ↑ to Fault ↓
Figure 22. OVP Turn ON delay: OVP ↓ to Output Ramp ↑
Figure 23. Hot-Short: Fast Trip Response and Current
Regulation
Figure 24. Hot-Short: Fast Trip Response (Zoomed)
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8 Parametric Measurement Information
5V
V(OUT)
VEN
10%
1V
5V
90%
90%
VEN
V(OUT)
0
time
0
time
tON(dly)
tOFF(dly)
5V
V(OVP)
I(FASTRIP)
50%
ILIMIT
I(IN)
90%
V(OUT)
0
time
tOVP(dly)
0
time
tFASTRIP(dly)
Figure 25. Timing Diagrams
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9 Detailed Description
9.1 Overview
TPS25921 is a smart eFuse with enhanced built-in protection circuitry. It provides robust protection for all
systems and applications powered from 4.5 V to 18 V.
For hot-plug-in boards, the device provides in-rush current control and programmable output ramp-rate.
TPS25921 integrates overcurrent and short circuit protection. The precision overcurrent limit helps to minimize
over design of the input power supply, while the fast response short circuit protection immediately isolates the
load from input when a short circuit is detected. The device allows the user to program the overcurrent limit
threshold between 0.4 A and 1.6 A via an external resistor. The device provides precise monitoring of voltage
bus for brown-out and overvoltage conditions and asserts fault for downstream system. Its threshold accuracy of
3% ensures tight supervision of bus, eliminating the need for a separate supply voltage supervisor chip.
TPS25921 is designed to protect systems such as White Goods, STBs, DTVs, Smart Meters and Gas Analyzers.
The additional features include:
•
•
•
Over temperature protection to safely shutdown in the event of an overcurrent event
Fault reporting for brown-out and overvoltage faults
A choice of latched or automatic restart mode
9.2 Functional Block Diagram
OUT
IN
5
8
OVP
1.39V
1.34V
+
Current
Sense
4.03V
OVP
4.26V
4
90m:
Charge
Pump
+
ENUV
I to V
+
3
EN
1.39V
FLT
UVLO
1.34V
6
TSD
Thermal
Shutdown
SWEN
S
Q
GATE
CONTROL
SWEN
R
Fault
Logic
26:
Retry Timer
+
(TPS25921A Only)
10uA
+
0.61V
1PA
ILIMIT
SS
ILIM
+
4.8x
2
7
+
70pF
SWEN
GND
1
70:
Fast Trip
Comp
I(FASTRIP)
TPS25921x
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9.3 Feature Description
9.3.1 Enable and Adjusting Undervoltage Lockout (UVLO)
The ENUV pin controls the ON/OFF state of the internal FET. A voltage V(ENUV) < V(ENF) on this pin turns off the
internal FET, thus disconnecting IN from OUT.
Toggling the ENUV pin below V(ENF_RST) resets the TPS25921L that has latched off due to a fault condition. The
internal de-glitch delay on ENUV falling edge is kept low for quick detection of power failure. For applications
where a higher de-glitch delay on ENUV is desired, or when the supply is particularly noisy, it is recommended to
use an external filter capacitor from the ENUV terminal to GND.
The undervoltage lockout threshold can be programmed by using an external resistor divider from the supply IN
terminal to the ENUV terminal to GND as shown in Figure 26. When an undervoltage or input power fail event is
detected, the internal FET is quickly turned off, and FLT is asserted. If the undervoltage lockout function is not
needed, the ENUV pin should be connected to the IN terminal. The ENUV terminal should not be left floating.
TPS25921 also implements internal undervoltage lockout (UVLO) circuitry on the IN pin. The device gets
disabled when the IN terminal voltage falls below internal UVLO Threshold V(UVF).
V(IN)
IN
TPS25921x
R1
ENUV
+
EN
1.39V
R2
1.34V
OVP
+
OVP
1.39V
R3
GND
1.34V
Figure 26. UVLO and OVP Thresholds Set By R1, R2 and R3
9.3.2 Overvoltage Protection (OVP)
TPS25921 incorporates circuits to protect the system during overvoltage conditions. A resistor divider, connected
from the supply to OVP terminal to GND (as shown in Figure 26), programs the overvoltage threshold. A voltage
more than V(OVPR) on the OVP pin turns off the internal FET and protects the downstream load. This pin should
be tied to GND when not used.
