TPS79418 [TI]
ULTRALOW-NOISE, HIGH PSRR, FAST RF 250-mA LOW-DROPOUT LINEAR REGULATORS; 超低噪声，高PSRR ，快速射频250 mA低压降线性稳压器
| 型号： | TPS79418 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | ULTRALOW-NOISE, HIGH PSRR, FAST RF 250-mA LOW-DROPOUT LINEAR REGULATORS |
| 文件： | 总15页 (文件大小：478K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
ULTRALOW-NOISE, HIGH PSRR, FAST RF 250-mA LOW-DROPOUT LINEAR
REGULATORS
FEATURES
DESCRIPTION
•
250-mA Low-Dropout Regulator With Enable
The TPS794xx family of low-dropout (LDO) linear
voltage regulators features high power-supply rejec-
tion ratio (PSRR), ultralow-noise, fast start-up, and
excellent line and load transient responses in small
outline, MSOP-8 PowerPAD™ and SOT223-6 pack-
ages. Each device in the family is stable with a small
2.2-µF ceramic capacitor on the output. The family
uses an advanced, proprietary BiCMOS fabrication
process to yield extremely low dropout voltages (e.g.,
155 mV at 250 mA). Each device achieves fast
start-up times (approximately 50 µs with a 0.001-µF
bypass capacitor) while consuming low quiescent
current (170 µA typical). Moreover, when the device
is placed in standby mode, the supply current is
reduced to less than 1 µA. The TPS79428 exhibits
approximately 32 µVRMS of output voltage noise at
2.8 V output with a 0.1-µF bypass capacitor. Appli-
•
Available in 1.8 V, 2.5 V, 2.8 V, 3 V, 3.3 V, and
Adjustable (1.2 V to 5.5 V)
•
•
•
•
•
•
High PSRR (60 dB at 10 kHz)
Ultralow Noise (32 µVrms, TPS79428)
Fast Start-Up Time (50 µs)
Stable With a 2.2-µF Ceramic Capacitor
Excellent Load/Line Transient Response
Very Low Dropout Voltage (155 mV at Full
Load)
•
Available in MSOP-8 and SOT223-6 Packages
APPLICATIONS
•
•
•
•
•
RF: VCOs, Receivers, ADCs
Audio
Bluetooth™, Wireless LAN
Cellular and Cordless Telephones
Handheld Organizers, PDAs
cations with analog components
that
are
noise-sensitive, such as portable RF electronics,
benefit from the high PSRR and low noise features as
well as the fast response time.
DGN PACKAGE
MSOP PowerPAD
(TOP VIEW)
TPS79433
TPS79428
RIPPLE REJECTION
vs
OUTPUT SPECTRAL NOISE DENSITY
vs
OUT
NC
FB
IN
NC
EN
1
2
3
4
8
7
6
5
FREQUENCY
FREQUENCY
90
0.35
0.30
C
C
= 2.2 µF,
OUT
= 0.1 µF,
80
70
NR
GND
NR
= 3.8 V
I
= 10 mA
OUT
V
IN
NC − No internal connection
I
= 250 mA
OUT
0.25
0.20
60
50
40
30
20
10
0
I
= 250 mA
OUT
DCQ PACKAGE
SOT223-6
(TOP VIEW)
0.15
0.10
V
V
C
C
C
= 4.3 V,
1
IN
EN
IN
= 3.3 V,
= 1 µF,
= 10 µF,
OUT
2
IN
I
= 1 mA
OUT
6
0.05
0
3
4
GND
OUT
NR
OUT
GND
= 0.01 µF
NR
100
1000
10000
100000
10
100
1 k
10 k 100 k 1 M 10 M
5
Frequency (Hz)
Frequency (Hz)
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.
Bluetooth is a trademark of Bluetooth SIG, Inc.
PowerPAD is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
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 © 2001–2004, Texas Instruments Incorporated
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
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.
