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TPS54335, TPS54336
SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
TPS5433x 4.5- to 28-V Input, 3-A Output, Synchronous SWIFT™
Step-Down DC-DC Converter
1 Features
3 Description
•
The TPS5433x family of devices are synchronous
converters with an input-voltage range of 4.5 to 28 V.
These devices include an integrated low-side
switching FET that eliminates the need for an
external diode which reduces component count.
1
•
•
•
•
•
•
•
•
•
•
Synchronous 128-mΩ and 84-mΩ MOSFETs for
3-A Continuous Output Current
TPS54335: Internal 2-ms Soft-Start,
50-kHz to 1.5-MHz Adjustable Frequency
TPS54336: Adjustable Soft-Start,
Fixed 340-kHz Frequency
Low 2-µA Shutdown, Quiescent Current
0.8-V Voltage Reference with ±0.8% Accuracy
Current Mode Control
Monotonic Startup into Pre-Biased Outputs
Pulse Skipping for Light-Load Efficiency
Hiccup Mode Overcurrent Protection
Thermal Shutdown (TSD) and
Overvoltage Transition Protection
8-Pin SO PowerPAD™ and 10-Pin VSON
Packages
2 Applications
•
•
•
•
Consumer Applications such as a Digital TV
(DTV), Set Top Box (STB, DVD/Blu-ray Player),
LCD Display, CPE (Cable Modem, WiFi Router),
DLP Projectors, Smart Meters
Battery Chargers
Industrial and Car Audio Power Supplies
5-V, 12-V, and 24-V Distributed Power Bus Supply
Efficiency is maximized through the integrated 128mΩ and 84-mΩ MOSFETs, low IQ and pulse skipping
at light loads. Using the enable pin, the shutdown
supply current is reduced to 2 μA. This step-down
(buck) converter provides accurate regulation for a
variety of loads with a well-regulated voltage
reference that is 1.5% over temperature.
Cycle-by-cycle current limiting on the high-side
MOSFET protects the TPS5433x family of devices in
overload situations and is enhanced by a low-side
sourcing current limit which prevents current
runaway. A low-side sinking current-limit turns off the
low-side MOSFET to prevent excessive reverse
current. Hiccup protection is triggered if the
overcurrent condition continues for longer than the
preset time. Thermal shutdown disables the device
when the die temperature exceeds the threshold and
enables the device again after the built-in thermal
hiccup time.
Device Information(1)
PART NUMBER
TPS54335
TPS54336
PACKAGE
BODY SIZE (NOM)
SO PowerPAD (8)
4.89 mm × 3.90 mm
VSON (10)
3.00 mm × 3.00 mm
SO PowerPAD (8)
4.89 mm × 3.90 mm
VSON (10)
3.00 mm × 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
4 Simplified Schematic
VIN
VIN
VIN
VIN
C1
C1
TPS54335
TPS54336
BOOT
EN
C BOOT
C BOOT
PH
RT
R RT
C2
SS
COMP
R O1
CC
VSENSE
RC
GND
C2
R O2
VOUT
CO
R O1
CC
LO
PH
VOUT
CO
COMP
BOOT
EN
LO
C SS
VSENSE
R O2
RC
GND
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.
TPS54335, TPS54336
SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Simplified Schematic.............................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
1
2
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
4
4
4
5
5
6
6
Absolute Maximum Ratings .....................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description .............................................. 9
8.1 Overview ................................................................... 9
8.2 Functional Block Diagram ....................................... 10
8.3 Feature Description................................................. 10
8.4 Device Functional Modes........................................ 18
9
Application and Implementation ........................ 19
9.1 Application Information............................................ 19
9.2 Typical Applications ................................................ 19
10 Power Supply Recommendations ..................... 31
11 Layout................................................................... 32
11.1 Layout Guidelines ................................................. 32
11.2 Layout Example .................................................... 32
12 Device and Documentation Support ................. 33
12.1
12.2
12.3
12.4
12.5
12.6
Device Support......................................................
Documentation Support ........................................
Related Links ........................................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
33
33
33
33
33
33
13 Mechanical, Packaging, and Orderable
Information ........................................................... 33
5 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (September 2013) to Revision C
•
Page
Added the ESD Ratings table and the following sections:Pin Configuration and Functions, Feature Description,
Device Functional Modes, Application and Implementation, Power Supply Recommendations, Layout, Device and
Documentation Support, and Mechanical, Packaging, and Orderable Information................................................................ 1
Changes from Revision A (July 2013) to Revision B
Page
•
Deleted PREVIEW watermark from TPS54335 DRC pinout image. ...................................................................................... 3
•
Corrected Equation 27.......................................................................................................................................................... 23
Changes from Original (May 2013) to Revision A
Page
•
Changed title from "....Step Down SWIFT™ Converter" to "....SWIFT™ Step-Down Voltage Regulator" and changed
product status from "Production Data" to "Product Mix"......................................................................................................... 1
•
Changed Feature bullet from "Thermal and Overvoltage Transient Protection" to "Thermal Shutdown and
Overvoltage Transition Protection" ......................................................................................................................................... 1
•
Added text "...and 10-pin SON" to Feature bullet................................................................................................................... 1
•
Changed Applications bullet from "...such as DTV, Set Top Boxes, LCD displays, CPE Equipment" to "....such as a
Digital TV (DTV), Set Top Box (STB, DVD/Blu-ray Player), LCD Display, CPE (Cable Modem, WiFi Router), DLP
Projectors, Smart Meters"....................................................................................................................................................... 1
•
Changed Applications bullet from "...Distributed Power Systems" to "...Distributed Power Bus Supply................................ 1
•
Changed Simplified Schematic images for readability ........................................................................................................... 1
•
Added SON (DRC) pin assignment drawings and pin descriptions ....................................................................................... 3
•
Added DRC package to Thermal Information table................................................................................................................ 5
•
Changed Reference voltage MIN spec from "0.792" to "0.7936" and MAX from "0.808" to "0.8064" for TJ =25°C
condition ................................................................................................................................................................................. 5
•
Deleted "Error amplifier dc gain" spec from Electrical Characteristics table .......................................................................... 5
•
Added TPS54336 DRC Load and Line Regulation characteristics graphs .......................................................................... 29
2
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SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
6 Pin Configuration and Functions
DDA Package
8-Pin SO PowerPAD
TPS54335 Top View
BOOT
1
VIN
2
PH
GND
DDA Package
8-Pin SO PowerPAD
TPS54336 Top View
8
RT
BOOT
1
7
PowerPAD
(9)
6
3
EN
VIN
2
COMP
PH
5
4
VSENSE
GND
DRC Package
10-Pin VSON With Exposed Thermal Pad
TPS54335 Top View
VIN 1
Exposed
Thermal
Pad
(11)
GND 3
GND 4
GND 5
SS
7
PowerPAD
(9)
6
3
EN
COMP
5
4
VSENSE
DRC Package
10-Pin VSON With Exposed Thermal Pad
TPS54336 Top View
10 RT
PH 2
8
VIN 1
9 BOOT
PH 2
8 EN
GND 3
7 COMP
GND 4
6 VSENSE
GND 5
10 SS
Exposed
Thermal
Pad
(11)
9 BOOT
8 EN
7 COMP
6 VSENSE
Pin Functions
PIN
SO
Power
PAD
VSON
BOOT
1
9
O
A bootstrap capacitor is required between the BOOT and PH pins. If the voltage on this
capacitor is below the minimum required by the output device, the output is forced to
switch off until the capacitor is refreshed.
COMP
6
7
O
This pin is the error-amplifier output and the input to the output switch-current comparator.
Connect frequency compensation components to this pin.
EN
7
8
I
This pin is the enable pin. Float the EN pin to enable.
GND
4
NAME
I/O
DESCRIPTION
3
4
—
Ground
O
The PH pin is the source of the internal high-side power MOSFET.
5
PH
3
2
Connect the RT pin to an external timing resistor to adjust the switching frequency of the
device.
RT (TPS54335)
8
10
O
The SS pin is the soft-start and tracking pin. An external capacitor connected to this pin
sets the internal voltage-reference rise time. The voltage on this pin overrides the internal
reference.
VIN
2
1
—
This pin is the 4.5- to 28-V input supply voltage.