9.3.3 Hot Plug-in and In-Rush Current Control
TPS25921 is designed to control the in-rush current upon insertion of a card into a live backplane or other "hot"
power source. This limits the voltage sag on the backplane’s supply voltage and prevents unintended resets of
the system power. A slew rate controlled startup (SS) also helps to eliminate conductive and radiated
interference. An external capacitor from the SS pin to GND defines the slew rate of the output voltage at poweron (as shown in Figure 27). The equation governing slew rate at start-up is shown in Equation 1 :
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Feature Description (continued)
TPS25921x
1 PA
SS
70 :
C(SS)
SWEN
C(INT)
GND
Figure 27. Output Ramp Up Time tdVdT is Set by C(dVdT)
I(SS) =
(C(SS) + C(INT) ) dV(OUT)
x
Gain(SS)
dt
(1)
Where:
• I(SS) = 1 µA (typical)
space
dV(OUT)
•
•
dt
= Desired output slew rate
GAIN(SS) = ΔV(OUT)/ΔV(SS) gain = 4.85
The total ramp time (tSS) of V(OUT) for 0 to V(IN) can be calculated using Equation 2:
tSS = 20.6 x 104 x V(IN) x (C(SS) + 70 pF )
(2)
Where C(ss) is in Farad.
The inrush current, I(INRUSH) can be calculated as
V
I(INRUSH) = C(OUT) x (IN)
tSS
(3)
The SS pin can be left floating to obtain a predetermined slew rate (tSS) on the output. When terminal is left
floating, the device sets an internal ramp rate of ~50V/ms for output (V(OUT)) ramp.
Figure 36 and Figure 37 illustrate the inrush current control behavior of the device. For systems where load is
present during start-up, the current never exceeds the overcurrent limit set by R(ILIM) resistor for the application.
For defining appropriate charging time/rate under different load conditions, refer to the Setting Output Voltage
Ramp time (tSS) section.
9.3.4 Overload and Short Circuit Protection :
At all times load current is monitored by sensing voltage across an internal sense resistor. During overload
events, current is limited to the current limit (ILIMIT) programmed by R(ILIM) resistor
ILIMIT = 10.73 x 10-3 x R(ILIM) - 0.018
R(ILIM) =
•
•
(4)
ILIMIT + 0.018
10.73 x 10-3
(5)
ILIMIT is overload current limit in Ampere
R(ILIM) is the current limit programming resistor in kΩ
TPS25921 incorporates two distinct overcurrent protection levels: the current limit (ILIMIT) and the fast-trip
threshold (I(FASTRIP)). The fast trip and current limit operations are shown in Figure 28.
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Feature Description (continued)
Bias current on ILIM pin directly controls current-limiting behavior of the device, and PCB routing of this node
must be kept away from any noisy (switching) signals.
9.3.4.1 Overload Protection
For overload conditions, the internal current-limit amplifier regulates the output current to ILIMIT. The output
voltage droops during current limit regulation, resulting in increased power dissipation in the device. If the device
junction temperature reaches the thermal shutdown threshold (T(TSD)), the internal FET is turned off. Once in
thermal shutdown, The TPS25921L version stays latched off, whereas TPS25921A commences an auto-retry
cycle tTSD(dly) ms after TJ < [T(TSD) - 20°C]. During thermal shutdown, the fault pin FLT pulls low to signal a fault
condition. Figure 40 and Figure 41 illustrate overload behavior.
9.3.4.2 Short Circuit Protection
During a transient short circuit event, the current through the device increases very rapidly. As current-limit
amplifier cannot respond quickly to this event due to its limited bandwidth, the device incorporates a fast-trip
comparator, with a threshold I(FASTRIP). When the current through the internal FET exceeds I(FASTRIP) (I(OUT) >
I(FASTRIP)), this comparator shuts down the pass device within 3 µs and terminates the rapid short-circuit peak
current. The I(FASTRIP) threshold is dependent on programmed overload current limit and function of R(ILIM). See
Equation 6 for the calculation.
I(FASTRIP) = 1.42 x 10-2 x R(ILIM) + 0.36
where
•
•
I(FASTRIP) is fast trip current limit in Ampere
R(ILIM) is the current limit resistor in kΩ
(6)
The fast-trip circuit holds the internal FET off for only a few microseconds, after which the device attempts to turn
back on normally, allowing the current-limit loop to regulate the output current to ILIMIT. Then, device behaves
similar to overload condition. Figure 42 through Figure 44 illustrate the behavior of the system when the current
exceeds the fast-trip threshold.