ORDERING INFORMATION
TRANSPORT MEDIA,
PRODUCT
VOLTAGE
PACKAGE
TJ
SYMBOL
PART NUMBER
QUANTITY
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
TPS79401DGNR
TPS79401DGNT
TPS79401DCQR
TPS79401DCQ
TPS79418DGNR
TPS79418DGNT
TPS79418DCQR
TPS79418DCQ
TPS79425DGNR
TPS79425DGNT
TPS79425DCQR
TPS79425DCQ
TPS79428DGNR
TPS79428DGNT
TPS79428DCQR
TPS79428DCQ
TPS79430DGNR
TPS79430DGNT
TPS79430DCQR
TPS79430DCQ
TPS79433DGNR
TPS79433DGNT
TPS79433DCQR
TPS79433DCQ
MSOP-8
AXL
TPS79401
Adjustable
SOT223-6
MSOP-8
PS79401
AXM
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
TPS79418
TPS79423
TPS79428
TPS79430
TPS79433
1.8 V
2.5 V
2.8 V
3 V
SOT223-6
MSOP-8
PS79418
AYB
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
SOT223-6
MSOP-8
PS79425
AYC
-40°C to 125°C
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
SOT223-6
MSOP-8
PS79428
AYD
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
SOT223-6
MSOP-8
PS79430
AYE
Tape and Reel, 2500
Tape and Reel, 250
Tape and Reel, 2500
Tube, 78
3.3 V
SOT223-6
PS79433
2
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
ABSOLUTE MAXIMUM RATINGS
over operating temperature range unless otherwise noted(1)
VALUE
-0.3 V to 6 V
VIN range
VEN range
-0.3 V to VIN + 0.3 V
-0.3 V to 6 V
VOUT range
Peak output current
ESD rating, HBM
Internally limited
2 kV
ESD rating, CDM
500 V
Continuous total power dissipation
Junction temperature range, TJ
Storage temperature range, Tstg
See Dissipation Ratings Table
-40°C to 150°C
-65°C to 150°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.
PACKAGE DISSIPATION RATINGS
AIR FLOW
(CFM)
T
A ≤ 25°C
TA = 70°C
TA = 85°C
PACKAGE
RθJC(°C/W)
RθJA(°C/W)
POWER RATING POWER RATING POWER RATING
0
8.47
8.21
8.20
55.09
49.97
48.10
2.27 W
2.50 W
2.60 W
1.45 W
1.60 W
1.66 W
1.18 W
1.30 W
1.35 W
DGN
150
250
6
5
4
3
2
1
0
Condition 1
CONDITIONS PACKAGE
PCB AREA
θJA
2
SOT223
SOT223
4in Top Side Only
53°C/W
1
2
Condition 2
2
0.5in Top Side Only
110°C/W
0
25
50
75
100
125
150
T
A
(°C)
Figure 1. SOT223 Power Dissipation
3
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
ELECTRICAL CHARACTERISTICS
Over recommended operating temperature range (TJ = -40°C to 125°C), VEN = VIN, VIN = VOUT(nom) + 1 V(1), IOUT = 1mA,
COUT = 10µF, CNR = 0.01 µF, unless otherwise noted. Typical values are at 25°C.
PARAMETER
Input voltage(1)
IOUT Continuous output current
VFB Internal reference
TEST CONDITIONS
MIN
2.7
TYP
MAX UNIT
VIN
5.5
250
V
mA
V
0
TPS79401
TPS79401
TJ = 25°C
1.220
VFB
-3.0
1.225
1.230
VOUT Output voltage range
Accuracy(1)
5.5 - VDO
+3.0
V
VOUT + 1 V ≤ VIN ≤ 5.5 V 0 mA ≤ IOUT ≤ 250 mA
VOUT + 1 V < VIN ≤ 5.5 V
%
Output voltage line regulation
0.05
0.12
%/V
mV
(1)
(∆VOUT%/∆VIN
)
Load regulation (∆VOUT%/∆IOUT
)
0 µA < IOUT < 250 mA
IOUT = 250 mA
10
155
155
145
925
170
0.07
TPS79428
TPS79430
TPS79433
210
210
200
Dropout voltage(2)
VIN = VOUT(nom) - 0.1 V
IOUT = 250 mA
mV
IOUT = 250 mA
Output current limit
Ground pin current
Shutdown current(3)
FB pin current
VOUT = 0 V
mA
µA
µA
µA
0 µA < IOUT < 250 mA
220
1
VEN = 0 V
VFB = 1.8 V
f = 100 Hz
f = 10 kHz
f = 100 kHz
2.7 V < VIN < 5.5 V
1
IOUT = 250 mA
IOUT = 250 mA
IOUT = 250 mA
CNR = 0.001 µF
CNR = 0.0047 µF
CNR = 0.01 µF
CNR = 0.1 µF
65
60
40
55
36
33
32
50
70
100
Power-supply ripple
rejection
TPS79428
dB
µVRMS
µs
BW = 100 Hz to 100
kHz, IOUT = 250 mA
Output noise voltage (TPS79428)
CNR = 0.001 µF
Time, start-up (TPS79428)
RL - 14 Ω, COUT = 1 µF CNR = 0.0047 µF
CNR = 0.01 µF
High-level enable input voltage
Low-level enable input voltage
EN pin current
2.7 V < VIN < 5.5 V
2.7 V < VIN < 5.5 V
VEN = 0
1.7
0
VIN
0.7
1
V
V
1
µA
V
UVLO threshold
VCC rising
2.25
2.65
UVLO hysteresis
100
mV
(1) Minimum VIN is 2.7 V or VOUT + VDO, whichever is greater.