VSENSE
5
6
I
PowerPAD (SO
only)
9
—
Thermal pad
(VSON only)
—
SS (TPS54336)
This pin is the inverting node of the transconductance (gm) error amplifier.
For proper operation, connect the GND pin to the exposed thermal pad. This thermal pad
should be connected to any internal PCB ground plane using multiple vias for good
thermal performance.
—
11
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7 Specifications
7.1 Absolute Maximum Ratings (1)
Input voltage
Output voltage
MIN
MAX
VIN
–0.3
30
EN
–0.3
6
BOOT
–0.3
(PH + 7.5)
VSENSE
–0.3
3
COMP
–0.3
3
RT
–0.3
3
SS
–0.3
3
0
7.5
PH
–1
30
PH, 10-ns transient
Source current
V
BOOT-PH
–3.5
30
–0.2
0.2
EN
100
100
RT
100
100
VDIFF (GND to exposed thermal pad)
UNIT
V
V
µA
PH
Current-limit
PH
Current-limit
A
200
200
µA
Operating junction temperature
–40
150
°C
Storage temperature, Tstg
–65
150
°C
Sink current
(1)
COMP
A
Stresses beyond those listed under the 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 other conditions beyond those indicated under the recommended
operating conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS–001, all pins (1)
2000
Charged device model (CDM), per JEDEC specification JESD22-C101,
all pins (2)
500
UNIT
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.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
VSS
Supply input voltage
VOUT Output voltage
IOUT
Output current
TJ
Operating junction temperature
4
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MIN
MAX
4.5
28
UNIT
V
0.8
24
V
0
3
A
–40
150
°C
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SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
7.4 Thermal Information
THERMAL METRIC (1)
DDA
DRC
8 PINS
10 PINS
RθJA
Junction-to-ambient thermal resistance
42.1
43.9
RθJC(top)
Junction-to-case (top) thermal resistance
50.9
55.4
RθJB
Junction-to-board thermal resistance
31.8
18.9
ψJT
Junction-to-top characterization parameter
8
0.7
ψJB
Junction-to-board characterization parameter
13.5
19.1
RθJC(bot)
Junction-to-case (bottom) thermal resistance
7.1
5.3
(1)
UNIT
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
7.5 Electrical Characteristics
The electrical ratings specified in this section apply to all specifications in this document unless otherwise noted. These
specifications are interpreted as conditions that will not degrade the parametric or functional specifications of the device for
the life of the product containing it. TJ = –40°C to 150°C, VIN = 4.5 to 28 V, (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
4
4.5
V
180
400
mV
2
10
µA
310
800
µA
1.21
1.28
V
SUPPLY VOLTAGE AND UVLO (VIN PIN)
Operating input voltage
4.5
Input UVLO threshold
Rising VIN
Input UVLO hysteresis
VIN-shutdown supply current
EN = 0 V
VIN-operating non-switching supply
current
VSENSE = 810 mV
28
V
ENABLE (EN PIN)
Enable threshold
Rising
Enable threshold
Falling
Input current
Hysteresis current
1.1
1.17
V
EN = 1.1 V
1.15
µA
EN = 1.3 V
3.3
µA
VOLTAGE REFERENCE
TJ =25°C
Reference
0.7936
0.788
0.8 0.8064
V
0.8
0.812
BOOT-PH = 3 V
160
280
mΩ
BOOT-PH = 6 V
128
230
mΩ
84
170
mΩ
MOSFET
High-side switch resistance (1)
Low-side switch resistance
(1)
VIN = 12 V
ERROR AMPLIFIER
Error-amplifier transconductance (gm)
–2 µA < ICOMP < 2 µA, VCOMP = 1 V
Error-amplifier source and sink
VCOMP = 1 V, 100-mV overdrive
Start switching peak current threshold
1300
µmhos
100
µA
0.5
COMP to ISWITCH gm
A
8
A/V
CURRENT-LIMIT
High-side switch current-limit threshold
Low-side switch sourcing current-limit
Low-side switch sinking current-limit
4.9
6.5
A
4.7
6.1
A
0
Hiccup wait time
Hiccup time before restart
(1)
4
3.5
A
512
Cycles
16384
Cycles
Measured at pins
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Electrical Characteristics (continued)
The electrical ratings specified in this section apply to all specifications in this document unless otherwise noted. These
specifications are interpreted as conditions that will not degrade the parametric or functional specifications of the device for
the life of the product containing it. TJ = –40°C to 150°C, VIN = 4.5 to 28 V, (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
160
175
MAX
UNIT
THERMAL SHUTDOWN
Thermal shutdown
Thermal shutdown hysteresis
°C
10
Thermal shutdown hiccup time
°C
32768
Cycles
PH PIN
Minimum on time
Measured at 90% to 90% of VIN, IPH = 2 A
Minimum off time
BOOT-PH ≥ 3 V
94
145
ns
3
V
0%
BOOT PIN
BOOT-PH UVLO
2.1
SOFT START
Internal soft-start time
TPS54335
2
ms
soft-start charge current
TPS54336
2.3
µA
7.6 Timing Requirements
MIN
TYP
MAX
UNIT
1500
kHz
576
kHz
SWITCHING FREQUENCY
TPS54335
50
TPS54335, RRT = 100 kΩ
Switching frequency range
384
TPS54335, RRT = 1000 kΩ, –40°C to 105°C
TPS54335, RRT = 30 kΩ
Internal switching frequency
TPS54336
480
40
50
60
kHz
1200
1500
1800
kHz
272
340
408
kHz
7.7 Typical Characteristics
140
210
130
On Resistance (m
On Resistance (m
190
170
150
130
110
110
100
90
80
70
90
60
50
70
±50
±25
0
25
50
75
100
Junction Temperature (C)
125
150
±25
0
25
50
75
100
Junction Temperature (C)
125
150
C002
VIN = 12 V
Figure 1. High-Side MOSFET on Resistance vs Junction
Temperature
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±50
C001
VIN = 12 V
6
120
Figure 2. Low-Side MOSFET on Resistance vs Junction
Temperature
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SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
Typical Characteristics (continued)
495
Oscillator Frequency (kHz)
Voltage Reference (V)
0.808
0.804
0.800
0.796
0.792
490
485
480
475
470
465
±50
±25
0
25
50
75
100
125
Junction Temperature (C)
±50
150
±25
0
25
50
75
100
125
150
Junction Temperature (C)
C003
Figure 3. Voltage Reference vs Junction Temperature
C004
Figure 4. Oscillator Frequency vs Junction Temperature
1.230
3.50
Hysteresis Current ( A)
EN-UVLO Threshold (V)
3.45
1.225
1.220
1.215
3.40
3.35
3.30
3.25
1.210
3.20
±50
±25
0
25
50
75
100
125
Junction Temperature (C)
±50
150
0
25
50
75
100
125
150
Junction Temperature (C)
VIN = 12 V
C006
VIN = 12 V
Figure 5. UVLO Threshold vs Junction Temperature
Figure 6. Hysteresis Current vs Junction Temperature
400
Non-Switching Operating
Quiescent Current ( A)
1.2
Pullup Current ( A)
±25
C005
1.175
1.15
1.125
1.1
350
300
250
T
TJ
= ±40C
±40C
J =
T
TJ
= 25C
25C
J =
T
TJ
= 150C
150C
J =
200
±50
±25
0
25
50
75
100
Junction Temperature (C)
125
150
4
8
12
16
20
24
Input Voltage (V)
C007
28
C008
VIN = 12 V
Figure 7. Pullup Current vs Junction Temperature
Figure 8. Non-Switching Operating Quiescent Current vs
Input Voltage
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Typical Characteristics (continued)
2.40
±40C
TTJ
J ==±40C
25C
TTJ
J ==25C
TTJ
150C
J ==150C
8
SS Charge Current ( A)
Shutdown Quiescent Current ( A)
10
6
4
2
0
2.35
2.30
2.25
2.20
4
8
12
16
20
24
Input Voltage (V)
±50
28
±25
0
25
50
75
100
125
150
Junction Temperature (C)
C009
C010
EN = 0 V
Figure 9. Shutdown Quiescent Current vs Input Voltage
Figure 10. SS Charge Current vs Junction Temperature
6.0
Minimum Controllable Duty Ratio (%)
Minimum Controllable On Time (ns)
120
110
100
90
80
70
5.0
4.0
3.0
±50
±25
0
25
50
75
100
125
Junction Temperature ()
±50
150
25
50
75
100
125
150
C012
VIN = 12 V
Figure 11. Minimum Controllable On Time vs Junction
Temperature
Figure 12. Minimum Controllable Duty Ratio vs Junction
Temperature
2.3
6.0
Current-Limit Threshold (A)
BOOT-PH UVLO Threshhold ( A)
0
Junction Temperature (C)
VIN = 12 V
2.2
2.1
= -40ƒ
TJTJ
= –40°C
TJTJ
= 25
°C
= 25ƒ
TJTJ
= 150
°C
= 150ƒ
5.5
5.0
4.5
4.0
2.0
±50
±25
0
25
50
75
100
Junction Temperature (C)
125
150
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4
8
12
16
20
Input Voltage (V)
C013
Figure 13. BOOT-PH UVLO Threshold vs Junction
Temperature
8
±25
C011
24
28
C014
Figure 14. Current-Limit Threshold vs Input Voltage
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8 Detailed Description
8.1 Overview
The device is a 28-V, 3-A, synchronous step-down (buck) converter with two integrated n-channel MOSFETs. To
improve performance during line and load transients the device implements a constant-frequency, peak currentmode control which reduces output capacitance and simplifies external frequency-compensation design.
