TPS2556-Q1, TPS2557-Q1
SLVSC97B – MARCH 2014 – REVISED SEPTEMBER 2020
TPS255x-Q1 Precision Automotive Adjustable Current-Limited Power-Distribution
Switches
1 Features
3 Description
•
The TPS2556-Q1 and TPS2557-Q1 powerdistribution switches are specialized for automotive
applications which require precision current limiting or
capacity to handle heavy capacitive loads and short
circuits. These devices offer a programmable currentlimit threshold between 500 mA and 5 A (typical) via
an external resistor. Control of the power-switch rise
and fall times minimizes current surges during turnon
or turnoff.
•
•
•
•
•
•
•
•
•
•
•
AEC-Q100 Qualified
– Device HBM ESD Classification Level H2
– Device CDM ESD Classification Level C5
Functional Safety-Capable
– Documentation available to aid functional safety
system design
Meets USB current-limiting requirements
Adjustable current limit, 500 mA – 5 A (typ.)
±6.5% current-limit accuracy at 4.5 A
Fast short-circuit response – 3.5 μs (typ.)
22-mΩ high-side MOSFET
Operating range: 2.5 V to 6.5 V
2-μA maximum standby supply current
Built-in soft-start
15-kV and 8-kV system-level ESD capable
Safety-related certifications:
– UL Recognized for UL 2367
– CB Certification for IEC 60950
– CB Certification for IEC 62368
TPS2556-Q1 and TPS2557-Q1 devices limit the
output current to a safe level by switching into a
constant-current mode when the output load exceeds
the current-limit threshold. The FAULT logic output
asserts low during overcurrent and overtemperature
conditions.
Use with the TPS2511-Q1 or TPS2513A-Q1 for a lowloss, automotive-qualified, USB charging-port solution
capable of charging all of today's popular phones and
tablets.
2 Application
Device Information
Automotive USB Charging Ports
ORDER NUMBER
PACKAGE(1)
BODY SIZE
TPS2556QDRB
S-PVSON (8)
3 mm × 3 mm
TPS2557QDRB
S-PVSON (8)
3 mm × 3 mm
(1)
5 V OUT
0.1 μF
IN
IN
For all available packages, see the orderable addendum at
the end of the data sheet.
OUT
OUT
TPS2556-Q1
100 kΩ
TPS2557-Q1
FAULT
DC to DC
Converter
or Controller
(LM25117-Q1,
TPS54340-Q1,
TPS54240-Q1,
TPS40170-Q1)
Control Signal
COUT
ILIM
USB
Connector
RILIM
VBUS
EN
GND
Thermal Pad
VIN
DM1
D–
D+
GND
DP1
TPS2513A-Q1
DM2
GND
CUSB
DP2
Recommend TPS2561A-Q1
for the Dual Port Solution
Typical Application as Power Switch of Single-Port Automotive USB Charge Port
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.
TPS2556-Q1, TPS2557-Q1
www.ti.com
SLVSC97B – MARCH 2014 – REVISED SEPTEMBER 2020
Table of Contents
1 Features............................................................................1
2 Application....................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Device Comparison Table...............................................3
6 Terminal Configuration and Functions..........................3
Terminal Functions............................................................3
7 Specifications.................................................................. 3
7.1 Absolute Maximum Ratings........................................ 3
7.2 Handling Ratings.........................................................4
7.3 Recommended Operating Conditions.........................4
7.4 Thermal Information....................................................4
7.5 Electrical Characteristics.............................................5
7.6 Switching Characteristics............................................5
7.7 Typical Characteristics................................................ 6
Parameter Measurement Information............................... 8
8 Detailed Description........................................................8
8.1 Overview..................................................................... 8
8.2 Functional Block Diagram......................................... 10
8.3 Feature Description...................................................10
8.4 Device Functional Modes..........................................11
9 Applications and Implementation................................ 13
9.1 Application Information............................................. 13
9.2 Typical Application, Design for Current Limit............ 13
10 Power Supply Recommendations..............................18
11 Layout........................................................................... 19
11.1 Layout Guidelines................................................... 19
11.2 Layout Example...................................................... 19
12 Device and Documentation Support..........................20
12.1 Related Links.......................................................... 20
12.2 Trademarks............................................................. 20
12.3 Electrostatic Discharge Caution..............................20
12.4 Glossary..................................................................20
13 Mechanical, Packaging, and Orderable
Information.................................................................... 21
4 Revision History
Changes from Revision A (March 2014) to Revision B (September 2020)
Page
• Added functional safety link and safety-related certifications bullet to the Features section ............................. 1
• Updated the numbering format for tables, figures and cross-references throughout the document...................1