(2) Dropout is not measured for the TPS79418 and TPS79425 since minimum VIN = 2.7 V.
(3) For adjustable versions, this applies only after VIN is applied; then VEN transitions high to low.
4
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
FUNCTIONAL BLOCK DIAGRAM—ADJUSTABLE VERSION
OUT
IN
Current
Sense
UVLO
SHUTDOWN
ILIM
R1
_
GND
EN
+
FB
UVLO
R2
Thermal
Shutdown
Quickstart
External to
the Device
Bandgap
Reference
1.225 V
250 kΩ
V
ref
(1)
V
IN
NR
(1) Not Available on DCQ (SOT223) options.
FUNCTIONAL BLOCK DIAGRAM—FIXED VERSION
OUT
IN
UVLO
Current
Sense
GND
EN
SHUTDOWN
ILIM
R1
R2
_
+
UVLO
Thermal
Shutdown
Quickstart
R = 40k
2
Bandgap
Reference
1.225 V
250 kΩ
V
ref
V
IN
NR
Terminal Functions
TERMINAL
DESCRIPTION
DGN
(MSOP)
DCQ
(SOT223)
NAME
NR
4
5
Connecting an external capacitor to this pin bypasses noise generated by the internal bandgap. This
improves power-supply rejection and reduces output noise.
EN
6
1
The EN terminal is an input which enables or shuts down the device. When EN goes to a logic high, the
device will be enabled. When the device goes to a logic low, the device is in shutdown mode.
FB
GND
IN
3
5, PAD
8
5
3
2
This terminal is the feedback input voltage for the adjustable device.
Regulator ground.
Unregulated input to the device.
No internal connection.
NC
2, 7
1
OUT
4
Output of the regulator.
5
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
TYPICAL CHARACTERISTICS
TPS79433 OUTPUT VOLTAGE
TPS79428 OUTPUT VOLTAGE
vs
JUNCTION TEMPERATURE
TPS79428 GROUND CURRENT
vs
JUNCTION TEMPERATURE
vs
OUTPUT CURRENT
3.290
3.285
3.280
3.275
3.270
3.265
3.260
3.255
3.250
190
185
2.800
V
C
= 3.8 V,
IN
I
= 1 mA
OUT
= 10 µF
OUT
2.795
2.790
180
175
170
I
= 1 mA
OUT
V
C
= 3.8 V
IN
= 10 µF
OUT
2.785
2.780
I
= 250 mA
OUT
165
160
155
150
2.775
I
= 200 mA
OUT
2.770
2.765
−40 −25 −10 5 20 35 50 65 80 95 110 125
(°C)
−40 −25 −10
5
20 35 50 65 80 95 110 125
(°C)
0
50
100
(mA)
200
250
T
J
I
T
J
OUT
Figure 2.
Figure 3.
Figure 4.
TPS79428 OUTPUT SPECTRAL
TPS79428 OUTPUT SPECTRAL
TPS79428 OUTPUT SPECTRAL
NOISE DENSITY
vs
NOISE DENSITY
vs
NOISE DENSITY
vs
FREQUENCY
FREQUENCY
FREQUENCY
0.35
0.30
0.25
0.20
1.8
1.6
1.4
1.2
0.35
0.30
C
I
= 10 µF,
= 250 mA
= 3.8 V
OUT
C
C
V
= 2.2 µF,
C
C
V
= 10 µF,
OUT
= 0.1 µF,
OUT
= 0.1 µF,
OUT
NR
= 3.8 V
NR
= 3.8 V
V
IN
IN
IN
C
= 0.001 µF
NR
0.25
0.20
C
= 0.0047 µF
= 0.01 µF
NR
1.0
0.8
0.6
0.4
I
= 250 mA
C
OUT
NR
I
= 1 mA
OUT
0.15
0.10
0.15
0.10
C
NR
= 0.1 µF
I
= 250 mA
I
= 1 mA
OUT
OUT
0.05
0
0.05
0
0.2
0
100
1000
10000
100000
100
1000
10000
100000
100
1000
10000
100000
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Figure 5.
Figure 6.
Figure 7.