9.3.4.3 Start-Up with Short on Output
During start-up into a short circuit current is limited to ILIMIT. Figure 45 and Figure 46 illustrate start-up with a
short on the output. This feature helps in quick fault isolation and hence ensures stability of the DC bus.
9.3.4.4 Constant Current Limit Behavior during Overcurrent Faults
When power dissipation in the internal FET [PD = (V(IN) - V(OUT)) × I(OUT)] > 2 W, there is a ~1 to 20 % thermal fold
back in the current limit value so that the regulated current drops from ILIMIT to IOS. Eventually, the device shuts
down due to over temperature.
Current (A)
I(FASTRIP)
I(FASTRIP) = 1.42 x 10-2 x R(ILIM) + 0.36
Thermal Foldback
1-20%
ILIMIT
IOS
Figure 28. Overcurrent Protection Levels
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Feature Description (continued)
9.3.5 FAULT Response
The FLT open-drain output is asserted (active low) during undervoltage, overvoltage and thermal shutdown
conditions. The FLT signal remains asserted until the fault condition is removed and the device resumes normal
operation. During thermal shutdown, TPS25921L version stays latched off, whereas TPS25921A commences an
auto-retry cycle tTSD(dly) millisecond after TJ < [T(TSD) - 20°C]. For TPS25921L, thermal fault latch can be reset by
cycling the ENUV pin below V(ENF_RST) threshold. A nuisance fast trip does not trigger fault.
Connect FLT with a pull up resistor to Input or Output voltage rail. FLT may be left open or tied to ground when
not used.
9.3.6 IN, OUT and GND Pins
The IN pin should be connected to the power source. A ceramic bypass capacitor close to the device from IN to
GND is recommended to alleviate bus transients. The recommended operating voltage range is 4.5 V – 18 V.
The OUT pin should be connected to the load. V(OUT) in the ON condition, is calculated using the Equation 7
(
V(OUT) = V(IN) - RDS(ON) x I(OUT)
)
(7)
where, RDS(ON) is the ON resistance of the internal FET.
GND terminal is the most negative voltage in the circuit and is used as a reference for all voltage reference
unless otherwise specified.
9.3.7 Thermal Shutdown:
Internal over temperature shutdown disables/turns off the FET when TJ > 155°C (typical). The TPS25921L
version latches off the internal FET, whereas TPS25921A commences an auto-retry cycle tTSD(dly) milliseconds
after TJ drops below [T(TSD) - 20°C]. During the thermal shutdown, the fault pin FLT is pulled low to signal a fault
condition.
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9.4 Device Functional Modes
9.4.1 Shutdown Control
The internal FET and hence the load current can be remotely switched off by taking the ENUV pin below its 1.34
V threshold with an open collector or open drain device as shown in Figure 29. Upon releasing the ENUV pin the
device turns on with soft-start cycle.
V(IN)
IN
TPS25921x
R1
ENUV
+
1.39V
from µC
EN
R2
1.34V
GND
Figure 29. Shutdown Control
9.4.2 Operational Overview of Device Functions
The device functionality for various conditions are shown in Table 1.
Table 1. Operational Overview of Device Functions
Device
TPS25921
Inrush ramp controlled by capacitor at SS pin
Start Up
Inrush limited to ILIMIT level as set by R(ILIM)
If TJ > T(TSD) device shuts off
Current is limited to I(LIM) level as set by R(ILIM)
Power dissipation increases as V(IN) - V(OUT) grows
Overcurrent Response
Device turns off when TJ > T(TSD)
‘L' Version remains off
'A' Version will attempt restart tTSD(dly) ms after TJ < [T(TSD) -20°C]
Fast shut off when I(LOAD) > I(FASTRIP)
Short-Circuit Response
Quick restart and current limited to ILIMIT, follows standard startup cycle
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10 Applications and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
The TPS25921x is a smart eFuse. It is typically used for Hot-Swap and Power rail protection applications. It
operates from 4.5 V to 18 V with programmable current limit, overvoltage and undervoltage protection. The
device aids in controlling the in-rush current and provides precise current limiting during overload conditions for
systems such as White Goods, Set-Top-Box, DTVs, Gaming Consoles, SSDs/HDDs and Smart Meters. The
device also provides robust protection for multiple faults on the sub-system rail.
Alternatively, the WEBENCH® software may be used to generate a complete design. The WEBENCH® software
uses an iterative design procedure and accesses a comprehensive database of components when generating a
design. Additionally, a spreadsheet design tool TPS25921 Design Calculator is available on web folder.