Changes from Revision * (March 2014) to Revision A (March 2014)
Page
• Changed part number in Description from TPS2511-Q to TPS2511-Q1............................................................ 1
• Changed CURRENT LIMIT values in Electrical Characteristics table ............................................................... 5
• Changed Equation 1 ........................................................................................................................................ 13
• Revised Figure 9-2 graph................................................................................................................................. 13
• Changed Equation 2 ........................................................................................................................................ 14
• Changed resistor value from 33.2 kΩ to 33.6 kΩ .............................................................................................14
• Changed Equation 3 ........................................................................................................................................ 14
• Changed Equation 4 ........................................................................................................................................ 15
• Changed current-limit threshold from 4 316 mA to 4 406 mA ..........................................................................15
• Changed values in Table 9-2 ........................................................................................................................... 15
2
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5 Device Comparison Table
DEVICE
MAX. OPERATING
CURRENT (A)
OUTPUTS
TPS2556-Q1
5
TPS2557-Q1
5
TPS2561A-Q1
2.5
ENABLES
TYPICAL rDS(on) (mΩ)
1
Active-low
22
1
Active-high
22
2
Active-high
44
6 Terminal Configuration and Functions
GND
1
IN
2
IN
3
EN
4
Thermal
Pad
8
FAULT
7
OUT
6
OUT
5
ILIM
EN = Active-low for the TPS2556-Q1
EN = Active-high for the TPS2557-Q1
Figure 6-1. 8-Terminal S-PVSON With Thermal Pad DRB Package (Top View)
Terminal Functions
TERMINAL
NAME
I/O
DESCRIPTION
TPS2556-Q1
TPS2557-Q1
EN
4
–
I
Enable input, logic low turns on power switch.
EN
–
4
I
Enable input, logic high turns on power switch.
GND
1
1
–
Ground connection; connect externally to PowerPAD.
2, 3
2, 3
I
Input voltage; connect a 0.1 μF or greater ceramic capacitor from
IN to GND as close to the IC as possible.
8
8
O
Active-low open-drain output, asserted during overcurrent or
overtemperature conditions.
OUT
6, 7
6, 7
O
Power-switch output.
ILIM
5
5
O
External resistor used to set current-limit threshold; recommended
20 kΩ ≤ R(ILIM) ≤ 187 kΩ.
Thermal pad
–
–
–
Internally connected to GND; used to heat-sink the part to
the circuit board traces. Connect therma pad to GND terminal
externally.
IN
FAULT
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range unless otherwise noted(1) (2)
Voltage range on IN, OUT, EN or EN, ILIM, FAULT
Voltage range from IN to OUT
I
MIN
MAX(2)
–0.3
7
V
7
V
–7
Continuous output current
Internally limited
Continuous FAULT sink current
ILIM source current
TJ
(1)
UNIT
Maximum junction temperature
–40
25
mA
Internally limited
mA
Internally limited
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress
ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under
Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device
reliability.
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(2)
Voltages are referenced to GND unless otherwise noted.
7.2 Handling Ratings
PARAMETER
Tstg
Storage temperature range
Human-body model (HBM) ESD stress
V(ESD) (1)
voltage(2)
Charged-device model (CDM) ESD stress voltage(3)
Contact discharge
System level(4)
(1)
(2)
(3)
(4)
Air discharge
MIN
MAX
UNIT
–65
150
°C
–2
2
kV
–750
750
V
–8
8
–15
15
kV
Electrostatic discharge (ESD) to measure device sensitivity or immunity to damage caused by assembly-line electrostatic discharges
into the device.
The passing level per AEC-Q100 Classification H2.
The passing level per AEC-Q100 Classification C5.
Surges per EN61000-4-2, 1999 applied between USB connection for V(BUS) and ground of the TPS2556EVM (HPA423, replacing
TPS2556 with TPS2556-Q1) evaluation module (SLUU393). These were the test levels, not the failure threshold.
7.3 Recommended Operating Conditions
V(IN)
MIN
MAX
2.5
6.5
TPS2556-Q1
0
6.5
TPS2557-Q1
0
6.5
Input voltage, IN
V( EN )
V(EN)
Enable voltage
1.1
UNIT
V
V
VIH
High-level input voltage on EN or EN
VIL
Low-level input voltage on EN or EN
I(OUT)
Continuous output current, OUT
0
5
A
Continuous FAULT sink current
0
10
mA
TJ
Operating junction temperature
–40
125
°C
R(ILIM)
Recommendedlimit-resistor range
20
187
kΩ
0.66
V
7.4 Thermal Information
THERMAL METRIC(1)
TPS2556-Q1,
TPS2557-Q1
DRB
UNIT
8 TERMINALS
RθJA
Junction-to-ambient thermal resistance
RθJC(top)
Junction-to-case (top) thermal resistance
RθJB
Junction-to-board thermal resistance
ψJT
ψJB
RθJC(bot)
(1)
4
41.5
°C/W
56
°C/W
16.4
°C/W
Junction-to-top characterization parameter
0.7
°C/W
Junction-to-board characterization parameter
16.5
°C/W
Junction-to-case (bottom) thermal resistance
3.5
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report (SPRA953).
