TI TPS40210SKGD1

TPS40210-HT
www.ti.com
SLVSAD8 – JUNE 2010
5.5-V TO 52-V INPUT, CURRENT-MODE BOOST CONTROLLER
Check for Samples: TPS40210-HT
FEATURES
1
•
APPLICATIONS
•
•
Down-Hole Drilling
High Temperature Environments
SUPPORTS EXTREME TEMPERATURE
APPLICATIONS
•
•
•
•
•
•
•
•
(1)
CONTENTS
Device Ratings
2
Electrical Characteristics
3
Typical Characteristics
5
Terminal Information
10
Application Information
12
Additional References
25
Design Examples
26
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•
•
•
•
•
•
•
•
•
•
For Boost, Flyback, SEPIC, LED Driver
Applications
Wide Input Operating Voltage: 5.5 V to 52 V
Adjustable Oscillator Frequency
Fixed-Frequency Current-Mode Control
Internal Slope Compensation
Integrated Low-Side Driver
Programmable Closed-Loop Soft Start
Overcurrent Protection
External Synchronization Capable
Reference Voltage: 700 mV
Low-Current Disable Function
Controlled Baseline
One Assembly/Test Site
One Fabrication Site
Available in Extreme (–55°C/210°C)
Temperature Range (1)
Extended Product Life Cycle
Extended Product-Change Notification
Product Traceability
Texas Instruments high temperature products
utilize highly optimized silicon (die) solutions
with design and process enhancements to
maximize performance over extended
temperatures.
DESCRIPTION
The TPS40210 is a wide input voltage (5.5 V to 52 V)
non-synchronous boost controller. It is suitable for
topologies that require a grounded source N-channel
FET, including boost, flyback, SEPIC, and various
LED driver applications. Device features include
programmable soft start, overcurrent protection with
automatic retry, and programmable oscillator
frequency. Current-mode control provides improved
transient response and simplified loop compensation.
VIN
TPS40210
1
RC
VDD 10
2
SS
BP
9
3
DIS/EN
GDRV
8
4
COMP
ISNS
7
5
FB
GND
6
VOUT
RSENSE
UDG-07110
Custom temperature ranges available
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2010, Texas Instruments Incorporated
TPS40210-HT
SLVSAD8 – JUNE 2010
www.ti.com
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.
BARE DIE INFORMATION
DIE THICKNESS
BACKSIDE FINISH
BACKSIDE
POTENTIAL
BOND PAD
METALLIZATION COMPOSITION
BOND PAD
THICKNESS
15 mils.
Silicon with backgrind
GND
Al-Cu (0.5%)
0.6 µm
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1238.4 µm
NC
(4)
NC
(5)
1
NC
(3)
NC
(2)
NC
(1)
10
3
1245.6 µm
2
9
8
7
4
52.8 µm
6
5
0.0
52.2 µm
0.0
Table 1. Bond Pad Coordinates in Microns
2
DISCRIPTION
PAD NUMBER
X min
Y min
X max
Y max
RC
1
67.95
1089.45
168.75
1190.25
SS
2
28.8
714.15
129.6
814.95
DIS/EN
3
28.8
595.35
129.6
696.15
COMP
4
28.8
306.45
129.6
407.25
FB
5
28.8
115.29
129.6
216.09
GND
6
1108.62
117.45
1209.42
218.25
ISNS
7
1108.62
332.91
1209.42
433.71
GDRV
8
1108.62
451.71
1209.42
552.51
BP
9
1108.62
570.51
1209.42
671.31
VDD
10
1057.68
1114.02
1158.48
1214.82
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Table 1. Bond Pad Coordinates in Microns (continued)
DISCRIPTION
PAD NUMBER
X min
Y min
X max
Y max
NC (1)
962.55
1147.32
1030.05
1214.82
NC (2)
868.59
1147.32
936.09
1214.82
NC (3)
764.73
1147.32
832.23
1214.82
NC (4)
643.68
1147.32
711.18
1214.82
NC (5)
403.74
1147.23
471.24
1214.73
ORDERING INFORMATION (1)
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TA
–55°C to 210°C
(1)
(2)
PACKAGE (2)
ORDERABLE PART NUMBER
KGD (bare die)
TPS40210SKGD1
NA
HKK
TPS40210SHKK
TPS40210SHKK
TOP-SIDE MARKING
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
Package drawings, thermal data, and symbolization are available at www.ti.com/packaging.
DEVICE RATINGS
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range unless otherwise noted (1)
Input voltage range
Output voltage range
VDD
–0.3 V to 52 V
RC, SS, FB, DIS/EN
–0.3 V to 10 V
ISNS
–0.3 V to 8 V
COMP, BP, GDRV
–0.3 V to 9 V
TJ
Operating junction temperature range
–55°C to 210°C
Tstg
Storage temperature range
–55°C to 210°C
(1)
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating
conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
MIN
MAX
VVDD
Input voltage
5.5
52
UNIT
V
TJ
Operating junction temperature
–55
210
°C
THERMAL CHARACTERISTICS FOR HKK PACKAGE
over operating free-air temperature range (unless otherwise noted)
PARAMETER
qJC
Junction-to-case thermal
resistance
TEST CONDITIONS
to bottom of case
to top of case - as if formed dead bug
MIN
TYP
MAX
4.6
12.9
UNIT
°C/W
ELECTROSTATIC DISCHARGE (ESD) PROTECTION
TYP
Human-Body Model (HBM)
1500
Charged-Device Model (CDM)
1500
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UNIT
V
3
TPS40210-HT
SLVSAD8 – JUNE 2010
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ELECTRICAL CHARACTERISTICS
TJ = –55°C to 210°C, VVDD= 12 Vdc, all parameters at zero power dissipation (unless otherwise noted)
PARAMETER
TEST CONDITIONS
TA = –55°C to 125°C
TA = 210°C
UNIT
MIN
TYP
MAX
MIN
TYP
MAX
686
700
720
686
702
725
mV
52
5.5
52
V
Voltage Reference
Feedback voltage
range
VFB
COMP = FB,
5.5 ≤ VVDD ≤ 52 V
Input Supply
Input voltage range
IVDD
Operating current
4.5
5.5 ≤ VVDD ≤ 52 V, no switching, VDIS < 0.8
1.5
2.5
1.5
3
mA
2.5 ≤ VDIS ≤ 7 V
10
20
23
90
mA
430
530
460
700
mA
4
4.25
4.50
4.60
V
140
195
240
195
mV
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VVDD
VVDD < VUVLO(on), VDIS < 0.8
Undervoltage Lockout (UVLO)
VUVLO(on)
Turn on threshold
voltage
VUVLO(hyst)
UVLO hysteresis
Oscillator
Oscillator frequency
range (1)
fOSC
35
Oscillator frequency
RRC = 200 kΩ, CRC = 470 pF
260
Frequency line
regulation
5.5 ≤ VDD ≤ 52 V
–20
Slope compensation
ramp
VSLP
PWM
520
VVDD = 12 V (1)
300
620
1000
35
340
260
7
–20
720
480
1000
300
640
kHz
400
7
%
750
mV
275
400
500
90
200
120
Minimum off time
170
200
100
Valley voltage
1.2
VSS(ofst)
Offset voltage from
SS pin to error
amplifier input
700
RSS(chg)
Soft-start charge
resistance
320
450
600
305
375
600
kΩ
RSS(dchg)
Soft-start discharge
resistance
840
1200
1600
700
968
1600
kΩ
1.5
3
tON(min)
Minimum pulse width
tOFF(min)
VVLY
Soft-Start
VVDD = 30 V
ns
ns
V
700
mV
Error Amplifier
GBWP
Unity gain bandwidth
product (1)
1.5
3
AOL
Open loop gain (1)
60
80
IIB(FB)
Input bias current
(current out of FB pin)
ICOMP(src)
Output source current VFB = 0.6 V, VCOMP = 1 V
100
265
ICOMP(snk)
Output sink current
1.2
2.3
120
150
111
VFB = 1.2 V, VCOMP = 1 V
300
MHz
dB
65
nA
100
280
mA
0.9
1.3
mA
120
150
Overcurrent Protection
VISNS(oc)
Overcurrent detection
threshold (at ISNS
5.5 ≤ VDD < 52 V, –55°C ≤ TJ ≤ 210°C
pin)
DOC
Overcurrent duty
cycle (1)
(1)
4
180
2
180
mV
2
%
Specified by design
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ELECTRICAL CHARACTERISTICS (continued)
TJ = –55°C to 210°C, VVDD= 12 Vdc, all parameters at zero power dissipation (unless otherwise noted)
PARAMETER
TA = –55°C to 125°C
TEST CONDITIONS
VSS(rst)
Overcurrent reset
threshold voltage (at
SS pin)
TBLNK
Leading edge
blanking
TA = 210°C
MIN
TYP
MAX
MIN
TYP
MAX
100
150
350
100
150
350
75
UNIT
mV
ns
Current-Sense Amplifier
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ACS
Current sense
amplifier gain
IB(ISNS)
Input bias current
Driver
4.2
5.6
7.2
1
3
4
4.8
7.2
V/V
1
3
mA
IGDRV(src)
Gate driver source
current
VGDRV = 4 V, TJ = 25°C
280
335
180
280
mA
IGDRV(snk)
Gate driver sink
current
VGDRV = 4 V, TJ = 25°C
300
330
230
290
mA
7
8
9
4.8
8.45
Linear Regulator
VBP
Bypass voltage
output
0 mA < IBP < 15 mA
10
V
Disable/Enable
VDIS(en)
Turn-on voltage
0.7
1
1.3
0.7
1
1.3
V
VDIS(hys)
Hysteresis voltage
25
145
220
25
155
220
mV
RDIS
DIS pin pulldown
resistance
0.7
1.1
1.5
0.5
0.9
1.5
MΩ
1000
Estimated Life (Years)
100
10
Electromigration Fail Mode
1
0
110
130
150
170
190
210
230
Continuous TJ (°C)
Notes:
1.