10.2 Typical Application
10.2.1 Precision Current Limiting and Protection for White Goods
V(IN)
4.5 to 18 V
IN
V(OUT)
OUT
(Note 1)
CIN
0.1µF
R1
470kO
90mO
COUT
100µF
R4
ENUV
R2
53kO
FLT
OVP
Fault Monitor
SS
ILIM
R3
47kO
(1)
CSS
1nF
GND
TPS25921x
RILIM
95.3kO
CIN: Optional and only for noise suppression.
Figure 30. Typical Application Schematics: eFuse for White Goods
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Typical Application (continued)
10.2.1.1 Design Requirements
For this design example, use the parameters shown in Table 2.
Table 2. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range, V(IN)
12 V
Undervoltage lockout set point, V(UV)
8V
Overvoltage protection set point , V(OV)
17 V
Load at Start-Up , RL(SU)
24 Ω
Current limit, ILIMIT
1A
Load capacitance , C(OUT)
100 µF
Maximum ambient temperatures , TA
85°C
10.2.1.2 Detailed Design Procedure
The following design procedure can be used to select component values for the TPS25921A and TPS25921L.
10.2.1.2.1 Step by Step Design Procedure
To
•
•
•
•
•
begin the design process a few parameters must be decided upon. The designer needs to know the following:
Normal input operation voltage
Maximum output capacitance
Maximum current Limit
Load during start-up
Maximum ambient temperature of operation
This design procedure below seeks to control the junction temperature of device under both static and transient
conditions by proper selection of output ramp-up time and associated support components. The designer can
adjust this procedure to fit the application and design criteria.
10.2.1.2.2 Programming the Current-Limit Threshold: R(ILIM) Selection
The R(ILIM) resistor at the ILIM pin sets the over load current limit, this can be set using Equation 5.
R(ILIM) =
1 + 0.018
10.73 x 10-3
= 94.8 kW
(8)
Choose closest standard value: 95.3 kΩ, 1% standard value resistor.
10.2.1.2.3 Undervoltage Lockout and Overvoltage Set Point
The undervoltage lockout (UVLO) and overvoltage trip point are adjusted using the external voltage divider
network of R1, R2 and R3 as connected between IN, ENUV, OVP and GND pins of the device. The values
required for setting the undervoltage and overvoltage are calculated solving Equation 9 and Equation 10.
V(OVPR) =
R3
x V(OV)
R1 + R2 + R3
(9)
R 2 + R3
V(ENR) =
x V(UV)
R1 + R2 + R3
(10)
For minimizing the input current drawn from the power supply {I(R123) = V(IN)/(R1 + R2 + R3)}, it is recommended to
use higher values of resistance for R1, R2 and R3.
However, leakage currents due to external active components connected to the resistor string can add error to
these calculations. So, the resistor string current, I(R123) must be chosen to be 20x greater than the leakage
current expected.
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From the device electrical specifications, V(OVPR) = 1.40 V and V(ENR) = 1.40 V. For design requirements, V(OV) is
17 V and V(UV) is 8 V. To solve the equation, first choose the value of R3 = 47 kΩ and use Equation 9 to solve for
(R1 + R2) = 523.71 kΩ. Use Equation 10 and value of (R1 + R2) to solve for R2 = 52.88 kΩ and finally R1= 470.83
kΩ.
Using the closest standard 1% resistor values gives R1 = 470 kΩ, R2 = 53 kΩ, and R3 = 47 kΩ.
The power failure threshold is detected on the falling edge of supply. This threshold voltage is 4% lower than the
rising threshold, V(UV). This is calculated using Equation 11.
V(PFAIL) = 0.96 x V(UV)
(11)
Power fail threshold set is : 7.68 V
10.2.1.2.4 Setting Output Voltage Ramp time (tSS)
For a successful design, the junction temperature of device should be kept below the absolute-maximum rating
during both dynamic (start-up) and steady state conditions. Dynamic power stresses often are an order of
magnitude greater than the static stresses, so it is important to determine the right start-up time and in-rush
current limit required with system capacitance to avoid thermal shutdown during start-up with and without load.