The device has been designed for safe monotonic startup into pre-biased loads. The device has a typical default
startup voltage of 4 V. The EN pin has an internal pullup-current source that can provide a default condition when
the EN pin is floating for the device to operate. The total operating current for the device is 310 µA (typical) when
not switching and under no load. When the device is disabled, the supply current is less than 5 μA.
The integrated 128-mΩ and 84-mΩ MOSFETs allow for high-efficiency power-supply designs with continuous
output currents up to 3 A.
The device reduces the external component count by integrating the boot recharge diode. The bias voltage for
the integrated high-side MOSFET is supplied by a capacitor between the BOOT and PH pins. The boot capacitor
voltage is monitored by an UVLO circuit and turns off the high-side MOSFET when the voltage falls below a
preset threshold. The output voltage can be stepped down to as low as the 0.8-V reference voltage.
The device minimizes excessive output overvoltage transients by taking advantage of the overvoltage powergood comparator. When the regulated output voltage is greater than 106% of the nominal voltage, the
overvoltage comparator is activated, and the high-side MOSFET is turned off and masked from turning on until
the output voltage is lower than 104%.
The TPS54335 device has a wide switching frequency of 50 kHz to 1500 kHz which allows for efficiency and size
optimization when selecting the output filter components. The internal 2-ms soft-start time is implemented to
minimize inrush currents.
The TPS54336 device has a fixed 340-kHz switching frequency. The device adjusts the soft-start time with the
SS pin.
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8.2 Functional Block Diagram
VIN
EN
Ip
Ih
Enable
Comparator
Thermal
Hiccup
UVLO
Shutdown
Logic
Hiccup
Shutdown
Enable
Threshold
OV
Boot
Charge
Current
Sense
Minimum Clamp
Pulse Skip
ERROR
AMPLIFIER
VSENSE
SS
(TPS54336)
BOOT
Boot
UVLO
+
+
HS MOSFET
Current
Comparator
Voltage
Reference
Power Stage
and
Deadtime
Control
Logic
PH
Slope
Compensation
VIN
Hiccup
Shutdown
Overload
Maximum
Recovery
Clamp
Oscillator
Regulator
LS MOSFET
Current-Limit
Current
Sense
GND
COMP
RT
(TPS54335)
EXPOSED THERMAL PAD
8.3 Feature Description
8.3.1 Fixed-Frequency PWM Control
The device uses a fixed-frequency, peak current-mode control. The output voltage is compared through external
resistors on the VSENSE pin to an internal voltage reference by an error amplifier which drives the COMP pin.
An internal oscillator initiates the turn on of the high-side power switch. The error amplifier output is compared to
the current of the high-side power switch. When the power-switch current reaches the COMP voltage level the
high-side power switch is turned off and the low-side power switch is turned on. The COMP pin voltage increases
and decreases as the output current increases and decreases. The device implements a current-limit by
clamping the COMP pin voltage to a maximum level and also implements a minimum clamp for improved
transient-response performance.
8.3.2 Light-Load Operation
The device monitors the peak switch current of the high-side MOSFET. When the peak switch current is lower
than 0.5 A (typical), the device stops switching to boost the efficiency until the peak switch current again rises
higher than 0.5 A (typical).
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Feature Description (continued)
8.3.3 Voltage Reference
The voltage-reference system produces a precise ±1.5% voltage-reference over temperature by scaling the
output of a temperature-stable bandgap circuit.
8.3.4 Adjusting the Output Voltage
The output voltage is set with a resistor divider from the output node to the VSENSE pin. Using divider resistors
with 1% tolerance or better is recommended. Begin with a value of 10 kΩ for the upper resistor divider, R1, and
use Equation 1 to calculate the value of R2. Consider using larger value resistors to improve efficiency at light
loads. If the values are too high then the regulator is more susceptible to noise and voltage errors from the
VSENSE input current are noticeable.
VREF
R2 =
´ R1
VOUT - VREF
(1)
8.3.5 Enabling and Adjusting Undervoltage Lockout
The EN pin provides electrical on and off control of the device. When the EN pin voltage exceeds the threshold
voltage, the device begins operation. If the EN pin voltage is pulled below the threshold voltage, the regulator
stops switching and enters the low-quiescent (IQ) state.
The EN pin has an internal pullup-current source which allows the user to float the EN pin to enable the device. If
an application requires control of the EN pin, use open-drain or open-collector output logic to interface with the
pin.
The device implements internal undervoltage-lockout (UVLO) circuitry on the VIN pin. The device is disabled
when the VIN pin voltage falls below the internal VIN UVLO threshold. The internal VIN UVLO threshold has a
hysteresis of 180 mV.
If an application requires a higher UVLO threshold on the VIN pin, then the EN pin can be configured as shown
in Figure 15. When using the external UVLO function, setting the hysteresis at a value greater than 500 mV is
recommended.
The EN pin has a small pullup-current, Ip, which sets the default state of the pin to enable when no external
components are connected. The pullup current is also used to control the voltage hysteresis for the UVLO
function because it increases by Ih when the EN pin crosses the enable threshold. Use Equation 2, and
Equation 3 to calculate the values of R1 and R2 for a specified UVLO threshold.
Device
VIN
Ip
Ih
R1
EN
R2
Figure 15. Adjustable VIN Undervoltage Lockout
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Feature Description (continued)
æ VENfalling ö
VSTART ç
÷ - VSTOP
ç VENrising ÷
è
ø
R1 =
æ VENfalling ö
Ip ç1 ÷ + Ih
ç
VENrising ÷ø
è
where
IP = 1.15 μA
IH = 3.3 μA
VENfalling = 1.17 V
VENrising = 1.21 V
•
•
•
•
(2)
R1´ VENfalling
R2 =
VSTOP - VENfalling + R1(Ip + Ih )
where
•
•
•
•
IP = 1.15 μA
IH = 3.3 μA
VENfalling = 1.17 V
VENrising = 1.21 V
(3)
8.3.6 Error Amplifier
The device has a transconductance amplifier as the error amplifier. The error amplifier compares the VSENSE
voltage to the lower of the internal soft-start voltage or the internal 0.8-V voltage reference. The
transconductance of the error amplifier is 1300 μA/V (typical). The frequency compensation components are
placed between the COMP pin and ground.
8.3.7 Slope Compensation and Output Current
The device adds a compensating ramp to the signal of the switch current. This slope compensation prevents
subharmonic oscillations as the duty cycle increases. The available peak inductor current remains constant over
the full duty-cycle range.
8.3.8 Safe Startup into Pre-Biased Outputs
The device has been designed to prevent the low-side MOSFET from discharging a pre-biased output. During
monotonic pre-biased startup, both high-side and low-side MOSFETs are not allowed to be turned on until the
internal soft-start voltage (TPS54335), or SS pin voltage (TPS54336) is higher than VSENSE pin voltage.