See datasheet for absolute maximum and minimum recommended operating conditions.
2.
Silicon operating life design goal is 10 years at 105°C junction temperature (does not include package
interconnect life).
Figure 1. TPS40210SKGD1/TPS40210SHKK
Operating Life Derating Chart
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TYPICAL CHARACTERISTICS
FREQUENCY
vs
TIMING RESISTANCE
SWITCHING FREQUENCY
vs
DUTY CYCLE
1200
68 pF
fSW - Frequency - kHz
220 pF
400
200
800
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100pF
600
1000
fSW - Frequency - kHz
470
220
100
68
33
1000
800
1200
CT(pF)
33pF
600
400
200
470 pF
1.8
IVDD - Quiescent Current - mA
1.6
1.4
1.2
1
0.8
200
300 400 500 600 700 800
RT - Timing Resistance - kW
0.4
0.2
0
-55
0
0.2
0.4
0.6
0.8
D - Duty Cycle
Figure 2.
Figure 3.
QUIESCENT CURRENT
vs
JUNCTION TEMPERATURE
SHUTDOWN CURRENT
vs
JUNCTION TEMPERATURE
1.0
1.2
50
52 V
12 V
4.5 V
0.6
0
900 1000
IVDD - Shutdown Current - µA
0
100
40
30
20
10
0
-55
-25
5
35
65
95
-25
5
35
65
95
125 155 185 215
125 155 185 215
TJ - Junction Temperature - °C
TJ - Junction Temperature - °C
Figure 4.
6
Figure 5.
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TYPICAL CHARACTERISTICS (continued)
REFERENCE VOLTAGE CHANGE
vs
JUNCTION TEMPERATURE
REFERENCE VOLTAGE CHANGE
vs
INPUT VOLTAGE
0.3
0.2
0.4
VFB – Reference Voltage Change – %
52 V
4.5 V
0.1
0
12 V
-0.1
-0.2
-0.3
-0.4
0.3
0.2
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VFB - Reference Voltage Change - %
0.5
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-55
-25
5
35
65
95
-0.5
125 155 185 215
10
0
20
30
40
VVDD – Input Voltage – V
TJ - Junction Temperature - °C
Figure 6.
Figure 7.
UNDERVOLTAGE LOCKOUT THRESHOLD
vs
JUNCTION TEMPERATURE
OVERCURRENT THRESHOLD
vs
JUNCTION TEMPERATURE
50
60
165
4.25
4.20
4.15
4.10
4.05
UVLO
164
Off
On
UVLO On
UVLO Off
4.00
-40 -25 -10 5 20 35 50 65 80 95 110 125
TJ – Junction Temperature – ° C
VISNS(OC) - Overcurrent Threshold - mV
VUVLO – Undervoltage Lockout Threshold – V
4.30
163
4.5 V
162
161
160
12 V
52 V
159
158
157
156
155
-55
-25
Figure 8.
5
35
65
95
125 155 185 215
TJ - Junction Temperature - °C
Figure 9.
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TYPICAL CHARACTERISTICS (continued)
OVERCURRENT THRESHOLD
vs
INPUT VOLTAGE
SWITCHING FREQUENCY CHANGE
vs
JUNCTION TEMPERATURE
5
155
fosc - Switching Frequency Change - %
153
152
151
150
149
148
147
146
3
2
4.5 V
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VISNS(OC) – Overcurrent Threshold – mV
4
154
1
0
-1
52 V
-2
-3
-4
-5
-55
145
0
5
10
15
20
25
30 35
VVDD – Input Voltage – V
40
12 V
-25
5
35
65
95
125 155 185 215
45
TJ - Junction Temperature - °C
Figure 10.
Figure 11.
OSCILLATOR AMPLITUDE
vs
JUNCTION TEMPERATURE
SOFT-START CHARGE/DISCHARGE RESISTANCE
vs
JUNCTION TEMPERATURE
Slope Compensation Ratio (VVDD/VSLP)
27
25
23
21
19
4.5 V
6.5 V
36 V
12 V
17
15
-55
RSS - Soft Start Charge/Discharge Resistance - kW
1600
29
-25
5
35
65
95
125
155
185
215
RSS(DSCH) Discharge
1400
1200
1000
800
600
400
RSS(CHG) Charge
200
0
-65
-40
-15
TJ - Junction Temperature - °C
Figure 12.
8
10
35
60
85
110
135
160
185
210
TJ - Junction Temperature - °C
Figure 13.
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TYPICAL CHARACTERISTICS (continued)
FB BIAS CURRENT
vs
JUNCTION TEMPERATURE
COMPENSATION SOURCE CURRENT
vs
JUNCTION TEMPERATURE
180
ICOMP(SRC) - Compensation Source Current - µA
300
140
120
100
80
60
40
20
0
-55
2 50
200
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IIB(FB) - Feedback Bias Current - nA
160
-25
5
35
65
95
125
155 185
215
150
10 0
50
0
- 55
-25
TJ - Junction Temperature - °C
35
65
95
12 5
155
18 5
2 15
185
215
TJ - Junction Temperature - °C
Figure 14.
Figure 15.
COMPENSATION SINK CURRENT
vs
JUNCTION TEMPERATURE
VALLEY VOLTAGE CHANGE
vs
JUNCTION TEMPERATURE
3
2
4
3
2
1
VVLY - Valley Voltage Change - %
ICOMP(SNK) - Compensation Sink Current - mA
5
5
1
0
-1
-2
-3
-4
-5
0
-55
-25
5
35
65
95
125 155 185 215
-6
-55
-25
TJ - Junction Temperature - °C
Figure 16.
5
35
65
95
125
155
TJ - Junction Temperature - °C
Figure 17.
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TYPICAL CHARACTERISTICS (continued)
REGULATOR VOLTAGE
vs
JUNCTION TEMPERATURE
DIS/EN TURN-ON THRESHOLD
vs
JUNCTION TEMPERATURE
1.2
–
– - DIS/EN Turn-On Threshold - V
VDIS(EN)
9
8.6
8.4
8.2
8
7.8
7.6
ILOAD = 0 m A
1.18
1.16
1.14
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VBP - Regulator Voltage - V
8.8
ILOAD = 5 m A
7.4
-65 -40 -15 10 35 60 85 110 135 160 185 210
1.12
1.1
1.08
1.06
1.04
1.02
1
-55 -25
TJ - Junction Temperature - °C
5
35
65
95
125 155 185 215
TJ - Junction Temperature - °C
Figure 18.
Figure 19.
CURRENT SENSE AMPLIFIER GAIN
vs
JUNCTION TEMPERATURE
ACS - Current Sense Amplifier Gain - V/V
7
6
5
4
3
2
1
0
-55
-25
5
35
65
95
125
155
185
215
TJ - Junction Temperature - °C
Figure 20.
10
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DEVICE INFORMATION
TERMINAL FUNCTIONS
TERMINAL
NAME
NO.
I/O
DESCRIPTION
9
O
Regulator output. Connect a 1.0-mF bypass capacitor from this pin to GND.