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7.5 Electrical Characteristics
over recommended operating conditions, VEN = 0 V, or VEN = VIN (unless otherwise noted)
TEST CONDITIONS(1)
PARAMETER
MIN
TYP
MAX
22
25
UNIT
POWER SWITCH
Static drain-source on-state
resistance
rDS(on)
TJ = 25°C
–40 °C ≤ TJ ≤ 125°C
35
mΩ
ENABLE INPUT EN OR EN
Enable terminal turnon or turnoff
threshold
0.66
55(2)
Hysteresis
I(EN)
Input current
1.1
V(EN) = 0 V or 6.5 V, or V( EN) = 0 V or 6.5 V
–0.5
V
mV
0.5
μA
CURRENT LIMIT
R(ILIM) = 24.9 kΩ
Current-limit threshold (maximum dc output current I(OUT) delivered to
R(ILIM) = 61.9 kΩ
load) and short-circuit current, OUT connected to GND
R(ILIM) = 100 kΩ
IOS
4180
4500
4745
1610
1805
1980
945
1110
1270
0.1
2.5
μA
R(ILIM) = 24.9 kΩ
95
120
μA
R(ILIM) = 100 kΩ
85
110
μA
0.01
1
μA
2.35
2.45
V
mA
SUPPLY CURRENT
I(IN_off)
Supply current, low-level output
V(IN) = 6.5 V, no load on OUT, V( EN) = 6.5 V or V(EN) = 0 V
I(IN_on)
Supply current, high-level output
V(IN) = 6.5 V, no load on OUT
I(REV)
Reverse leakage current
V(OUT) = 6.5 V, VIN = 0 V
TJ = 25 °C
UNDERVOLTAGE LOCKOUT
V(UVLO)
Low-level input voltage, IN
V(IN) rising
35(2)
Hysteresis, IN
mV
FAULT FLAG
VOL
Output low voltage, FAULT
I( FAULT) = 1 mA
Off-state leakage
V( FAULT) = 6.5 V
180
FAULT deglitch
FAULT assertion or de-assertion due to overcurrent condition
6
9
mV
1
μA
13
ms
THERMAL SHUTDOWN
T(OTSD2)
Thermal shutdown threshold
155
°C
T(OTSD)
Thermal shutdown threshold in
current-limit
135
°C
20(2)
Hysteresis
(1)
(2)
°C
Pulse-testing techniques maintain junction temperature close to ambient temperature; thermal effects must be taken into account
separately.
These parameters are provided for reference only, and do no constitute part of TI's published specifications for purposes of TI's
product warranty.
7.6 Switching Characteristics
MIN
tr
Rise time, output
tf
Fall time, output
ton
Turnon time
toff
Turnoff time
t(IOS)
Response time to short circuit
(1)
VIN = 6.5 V
VIN = 2.5 V
VIN = 6.5 V
2
CL = 1 μF, RL = 100 Ω,
(see Figure 8-1)
VIN = 2.5 V
TYP MAX UNIT
3
1
2
3
0.6
0.8
1.0
0.4
0.6
0.8
CL = 1 μF, RL = 100 Ω, (see Figure 8-1)
V(IN) = 5 V (see Figure 8-2)
4
ms
9
ms
6
ms
3.5(1)
μs
These parameters are provided for reference only, and do no constitute part of TI's published specifications for purposes of TI's
product warranty
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7.7 Typical Characteristics
700
Supply Current, Output Disabled (nA)
2.335
Undervoltage Lockout (V)
2.330
2.325
2.320
UVLO Rising
2.315
UVLO Falling
2.310
2.305
2.300
2.295
2.290
50
100
300
200
100
0
120
100
80
60
40
VIN
V(IN)==2.5
2.5VV
VIN
V(IN)==3.3
3.3VV
V(IN)==55VV
VIN
V(IN)==6.5
6.5VV
VIN
20
0
±50
0
50
0
±50
100
Junction Temperature (ƒC)
150
C003
50
100
150
Junction Temperature (ƒC)
C001
Figure 7-1. UVLO – Undervoltage Lockout – V
Supply Current, Output Enabled (µA)
400
150
C002
Figure 7-2. IIN – Supply Current, Output Disabled –
nA
Supply Current versus VIN, Output Enabled (µA)
0
Junction Temperature (ƒC)
1.20E-04
1.10E-04
1.00E-04
9.00E-05
8.00E-05
= ±40
TTJ
J = t40ƒC
25
TTJ
J ==25ƒC
TTJ
J ==125ƒC
125
7.00E-05
6.00E-05
2
3
4
5
6
7
Input Voltage (V)
C004
R(ILIM) = 24.9 kΩ
R(ILIM) = 24.9 kΩ
Figure 7-3. IIN – Supply Current, Output Enabled –
μA
Figure 7-4. IIN – Supply Current, Output Enabled –
μA
1.200
Static Drain-Source Current (A)
35
Static Drain-Source On-State Resistance (mŸ
500
±100
±50
30
25
20
15
10
5
0
1.000
0.800
0.600
0.400
TA
T
==-40°C
t40ƒC
TJA=
t40ƒC
T
25ƒC
TA
TJA==25°C