The ramp-up capacitor C(SS) needed is calculated considering the two possible cases:
10.2.1.2.4.1 Case1: Start-up Without Load: Only Output Capacitance C(OUT) Draws Current During Start-up
7
14
Input Current
Power Dissipation
Output Voltage
6
12
5
10
4
8
3
6
2
4
1
2
Output Voltage (V)
Input Current (A), Power Dissipation (W)
During start-up, as the output capacitor charges, the voltage difference across the internal FET decreases, and
the power dissipated decreases as well. Typical ramp-up of output voltage V(OUT) with inrush current limit of 0.5A
and power dissipated in the device during start-up is shown in Figure 31. The average power dissipated in the
device during start-up is equal to area of triangular plot (red curve in Figure 32) averaged over tSS.
0
0
0
20
40
60
80
100
Start-Up Time, tSS (%)
V(IN) = 12 V
C(SS) = 1 nF
C(OUT)=100 µF
Figure 31. Start-up Without Load
V(IN) = 12 V
C(SS) = 1 nF
C013
C(OUT)=100 µF
Figure 32. PD(INRUSH) Due to Inrush Current
For TPS25921 device, the inrush current is determined as,
I=C x
V(IN)
dV
=> I(INRUSH) = C(OUT) x
dT
tSS
(12)
Power dissipation during start-up is:
PD(INRUSH) = 0.5 x V(IN) x I(INRUSH)
(13)
Equation 13 assumes that load does not draw any current until the output voltage has reached its final value.
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10.2.1.2.4.2 Case 2: Start-up With Load: Output Capacitance C(OUT) and Load Draws Current During Start-up
When load draws current during the turn-on sequence, there will be additional power dissipated. Considering a
resistive load RL(SU) during start-up, load current ramps up proportionally with increase in output voltage during
tSS time. Typical ramp-up of output voltage, load current and power dissipation in the device is shown in
Figure 33 and power dissipation with respect to time is plotted in Figure 34. The additional power dissipation
during start-up phase is calculated as follows.
æ
t ÷÷ö
(VI - VO )(t) = V(IN) x ççç1÷
çè
tSS ÷ø
(14)
æ V
ö
t
ç (IN) ÷÷
IL (t) = çç
÷x
ççè RL(SU) ÷÷ø tSS
(15)
Where RL(SU) is the load resistance present during start-up. Average energy loss in the internal FET during
charging time due to resistive load is given by:
tss
ò0
æ
t ÷÷ö çæç V(IN)
t ÷ö÷
V(IN) x ççç1 x
÷ dt
÷xç
çè
tSS ÷ø çèç RL(SU)
tSS ø÷÷
(16)
Load Current (A), Power Dissipation (W)
Wt =
2.0
14
Power Dissipation
Load Current
Output Voltage
1.8
1.6
12
10
1.4
1.2
8
1.0
6
0.8
0.6
4
0.4
2
0.2
0
0.0
0
10
20
30
40
50
60
70
80
90
100
Start-Up Time, tSS (%)
V(IN) = 12 V
C(SS) = 1 nF ,
C(OUT)=100 µF
RL(SU) = 24 Ω
Figure 33. Start-up With Load
V(IN) = 12 V
C(SS) = 1 nF
C013
RL(SU) = 24 Ω
Figure 34. PD(LOAD) in Device during Start-up with Load
On solving Equation 16 the average power loss in the internal FET due to load is:
V 2(IN)
æ 1ö
PD(LOAD) = çç ÷÷÷ x
çè 6 ø R
L(SU)
(17)
Total power dissipated in the device during startup is:
PD(STARTUP) = PD(INRUSH) + PD(LOAD)
(18)
Total current during startup is given by:
I(STARTUP) = I(INRUSH) + IL (t)
(19)
If I(STARTUP) > ILIMIT, the device limits the current to ILIMIT and the current limited charging time is determined by:
é
æ
öù
ê
÷÷÷ú
ççç
ê I
ú
÷
ç
I(INRUSH)
÷
ê (LIMIT)
÷÷÷úú
- 1 + LNççç
tSS(current-limited) = C(OUT) x RL(SU) x ê
V(IN) ÷÷ú
ç
êI
ççI(LIMIT) ê (INRUSH)
÷÷ú
ê
RL(SU) ÷ø÷ú
çèç
ë
û
(20)
The power dissipation, with and without load, for selected start-up time should not exceed the shutdown limits as
shown in Figure 35.
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Thermal Shutdown Time (ms)
100000
TA -40C
= -40oC
TA 25C
= 25oC
10000
TA 85C
= 85oC
TA 125C
= 125oC
1000
100
10
1
0.1
0.1
1
10
100
Power Dissipation (W)
C014
Figure 35. Thermal Shutdown Limit Plot
For the design example under discussion,
Select ramp-up capacitor C(SS) = 1nF, using Equation 2.