COMP
4
O
Error amplifier output. Connect control loop compensation network between COMP pin and FB pin.
DIS/EN
3
I
Disable/enable. Pulling this pin high places the part into a shutdown mode. Shutdown mode is characterized
by a very low quiescent current. While in shutdown mode, the functionality of all blocks is disabled, and the
BP regulator is shut down. This pin has an internal 1-MΩ pulldown resistor to GND. Leaving this pin
unconnected enables the device.
FB
GDRV
GND
ISNS
RC
SS
VDD
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BP
Error amplifier inverting input. Connect a voltage divider from the output to this pin to set the output voltage.
Compensation network is connected between this pin and COMP.
5
I
8
O
Connect the gate of the power N-channel MOSFET to this pin.
6
–
Device ground
7
I
Current sense. Connect an external current sensing resistor between this pin and GND. The voltage on this
pin is used to provide current feedback in the control loop and detect an overcurrent condition. An
overcurrent condition is declared when ISNS pin voltage exceeds the overcurrent threshold voltage, 150 mV
typical.
1
I
Switching frequency setting. Connect capacitor from RC pin to GND. Connect a resistor from RC pin to VDD
of the IC power supply and a capacitor from RC to GND.
2
I
Soft-start time programming. Connect capacitor from SS pin to GND to program converter soft-start time.
This pin also functions as a timeout timer when the power supply is in an overcurrent condition.
10
I
System input voltage. Connect a local bypass capacitor from this pin to GND. Depending on the amount of
required slope compensation, this pin can be connected to the converter output. See Application Information
section for additional details.
DGQ PHKK
owerPAD
PACKAGE
PACKAGE
(Top V
iew)
(TOP
VIEW)
RC
1
10
VDD
SS
2
9
BP
DIS/EN
3
8
GDRV
COMP
4
7
ISNS
FB
5
6
GND
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FUNCTIONAL BLOCK DIAGRAM
DIS/EN
3
COMP
4
FB
5
10 VDD
+
+
2
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SS
OC Fault
Soft Start
and
Overcurrent
E/A
SS Ref
700 mV
LDO
1
BP
8
GDRV
6
GND
7
ISNS
Driver
Enable E/A
RC
9
Oscillator
and
Slope
Compensation
PWM
Logic
+
Gain = 6
OC Fault
UVLO
150 mV
+
LEB
12
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UDG-07107
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APPLICATION INFORMATION
Minimum On-Time and Off-Time Considerations
The TPS40210 has a minimum off time of approximately 200 ns and a minimum on time of 300 ns. These two
constraints place limitations on the operating frequency that can be used for a given input-to-output conversion
ratio. See Figure 3 for the maximum frequency that can be used for a given duty cycle.
The duty cycle at which the converter operates is dependent on the mode in which the converter is running. If the
converter is running in discontinuous conduction mode, the duty cycle varies with changes to the load much
more than it does when running in continuous conduction mode.
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In continuous conduction mode, the duty cycle is related primarily to the input and output voltages.
VOUT + VD
1
=
VIN
1- D
æ æ
VIN
D = ç1 - ç
ç
V
è è OUT + VD
öö
÷ ÷÷
øø
(1)
(2)
In discontinuous mode, the duty cycle is a function of the load, input and output voltages, inductance, and
switching frequency.
D=
2 ´ (VOUT + VD )´ IOUT ´ L ´ fSW
(VIN )2
(3)
All converters using a diode as the freewheeling or catch component have a load current level at which they
transition from discontinuous conduction to continuous conduction. This is the point at which the inductor current
falls to zero. At higher load currents, the inductor current does not fall to zero but remains flowing in a positive
direction and assumes a trapezoidal wave shape as opposed to a triangular wave shape. This load boundary
between discontinuous conduction and continuous conduction can be found for a set of converter parameters as
shown in Equation 4.
2
VOUT + VD - VIN )´ (VIN )
(
IOUT(crit) =
2
2 ´ (VOUT + VD ) ´ fSW ´ L
(4)
For loads higher than the result of Equation 4, the duty cycle is given by Equation 2, and for loads less than the
results of Equation 4, the duty cycle is given Equation 3. For Equation 1 through Equation 4, the variable
definitions are as follows:
• VOUT is the output voltage of the converter in V
• VD is the forward conduction voltage drop across the rectifier or catch diode in V
• VIN is the input voltage to the converter in V
• IOUT is the output current of the converter in A
• L is the inductor value in H
• f SW is the switching frequency in Hz
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Setting the Oscillator Frequency
The oscillator frequency is determined by a resistor and capacitor connected to the RC pin of the TPS40210. The
capacitor is charged to a level of approximately VVDD/20 by current flowing through the resistor and is then
discharged by a transistor internal to the TPS40210. The required resistor for a given oscillator frequency is
found from either Figure 2 or Equation 5.
RT =
1
5.8 ´ 10
-8
´ fSW ´ C T + 8 ´ 10
- 10
2
´ fSW + 1.4 ´ 10
-7
´ fSW - 1.5 ´ 10 - 4 + 1.7 ´ 10 - 6 ´ C T - 4 ´ 10 - 9 ´ C T 2
where
RT is the timing resistance in kΩ
f SW is the switching frequency in kHz
CT is the timing capacitance in pF
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•
•
•
(5)
For most applications, a capacitor in the range of 68 pF to 120 pF gives the best results. Resistor values should
be limited to between 100 kΩ and 1 MΩ as well. If the resistor value falls below 100 kΩ, decrease the capacitor
size and recalculate the resistor value for the desired frequency. As the capacitor size decreases below 47 pF,
the accuracy of Equation 5 degrades, and empirical means may be needed to fine tune the timing component
values to achieve the desired switching frequency.
Synchronizing the Oscillator
The TPS40210 can be synchronized to an external clock source. Figure 21 shows the functional diagram of the
oscillator. When synchronizing the oscillator to an external clock, the RC pin must be pulled below 150 mV for 20
ns or more. The external clock frequency must be higher than the free running frequency of the converter as
well. When synchronizing the controller, if the RC pin is held low for an excessive amount of time, erratic
operation may occur. The maximum amount of time that the RC pin should be held low is 50% of a nominal
output pulse, or 10% of the period of the synchronization frequency.
Under circumstances where the duty cycle is less than 50%, a Schottky diode connected from the RC pin to an
external clock may be used to synchronize the oscillator. The cathode of the diode is connected to the RC pin.
The trip point of the oscillator is set by an internal voltage divider to be 1/20 of the input voltage. The clock signal
must have an amplitude higher than this trip point. When the clock goes low, it allows the reset current to restart
the RC ramp, synchronizing the oscillator to the external clock. This provides a simple single-component method
for clock synchronization.
VDD
8
10
VIN
+
RRC
External Frequency
Synchronization
(optional)
RC
Q
R
Q
CLK
+
1
+
CRC
S
150 mV
GND
65
TPS40210/11
UDG-08063
Figure 21. Oscillator Functional Diagram
14
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VDD
Amplitude >
8
10
VIN
VIN
+
20
RRC
Duty Cycle < 50%
RC
S
Q
R
Q
+
1
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Frequency > Controller
Frequency
+
CRC
CLK
150 mV
GND
65
TPS40210/11
UDG-08064
Figure 22. Diode Connected Synchronization
Current Sense and Overcurrent
The TPS40210 are current-mode controllers and use a resistor in series with the source terminal power FET to
sense current for both the current-mode control and overcurrent protection. The device enters a current-limit
state if the voltage on the ISNS pin exceeds the current-limit threshold voltage VISNS(oc) from the electrical
specifications table. When this happens, the controller discharges the SS capacitor through a relatively high
impedance and then attempts to restart. The amount of output current that causes this to happen is dependent
on several variables in the converter.
TPS40210/11
VIN
10 VDD
TPS40210/11
RT
L
VOUT
VDD 10
1
RC
CT
6
GDRV
8
ISNS
7
GND
UDG-07119
RIFLT
CIFLT
GND
RISNS
6
UDG-07120
Figure 23. Oscillator Components
Figure 24. Current Sense Components
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The load current overcurrent threshold is set by proper choice of RISNS. If the converter is operating in
discontinuous mode the current sense resistor is found in Equation 6.
RISNS =
fSW ´ L ´ VISNS(oc)
2 ´ L ´ fSW ´ IOUT(oc) ´ (VOUT + VD - VIN )
(6)
If the converter is operating in continuous conduction mode RISNS can be found in Equation 7.