8.3.9 Bootstrap Voltage (BOOT)
The device has an integrated boot regulator. The boot regulator requires a small ceramic capacitor between the
BOOT and PH pins to provide the gate-drive voltage for the high-side MOSFET. The boot capacitor is charged
when the BOOT pin voltage is less than the VIN voltage and when the BOOT-PH voltage is below regulation.
The value of this ceramic capacitor should be 0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric
with a voltage rating of 10 V or higher is recommended because of the stable characteristics over temperature
and voltage. When the voltage between BOOT and PH pins drops below the BOOT-PH UVLO threshold, which
is 2.1 V (typical), the high-side MOSFET turns off and the low-side MOSFET turns on, allowing the boot
capacitor to recharge.
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Feature Description (continued)
8.3.10 Adjustable Switching Frequency (TPS54335 Only)
To determine the RT resistance, RRT, for a given switching frequency, use Equation 4 or the curve in Figure 16.
To reduce the solution size, set the switching frequency as high as possible, but consider the tradeoffs of the
supply efficiency and minimum controllable on time.
RRT (kW) = 55300 ´ ƒSW -1.025 (kHz)
(4)
RT Set Resistance (k
)
1000
800
600
400
200
0
0
250
500
750
1000
1250
Oscillator Frequency (kHz)
1500
C026
Figure 16. RT Set Resistor vs Switching Frequency
8.3.11 Soft-Start (TPS54336 Only)
The TPS54336 device uses the lower voltage of the internal voltage reference or the SS pin voltage as the
reference voltage and regulates the output accordingly. A capacitor on the SS pin to ground implements a softstart time. The device has an internal pullup current source of 2.3 μA that charges the external soft-start
capacitor. Use Equation 5 to calculate the soft time (tSS, 10% to 90%) and soft capacitor (CSS).
C (nF) ´ VREF (V)
t SS (ms) = SS
ISS (µA)
where
•
•
VREF is the voltage reference (0.8 V)
ISS is the soft-start charge current (2.3 μA)
(5)
When the input UVLO is triggered, the device stops switching and enters low-current operation when either the
EN pin is pulled below 1.21 V or a thermal-shutdown event occurs. At the subsequent power-up, when the
shutdown condition is removed, the device does not begin switching until it has discharged the SS pin to ground
ensuring proper soft-start behavior.
8.3.12 Output Overvoltage Protection (OVP)
The device incorporates an output overvoltage-protection (OVP) circuit to minimize output voltage overshoot. For
example, when the power-supply output is overloaded, the error amplifier compares the actual output voltage to
the internal reference voltage. If the VSENSE pin voltage is lower than the internal reference voltage for a
considerable time, the output of the error amplifier demands maximum output current. When the condition is
removed, the regulator output rises and the error-amplifier output transitions to the steady-state voltage. In some
applications with small output capacitance, the power-supply output voltage can respond faster than the error
amplifier which leads to the possibility of an output overshoot. The OVP feature minimizes the overshoot by
comparing the VSENSE pin voltage to the OVP threshold. If the VSENSE pin voltage is greater than the OVP
threshold, the high-side MOSFET is turned off which prevents current from flowing to the output and minimizes
output overshoot. When the VSENSE voltage drops lower than the OVP threshold, the high-side MOSFET is
allowed to turn on at the next clock cycle.
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Feature Description (continued)
8.3.13 Overcurrent Protection
The device is protected from overcurrent conditions by cycle-by-cycle current limiting on both the high-side
MOSFET and the low-side MOSFET.
8.3.13.1 High-Side MOSFET Overcurrent Protection
The device implements current mode control which uses the COMP pin voltage to control the turn off of the highside MOSFET and the turn on of the low-side MOSFET on a cycle-by-cycle basis. During each cycle, the switch
current and the current reference generated by the COMP pin voltage are compared. When the peak switch
current intersects the current reference the high-side switch turns off.
8.3.13.2 Low-Side MOSFET Overcurrent Protection
While the low-side MOSFET is turned on, the conduction current is monitored by the internal circuitry. During
normal operation the low-side MOSFET sources current to the load. At the end of every clock cycle, the low-side
MOSFET sourcing current is compared to the internally set low-side sourcing current-limit. If the low-side
sourcing current-limit is exceeded, the high-side MOSFET does not turn on and the low-side MOSFET stays on
for the next cycle. The high-side MOSFET turns on again when the low-side current is below the low-side
sourcing current-limit at the start of a cycle.
The low-side MOSFET can also sink current from the load. If the low-side sinking current-limit is exceeded the
low-side MOSFET turns off immediately for the remainder of that clock cycle. In this scenario, both MOSFETs
are off until the start of the next cycle.
Furthermore, if an output overload condition (as measured by the COMP pin voltage) occurs for more than the
hiccup wait time, which is programmed for 512 switching cycles, the device shuts down and restarts after the
hiccup time of 16384 cycles. The hiccup mode helps to reduce the device power dissipation under severe
overcurrent conditions.
8.3.14 Thermal Shutdown
The internal thermal-shutdown circuitry forces the device to stop switching if the junction temperature exceeds
175°C typically. When the junction temperature drops below 165°C typically, the internal thermal-hiccup timer
begins to count. The device reinitiates the power-up sequence after the built-in thermal-shutdown hiccup time
(32768 cycles) is over.
8.3.15 Small-Signal Model for Loop Response
Figure 17 shows an equivalent model for the device control loop which can be modeled in a circuit-simulation
program to check frequency and transient responses. The error amplifier is a transconductance amplifier with a
gm of 1300 μA/V. The error amplifier can be modeled using an ideal voltage-controlled current source. The
resistor, Roea (3.07 MΩ), and capacitor, Coea (20.7 pF), model the open-loop gain and frequency response of the
error amplifier. The 1-mV AC-voltage source between the nodes a and b effectively breaks the control loop for
the frequency response measurements. Plotting ac-c and c-b show the small-signal responses of the power
stage and frequency compensation respectively. Plotting a-b shows the small-signal response of the overall loop.
The dynamic loop response can be checked by replacing the load resistance, RL, with a current source with the
appropriate load-step amplitude and step rate in a time-domain analysis.
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Feature Description (continued)
PH
Power Stage
8 A/V
VOUT
a
RESR
b
R1
c
COMP
RL
VSENSE
+
VREF
R3
C2
CO
Coea
C1
Roea
gmea
1300 µA/V
R2
Figure 17. Small-Signal Model For Loop Response
8.3.16 Simple Small-Signal Model for Peak Current-Mode Control
Figure 18 is a simple small-signal model that can be used to understand how to design the frequency
compensation. The device power stage can be approximated to a voltage-controlled current-source (duty-cycle
modulator) supplying current to the output capacitor and load resistor. The control-to-output transfer function is
shown in Equation 6 and consists of a DC gain, one dominant pole and one ESR zero. The quotient of the
change in switch current and the change in the COMP pin voltage (node c in Figure 17) is the power-stage
transconductance (gmps) which is 8 A/V for the device. The DC gain of the power stage is the product of gmps
and the load resistance, RL, with resistive loads as shown in Equation 7. As the load current increases, the DC
gain decreases. This variation with load may seem problematic at first glance, but fortunately the dominant pole
moves with the load current (see Equation 8). The combined effect is highlighted by the dashed line in Figure 19.
As the load current decreases, the gain increases and the pole frequency lowers, keeping the 0-dB crossover
frequency the same for the varying load conditions which makes designing the frequency compensation easier.
VOUT
VC
RESR
RL
gmps
CO
Figure 18. Simplified Small-Signal Model for Peak Current-Mode Control
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Feature Description (continued)
VOUT
Adc
VC
RESR
ƒp
RL
gmps
CO
ƒz
Figure 19. Simplified Frequency Response for Peak Current-Mode Control
æ
ö
s
ç1 +
÷
2p ´ ƒ z ø
VOUT
è
= Adc ´
VC
æ
ö
s
ç1 +
÷
ç
2p ´ ƒp ÷ø
è
Adc = gmps ´ RL
(6)
where
•
•
gmps is the power stage gain (8 A/V)
RL is the load resistance
ƒp =
CO
(7)
1
´ RL ´ 2p
where
•
CO is the output capacitance
(8)
1
CO ´ RESR ´ 2p
ƒz =
where
•
RESR is the equivalent series resistance of the output capacitor
(9)
8.3.17 Small-Signal Model for Frequency Compensation
The device uses a transconductance amplifier for the error amplifier and readily supports two of the commonly
used Type II compensation circuits and a Type III frequency compensation circuit, as shown in Figure 20. In
Type 2A, one additional high frequency pole, C6, is added to attenuate high frequency noise. In Type III, one
additional capacitor, C11, is added to provide a phase boost at the crossover frequency. See Designing Type III
Compensation for Current Mode Step-Down Converters (SLVA352) for a complete explanation of Type III
compensation.