)
(
tSS = 20.6 x 104 x 12 x 1 x 10-9 + 70 x 10-12 = 2.64 ms
(21)
The inrush current drawn by the load capacitance (C(OUT)) during ramp-up using Equation 3.
(
)
æ
I(INRUSH) = 100 x 10-6 x ç
ö
12
÷
è 2.64 x 10-3 ø
= 0.454 A
(22)
The inrush Power dissipation is calculated, using Equation 13.
PD(INRUSH) = 0.5 x 12 x 0.454 = 2.72 W
(23)
For 2.72 W of power loss, the thermal shut down time of the device should not be less than the ramp-up time tSS
to avoid the false trip at maximum operating temperature. From thermal shutdown limit graph Figure 35 at
TA = 85°C, for 2.72 W of power the shutdown time is ~170 ms. So it is safe to use 2.64 ms as start-up time
without any load on output.
Considering the start-up with load 24 Ω, the additional power dissipation, when load is present during start up is
calculated, using Equation 17.
PD(LOAD) = æç ö÷ x æç
è6ø è
1
12 x 12 ö
÷ =1W
24 ø
(24)
The total device power dissipation during start up is:
PD(STARTUP) = 2.72 + 1 = 3.72 W
(25)
From thermal shutdown limit graph at TA = 85°C, the thermal shutdown time for 3.72 W is close to 60 ms. It is
safe to have 30% margin to allow for variation of system parameters such as load, component tolerance, and
input voltage. So it is well within acceptable limits to use the 1 nF capacitor with start-up load of 24 Ω.
If there is a need to decrease the power loss during start-up, it can be done with increase of C(SS) capacitor.
To illustrate, choose C(SS) = 4.7 nF as an option and recalculate:
)
(
æ
ö
12
I(INRUSH) = (100 x 10-6 )x ç
÷ = 0.102 A
è 11.8 x 10-3 ø
tSS = 20.6 x 104 x 12 x 4.7 x 10-9 + 70 x 10-12 = 11.8 ms
22
(26)
(27)
PD(INRUSH) = 0.5 x 12 x 0.102 = 0.61 W
(28)
1
12 x 12 ö
PD(LOAD) = æç ö÷ x æç
÷ =1W
è 6 ø è 24 ø
(29)
PD(STARTUP) = 0.61 + 1 = 1.61 W
(30)
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From thermal shutdown limit graph at TA = 85°C, the shutdown time for 1.61 W power dissipation is ~1000 ms,
which increases the margins further for shutdown time and ensures successful operation during start up and
steady state conditions.
The spreadsheet tool available on the web can be used for iterative calculations.
10.2.1.2.5 Support Component Selections - R4 and CIN
Reference to application schematics, R4 is required only if FLT is used; The resistor serves as pull-up for the
open-drain output driver. The current sunk by this pin should not exceed 100 mA (refer to the Absolute Maximum
Ratings table). CIN is a bypass capacitor to help control transient voltages, unit emissions, and local supply noise.
Where acceptable, a value in the range of 0.001 μF to 0.1 μF is recommended for C(IN).
10.2.1.3 Application Curves
Figure 36. Hot-Plug Start-Up: Output Ramp Without Load
on Output
Figure 37. Hot-Plug Start-Up: Output Ramp With 24 Ω Load
at Start Up
Figure 38. Overvoltage Shutdown
Figure 39. Overvoltage Recovery
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24
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Figure 40. Over Load: Step Change in Load from 19 Ω to
9 Ω Back
Figure 41. Overload Condition: Auto Retry and Recovery TPS25921A
Figure 42. Hot Short: Fast Trip and Current Regulation
Figure 43. Hot Short: Latched - TPS25921L
Figure 44. Hot Short: Auto-Retry and Recovery from Short
Circuit - TPS25921A
Figure 45. Hot Plug-in with Short on Output: Latched TPS25921L
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Figure 46. Hot Plug-in with Short on Output: Auto-Retry - TPS25921A
10.3 System Examples
The TPS25921 provides a simple solution for current limiting, inrush current control and supervision of power
rails for wide range of applications operating at 4.5 V to 18 V and delivering up to 1.5 A.