RISNS =
•
•
•
•
•
•
•
•
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where
VISNS
VISNS
=
æ IOUT ö æ IRIPPLE ö æ IOUT ö æ D ´ VIN ö
+
ç 1- D ÷ + ç
2 ÷ø çç (1 - D ) ÷÷ ç 2 ´ fSW ´ L ÷
è
ø è
ø
è
ø è
RISNS is the value of the current sense resistor in Ω.
VISNS(oc) is the overcurrent threshold voltage at the ISNS pin (from electrical specifications)
D is the duty cycle (from Equation 2)
f SW is the switching frequency in Hz
VIN is the input voltage to the power stage in V (see text)
L is the value of the inductor in H
IOUT(oc) is the desired overcurrent trip point in A
VD is the drop across the diode in Figure 24
(7)
The TPS40210 have a fixed undervoltage lockout (UVLO) that allows the controller to start at a typical input
voltage of 4.25 V. If the input voltage is slowly rising, the converter might have less than its designed nominal
input voltage available when it has reached regulation. As a result, this may decreases the apparent current-limit
load current value and must be taken into consideration when selecting RISNS. The value of VIN used to calculate
RISNS must be the value at which the converter finishes startup. The total converter output current at startup is
the sum of the external load current and the current required to charge the output capacitor(s). See the Soft Start
section of this data sheet for information on calculating the required output capacitor charging current.
The topology of the standard boost converter has no method to limit current from the input to the output in the
event of a short circuit fault on the output of the converter. If protection from this type of event is desired, it is
necessary to use some secondary protection scheme such as a fuse or rely on the current limit of the upstream
power source.
Current Sense and Sub-Harmonic Instability
A characteristic of peak current-mode control results in a condition where the current control loop can exhibit
instability. This results in alternating long and short pulses from the pulse-width modulator. The voltage loop
maintains regulation and does not oscillate, but the output ripple voltage increases. The condition occurs only
when the converter is operating in continuous conduction mode, and the duty cycle is 50% or greater. The cause
of this condition is described in Texas Instruments literature number SLUA101, available at www.ti.com. The
remedy for this condition is to apply a compensating ramp from the oscillator to the signal going to the
pulse-width modulator. In the TPS40210, the oscillator ramp is applied in a fixed amount to the pulse-width
modulator. The slope of the ramp is given in Equation 8.
æV
ö
s e = fSW ´ ç VDD ÷
è 20 ø
(8)
To ensure that the converter does not enter into sub-harmonic instability, the slope of the compensating ramp
signal must be at least half of the down slope of the current ramp signal. Because the compensating ramp is
fixed in the TPS40210, this places a constraint on the selection of the current sense resistor.
The down slope of the current sense wave form at the pulse-width modulator is described in Equation 9.
m2 =
16
A CS ´ RISNS ´ (VOUT + VD - VIN )
L
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Since the slope compensation ramp must be at least half, and preferably equal to the down slope of the current
sense waveform seen at the pulse-width modulator, a maximum value is placed on the current sense resistor
when operating in continuous mode at 50% duty cycle or greater. For design purposes, some margin should be
applied to the actual value of the current sense resistor. As a starting point, the actual resistor chosen should be
80% or less that the value calculated in Equation 10. This equation calculates the resistor value that makes the
slope compensation ramp equal to one half of the current ramp downslope. Values no more than 80% of this
result are acceptable.
RISNS(max) =
•
•
•
•
•
•
•
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where
VVDD ´ L ´ fSW
60 ´ (VOUT + VD - VIN )
Se is the slope of the voltage compensating ramp applied to the pulse-width modulator in V/s
f SW is the switching frequency in Hz
VVDD is the voltage at the VDD pin in V
m2 is the down slope of the current sense waveform seen at the pulse-width modulator in V/s
RISNS is the value of the current sense resistor in Ω
VOUT is the converter output voltage VIN is the converter power stage input voltage
VD is the drop across the diode in Figure 24
(10)
It is possible to increase the voltage compensation ramp slope by connecting the VDD pin to the output voltage
of the converter instead of the input voltage as shown in Figure 24. This can help in situations where the
converter design calls for a large ripple current value in relation to the desired output current limit setting.
NOTE
Connecting the VDD pin to the output voltage of the converter affects the startup voltage
of the converter since the controller undervoltage lockout (UVLO) circuit monitors the VDD
pin and senses the input voltage less the diode drop before startup. The effect is to
increase the startup voltage by the value of the diode voltage drop.
If an acceptable RISNS value is not available, the next higher value can be used and the signal from the resistor
divided down to an acceptable level by placing another resistor in parallel with CISNS.
Current Sense Filtering
In most cases, a small filter placed on the ISNS pin improves performance of the converter. These are the
components RIFLT and CIFLT in Figure 24. The time constant of this filter should be approximately 10% of the
nominal pulse width of the converter. The pulse width can be found using Equation 11.
tON =
D
fSW
(11)
The suggested time constant is then
RIFLT ´ CIFLT = 0.1´ tON
(12)
The range of RIFLT should be from about 1 kΩ to 5 kΩ for best results. Higher values can be used, but this raises
the impedance of the ISNS pin connection more than necessary and can lead to noise-pickup issues in some
layouts. CISNS should be located as close as possible to the ISNS pin as well to provide noise immunity.
Soft Start
The soft-start feature of the TPS40210 is a closed-loop soft start, meaning that the output voltage follows a linear
ramp that is proportional to the ramp generated at the SS pin. This ramp is generated by an internal resistor
connected from the BP pin to the SS pin and an external capacitor connected from the SS pin to GND. The SS
pin voltage (VSS) is level shifted down by approximately VSS(ofst) (approximately 1 V) and sent to one of the “+”
inputs (the “+” input with the lowest voltage dominates) of the error amplifier. When this level-shifted voltage
(VSSE) starts to rise at time t1 (see Figure 25), the output voltage that the controller expects rises as well. Since
VSSE starts at near 0 V, the controller attempts to regulate the output voltage from a starting point of zero volts. It
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cannot do this, due to the converter architecture. The output voltage starts from the input voltage less the drop
across the diode (VIN – VD) and rises from there. The point at which the output voltage starts to rise (t2) is when
the VSSE ramp passes the point where it is commanding more output voltage than (VIN – VD). This voltage level is
labeled VSSE(1). The time required for the output voltage to ramp from a theoretical zero to the final regulated
value (from t1 to t3) is determined by the time it takes for the capacitor connected to the SS pin (CSS) to rise
through a 700-mV range, beginning at VSS(ofst) above GND.
TPS40210/11
VSS
RSS(chg)
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700 mV REF
SS
VSS(ofst)+700 mV
VSSE
VSS(ofst)
2
+
+
RSS(dchg)
VSSE(1)
t0
Error Amplifier
t1
VIN - VD
VOUT
t2
t3
DIS
UVLO
OC Fault
FB
5
COMP
4
Figure 25. SS Pin Voltage and Output Voltage
18
UDG-07121
Figure 26. SS Pin Functional Circuit
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The required capacitance for a given soft start time t3 – t1 in Figure 25 is calculated in Equation 13.
CSS =
tSS
æ
VBP - VSS(ofst)
RSS ´ ln ç
çV - V
SS(ofst) + VFB
è BP
(
ö
÷
÷
ø
)
where
tSS is the soft-start time
RSS(chg) is the SS charging resistance in Ω, typically 500 kΩ
CSS is the value of the capacitor on the SS pin, in F
VBP is the value of the voltage on the BP pin in V
VSS(ofst) is the approximate level shift from the SS pin to the error amplifier (~1 V)
VFB is the error amplifier reference voltage, 700 mV typical
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•
•
•
•
•
•
(13)
Note that tSS is the time it takes for the output voltage to rise from 0 V to the final output voltage. Also note the
tolerance on RSS(chg) given in the electrical specifications table. This contributes to some variability in the output
voltage rise time, and margin must be applied to account for it in design.
Also take note of VBP. Its value varies depending on input conditions. For example, a converter operating from a
slowly rising input initializes VBP at a fairly low value and increases during the entire startup sequence. If the
controller has a voltage above 8 V at the input and the DIS pin is used to stop and then restart the converter, VBP
is approximately 8 V for the entire startup sequence. The higher the voltage on BP, the shorter the startup time is
and conversely, the lower the voltage on BP, the longer the startup time is.