The following design guidelines are provided for advanced users who prefer to compensate using the general
method. The following equations only apply to designs whose ESR zero is above the bandwidth of the control
loop which is usually true with ceramic output capacitors.
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Feature Description (continued)
VOUT
C11
R8
VSENSE
COMP
Type III
R9
VREF
Type 2A
Type 2B
+
R4
gmea
Roea
Coea
C6
R4
C4
C4
Figure 20. Types of Frequency Compensation
The general design guidelines for device loop compensation are as follows:
1. Determine the crossover frequency, ƒc. A good starting value for ƒc is 1/10th of the switching frequency, ƒSW.
2. Use Equation 10 to calculate the value of R4.
2p ´ ƒc ´ VOUT ´ CO
R4 =
gmea ´ VREF ´ gmps
where
•
•
•
gmea is the GM amplifier gain (1300 μA/V)
gmps is the power stage gain (8 A/V)
VREF is the reference voltage (0.8 V)
(10)
3. Place a compensation zero at the dominant pole and use Equation 11 to calculate the value of ƒp.
æ
ö
1
ç ƒp =
÷
CO ´ RL ´ 2p ø
è
(11)
4. Use Equation 12 to calculate the value of C4.
R ´ CO
C4 = L
(12)
R4
5. The use of C6 is optional. C6 can be used to cancel the zero from the ESR (equivalent series resistance) of
the output capacitor CO. If used, use Equation 13 to calculate the value of C6.
´ CO
R
C6 = ESR
(13)
R4
6. Type III compensation can be implemented with the addition of one capacitor, C11. The use of C11 allows
for slightly higher loop bandwidths and higher phase margins. If used, use Equation 14 to calculate the value
of C11.
1
C11 =
(2 ´ p ´ R8 ´ ƒC )
(14)
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8.4 Device Functional Modes
8.4.1 Operation With VI < 4.5 V (minimum VI)
The device is designed to operate with input voltages above 4.5 V. The typical VIN UVLO threshold is 4V and if
VIN falls below this threshold the device stops switching. If the EN pin voltage is above EN threshold the device
becomes active when the VIN pin passes the UVLO threshold. .
8.4.2 Operation With EN Control
The enable threshold is 1.2-V typical. If the EN pin voltage is below this threshold the device does not switch
even though the Vin is above the UVLO threshold. The IC quiescent current is reduced in this state. Once the
EN is above the threshold with VIN above UVLO threshold the device is active again and the soft-start sequence
is initiated.
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9 Application 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.
9.1 Application Information
The TPS5433x are integrated synchronous step-down DC-DC converters which operate with a Vin of 4.5 V to
28 V. WEBENCH software is available to aid in the design and analysis of an application circuit.
9.2 Typical Applications
9.2.1 TPS54335 Application
U1
TPS54335DDA
VIN = 8 to 28 V
2
VIN
C1
10 µF
5
VSENSE
C2
0.1 µF
7
R1
220 kΩ
8
VIN
VSENSE
BOOT
PH
EN
COMP
RT
GND
PAD
L1 15 µH
C3 0.1 µF
VOUT = 5 V, 3 A max
1
VOUT
3
C6
47 µF
6
R4
51.1 Ω
4
R3
3.74 kΩ
R5
100 kΩ
C5
120 pF
R2
43.2 kΩ
C7
47 µF
R7
143 kΩ
VSENSE
C4
0.012 µF
R6
19.1 kΩ
Figure 21. Typical Application Schematic, TPS54335
9.2.1.1 Design Requirements
For this design example, use the parameters listed in Table 1.
Table 1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
8 to 28 V
Output voltage
5V
Transient response, 1.5-A load step
ΔVOUT = ±5 %
Input ripple voltage
400 mV
Output ripple voltage
30 mV
Output current rating
3A
Operating Frequency
340 kHz
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9.2.1.2 Detailed Design Procedure
The following design procedure can be used to select component values for the TPS54335 and TPS54336
devices. Alternately, 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. This section presents a simplified discussion of the design process using the TPS54335
device.
For this design example, use the input parameters listed in Table 1.
9.2.1.2.1 Switching Frequency
The switching frequency of the TPS54335 device is set at 340 kHz to match the internally set frequency of the
TPS54336 device for this design. Use Equation 4 to calculate the required value for R7. The calculated value is
140.6 kΩ. Use the next higher standard value of 143 kΩ for R7.
9.2.1.2.2 Output Voltage Set Point
The output voltage of the TPS54335 device is externally adjustable using a resistor divider network. In the
application circuit of Figure 21, this divider network is comprised of R5 and R6. Use Equation 15 and Equation 16
to calculate the relationship of the output voltage to the resistor divider.
R5 ´ Vref
R6 =
VOUT - Vref
(15)
é R5 ù
VOUT = Vref ´ ê
+1ú
ë R6 û
(16)
Select a value of R5 to be approximately 100 kΩ. Slightly increasing or decreasing R5 can result in closer outputvoltage matching when using standard value resistors. In this design, R5 = 100 kΩ and R6 = 19.1 kΩ which
results in a 4.988-V output voltage. The 51.1-Ω resistor, R4, is provided as a convenient location to break the
control loop for stability testing.
9.2.1.2.3 Undervoltage Lockout Set Point
The undervoltage lockout (UVLO) set point can be adjusted using the external-voltage divider network of R1 and
R2. R1 is connected between the VIN and EN pins of the TPS54335 device. R2 is connected between the EN
and GND pins. The UVLO has two thresholds, one for power up when the input voltage is rising and one for
power down or brown outs when the input voltage is falling. For the example design, the minimum input voltage
is 8 V, so the start-voltage threshold is set to 7.15 V with 1-V hysteresis. Use Equation 2 and Equation 3 to
calculate the values for the upper and lower resistor values of R1 and R2.
9.2.1.2.4 Input Capacitors
The TPS54335 device requires an input decoupling capacitor and, depending on the application, a bulk input
capacitor. The typical recommended value for the decoupling capacitor is 10 μF. A high-quality ceramic type X5R
or X7R is recommended. The voltage rating should be greater than the maximum input voltage. A smaller value
can be used as long as all other requirements are met; however a 10-μF capacitor has been shown to work well
in a wide variety of circuits. Additionally, some bulk capacitance may be needed, especially if the TPS54335
circuit is not located within about 2 inches from the input voltage source. The value for this capacitor is not critical
but should be rated to handle the maximum input voltage including ripple voltage, and should filter the output so
that input ripple voltage is acceptable. For this design, a 10-μF, X7R dielectric capacitor rated for 35 V is used for
the input decoupling capacitor. The ESR is approximately 2 mΩ, and the current rating is 3 A. Additionally, a
small 0.1-μF capacitor is included for high frequency filtering.
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Use Equation 17 to calculate the input ripple voltage (ΔVIN).
IOUT(MAX) ´ 0.25
DVIN =
+ IOUT(MAX) ´ ESRMAX
CBULK ´ ƒSW
(
)
where
•
•
•
•
CBULK is the bulk capacitor value
ƒSW is the switching frequency
IOUT(MAX) is the maximum load current
ESRMAX is the maximum series resistance of the bulk capacitor
(17)
The maximum RMS (root mean square) ripple current must also be checked. For worst case conditions, use
Equation 18 to calculate ICIN(RMS).
IO(MAX)
ICIN(RMS) =
(18)
2
In this case, the input ripple voltage is 227 mV and the RMS ripple current is 1.5 A.
NOTE
The actual input-voltage ripple is greatly affected by parasitics associated with the layout
and the output impedance of the voltage source.