10.3.1 Protection and Current Limiting for Primary-Side Regulated Power Supplies
Primary side regulated power supplies and adapters are dominant today in many of the applications such as
Smart-phones, Portable hand-held devices, White Goods, Set-Top-Box and Gaming consoles. These supplies
provide efficient, low cost and low component count solutions for power needs ranging from 5W to 30W. But,
these come with drawbacks of
•
•
•
No secondary side protection for immediate termination of critical faults such as short circuit and over voltage
Do not provide precise current limiting for overload transients
Have poor output voltage regulation for sudden change in AC input voltages - triggering output overvoltage
condition
Many of the above applications require precise output current limiting and secondary side protection, driving the
need for current sensing in the secondary side. This needs additional circuit implementation using precision
operational amplifiers. This increases the complexity of the solution and also results in sensing losses The
TPS25921 with its integrated low-ohmic N-channel FET provides a simple and efficient solution. Figure 47 shows
the typical implementation using TPS25921.
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System Examples (continued)
VAC(IN)
VDC
Rectifier + Noise
Filter
TPS25921
R1
CO
CB
R2
V(OUT)
ILIM
OVP
RILIM
UCC287xx
Primary Regulated
Fly-back Controller
Rs
Figure 47. Current Limiting and Protection for AC-DC Power Supplies
During short circuit conditions, the internal fast comparator of TPS25921 turns OFF the internal FET in less than
3 µs (typical) as soon as current exceeds I(FASTRIP), set by the current limit R(ILIM) resistor. The OVP comparator
with 3% precision helps in quick isolation of the load from the input when inputs exceeds the set V(OVPR)
Figure 42 and Figure 38 shows short circuit and overvoltage response waveforms of implementation using
TPS25921. In addition to above, the TPS25921 provides inrush current limit when output is hot-plugged into any
of the system loads.
10.3.2 Precision Current Limiting in Intrinsic Safety Applications
Intrinsic safety (IS) is becoming prominent need for safe operation of electrical and electronic equipment in
hazardous areas. Intrinsic safety requires that equipment is designed such that the total amount of energy
available in the apparatus is simply not enough to ignite an explosive atmosphere. The energy can be electrical,
in the form of a spark, or thermal, in the form of a hot surface.
This calls for precise current limiting and precision shutdown of the circuit for over voltage conditions ensuring
that set voltage and current limits are not exceeded for wide operating temperature range and variable
environmental conditions. Applications such as Gas Analyzers, Medical equipment (such as
electrocardiographs), Portal Industrial Equipment, Cabled Power distribution systems and hand-held motor
operated tools need to meet these critical safety standards.
The TPS25921 device can be used as simple protection solution for each of the internal rails. Figure 48 shows
the typical implementation using TPS25921.
26
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System Examples (continued)
V(IN)
Sync Buck
DC-DC Converter
LO
CO
CB
R1
RILIM
V(OUT)
TPS25921
LDO
CO
CB
ILIM
OVP
R2
V(IN)
V(OUT)
TPS25921
R1
R2
ILIM
OVP
RILIM
Figure 48. Precision current Limit and Protection of Internal Rails
10.3.3 Smart Load Switch
A smart load switch is a series FET used for switching of the load (resistive or inductive). It also provides
protection during fault conditions. Typical discrete implementation is shown in Figure 49. Discrete solutions have
higher component count and require complex circuitry to implement each of the protection fault needs.
TPS25921 can be used as a smart power switch for applications ranging from 4.5 V to 18 V. TPS25921 provides
programmable soft start, programmable current limits, over-temperature protection, a fault flag, and undervoltage lockout.
Enable
V(IN)
Load
UVLO
OVP
R1
Cs
Enable
Over Current
Protection
Disable
Q2
R2
V(IN)
EN
TPS25921
R1
R2
OVP
Load
ILIM
RILIM
Q2
Figure 49. Smart Load Switch Implementation
Figure 49 shows typical implementation and usage as load switch. This configuration can be used for driving a
solenoid and FAN control. It is recommended to use a freewheeling diode across the load when load is highly
inductive.
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System Examples (continued)
Figure 50 shows load switching waveforms using TPS25921 for 12 V Bus
Figure 50. Smart Load Switch (100 Hz Operation)
11 Power Supply Recommendations
The device is designed for supply voltage range of 4.5 V ≤ VIN ≤ 18 V. If the input supply is located more than a
few inches from the device an input ceramic bypass capacitor higher than 0.1 μF is recommended. Power supply
should be rated higher than the current limit set to avoid voltage droops during over current and short-circuit
conditions.