The soft-start time (tSS) must be chosen long enough so that the converter can start up without going into an
overcurrent state. Since the overcurrent state is triggered by sensing the peak voltage on the ISNS pin, that
voltage must be kept below the overcurrent threshold voltage VISNS(oc). The voltage on the ISNS pin is a function
of the load current of the converter, the rate of rise of the output voltage and the output capacitance, and the
current sensing resistor. The total output current that must be supported by the converter is the sum of the
charging current required by the output capacitor and any external load that must be supplied during startup. This
current must be less than the IOUT(oc) value used in Equation 6 or Equation 7 (depending on the operating mode
of the converter) to determine the current sense resistor value.
In these equations, the actual input voltage at the time that the controller reaches the final output voltage is the
important input voltage to use in the calculations. If the input voltage is slowly rising and is at less than the
nominal input voltage when the startup time ends, the output current limit is less than IOUT(oc) at the nominal input
voltage. The output capacitor charging current must be reduced (decrease COUT or increase the tSS) or IOUT(oc)
must be increased and a new value for RISNS calculated.
IC(chg) =
COUT ´ VOUT
tSS
(14)
COUT ´ VOUT
(IOUT(oc) - IEXT)
tSS >
where
•
•
•
•
•
•
IC(chg) is the output capacitor charging current in A
COUT is the total output capacitance in F
VOUT is the output voltage in V
tSS is the soft start time from Equation 13
IOUT(oc) is the desired over current trip point in A
IEXT is any external load current in A
(15)
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The capacitor on the SS pin (CSS) also plays a role in overcurrent functionality. It is used as the timer between
restart attempts. The SS pin is connected to GND through a resistor, RSS(dchg), when the controller senses an
overcurrent condition. Switching stops and nothing else happens until the SS pin discharges to the soft-start
reset threshold, VSS(rst). At this point, the SS pin capacitor is allowed to charge again through the charging
resistor RSS(chg), and the controller restarts from that point. The shortest time between restart attempts occurs
when the SS pin discharges from VSS(ofst) (approximately 1 V) to VSS(rst) (150 mV) and then back to VSS(ofst) and
switching resumes. In actuality, this is a conservative estimate since switching does not resume until the VSSE
ramp rises to a point where it is commanding more output voltage than exists at the output of the controller. This
occurs at some SS pin voltage greater than VSS(ofst) and depends on the voltage that remains on the output
overvoltage the converter while switching has been halted. The fastest restart time can be calculated by using
Equation 16, Equation 17, and Equation 18.
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æ VSS(ofst)
tDCHG = RSS(dchg) ´ CSS ´ ln ç
ç VSS(rst)
è
(
(
ö
÷
÷
ø
) ö÷
)÷ø
æ V -V
BP
SS(rst)
tCHG = RSS(chg) ´ CSS ´ ln ç
ç V -V
SS(ofst)
è BP
tRSTRT(min ) = tCHG + tDCHG
(16)
(17)
(18)
VBP
VSS
tRSTR(min)
VSS(ofst)
VSS(rst)
T - Time
Figure 27. Soft Start During Overcurrent
20
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BP Regulator
The TPS40210 has an on-board linear regulator that supplies power for the internal circuitry of the controller,
including the gate driver. This regulator has a nominal output voltage of 8 V and must be bypassed with a 1-mF
capacitor. If the voltage at the VDD pin is less than 8 V, the voltage on the BP pin is also less, and the gate drive
voltage to the external FET is reduced from the nominal 8 V. This should be considered when choosing a FET
for the converter.
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Connecting external loads to this regulator can be done, but care must be taken to ensure that the thermal rating
of the device is observed, because there is no thermal shutdown feature in this controller. Exceeding the thermal
ratings causes out-of-specification behavior and can lead to reduced reliability. The controller dissipates more
power when there is an external load on the BP pin and is tested for dropout voltage for up to 5-mA load. When
the controller is in the disabled state, the BP pin regulator also shuts off so loads connected there power down
as well. When the controller is disabled with the DIS/EN pin, this regulator is turned off.
The total power dissipation in the controller can be calculated as follows. The total power is the sum of PQ, PG
and PE.
PQ = VVDD ´ IVDD(en)
PG = VVDD ´ Qg ´ fSW
(19)
(20)
PE = VVDD ´ IEXT
where
•
•
•
•
•
•
•
•
PQ is the quiescent power of the device in W
VVDD is the VDD pin voltage in V
IVDD(en) is the quiescent current of the controller when enabled but not switching in A
PG is the power dissipated by driving the gate of the FET in W
Qg is the total gate charge of the FET at the voltage on the BP pin in C
f SW is the switching frequency in Hz
PE is the dissipation caused be external loading of the BP pin in W
IEXT is the external load current in A
(21)
Shutdown (DIS/EN Pin)
The DIS/EN pin is an active-high shutdown command for the controller. Pulling this pin above 1.2 V causes the
controller to completely shut down and enter a low current consumption state. In this state, the regulator
connected to the BP pin is turned off. There is an internal 1.1-MΩ pull-down resistor connected to this pin that
keeps the pin at GND level when left floating. If this function is not used in an application, it is best to connect
this pin to GND
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Control Loop Considerations
There are two methods to design a suitable control loop for the TPS40210. The first (and preferred, if equipment
is available) is to use a frequency-response analyzer to measure the open-loop modulator and power stage gain
and to then design compensation to fit that. The usage of these tools for this purpose is well documented with
the literature that accompanies the tool and is not discussed here.
The second option is to make an initial guess at compensation, and then evaluate the transient response of the
system to see if the compensation is acceptable to the application or not. For most systems, an adequate
response can be obtained by simply placing a series resistor and capacitor (RFB and CFB) from the COMP pin to
the FB pin as shown in Figure 28.
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VIN
TPS40210
1
RC
2
SS
3
DIS/EN
L
VDD 10
BP
9
GDRV
8
VOUT
CHF
CFB
RFB
COUT
RIFLT
4
COMP
5
FB
ISNS
7
GND
6
CIFLT
ROUT
RSENSE
R1
R2
UDG-07177
Figure 28. Basic Compensation Network
The natural phase characteristics of most capacitors used for boost outputs combined with the current mode
control provide adequate phase margin when using this type of compensation. To determine an initial starting
point for the compensation, the desired crossover frequency must be considered when estimating the control to
output gain. The model used is a current source into the output capacitor and load.
When using these equations, the loop bandwidth should be no more than 20% of the switching frequency, f SW. A
more reasonable loop bandwidth would be 10% of the switching frequency. Be sure to evaluate the transient
response of the converter over the expected load range to ensure acceptable operation.
K CO = gM ´ ZOUT (fCO ) = 19.1A
0.13 ´ L ´
gM =
22
fSW
ROUT
2
V
´ 0.146 W = 2.80
0.13 ´ 10 mH ´
=
600kHz
240 W
2
(RISNS ) ´ (120 ´ RISNS + L ´ fSW ) (12mW ) ´ (120 ´ 12mW + 10 mH ´ 600kHz )
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= 19.1 A
(22)
V
(23)
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(1+ (2p ´ f ´ R
L
ZOUT = ROUT ´
(
2
ESR
2
´ COUT )
2
)
)
2
1 + (ROUT ) + 2 ´ ROUT ´ RESR + (RESR ) ´ (2p ´ fL ´ COUT )
where
KCO is the control to output gain of the converter, in V/V
gM is the transconductance of the power stage and modulator, in S
ROUT is the output load equivalent resistance, in Ω
ZOUT is the output impedance, including the output capacitor, in Ω
RISNS is the value of the current sense resistor, in Ω
L is the value of the inductor, in H
COUT is the value of the output capacitance, in mF
RESR is the equivalent series resistance of COUT, in Ω
f SW is the switching frequency, in Hz
f L is the desired crossover frequency for the control loop, in Hz
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•
•
•
•
•
•
•
•
•
•
(24)
These equations assume that the operation is discontinuous and that the load is purely resistive. The gain in
continuous conduction can be found by evaluating Equation 23 at the resistance that gives the critical conduction
current for the converter. Loads that are more like current sources give slightly higher gains than predicted here.
To find the gain of the compensation network required for a control loop of bandwidth f L, take the reciprocal of
Equation 22.
K COMP =
1
K CO
=
1
= 0.356
2.80
(25)
The GBWP of the error amplifier is only specified to be at least 1.5 MHz. If KCOMP multiplied by the fL is greater
than 750 kHz, reduce the desired loop crossover frequency until this condition is satisfied. This ensures that the
high-frequency pole from the error amplifier response with the compensation network in place does not cause
excessive phase lag at the f L and decrease phase margin in the loop.