25ƒC
T
=
125ƒC
TJA==125ƒC
TA
125°C
0.200
0.000
±50
0
50
100
Junction Temperature (ƒC)
150
0
50
100
V(IN) t V(OUT) (mV)
C005
Figure 7-5. MOSFET rDS(on) Versus Junction
Temperature
6
VIN
= 2.5 V
V
(IN) = 2.5 V
V
= 6.5
6.5 V
V
(IN) =
VIN
600
150
200
C006
C007
R(ILIM) = 100 kΩ
Figure 7-6. Switch Current Versus Drain-Source
Voltage Across Switch
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2.0
5.000
1.8
4.500
Static Drain-Source Current (A)
Static Drain-Source Current (A)
www.ti.com
1.6
1.4
1.2
1.0
0.8
0.6
TA
= t40ƒC
±40ƒC
TJ =
TA
25°C
TJ = 25ƒC
TJ =
TA
= 125ƒC
125°C
0.4
0.2
0.0
0
50
100
150
V(IN) ± V(OUT) (mV)
4.000
3.500
3.000
2.500
2.000
1.500
= ±40ƒC
TTJ
J = t40ƒC
TTJ
25°C
J ==25ƒC
TJ = 125ƒC
TJ = 125°C
1.000
0.500
0.000
200
0
50
100
V(IN) ± V(OUT) (mV)
C007
150
200
C010
R(ILIM) = 24.9 kΩ
R(ILIM) = 61.9 kΩ
Figure 7-7. Switch Current Versus Drain-Source
Voltage Across Switch
Figure 7-8. Switch Current Versus Drain-Source
Voltage Across Switch
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Parameter Measurement Information
OUT
tr
V(OUT)
CL
RL
tf
90%
90%
10%
10%
TEST CIRCUIT
V(EN)
50%
50%
V(EN)
ton
n
toff
50%
50%
toff
ton
90%
90%
V(OUT)
V(OUT)
10%
10%
VOLTAGE WAVEFORMS
Figure 8-1. Test Circuit and Voltage Waveforms
IOS
I(OUT)
t(IOS)
Figure 8-2. Response Time to Short-Circuit Waveform
Decreasing
Load Resistance
V(OUT)
Decreasing
Load Resistance
I(OUT)
IOS
Figure 8-3. Output Voltage Versus Current-Limit Threshold
8 Detailed Description
8.1 Overview
The TPS2556-Q1 and TPS2557-Q1 are current-limited, power-distribution switches using N-channel MOSFETs
for applications that might encounter short circuits or heavy capacitive loads . This device allows the user to
program the current-limit threshold between 500 mA and 5 A (typical) via an external resistor. This device
incorporates an internal charge pump and the gate-drive circuitry necessary to drive the N-channel MOSFET.
8
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The charge pump supplies power to the driver circuit and provides the necessary voltage to pull the gate of the
MOSFET above the source. The charge pump operates from input voltages as low as 2.5 V and requires little
supply current. The driver controls the gate voltage of the power switch. The driver incorporates circuitry that
controls the rise and fall times of the output voltage to limit large current and voltage surges and provides built-in
soft-start functionality. The TPS2556-Q1 and TPS2557-Q1 family limits the output current to the programmed
current-limit threshold IOS during an overcurrent or short-circuit event by reducing the charge-pump voltage
driving the N-channel MOSFET and operating it in the linear range of operation. The result of limiting the output
current to IOS reduces the output voltage at OUT by no longer fully enhancing the N-channel MOSFET.
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8.2 Functional Block Diagram
CS
IN
OUT
Current
Sense
Charge
Pump
Driver
EN
Current
Limit
FAULT
UVLO
GND
Thermal
Sense
8-ms Deglitch
ILIM
8.3 Feature Description
8.3.1 Overcurrent Conditions
The TPS2556-Q1 and TPS2557-Q1 devices respond to overcurrent conditions by limiting their output current
to IOS. On detecting an overcurrent condition, the device maintains a constant output current, and the output
voltage reduces accordingly. Two possible overload conditions can occur.
The first condition is when a short circuit or partial short circuit is present on a powered-up and enabled device.