11.1 Transient Protection
In case of short circuit and over load current limit, when the device interrupts current flow, input inductance
generates a positive voltage spike on the input and output inductance generates a negative voltage spike on the
output. The peak amplitude of voltage spikes (transients) is dependent on value of inductance in series to the
input or output of the device. Such transients can exceed the Absolute Maximum Ratings of the device if steps
are not taken to address the issue.
Typical methods for addressing transients include
• Minimizing lead length and inductance into and out of the device
• Using large PCB GND plane
• Schottky diode across the output to absorb negative spikes
• A low value ceramic capacitor (C(IN) = 0.001 µF to 0.1 µF) to absorb the energy and dampen the transients.
The approximate value of input capacitance can be estimated with Equation 31.
VSPIKE(Absolute) = V(IN) + I(LOAD) x
L(IN)
C(IN)
(31)
Where:
• V(IN) is the nominal supply voltage
• I(LOAD) is the load current,
• L(IN) equals the effective inductance seen looking into the source
• C(IN) is the capacitance present at the input
Some applications may require the addition of a Transient Voltage Suppressor (TVS) to prevent transients from
exceeding the Absolute Maximum Ratings of the device.
The circuit implementation with optional protection components (a ceramic capacitor, TVS and schottky diode) is
shown in Figure 51.
28
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Transient Protection (continued)
IN
4.5 to 18 V
IN
OUT
OUT
(Note 1)
CIN
90mO
ENUV
(Note 1)
(Note 1)
FLT
OVP
SS
GND
(1)
ILIM
TPS25921x
Optional components needed for suppression of transients
Figure 51. Circuit Implementation With Optional Protection Components
11.2 Output Short-Circuit Measurements
It is difficult to obtain repeatable and similar short-circuit testing results. Source bypassing, input leads, circuit
layout and component selection, output shorting method, relative location of the short, and instrumentation all
contribute to variation in results. The actual short itself exhibits a certain degree of randomness as it
microscopically bounces and arcs. Care in configuration and methods must be used to obtain realistic results. Do
not expect to see waveforms exactly like those in the data sheet; every setup differs.
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12 Layout
12.1 Layout Guidelines
•
•
•
•
•
•
•
•
•
For all applications, a 0.01-uF or greater ceramic decoupling capacitor is recommended between IN terminal
and GND. For hot-plug applications, where input power path inductance is negligible, this capacitor can be
eliminated/minimized.
The optimum placement of decoupling capacitor is closest to the IN and GND terminals of the device. Care
must be taken to minimize the loop area formed by the bypass-capacitor connection, the IN terminal, and the
GND terminal of the IC. See Figure 52 for a PCB layout example.
High current carrying power path connections should be as short as possible and should be sized to carry at
least twice the full-load current.
The GND terminal must be tied to the PCB ground plane at the terminal of the IC. The PCB ground should be
a copper plane or island on the board.
Locate all TPS25921x support components: R(ILIM), CSS, and resistors for FLT, ENUV and OVP, close to their
connection pin. Connect the other end of the component to the GND pin of the device with shortest trace
length.
The trace routing for the RILIM and CSS components to the device should be as short as possible to reduce
parasitic effects on the current limit and soft start timing. These traces should not have any coupling to
switching signals on the board.
OVP and ENUV signal traces should be routed with sufficient spacing from FLT signal trace, to avoid
spurious coupling of FLT switching, during fault conditions.
Protection devices such as TVS, snubbers, capacitors, or diodes should be placed physically close to the
device they are intended to protect, and routed with short traces to reduce inductance. For example, a
protection Schottky diode is recommended to address negative transients due to switching of inductive loads,
and it should be physically close to the OUT pins.
Obtaining acceptable performance with alternate layout schemes is possible; however this layout has been
shown to produce good results and is intended as a guideline.
12.2 Layout Example
Top layer
Bottom Layer: GND plane (Optional)
Via to top layer ground plane (only for two layer board)
Ground
(Note 1)
GND
1
8
OVP
SS
2
7
ILIM
ENUV
3
6
FLT
IN
4
5
OUT
(Note 1)
Output
Input
(1)
Optional: Needed only to suppress the transients caused by inductive load switching.
Figure 52. Board Layout
30
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13 Device and Documentation Support
13.1 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 3. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
TPS25921A
Click here
Click here
Click here
Click here
Click here
TPS25921L
Click here
Click here
Click here
Click here
Click here
13.2 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
13.3 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
13.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
13.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
14 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
TPS25921AD
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
25921A
TPS25921ADR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
25921A
TPS25921LD
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
25921L
TPS25921LDR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 85
25921L
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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