Design Requirements shows the actual input voltage ripple for this circuit which is larger than the calculated
value. This measured value is still below the specified input limit of 400 mV. The maximum voltage across the
input capacitors is VIN(MAX) + ΔVIN / 2. The selected bypass capacitor is rated for 35 V and the ripple current
capacity is greater than 3 A. Both values provide ample margin. The maximum ratings for voltage and current
must not be exceeded under any circumstance.
9.2.1.2.5 Output Filter Components
Two components must be selected for the output filter, the output inductor (LO) and CO. Because the TPS54335
device is an externally compensated device, a wide range of filter component types and values can be
supported.
9.2.1.2.5.1 Inductor Selection
Use Equation 19 to calculate the minimum value of the output inductor (LMIN).
LMIN =
VOUT ´
(VIN(MAX) - VOUT )
VIN(MAX) ´ KIND ´ IOUT ´ ƒSW
where
•
KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output
current
(19)
In general, the value of KIND is at the discretion of the designer; however, the following guidelines may be used.
For designs using low-ESR output capacitors, such as ceramics, a value as high as KIND = 0.3 can be used.
When using higher ESR output capacitors, KIND = 0.2 yields better results.
For this design example, use KIND = 0.3. The minimum inductor value is calculated as 13.4 μH. For this design, a
close standard value of 15 µH was selected for LMIN.
For the output filter inductor, the RMS current and saturation current ratings must not be exceeded. Use
Equation 20 to calculate the RMS inductor current (IL(RMS)).
IL(RMS) =
2
IOUT(MAX)
(
)
æ VOUT ´ VIN(MAX) - VOUT ö
1
÷
´ ç
+
ç VIN(MAX) ´ LOUT ´ ƒSW ´ 0.8 ÷
12
è
ø
2
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Use Equation 21 to calculate the peak inductor current (IL(PK)).
IL(PK) = IOUT(MAX) +
VOUT ´
(VIN(MAX)
- VOUT
)
1.6 ´ VIN(MAX) ´ LOUT ´ ƒSW
(21)
For this design, the RMS inductor current is 3.002 A and the peak inductor current is 3.503 A. The selected
inductor is a Coilcraft 15 μH, XAL6060-153MEB. This inductor has a saturation current rating of 5.8 A and an
RMS current rating of 6 A which meets the requirements. Smaller or larger inductor values can be used
depending on the amount of ripple current the designer wants to allow so long as the other design requirements
are met. Larger value inductors have lower AC current and result in lower output voltage ripple. Smaller inductor
values increase AC current and output voltage ripple. In general, for the TPS54335 device, use inductors with
values in the range of 0.68 μH to 100 μH.
9.2.1.2.5.2 Capacitor Selection
Consider three primary factors when selecting the value of the output capacitor. The output capacitor determines
the modulator pole, the output voltage ripple, and how the regulator responds to a large change in load current.
The output capacitance must be selected based on the more stringent of these three criteria.
The desired response to a large change in the load current is the first criterion. The output capacitor must supply
the load with current when the regulator cannot. This situation occurs if the desired hold-up times are present for
the regulator. In this case, the output capacitor must hold the output voltage above a certain level for a specified
amount of time after the input power is removed. The regulator is also temporarily unable to supply sufficient
output current if a large, fast increase occurs affecting the current requirements of the load, such as a transition
from no load to full load. The regulator usually requires two or more clock cycles for the control loop to notice the
change in load current and output voltage and to adjust the duty cycle to react to the change. The output
capacitor must be sized to supply the extra current to the load until the control loop responds to the load change.
The output capacitance must be large enough to supply the difference in current for 2 clock cycles while only
allowing a tolerable amount of drop in the output voltage. Use Equation 22 to calculate the minimum required
output capacitance.
2 ´ DIOUT
CO >
ƒSW ´ DVOUT
where
•
•
•
ΔIOUT is the change in output current
ƒSW is the switching frequency of the regulator
ΔVOUT is the allowable change in the output voltage
(22)
For this example, the transient load response is specified as a 5% change in the output voltage, VOUT, for a load
step of 1.5 A. For this example, ΔIOUT = 1.5 A and ΔVOUT = 0.05 × 5 = 0.25 V. Using these values results in a
minimum capacitance of 35.3 μF. This value does not consider the ESR of the output capacitor in the output
voltage change. For ceramic capacitors, the ESR is usually small enough to ignore in this calculation.
Equation 23 calculates the minimum output capacitance required to meet the output voltage ripple specification.
In this case, the maximum output voltage ripple is 30 mV. Under this requirement, Equation 23 yields 12.3 µF.
1
1
CO >
´
V
8 ´ ƒSW
OUTripple
Iripple
where
•
•
•
ƒSW is the switching frequency
VOUTripple is the maximum allowable output voltage ripple
Iripple is the inductor ripple current
(23)
Use Equation 24 to calculate the maximum ESR an output capacitor can have to meet the output-voltage ripple
specification. Equation 24 indicates the ESR should be less than 29.8 mΩ. In this case, the ESR of the ceramic
capacitor is much smaller than 29.8 mΩ.
VOUTripple
RESR <
Iripple
(24)
22
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Additional capacitance deratings for aging, temperature, and DC bias should be considered which increases this
minimum value. For this example, two 47-μF 10-V X5R ceramic capacitors with 3 mΩ of ESR are used.
Capacitors generally have limits to the amount of ripple current they can handle without failing or producing
excess heat. An output capacitor that can support the inductor ripple current must be specified. Some capacitor
data sheets specify the RMS value of the maximum ripple current. Use Equation 25 to calculate the RMS ripple
current that the output capacitor must support. For this application, Equation 25 yields 116.2 mA for each
capacitor.
ICOUT(RMS) =
(
)
æ VOUT ´ VIN(MAX) - VOUT
´ ç
ç VIN(MAX) ´ LOUT ´ ƒSW ´ NC
12
è
1
ö
÷
÷
ø
(25)
9.2.1.2.6 Compensation Components
Several possible methods exist to design closed loop compensation for DC-DC converters. For the ideal currentmode control, the design equations can be easily simplified. The power stage gain is constant at low frequencies,
and rolls off at –20 dB/decade above the modulator pole frequency. The power stage phase is 0 degrees at low
frequencies and begins to fall one decade below the modulator pole frequency reaching a minimum of –90
degrees which is one decade above the modulator pole frequency. Use Equation 26 to calculate the simple
modulator pole (ƒp_mod).
IOUT max
ƒp_mod =
2p ´ VOUT ´ COUT
(26)
For the TPS54335 device, most circuits have relatively high amounts of slope compensation. As more slope
compensation is applied, the power stage characteristics deviate from the ideal approximations. The phase loss
of the power stage will now approach –180 degrees, making compensation more difficult. The power stage
transfer function can be solved but it requires a tedious calculation. Use the PSpice model to accurately model
the power-stage gain and phase so that a reliable compensation circuit can be designed. Alternately, a direct
measurement of the power stage characteristics can be used which is the technique used in this design
procedure. For this design, the calculated values are as follows:
L1 = 15 µH
C6 and C7 = 47 µF
ESR = 3 mΩ
Figure 22 shows the power stage characteristics.
60
180
40
120
20
60
0
0
–20
–60
–40
–120
Gain
Phase
–60
10
Phase (°)
Gain (dB)
Gain = 2.23 dB
at ƒ = 31.62 kHz
100
1000
10000
–180
100000
Frequency (Hz)
C020
Figure 22. Power Stage Gain and Phase Characteristics
For this design, the intended crossover frequency is 31.62 kHz (an actual measured data point exists for that
frequency). From the power stage gain and phase plots, the gain at 31.62 kHz is 2.23 dB and the phase is about
-106 degrees. For 60 degrees of phase margin, additional phase boost from a feed-forward capacitor in parallel
with the upper resistor of the voltage set point divider is not needed. R3 sets the gain of the compensated error
amplifier to be equal and opposite the power stage gain at crossover. Use Equation 27 to calculate the required
value of R3.
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10
R3 =
-GPWRSTG
20
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´
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VOUT
VREF
(27)
To maximize phase gain, the compensator zero is placed one decade below the crossover frequency of 31.62
kHz. Use Equation 28 to calculate the required value for C4.