With the output voltage held near zero potential with respect to ground, the TPS2556-Q1 or TPS2557-Q1 device
ramps the output current to IOS. The TPS2556-Q1 and TPS2557-Q1 devices limit the current to IOS until removal
of the overload condition or until the device begins to cycle thermally.
The second condition is when a short circuit, partial short circuit, or transient overload occurs while the device
is enabled and powered on. The device responds to the overcurrent condition within time t(IOS) (see Figure
8-2). Overdriving the current-sense amplifier during this time and momentarily disables the internal N-channel
MOSFET. The current-sense amplifier recovers and ramps the output current to IOS. Similar to the previous
case, the TPS2556-Q1 and TPS2557-Q1 devices limit the current to IOS until removal of the overload condition
or until the device begins to cycle thermally.
The TPS2556-Q1 and TPS2557-Q1 cycle thermally if an overload condition is present long enough to activate
thermal limiting in any of the above cases. The device turns off when the junction temperature exceeds 135°C
(minimum) while in current limit. The device remains off until the junction temperature cools 20°C (typical) and
then restarts. The TPS2556-Q1 and TPS2557-Q1 cycle on and off until removal of the overload (see Figure 9-7).
8.3.2 FAULT Response
Assertion (active-low) of the FAULT open-drain output occurs during an overcurrent or overtemperature
condition. The TPS2556-Q1 and TPS2557-Q1 devices assert the FAULT signal until removal of the fault
condition and the resumption of normal device operation. Design of the TPS2556-Q1 and TPS2557-Q1 devices
eliminates false FAULT reporting by using an internal delay (9-ms typical) deglitch circuit for overcurrent
conditions without the need for external circuitry. This avoids accidental FAULT assertion due to normal
operation, such as starting into a heavy capacitive load. The deglitch circuitry delays entering and leaving
current-limit-induced fault conditions. Deglitching of the FAULT signal does not occur when an overtemperature
condition disables the MOSFET, but does occur after the device has cooled and begins to turn on. This
unidirectional deglitch prevents FAULT oscillation during an overtemperature event.
8.3.3 Thermal Sense
The TPS2556-Q1 and TPS2557-Q1 devices self-protect by using two independent thermal sensing circuits
that monitor the operating temperature of the power switch and disable operation if the temperature exceeds
recommended operating conditions. The TPS2556-Q1 and TPS2557-Q1 devices operate in constant-current
mode during an overcurrent condition, which increases the voltage drop across power switch. The power
10
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dissipation in the package is proportional to the voltage drop across the power switch, which increases the
junction temperature during an overcurrent condition. The first thermal sensor (OTSD) turns off the power switch
when the die temperature exceeds 135°C (min) and the part is in current limit. Hysteresis is built into the thermal
sensor, and the switch turns on after the device has cooled approximately 20°C.
The TPS2556-Q1 and TPS2557-Q1 devices also have a second thermal sensor (OTSD2). This thermal sensor
turns off the power switch when the die temperature exceeds 155°C (minimum) regardless of whether the power
switch is in current limit, and turns on the power switch after the device has cooled approximately 20°C. The
TPS2556-Q1 and TPS2557-Q1 devices continue to cycle off and on until the fault is removed.
8.4 Device Functional Modes
8.4.1 Undervoltage Lockout (UVLO)
The undervoltage lockout (UVLO) circuit disables the power switch until the input voltage reaches the UVLO
turnon threshold. Built-in hysteresis prevents unwanted on-and-off cycling due to input voltage droop during
turnon.
8.4.2 Enable ( EN OR EN)
The logic enable controls the power switch and device supply current. The supply current is reduced to less than
2 μA when a logic high is present on EN or when a logic low is present on EN. A logic low input on EN or a logic
high input on EN enables the driver, control circuits, and power switch. The enable input is compatible with both
TTL and CMOS logic levels.
8.4.3 Auto-Retry Functionality
Some applications require that an overcurrent condition disable the device momentarily during a fault condition
and re-enables it after a preset time. This auto-retry functionality can be implemented with an external resistor
and capacitor. During a fault condition, FAULT pulls EN low. Pulling EN below the turnoff threshold disables
the part is disabled, and FAULT goes into the high-impedance state, allowing CRETRY to begin charging. The
device re-enables when the voltage on EN reaches the turnon threshold. The resistor-capacitor time constant
determines the auto-retry time. The device continues to cycle in this manner until removal of the fault condition.
TPS2557-Q1
Input
Output
0.1 µF
IN
OUT
CLOAD
RFAULT
100 kW
1 kW
CRETRY
0.22 µF
FAULT
EN
ILIM
GND
RLOAD
RILIM
20 kW
Thermal Pad
Figure 8-1. Auto-Retry Functionality
Some applications require auto-retry functionality and the ability to enable and disable with an external logic
signal. Figure 8-2 shows how an external logic signal can drive EN through RFAULT and maintain auto-retry
functionality. The resistor-capacitor time constant determines the auto-retry time-out period.