The R-C network connected from COMP to FB places a zero in the compensation response. That zero should be
approximately 1/10th of the desired crossover frequency, f L. With that being the case, RFB and CFB can be found
from Equation 26 and Equation 27
RFB =
CFB =
where
•
•
R1
= R1´ K COMP
K CO
(26)
10
2p ´ fL ´ RFB
R1 is in fL is the loop crossover frequency desired, in Hz.
RFB is the feedback resistor in CFB is the feedback capacitance in mF.
(27)
Thought not strictly necessary, it is recommended that a capacitor be added between COMP and FB to provide
high-frequency noise attenuation in the control loop circuit. This capacitor introduces another pole in the
compensation response. The allowable location of that pole frequency determines the capacitor value. As a
starting point, the pole frequency should be 10 × fL. The value of CHF can be found from Equation 28.
CHF =
1
20p ´ fL ´ RFB
(28)
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The error amplifier GBWP will usually be higher, but is ensured by design to be at least 1.5 MHz. If the gain
required in Equation 25 multiplied by 10 times the desired control loop crossover frequency, the high-frequency
pole introduced by CHF is overridden by the error amplifier capability and the effective pole is lower in frequency.
If this is the case, CHF can be made larger to provide a consistent high-frequency roll off in the control loop
design. Equation 29 calculates the required CHF in this case.
CHF =
1
6
2p ´ 1.5 ´ (10 ) ´ RFB
where
CHF is the high-frequency roll-off capacitor value in mF
RFB is the mid-band gain-setting resistor value in Ω
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•
•
(29)
Gate Drive Circuit
Some applications benefit from the addition of a resistor connected between the GDRV pin and the gate of the
switching MOSFET. In applications that have particularly stringent load regulation (under 0.75%) requirements
and operate from input voltages above 5 V, or are sensitive to pulse jitter in the discontinuous conduction region,
this resistor is recommended. The recommended starting point for the value of this resistor can be calculated
from Equation 30.
RG =
where
•
•
105
QG
QG is the MOSFET total gate charge at 8-V VGS in nC.
RG is the suggested starting point gate resistance in Ω.
(30)
VIN
L
TPS40210/11
VDD 10
VOUT
RG
GDRV
8
ISNS
7
GND
6
UDG-07196
Figure 29. Gate Drive Resistor
TPS40211
The only difference between the TPS40210 and the TPS40211 is the reference voltage that the error amplifier
uses to regulate the output voltage. The TPS40211 uses a 260-mV reference and is intended for applications
where the output is actually a current instead of a regulated voltage. A typical example of an application of this
type is an LED driver. An example schematic is shown in Figure 30.
24
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VIN
IOUT
TPS40210/11
1
RC
L
VDD 10
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2
SS
3 DIS/EN
4
COMP
BP
9
GDRV
8
ISNS 7
RIFB
5
GND
FB
6
UDG-07197
Figure 30. Typical LED Drive Schematic
The current in the LED string is set by the choice of the resistor RISNS as shown in Equation 31.
RIFB =
where
•
•
•
VFB
IOUT
RIFB is the value of the current sense resistor for the LED string in Ω.
VFB is the reference voltage for the TPS40211 in V (0.260 V typ).
IOUT is the desired DC current in the LED string in A.
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ADDITIONAL REFERENCES
References
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These references may be found on the web at www.power.ti.com under Technical Documents. Many design
tools and links to additional references, may also be found at www.power.ti.com
1. Design and Application Guide for High Speed MOSFET Gate Drive Circuits, SEM 1400, 2001 Seminar
Series
2. Designing Stable Control Loops, SEM 1400, 2001 Seminar Series
3. Additional PowerPADTM information may be found in Applications Briefs SLMA002 and SLMA004
4. QFN/SON PCB Attachment, Texas Instruments Literature Number SLUA271, June 2002
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DESIGN EXAMPLE 1
12-V to 24-V Non-Synchronous Boost Regulator
The following example illustrates the design process and component selection for a 12-V to 24-V
non-synchronous boost regulator using the TPS40210 controller.
+
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+
Figure 31. TPS40210 Design Example – 8-V to 24-V at 2-A
Table 2. TPS40210 Design Example Specifications
PARAMETER
CONDITIONS
MIN NOM MAX
UNIT
INPUT CHARACTERISTICS
VIN
Input voltage
IIN
Input current
8
12
No load input current
VIN(UVLO)
Input undervoltage lockout
14
4.4
0.05
4.5
V
A
V
OUTPUT CHARACTERISTICS
VOUT
Output voltage
23.5
24.0
Line regulation
24.5
Load regulation
1%
VOUT(ripple)
Output voltage ripple
500
IOUT
Output current
IOCP
Output overcurrent inception point
ΔI
Load step
8 V ≤ VIN ≤ 14 V
0.2
V
1%
1
2
3.5
mVPP
A
Transient response
Load slew rate
Overshoot threshold voltage
Settling time
1
A
1
A/ms
500
mV
5
ms
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Table 2. TPS40210 Design Example Specifications (continued)
PARAMETER
CONDITIONS
MIN NOM MAX
UNIT
600
kHz
SYSTEM CHARACTERISTICS
fSW
Switching frequency
hPK
Peak efficiency
VIN = 12 V, 0.2 A ≤ IOUT ≤ 2 A
95%
h
Full load efficiency
VIN = 12 V, IOUT = 2 A
94%
TOP
Operating temperature range
10 V ≤ VIN ≤ 14 V, 0.2 A ≤ IOUT ≤ 2 A
25
°C
MECHANICAL DIMENSIONS
Width
L
Length
1.5
1.5
h
Height
0.5
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W
in
Step-By-Step Design Procedure
Duty Cycle Estimation
The duty cycle of the main switching MOSFET is estimated using Equation 32 and Equation 33.
DMIN »
DMAX »
VOUT - VIN(max) + VFD
VOUT + VFD
=
24 V - 14 V + 0.5 V
= 42.8%
24 V + 0.5 V
(32)
VOUT - VIN(m in) + VFD
24 V - 8 V + 0.5 V
=
= 67.3%
VOUT + VFD
24 V + 0.5 V
(33)
Using and estimated forward drop of 0.5 V for a Schottky rectifier diode, the approximate duty cycle is 42.8%
(minimum) to 67.3% (maximum).
Inductor Selection
The peak-to-peak ripple is limited to 30% of the maximum output current.
ILrip(m ax) = 0.3 ´
IOUT(m ax)
1 - DMIN
= 0.3 ´
2
= 1.05 A
1 - 0.428
(34)
The minimum inductor size can be estimated using Equation 35.
VIN(max)
1
14 V
1
LMIN »
´ DMIN ´
=
´ 0.428 ´
= 9.5 mH
ILrip(max)
fSW 1.05 A
600kHz
(35)
The next higher standard inductor value of 10 mH is selected. The ripple current is estimated by Equation 36.
IRIPPLE »
VIN
1
12 V
1
´D´
=
´ 0.50 ´
= 1.02 A
L
10 m H
600 kHz
fSW
(36)
V
1
8V
1
IRIPPLE(Vinmin) » IN ´ D ´
=
´ 0.673 ´
= 0.89 A
fSW 10 mH
L
600kHz
(37)
The worst-case peak-to-peak ripple current occurs at 50% duty cycle and is estimated as 1.02 A. Worst-case
RMS current through the inductor is approximated by Equation 38.
ILrms =
(I ( ) ) + (
2
L avg
1 I
12 RIPPLE
)
2
æ IOUT(max)
» ç
ç 1- D
MAX
è
2
ö
÷÷ +
ø
(112IRIPPLE(VINmin) )
2
2
2
æ
ö
= ç
÷ +
è 1 - 0.673 ø
((112)´ 0.817A )
2
= 6.13 Arms
(38)
The worst case RMS inductor current is 6.13 Arms. The peak inductor current is estimated by Equation 39.
28
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ILpeak »
IOUT(max)
1 - DMAX
+ (12 )IRIPPLE(Vinmin) =
2
+ (12 )0.718 = 6.57 A
1 - 0.673
(39)
A 10-mH inductor with a minimum RMS current rating of 6.13 A and minimum saturation current rating of 6.57 A
must be selected. A TDK RLF12560T-100M-7R5 7.5-A 10-mH inductor is selected.
This inductor power dissipation is estimated by Equation 40.
2
PL » (ILrms ) ´ DCR
(40)
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The TDK RLF12560T-100M-7R5 12.4-mΩ DCR dissipates 466 mW of power.
Rectifier Diode Selection
A low-forward voltage drop Schottky diode is used as a rectifier diode to reduce its power dissipation and
improve efficiency. Using 80% derating, on VOUT for ringing on the switch node, the rectifier diode minimum
reverse break-down voltage is given by Equation 41.