1
C4 =
ƒ
2 ´ p ´ R3 ´ CO
10
(28)
To maximize phase gain the high frequency pole is placed one decade above the crossover frequency of 31.62
kHz. The pole can also be useful to offset the ESR of aluminum electrolytic output capacitors. Use Equation 29
to calculate the value of C5.
1
C5 =
2 ´ p ´ R3 ´ 10 ´ ƒCO
(29)
For this design the calculated values for the compensation components are as follows:
R3 = 3.74 kΩ
C4 = 0.012 µF
C5 = 120 pF
9.2.1.2.7 Bootstrap Capacitor
Every TPS54335 design requires a bootstrap capacitor, C3. The bootstrap capacitor value must 0.1 μF. The
bootstrap capacitor is located between the PH and BOOT pins. The bootstrap capacitor should be a high-quality
ceramic type with X7R or X5R grade dielectric for temperature stability.
9.2.1.2.8 Power Dissipation Estimate
The following formulas show how to estimate the device power dissipation under continuous-conduction mode
operations. These formulas should not be used if the device is working in the discontinuous conduction mode
(DCM) or pulse-skipping Eco-mode™.
The device power dissipation includes:
1. Conduction loss:
Pcon = IOUT2 × RDS(on) × VOUT / VIN
where
•
•
•
•
IOUT is the output current (A)
RDS(on) is the on-resistance of the high-side MOSFET (Ω)
VOUT is the output voltage (V)
VIN is the input voltage (V)
2. Switching loss:
Psw = 0.5 × 10–9 × VIN 2 × IOUT × ƒSW
where
•
ƒSW is the switching frequency (Hz)
3. Gate charge loss:
Pgc = 22.8 × 10–9 × ƒSW
4. Quiescent current loss:
Pq = 0.11 × 10-3 × VIN
24
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Therefore:
Ptot = Pcon + Psw + Pgc + Pq
where
•
Ptot is the total device power dissipation (W)
For given TA :
TJ = TA + Rth × Ptot
where
•
•
•
TA is the ambient temperature (°C)
TJ is the junction temperature (°C)
Rth is the thermal resistance of the package (°C/W)
For given TJMAX = 150°C:
TAMAX = TJMAX – Rth × Ptot
where
•
•
TAMAX is the maximum ambient temperature (°C)
TJMAX is the maximum junction temperature (°C)
100
100
90
90
80
80
70
70
Efficiency (%)
Efficiency (%)
9.2.1.3 Application Curves
60
50
40
30
60
50
40
30
20
20
VIN = 12 V
VIN = 24 V
10
0
0.0
0.5
1.0
1.5
2.0
2.5
Output Current (A)
0
0.001
3.0
0.01
0.1
0.5
10
C016
Figure 24. TPS54335 Low-Current Efficiency
0.10
VIN = 12 V
VIN = 24 V
0.4
1
Output Current (A)
C015
Figure 23. TPS54335 Efficiency
IOUT = 1.5 A
0.08
0.3
0.06
Line Regulation (%)
Load Regulation (%)
VIN = 12 V
VIN = 24 V
10
0.2
0.1
0.0
±0.1
±0.2
0.04
0.02
0.00
±0.02
±0.04
±0.3
±0.06
±0.4
±0.08
±0.5
±0.10
0.0
0.5
1.0
1.5
2.0
2.5
Output Current (A)
3.0
8
10
Figure 25. TPS54335 Load Regulation
12
14
16
18
20
22
24
26
Input Voltage (V)
C017
28
C018
Figure 26. TPS54335 Line Regulation
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Gain (dB)
VOUT = 200 mV/div (AC coupled)
IOUT = 1 A/div
60
180
40
120
20
60
0
0
–20
–60
–40
–120
Gain
Phase
–60
10
100
1000
VOUT = 20 mV/div (AC coupled)
10000
100000
–180
1000000
Frequency (Hz)
Time = 200 µs/div
0.75- to 2.25-A load step
Slew rate = 500 mA/µs
Figure 27. TPS54335 Transient Response
Phase (°)
SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
C019
Figure 28. TPS54335 Loop Response
VOUT = 20 mV/div (AC coupled)
PH = 10 V/div
PH = 10 V/div
Time = 2 µs/div
Time = 2 µs/div
Figure 29. TPS54335 Full-Load Output Ripple
Figure 30. TPS54335 100-mA Output Ripple
VIN = 200 mV/div (AC coupled)
VOUT = 20 mV/div (AC coupled)
PH = 10 V/div
PH = 10 V/div
Time = 100 µs/div
Time = 2 µs/div
Figure 31. TPS54335 No-Load Output Ripple
26
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Figure 32. TPS54335 Full-Load Input Ripple
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VIN = 10 V/div
VIN = 10 V/div
EN = 2 V/div
EN = 2 V/div
VOUT = 2 V/div
VOUT = 2 V/div
Time = 2 ms/div
Time = 2 ms/div
Figure 33. TPS54335 Startup Relative To VIN
Figure 34. TPS54335 Startup Relative To Enable
VIN = 10 V/div
VIN = 10 V/div
EN = 2 V/div
EN = 2 V/div
VOUT = 2 V/div
VOUT = 2 V/div
Time = 2 ms/div
Time = 2 ms/div
Figure 35. TPS54335 Shutdown Relative To VIN
Figure 36. TPS54335 Shutdown Relative To EN
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9.2.2 TPS54336 Typical Application
U1
TPS54336DDA
VIN = 8 to 28 V
2
VIN
C1
10 µF
VSENSE
C2
0.1 µF
R1
220 kΩ
5
7
8
VIN
VSENSE
BOOT
PH
EN
COMP
SS
GND
PAD
L1 15 µH
C3 0.1 µF
VOUT = 5 V, 3 A max
1
VOUT
3
C6
47 µF
6
R4
51.1 Ω
4
R3
3.74 kΩ
R5
100 kΩ
C5
120 pF
R2
43.2 kΩ
C7
47 µF
VSENSE
C4
0.012 µF
C8
0.01 µF
R6
19.1 kΩ
Figure 37. Typical Application Schematic, TPS54336
9.2.2.1 Design Requirements
For this design example, use the parameters listed in Table 2.
Table 2. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
8 to 28 V
Output voltage
5V
Transient response, 1.5-A load step
ΔVOUT = ±5 %
Input ripple voltage
400 mV
Output ripple voltage
30 mV
Output current rating
3A
Soft-start time
3.5 ms
9.2.2.2 Detailed Design Procedure
9.2.2.2.1 TPS54336 Design
The design procedure for the TPS54336 device is identical to the TPS54335 device, except that the TPS54336
device uses a soft-start circuit rather than an externally set switching frequency at pin 8. The switching frequency
is internally set for 340 kHz.
9.2.2.2.2 Soft-Start Capacitor
The soft-start capacitor determines the minimum amount of time required for the output voltage to reach the
nominal programmed value during power up. This feature is useful if a load requires a controlled-voltage slew
rate. This feature is also used if the output capacitance is very large and requires large amounts of current to
quickly charge the capacitor to the output voltage level. The large currents required to charge the capacitor can
cause the TPS54336 device to reach the current-limit. Excessive current draw from the input power supply can
cause the input voltage rail to sag. Limiting the output voltage slew rate solves both of these problems. Use
Equation 5 to calculate the value of the soft-start capacitor. For the example circuit, the soft-start time is not too
critical because the output capacitor value is 2 × 47 μF which does not require much current to charge to 5 V.
The example circuit has the soft-start time set to an arbitrary value of 3.5 ms which requires a 10-nF capacitor.