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TPS2557-Q1
Input
0.1 µF
External Logic
RFAULT
Signal and Driver
100 kΩ
IN
FAULT
EN
CRETRY
0.22 µF
Output
OUT
CLOAD
ILIM
RLOAD
RILIM
20 kΩ
GND
Thermal Pad
Figure 8-2. Auto-Retry Functionality With External EN Signal
8.4.4 Two-Level Current-Limit Circuit
Some applications require different current-limit thresholds depending on external system conditions. Figure 8-3
shows an implementation for an externally controlled, two-level current-limit circuit. The current-limit threshold is
set by the total resistance from ILIM to GND (see Programming the Current-Limit Threshold). A logic-level input
enables and disables MOSFET Q1 and changes the current-limit threshold by modifying the total resistance from
ILIM to GND. One can use additional MOSFET and resistor combinations in parallel with Q1 and R2 to increase
the number of additional current-limit levels.
CAUTION
Never drive ILIM directly with an external signal.
TPS2556-Q1, TPS2557-Q1
Input
0.1 µF
IN
RFAULT
100 kΩ
FAULT Signal
Control Signal
Output
OUT
CLOAD
FAULT
EN
ILIM
GND
Thermal Pad
R1
187 kΩ
RLOAD
R2
22.1 kΩ
Q1
Current-Limit
Control Signal
Figure 8-3. Two-Level Current-Limit Circuit
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9 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, as well as validating and testing their design
implementation to confirm system functionality.
9.1 Application Information
The devices are current-limited, power-distribution switches. They limit the output current to IOS when
encountering short circuits or heavy capacitive loads.
9.2 Typical Application, Design for Current Limit
The use of theTPS2556-Q1 and TPS2557-Q1 devices is as a power switch to limit the output current. FAULT is
an open drain pulled high to V(IN) with a resistor, a host can use to monitor overcurrent or thermal shutdown.
TPS2556-Q1
V(IN) = 5 V
0.1 µF
IN
OUT
RFAULT
100 kW
RLOAD
V(OUT)
150 µF
FAULT Signal
FAULT
Enable Signal
EN
ILIM
GND
24.9 kW
Thermal Pad
Figure 9-1. Application Schematic for Current Limit, TPS2556-Q1
9.2.1 Design Requirements
For this design example, use the following as the input parameters.
Table 9-1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage
5V
Minimum current limit
3A
Maximum current limit
5A
9.2.2 Detailed Design Procedure
9.2.2.1 Determine Design Parameters
Beginning the design process requires deciding on a few parameters. The designer must know the following:
•
•
•
Input voltage
Minimum current limit
Maximum current limit
9.2.2.2 Programming the Current-Limit Threshold
The overcurrent threshold is user-programmable via an external resistor. The TPS2556-Q1 and TPS2557-Q1
devices use an internal regulation loop to provide a regulated voltage on the ILIM terminal. The current-limit
threshold is proportional to the current sourced out of ILIM. The recommended 1% resistor range for RILIM is
20 kΩ ≤ R(ILIM) ≤ 187 kΩ to ensure stability of the internal regulation loop. Many applications require that the
minimum current limit be above a certain current level or that the maximum current limit be below a certain
current level, so it is important to consider the tolerance of the overcurrent threshold when selecting a value
for RILIM. The following equations approximate the resulting overcurrent threshold for a given value of external
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resistor RILIM. Consult the Electrical Characteristics table for specific current-limit settings. The traces routing the
RILIM resistor to the TPS2556-Q1 and TPS2557-Q1 devices should be as short as possible to reduce parasitic
effects on the current-limit accuracy.
I OS(max) (mA) =
I OS(nom) (mA) =
I OS(min) (mA) =
101 810 V
R(ILIM)0.9538 kW
113 849 V
R(ILIM)1.0049 kW
125 477 V
R(ILIM)1.058 kW
(1)
6000
(min)
IPower
OS(min)
(typ)
IPower
OS(typ)
IPower
(max)
OS(max)
Current-Limit Threshold (mA)
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
20 30 40 50 60 70 80 90 100 110 120 130 140 150
RILIM N
C002
Figure 9-2. Current-Limit Threshold versus R(ILIM)
9.2.2.3 Selecting Current-Limit Resistor 1
Some applications require that current limiting not occur below a certain threshold. For this example, assume
that 3 A must be delivered to the load so that the minimum desired current-limit threshold is 3 000 mA. Use the
IOS equations and Figure 9-2 to select R(ILIM).