V
V(BR)R(min) ³ OUT = 1.25 ´ VOUT = 1.25 ´ 24 V = 30 V
0.8
(41)
The diode must have reverse breakdown voltage greater than 30 V. The rectifier diode peak and average
currents are estimated by Equation 42 and Equation 43.
ID (avg ) » IOUT (m ax ) = 2 A
ID(peak ) = IL(peak ) = 6.57 A
(42)
(43)
For this design, 2-A average and 6.57-A peak is
The power dissipation in the diode is estimated by Equation 44.
PD(max) » VF ´ IOUT(max) = 0.5 V ´ 2 A = 1W
(44)
For this design, the maximum power dissipation is estimated as 1 W. Reviewing 30-V and 40-V Schottky diodes,
the MBRS340T3 40-V 3-A diode in an SMC package is selected. This diode has a forward voltage drop of 0.48 V
at 6 A, so the conduction power dissipation is approximately 960 mW, less than half its rated power dissipation.
Output Capacitor Selection
Output capacitors must be selected to meet the required output ripple and transient specifications.
COUT = 8
ESR =
IOUT ´ D
æ 2 A ´ 0.673 ö
1
1
´
= 8ç
= 35 mF
÷´
VOUT(ripple) fSW
è 500mV ø 600kHz
VOUT(ripple )
7
7
500mV
´
= ´
= 95mW
8 IL(peak ) - IOUT 8 6.57 A - 2 A
(45)
(46)
A Panasonic EEEFC1V330P 35-V 33-mF, 120-mΩ bulk capacitor and 6.8-mF ceramic capacitor is selected to
provide the required capacitance and ESR at the switching frequency. The combined capacitances of 39.8 mF
and 60 mΩ are used in compensation calculations.
Input Capacitor Selection
Since a boost converter has continuous input current, the input capacitor senses only the inductor ripple current.
The input capacitor value can be calculated by Equation 47 and Equation 48 .
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IL(ripple )
4 ´ VIN(ripple ) ´ fSW
ESR <
VIN(ripple )
2 ´ IL(ripple )
=
=
1.02 A
= 7.0 mF
4 ´ 60mV ´ 600kHz
(47)
60mV
= 30mW
2 ´ 1.02 A
(48)
For this design, to meet a maximum input ripple of 60 mV, a minimum 7.0-mF input capacitor with ESR less than
30 mΩ is needed. A 10-mF X7R ceramic capacitor is selected.
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Current Sense and Current Limit
The maximum allowable current sense resistor value is limited by both the current limit and sub-harmonic
stability. These two limitations are given by Equation 49 and Equation 50.
RISNS <
RISNS <
VOCP(min)
(
1.1´ IL(peak ) + IDrive
=
)
110mV
= 14.2mW
1.1´ 6.57 A + 0.50 A
VDDMAX ´ L ´ fSW
14 V ´ 10 mH ´ 600kHz
=
= 133mW
60 ´ (VOUT + Vfd - VIN ) 60 ´ (24 V + 0.48 V - 14 V)
(49)
(50)
The current limit requires a resistor less than 14.2 mΩ, and stability requires a sense resistor less than 133 mΩ.
A 10-mΩ resistor is selected. Approximately 2-mΩ of routing resistance is added in compensation calculations.
Current Sense Filter
To remove switching noise from the current sense, an R-C filter is placed between the current sense resistor and
the ISNS pin. A resistor with a value between 1 kΩ and 5 kΩ is selected, and a capacitor value is calculated by
Equation 51.
CIFLT =
0.1´ DMIN
0.1´ 0.428
=
= 71pF
fSW ´ RIFLT 600kHz ´ 1kW
(51)
For a 1-kΩ filter resistor, 71 pF is calculated and a 100-pF capacitor is selected.
Switching MOSFET Selection
The TPS40210 drives a ground referenced N-channel FET. The RDS(on) and gate charge are estimated based on
the desired efficiency target.
æ1 ö
æ1 ö
æ 1
ö
- 1÷ = 2.526 W
PDISS(total) » POUT ´ ç - 1÷ = VOUT ´ IOUT ´ ç - 1÷ = 24 V ´ 2 A ´ ç
0.95
h
h
è
ø
è
ø
è
ø
(52)
For a target of 95% efficiency with a 24-V input voltage at 2 A, maximum power dissipation is limited to 2.526 W.
The main power dissipating devices are the MOSFET, inductor, diode, current sense resistor and the integrated
circuit, the TPS40210.
PFET < PDISS(total) - PL - PD - PRisns - VIN(max) ´ IVDD
(53)
This leaves 740 mW of power dissipation for the MOSFET. This can likely cause an SO-8 MOSFET to get too
hot, so power dissipation is limited to 500 mW. Allowing half for conduction and half for switching losses, we can
determine a target RDS(on) and QGS for the MOSFET by Equation 54 and Equation 55.
QGS <
3 ´ PFET ´ IDRIVE
3 ´ 0.50 W ´ 0.50 A
=
= 13.0nC
2 ´ VOUT ´ IOUT ´ fSW 2 ´ 24 V ´ 2 A ´ 600kHz
(54)
A target MOSFET gate-to-source charge of less than 13.0 nC is calculated to limit the switching losses to less
than 250 mW.
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RDS(on ) <
PFET
=
2
2 ´ (IRMS ) ´ D
0.50 W
2 ´ 6.132 ´ 0.674
= 9.8mW
(55)
A target MOSFET RDS(on) of 9.8 mΩ is calculated to limit the conduction losses to less than 250 mW. Reviewing
30-V and 40-V MOSFETs, an Si4386DY 9-mΩ MOSFET is selected. A gate resistor was added per Equation 30.
The maximum gate charge at Vgs = 8 V for the Si4386DY is 33.2 nC, this implies RG = 3.3 Ω.
Feedback Divider Resistors
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The primary feedback divider resistor (RFB) from VOUT to FB should be selected between 10-kΩ and 100-kΩ to
maintain a balance between power dissipation and noise sensitivity. For a 24-V output a high feedback
resistance is desirable to limit power dissipation so RFB = 51.1 kΩ is selected.
RBIAS =
VFB ´ RFB
0.700 V ´ 51.1kW
=
= 1.53kW
VOUT - VFB
24 V - 0.700 V
(56)
RBIAS = 1.50 kΩ is selected.
Error Amplifier Compensation
While current mode control typically requires only Type II compensation, it is desirable to layout for Type III
compensation to increase flexibility during design and development.
Current mode control boost converters have higher gain with higher output impedance, so it is necessary to
calculate the control loop gain at the maximum output impedance, estimated by Equation 57.
ROUT(max ) =
VOUT
IOUT(min )
=
24 V
= 240 W
0.1A
(57)
The transconductance of the TPS40210 current mode control can be estimated by Equation 58.
0.13 ´ L ´
gM =
fSW
ROUT
0.13 ´ 10 mH ´
=
2
(RISNS ) ´ (120 ´ RISNS + L ´ fSW )
600kHz
240 W
= 19.1 A
2
(12mW ) ´ (120 ´ 12mW + 10 mH ´ 600kHz )
V
(58)
The maximum output impedance ZOUT, can be estimated by Equation 59.
(1+ (2p ´ f ´ R
ESR
ZOUT (f ) = ROUT ´
(
2
)
) )´ (2p ´ f ´ C
2
´ COUT )
1 + (ROUT ) + 2 ´ ROUT ´ RESR + (RESR
2
OUT
)2
(59)
(1+ (2p ´ 20kHz ´ 60mW ´ 39.8 mF) )
1 + ((240 W ) + 2 ´ 240 W ´ 60mW + (60mW ) )´ (2p ´ 20kHz ´ 39.8 mF )
2
ZOUT (fCO ) = 240 W ´
2
2
2
= 0.146 W
(60)
The modulator gain at the desired cross-over can be estimated by Equation 61.
K CO = gM ´ ZOUT (fCO ) = 19.1A
V
´ 0.146 W = 2.80
(61)
The feedback compensation network needs to be designed to provide an inverse gain at the cross-over
frequency for unit loop gain. This sets the compensation mid-band gain at a value calculated in Equation 62.
K COMP =
1
K CO
=
1
= 0.356
2.80
(62)
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To set the mid-band gain of the error amplifier to KCOMP use Equation 63.
R4 = R7 ´ K COMP =
R7
51.1kW
=
= 18.2kW
K CO
2.80
(63)
R4 = 18.7 kΩ selected.