For the TPS54336 device, the calculated values are as follows:
ISS = 2.3 µA
VREF = 0.8 V
28
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100
100
90
90
80
80
70
70
Efficiency (%)
Efficiency (%)
9.2.2.3 Application Curves
60
50
40
30
60
50
40
30
20
20
VIN = 12 V
VIN = 24 V
10
0
0.0
0.5
1.0
1.5
2.0
2.5
Output Current (A)
0
0.001
3.0
0.1
1
C022
Figure 39. TPS54336 Low-Current Efficiency
VIN = 12 V
VIN = 24 V
0.4
10
Output Current (A)
0.5
0.5
VIN = 12 V
VIN = 24 V
0.4
0.3
Load Regulation (%)
0.3
Load Regulation (%)
0.01
C021
Figure 38. TPS54336 Efficiency
0.2
0.1
0.0
±0.1
±0.2
0.2
0.1
0.0
–0.1
–0.2
±0.3
–0.3
±0.4
–0.4
–0.5
±0.5
0.0
0.5
1.0
1.5
2.0
2.5
Output Current (A)
0.0
3.0
0.5
1.0
0.10
2.0
2.5
3.0
C023
Figure 41. TPS54336 DRC Load Regulation
0.10
IOUT = 1.5 A
0.08
1.5
Output Current (A)
C023
Figure 40. TPS54336 DDA Load Regulation
0.08
0.06
Line Regulation (%)
0.06
Line Regulation (%)
VIN = 12 V
VIN = 24 V
10
0.04
0.02
0.00
±0.02
±0.04
0.04
0.02
0.00
–0.02
–0.04
±0.06
–0.06
±0.08
–0.08
–0.10
±0.10
8
12
16
20
24
Input Voltage (V)
28
8
10
12
14
16
18
20
22
24
26
Input Voltage (V)
C024
28
C023
IOUT = 1.5 A
Figure 42. TPS54336 DDA Line Regulation
Figure 43. TPS54336 DRC Line Regulation
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Gain (dB)
VOUT = 200 mV/div (AC coupled)
IOUT = 1 A/div
60
180
40
120
20
60
0
0
-20
-60
-40
-120
Gain
Phase
-60
10
100
1000
VOUT = 20 mV/div (AC coupled)
10000
100000
-180
1000000
Frequency (Hz)
Time = 200 µs/div
0.75- to 2.25-A load step
Slew rate = 500 mA/µs
Figure 44. TPS54336 Transient Response
Phase (°)
SLVSC03C – MAY 2013 – REVISED DECEMBER 2014
C025
Figure 45. TPS54336 Loop Response
VOUT = 20 mV/div (AC coupled)
PH = 10 V/div
PH = 10 V/div
Time = 2 µs/div
Time = 2 µs/div
Figure 46. TPS54336 Full-Load Output Ripple
Figure 47. TPS54336 100-mA Output Ripple
VIN = 200 mV/div (AC coupled)
VOUT = 20 mV/div (AC coupled)
PH = 10 V/div
PH = 10 V/div
Time = 2 µs/div
Time = 100 µs/div
Figure 48. TPS54336 No-Load Output Ripple
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Figure 49. TPS54336 Full- Load Input Ripple
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VIN = 20 V/div
VIN = 20 V/div
EN = 5 V/div
EN = 5 V/div
SS = 2 V/div
SS = 2 V/div
VOUT = 2 V/div
VOUT = 2 V/div
Time = 2 ms/div
Time = 2 ms/div
Figure 50. TPS54336 Startup Relative to VIN
Figure 51. TPS54336 Startup Relative to Enable
VIN = 20 V/div
VIN = 20 V/div
EN = 5 V/div
EN = 5 V/div
SS = 2 V/div
SS = 2 V/div
VOUT = 2 V/div
VOUT = 2 V/div
Time = 2 ms/div
Time = 2 ms/div
Figure 52. TPS54336 Shutdown Relative to VIN
Figure 53. TPA54336 Shutdown Relative to EN
10 Power Supply Recommendations
The devices are designed to operate from an input supply ranging from 4.5 V to 28 V. The input supply should
be well regulated. If the input supply is located more than a few inches from the converter an additional bulk
capacitance typically 100 µF may be required in addition to the ceramic bypass capacitors.
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11 Layout
11.1 Layout Guidelines
The VIN pin should be bypassed to ground with a low-ESR ceramic bypass capacitor. Care should be taken to
minimize the loop area formed by the bypass capacitor connection, the VIN pin, and the GND pin of the IC. The
typical recommended bypass capacitance is 10-μF ceramic with a X5R or X7R dielectric and the optimum
placement is closest to the VIN and GND pins of the device. See Figure 54 for a PCB layout example. The GND
pin should be tied to the PCB ground plane at the pin of the IC. To facilitate close placement of the input bypass
capacitors, the PH pin should be routed to a small copper area directly adjacent to the pin. Use vias to route the
PH signal to the bottom side or an inner layer. If necessary, allow the top-side copper area to extend slightly
under the body of the closest input bypass capacitor. Make the copper trace on the bottom or internal layer short
and wide as practical to reduce EMI issues. Connect the trace with vias back to the top side to connect with the
output inductor as shown after the GND pin. In the same way use a bottom or internal layer trace to route the PH
signal across the VIN pin to connect to the boot capacitor as shown. Make the circulating loop from the PH pin to
the output inductor and output capacitors and then back to GND as tight as possible while preserving adequate
etch width to reduce conduction losses in the copper . For operation at a full rated load, the ground area near the
IC must provide adequate heat dissipating area. Connect the exposed thermal pad to the bottom or internal layer
ground plane using vias as shown. Additional vias may be used adjacent to the IC to tie top-side copper to the
internal or bottom layer copper. The additional external components can be placed approximately as shown. Use
a separate ground trace to connect the feedback, compensation, UVLO, and RT (SS for TPS54336) returns.
Connect this ground trace to the main power ground at a single point to minimize circulating currents. 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.
11.2 Layout Example
Via to Power Ground Plane
Via to SW Copper Pour on Bottom
or Internal Layer
Connect to VIN on
internal or bottom
layer
Analog
Ground
Trace
VIN
VIN
Input
Bypass
Capacitor
VIN
High-frequency
Bypass
Capacitor
Frequency
Set Resistor
BOOT
Capacitor
BOOT
RT
VIN
EN
UVLO
Resistors
PH
COMP
GND
VSENSE
Compensation
Network
Exposed
Thermal Pad
Area
Power
Ground
SW node copper pour
area on internal or
bottom layer
Output
Inductor
Power
Ground
VOUT
Note:
Feedback
Resistors
Output
Filter
Capacitor
Pin 8 for the TPS54336 device is SS. Connect an SS capacitor instead of an RT resistor from pin 8 to GND.
Figure 54. TPS54335DDA Board Layout
32
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12 Device and Documentation Support
12.1 Device Support
12.1.1 Development Support
For the WEBENCH circuit design and selection simulation services, go to www.ti.com/WEBENCH.
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
Designing Type III Compensation for Current Mode Step-Down Converters (SLVA352)
12.3 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
TPS54335
Click here
Click here
Click here
Click here
Click here
TPS54336
Click here
Click here
Click here
Click here
Click here
12.4 Trademarks
PowerPAD, SWIFT, Eco-mode are trademarks of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.5 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.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 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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24-Nov-2014
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
TPS54335DDA
ACTIVE SO PowerPAD
DDA
8
75
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 85
54335
TPS54335DDAR
ACTIVE SO PowerPAD
DDA
8
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-2-260C-1 YEAR
-40 to 85
54335
TPS54335DRCR
ACTIVE
VSON
DRC
10
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
54335
TPS54335DRCT
ACTIVE
VSON
DRC
10
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
54335
TPS54336DDA
ACTIVE SO PowerPAD
DDA
8
75
Green (RoHS
& no Sb/Br)
CU NIPDAUAG
Level-2-260C-1 YEAR
-40 to 85
54336
TPS54336DDAR
ACTIVE SO PowerPAD
DDA
8
2500
Green (RoHS
& no Sb/Br)
CU NIPDAUAG
Level-2-260C-1 YEAR
-40 to 85
54336
TPS54336DRCR
ACTIVE
VSON
DRC
10
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
54336
TPS54336DRCT
ACTIVE
VSON
DRC
10
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 85
54336
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
(4)
24-Nov-2014
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
6-Nov-2014
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
TPS54336DRCT
Package Package Pins
Type Drawing
VSON
DRC
10
SPQ
250
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
180.0
12.4
Pack Materials-Page 1
3.3
B0
(mm)
K0
(mm)
P1
(mm)
3.3
1.1
8.0
W
Pin1
(mm) Quadrant
12.0
Q2
PACKAGE MATERIALS INFORMATION
www.ti.com
6-Nov-2014
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
TPS54336DRCT
VSON
DRC
10
250
210.0
185.0
35.0
Pack Materials-Page 2
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