I OS(min) (mA) = 3 000 mA
I OS(min) (mA) =
125 477 V
R (ILIM)1.058 kW
1
æ 125 477 V ö÷1.058
ç
÷÷
R (ILIM) (kW) = çç
çèI OS(min) mA ø÷÷
R (ILIM) (kW) = 34 kW
(2)
Select the closest 1% resistor less than the calculated value: R(ILIM) = 33.6 kΩ. This sets the minimum currentlimit threshold at 3 000 mA . Use the IOS equations, Figure 10-2, and the previously calculated value for R(ILIM) to
calculate the maximum resulting current-limit threshold.
RILIM (kW) = 33.6 kW
IOS(max) (mA) =
IOS(max) (mA) =
101810 V
R(ILIM)0.9538 kW
101810 V
33.60.9538 kW
IOS(max) (mA) = 3 564 mA
(3)
The resulting maximum current-limit threshold is 3 564 mA with a 33.6-kΩ resistor.
14
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9.2.2.4 Selecting Current-Limit Resistor 2
Some applications require that current limiting must occur below a certain threshold. For this example, assume
that the desired upper current-limit threshold must be below 5,000 mA to protect an upstream power supply. Use
the IOS equations and Figure 9-2 to select R(ILIM).
I OS(max) (mA) = 5 000 mA
I OS(max) (mA) =
101 810 V
R (ILIM)0.9538 kW
1
æ 101 810 V ö÷0.9538
ç
÷÷
R (ILIM) (kW) = çç
çèI OS(max) mA ø÷÷
R (ILIM) (kW) = 23.6 kW
(4)
Select the closest 1% resistor greater than the calculated value: R(ILIM) = 23.7 kΩ. This sets the maximum
current-limit threshold at 5 000 mA . Use the IOS equations, Figure 10-2, and the previously calculated value for
RILIM to calculate the minimum resulting current-limit threshold.
R (ILIM) (kW) = 23.7 kW
I OS(min) (mA) =
I OS(min) (mA) =
125 477 V
R(ILIM)1.058
125 477 V
23.71.058
I OS(min) (mA) = 4 406 mA
(5)
The resulting minimum current-limit threshold is 4 406 mA with a 23.7-kΩ resistor.
9.2.2.5 Accounting for Resistor Tolerance
The previous sections described the selection of RILIM given certain application requirements and the importance
of understanding the current-limit threshold tolerance. The analysis focused only on the TPS2556-Q1 and
TPS2557-Q1 device performance and assumed an exact resistor value. However, resistors sold in quantity
are not exact and are bounded by an upper and lower tolerance centered around a nominal resistance. The
additional RILIM resistance tolerance directly affects the current-limit threshold accuracy at a system level. The
following table shows a process that accounts for worst-case resistor tolerance assuming 1% resistor values.
Step one follows the selection process outlined in the foregoing application examples. Step two determines the
upper and lower resistance bounds of the selected resistor. Step three uses the upper and lower resistor bounds
in the IOS equations to calculate the threshold limits. It is important to use tighter tolerance resistors, for example
0.5% or 0.1%, when precision current limiting is desirable.
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Table 9-2. Common RILIM Resistor Selections
Desired Nominal
Current Limit (mA)
Ideal Resistor Closest 1%
(kΩ)
Resistor (kΩ)
Resistor Tolerance
1% low (kΩ)
1% high (kΩ)
Actual Limits
IOS MIN (mA)
IOS NOM (mA) IOS MAX (mA)
750
148.1
147
145.5
148.5
632
756
881
1000
111.3
110
108.9
111.1
859
1011
1161
1250
89.1
88.7
87.8
89.6
1079
1256
1426
1500
74.3
75
74.3
75.8
1289
1486
1673
1750
63.7
63.4
62.8
64.0
1540
1760
1964
2000
55.8
56.2
55.6
56.8
1749
1986
2203
2250
49.6
49.9
49.4
50.4
1983
2238
2468
2500
44.7
44.2
43.8
44.6
2255
2528
2770
2750
40.7
40.2
39.8
40.6
2493
2781
3033
3000
37.3
37.4
37.0
37.8
2691
2991
3249
3250
34.4
34.8
34.5
35.1
2904
3215
3480
3500
32.0
31.6
31.3
31.9
3216
3542
3816
3750
29.9
30.1
29.8
30.4
3386
3720
3997
4000
28.0
28
27.7
28.3
3655
4000
4282
4250
26.4
26.1
25.8
26.4
3937
4293
4579
4500
24.9
24.9
24.7
25.1
4138
4501
4789
4750
23.6
23.7
23.5
23.9
4360
4730
5020
5000
22.4
22.6
22.4
22.8
4585
4961
5253
5250
21.4
21.5
21.3
21.7
4834
5216
5509
5500
20.4
20.5
20.3
20.7
5083
5472
5765
9.2.2.6 Power Dissipation and Junction Temperature
The low on-resistance of the N-channel MOSFET allows small surface-mount packages to pass large currents.