Place the zero at 10th the desired cross-over frequency.
C2 =
10
10
=
= 2837pF
2p ´ fL ´ R4 2p ´ 30kHz ´ 18.7kW
(64)
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C2 = 2200 pF selected.
Place a high-frequency pole at about five times the desired cross-over frequency and less than one-half the unity
gain bandwidth of the error amplifier:
C4 »
C4 >
1
1
=
= 56.74pF
10p ´ fL ´ R4 10p ´ 30kHz ´ 18.7kW
1
1
=
= 11.35pF
p ´ GBW ´ R4 p ´ 1.5MHz ´ 18.7kW
(65)
(66)
C4 = 47 pF selected.
R-C Oscillator
The R-C oscillator calculation as shown in Equation 5 substitutes 100 for CT and 600 for fSW. For a 600-kHz
switching frequency, a 100-pF capacitor is selected and a 262-kΩ resistor is calculated (261 kΩ selected).
Soft-Start Capacitor
Because VDD > 8 V, the soft-start capacitor is selected by using Equation 67 to calculate the value.
CSS = 20 ´ TSS ´ 10-6
(67)
For TSS = 12 ms, CSS = 240 nF, a 220-nF capacitor selected.
Regulator Bypass
A regulator bypass capacitor of 1.0-mF is selected per the recommendation.
32
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SLVSAD8 – JUNE 2010
TEST DATA
GAIN AND PHASE
vs
FREQUENCY
FET Vds and Vgs VOLTAGES
vs
TIME
80
180
60
VIN = 8 V
VOUT = 24 V
IOUT = 2 A
135
Phase
40
90
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45
0
Phase – °
20
Gain – dB
GDRV
(5 V/ div)
0
Gain
-20
-45
-40
FET Vds
(20 V/ div)
-90
-60
-135
-80
100
-180
1M
1000
10 k
100 k
fSW – Frequency – Hz
T – Time – 400 ns
Figure 32.
Figure 33.
EFFICIENCY
vs
LOAD CURRENT
6
VIN (V)
14
12
8
98
96
94
92
5
VIN = 12 V
90
88
VIN = 8 V
86
84
VIN (V)
14
12
8
VIN = 14V
PLOSS – Power Loss – W
100
h – Efficiency – %
POWER LOSS
vs
LOAD CURRENT
VIN = 8 V
4
VIN = 12 V
3
2
VIN = 14 V
1
82
80
0
0
0.5
1.0
1.5
2.0
ILOAD – Load Current – A
2.5
0
Figure 34.
0.5
1.0
1.5
2.0
ILOAD – Load Current – A
2.5
Figure 35.
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TPS40210-HT
SLVSAD8 – JUNE 2010
www.ti.com
OUTPUT VOLTAGE
vs
LOAD CURRENT
24.820
VIN (V)
14
12
8
24.724
VIN = 8 V
24.676
24.628
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VOUT – Output Voltage – V
24.772
24.580
VIN = 14 V
24.532
VIN = 12 V
24.484
24.436
24.388
24.340
0
0.5
1.0
1.5
2.0
ILOAD – Load Current – A
2.5
Figure 36.
List of Materials
Table 3. List of Materials, Design Example 1
REFERENCE
DESIGNATOR
SIZE
PART
NUMBER
MANUFACTURER
0.406 x 0.457
EEEFC1V101P
Panasonic
2200 pF, ceramic capacitor, 25 V, X7R, 20%
0603
Std
Std
100 pF, ceramic capacitor, 16 V, C0G, 10%
0603
Std
Std
47 pF, ceramic capacitor, 16 V, X7R, 20%
0603
Std
Std
0.22 mF, ceramic capacitor, 16 V, X7R, 20%
0603
Std
Std
1.0 mF, ceramic capacitor, 16 V, X5R, 20%
0603
Std
Std
10 mF, ceramic capacitor, 25 V, X7R, 20%
0805
C3225X7R1E106M
TDK
0.1 mF, ceramic capacitor, 50 V, X7R, 20%
0603
Std
Std
100 pF, ceramic capacitor, 16 V, X7R, 20%
0603
Std
Std
Schottky diode, 3 A, 40 V
SMC
MBRS340T3
On Semi
0.325 x 0.318 inch
RLF12560T-100M-7R5
TDK
MOSFET, N-channel, 40 V, 14 A, 9 mΩ
SO-8
Si4840DY
Vishay
10 kΩ, chip resistor, 1/16 W, 5%
0603
Std
Std
18.7 kΩ, chip resistor, 1/16 W, 1%
0603
Std
Std
R5
1.5 kΩ, chip resistor, 1/16 W, 1%
0603
Std
Std
R6
261 kΩ, chip resistor, 1/16 W, 1%
0603
Std
Std
R7
51.1 kΩ, chip resistor, 1/16 W, 1%
0603
Std
Std
R9
3.3 Ω, chip resistor, 1/16 W, 5%
0603
Std
Std
R10
1.0 kΩ, chip resistor, 1/16 W, 5%
0603
Std
Std
R11
10 mΩ, chip resistor, 1/2 W, 2%
1812
Std
Std
U1
IC, 4.5 V-52 V I/P, current mode boost controller
DGQ10
TPS40210QDGQRQ1
TI
C1
C2
C3
C4
C5
C7
C8
C9
C10
D1
L1
Q1
R3
R4
34
DESCRIPTION
100 mF, aluminum capacitor, SM, ± 20%, 35 V
10 mH, inductor, SMT, 7.5 A, 12.4 mΩ
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SLVSAD8 – JUNE 2010
DESIGN EXAMPLE 2
12-V Input, 700-mA LED Driver, Up to 35-V LED String
Application Schematic
L1
VIN
D1
B2100
R2
GDRV
C3
C4
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C21
C1
C2
R1
R11
ISNS
VIN
R3
D2
C8
1
U1
TPS40210
TPS40211
VIN
RC
DD 10
C10
C9
Loop
Response
Injection
R23
LEDC
C6
R13
R4
DIS/EN
C11
BP
9
DIS/EN
GDRV
8
4
COMP
ISNS
7
5
FB
GND
6
2
SS
3
C6
GDRV
C13
LEDC
ISNS
R24
R6
D3
R15
C14
PWM Dimming
UDG-08015
Figure 37. 12-V Input, 700-mA LED Driver, Up to 35-V LED String
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TPS40210-HT
SLVSAD8 – JUNE 2010
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List of Materials
Table 4. List of Materials, Design Example 2
REFERENCE
DESIGNATOR
TYPE
DESCRIPTION
SIZE
10 mF, 25 V
1206
C3, C4
2.2 mF, 100 V
1210
C5
1 nF, NPO
0603
C6
100 pF, NPO
0603
C8
100 pF
0603
0.1 mF
0603
0.1 mF, 25 V
0805
1 mF, 25 V
1206
220 pF
0603
10 nF, X7R
0603
C9
C10
C11
C13
C14
C21
D1
D2
D3
L1
Q1
Q3
R1
R2
R3
R4
R6
R11
R13
R15
R24
R23
U1
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C1, C2
Capacitor
330 mF, 25 V electrolytic
B2100, Schottky, 100 V, 2 A
Diode
BZT52C43
MMBD7000
Inductor
MOSFET
Resistor
Wurth 7447709100, 10 mH, 6 A
Si7850DP, 60 V, 31 mΩ
2N7002, 60 V, 0.1 A
SOT-23
12 × 12 × 10 mm
SO-8
SOT-23
15 mΩ
2512
3.01 Ω
0805
402 kΩ
0603
14.3 kΩ
0603
0.36 Ω
2512
1 kΩ
0603
30.1 kΩ
0603
49.9 kΩ
0603
10 kΩ
0603
10 Ω
Integrated circuit
SMB
SOD-123
TPS40211
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0603
DGQ-10
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PACKAGE OPTION ADDENDUM
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PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
Samples
(Requires Login)
TPS40210SHKK
ACTIVE
CFP
HKK
10
150
TBD
AU
N / A for Pkg Type
Purchase Samples
TPS40210SKGD1
ACTIVE
XCEPT
KGD
0
400
TBD
Call TI
N / A for Pkg Type
Request Free Samples
(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.
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.
OTHER QUALIFIED VERSIONS OF TPS40210-HT :
• Catalog: TPS40210
• Automotive: TPS40210-Q1
NOTE: Qualified Version Definitions:
Addendum-Page 1
PACKAGE OPTION ADDENDUM
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• Catalog - TI's standard catalog product
• Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects
Addendum-Page 2
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