It is good design practice to estimate power dissipation and junction temperature. The following analysis gives
an approximation for calculating junction temperature based on the power dissipation in the package. However,
it is important to note that thermal analysis is strongly dependent on additional system-level factors. Such factors
include air flow, board layout, copper thickness and surface area, and proximity to other devices that dissipate
power. Good thermal design practice must include all system-level factors in addition to individual component
analysis.
Begin by determining the rDS(on) of the N-channel MOSFET relative to the input voltage and operating
temperature. As an initial estimate, use the highest operating ambient temperature of interest and read rDS(on)
from the typical characteristics graph. Using this value, calculate the power dissipation by:
PD = rDS(on) × IOUT 2
where:
PD = Total power dissipation (W)
rDS(on) = Power-switch on-resistance (Ω)
I(OUT) = Maximum current-limit threshold (A)
This step calculates the total power dissipation of the N-channel MOSFET.
Finally, calculate the junction temperature:
TJ = PD × RθJA + TA
where:
TA = Ambient temperature (°C)
16
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RθJA = Thermal resistance (°C/W)
PD = Total power dissipation (W)
Compare the calculated junction temperature with the initial estimate. If they are not within a few degrees,
repeat the calculation using the refined rDS(on) from the previous calculation as the new estimate. Two or three
iterations are generally sufficient to achieve the desired result. The final junction temperature is highly dependent
on thermal resistance RθJA, and thermal resistance is highly dependent on the individual package and board
layout. The Thermal Information table lists thermal resistances of the device that one can use to help calculate
the thermal performance of the board design.
9.2.3 Application Curves
VOUT
2 V/div
VOUT
2 V/div
VEN_bar
5 V/div
VEN_bar
5 V/div
IIN
2 A/div
IIN
2 A/div
t - Time - 2 ms/div
t - Time - 2 ms/div
Figure 9-3. Turnon Delay and Rise Time
Figure 9-4. Turnoff Delay and Fall Time
VEN_bar
5 V/div
VOUT
2 V/div
FAULT_bar
FAULT_bar
5 V/div
5 V/div
IIN
2 A/div
IIN
5 A/div
t - Time - 2 ms/div
t - Time - 5 ms/div
Figure 9-5. Device Enabled Into Short Circuit
Figure 9-6. Full-Load to Short-Circuit Transient
Response
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VOUT
2 V/div
FAULT_bar
5 V/div
IIN
5 A/div
t - Time - 5 ms/div
Figure 9-7. Short-Circuit to Full-Load Recovery Response
10 Power Supply Recommendations
Design of the devices is for operation from an input voltage supply range of 2.5 V to 6.5 V. The current capability
of the power supply should exceed the maximum current limit of the power switch.
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11 Layout
11.1 Layout Guidelines
•
•
•
•
For all applications, TI recommends a 0.1-µF or greater ceramic bypass capacitor between IN and GND as
close to the device as possible for local noise decoupling. This precaution reduces ringing on the input due to
power-supply transients. The application may require additional input capacitance on the input to prevent
voltage overshoot from exceeding the absolute-maximum voltage of the device during heavy transient
conditions.
Output capacitance is not required, but TI recommends placing a high-value electrolytic capacitor on the
output pin when there is an expectation of large transient currents on the output.
The traces routing the RILIM resistor to the device should be as short as possible to reduce parasitic effects
on the current limit accuracy.
Connect the thermal pad directly to PCB ground plane using wide and short copper trace.
11.2 Layout Example
VIA to Power Ground Plane
Power
Ground
High Frequency
Bypass Capacitor
FAULT
1
8
2
7
3
6
4
5
IN
OUT
ILIM
Figure 11-1. TPS2556-Q1 and TPS2557-Q1 Board Layout
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12 Device and Documentation Support
12.1 Related Links
The following table lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 12-1. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
TPS2556-Q1
Click here
Click here
Click here
Click here
Click here
TPS2557-Q1
Click here
Click here
Click here
Click here
Click here
12.2 Trademarks
All trademarks are the property of their respective owners.
12.3 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
12.4 Glossary
TI Glossary
20
This glossary lists and explains terms, acronyms, and definitions.
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13 Mechanical, Packaging, and Orderable Information
The following packaging information and addendum reflect the most-current data available for the designated
devices. This data is subject to change without notice and without revision of this document.
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PACKAGE OPTION ADDENDUM
www.ti.com
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)
TPS2556QDRBRQ1
ACTIVE
SON
DRB
8
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
2556Q
TPS2556QDRBTQ1
ACTIVE
SON
DRB
8
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
2556Q
TPS2557QDRBRQ1
ACTIVE
SON
DRB
8
3000
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
2557Q
TPS2557QDRBTQ1
ACTIVE
SON
DRB
8
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
2557Q
(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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