TPS79428 ROOT MEAN SQUARED
OUTPUT NOISE
TPS79433 OUTPUT IMPEDANCE
TPS79428 DROPOUT VOLTAGE
vs
JUNCTION TEMPERATURE
vs
CNR
vs
FREQUENCY
10
60
50
40
250
200
V
= 3.8 V,
V
C
= 4.3 V,
IN
IN
I
C
= 250 mA,
OUT
C
OUT
= 10 µF
= 10 µF,
OUT
= 10 µF
OUT
I
= 250 mA
OUT
I
= 1 mA
OUT
1
150
100
50
30
20
I
= 250 mA
0.100
0.020
OUT
10
0
I
= 1 mA
OUT
0
10
100
1 k
10 k 100 k 1 M 10 M
−40 −25 −10
5
20 35 50 65 80 95 110 125
(°C)
0.001
0.0047
0.01
0.1
C
(µF)
T
J
Frequency (Hz)
NR
Figure 8.
Figure 9.
Figure 10.
6
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
TYPICAL CHARACTERISTICS (continued)
TPS79433 RIPPLE REJECTION
TPS79433 RIPPLE REJECTION
TPS79433 RIPPLE REJECTION
vs
vs
vs
FREQUENCY
FREQUENCY
FREQUENCY
90
90
90
I
= 10 mA
OUT
80
70
60
80
70
60
50
40
30
20
10
0
80
70
I
= 10 mA
I
I
= 10 mA
I
OUT
OUT
= 250 mA
= 250 mA
OUT
I
= 250 mA
OUT
OUT
60
50
40
30
20
10
0
50
40
30
20
10
0
V
V
C
C
C
= 4.3 V,
V
V
C
C
C
= 4.3 V,
= 3.3 V,
= 1 µF,
= 10 µF,
= 0.01 µF
IN
V
V
C
C
C
= 4.3 V,
IN
IN
= 3.3 V,
= 1 µF,
OUT
= 3.3 V,
= 1 µF,
= 2.2 µF,
OUT
OUT
IN
IN
IN
= 2.2 µF,
= 0.01 µF
OUT
OUT
OUT
NR
= 0.1 µF
NR
NR
10
100
1 k
10 k 100 k 1 M 10 M
10
100
1 k
10 k 100 k 1 M 10 M
10
100
1 k
10 k 100 k 1 M 10 M
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Figure 11.
Figure 12.
Figure 13.
TPS79433 OUTPUT VOLTAGE,
ENABLE VOLTAGE
vs
TPS79433
LINE TRANSIENT RESPONSE
TPS79433
LOAD TRANSIENT RESPONSE
TIME (START-UP)
6.0
5.5
I
C
= 250 mA,C
= 10 µF,
= 0.1 µF, dv/dt = 1 V/µs
V_Enable
OUT
OUT
250
0
4
2
0
NR
V
V
= 4.3 V,
IN
OUT
= 250 mA,
= 3.3 V,
5.0
4.5
10
0
I
OUT
C
= 2.2 µF
OUT
50
0
3
2
1
0
C
NR
= 0.0047 µF
−10
−20
−30
−50
di
dt
0.02A
ms
C
= 0.001 µF
NR
V
C
= 4.3 V,
IN
+
= 10 µF
OUT
0
30
60
90
120 150 180 210
0
100
200
300
400
500
0
80 160 240 320 400 480 560 640 720 800
Time (µs)
Time (µs)
Time (µs)
Figure 14.
Figure 15.
Figure 16.
TPS79433 DROPOUT VOLTAGE
TPS79401 DROPOUT VOLTAGE
TPS79425
POWER-UP/POWER-DOWN
vs
vs
OUTPUT CURRENT
INPUT VOLTAGE
250
200
150
100
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
200
150
V
R
= 2.5 V,
T
= 125°C
OUT
= 10 Ω
A
T = 125°C
A
L
T
A
= 25°C
V
IN
T
A
= 25°C
V
OUT
100
50
0
T
A
= −40°C
T
A
= −40°C
C
OUT
= 10 µF,
50
0
C
NR
= 0.01 µF,
0
I
= 250 mA
OUT
−0.5
0
25 50 75 100 125 150 175 200 225 250
(mA)
2.5
3.0
3.5
4.5
0
1.4
2.8
4.2 5.6
7.0 8.4 9.8
4.0
5.0
I
V (V)
IN
t (ms)
OUT
Figure 17.
Figure 18.
Figure 19.
7
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
TYPICAL CHARACTERISTICS (continued)
TPS79428 TYPICAL REGIONS OF
STABILITY EQUIVALENT SERIES
RESISTANCE (ESR)
vs
TPS79428 TYPICAL REGIONS OF
STABILITY EQUIVALENT SERIES
RESISTANCE (ESR)
vs
OUTPUT CURRENT
OUTPUT CURRENT
100
100
C
T
A
= 2.2 µF
OUT
= −40 to 85°C
C
T
A
= 10 µF
OUT
= −40 to 85°C
10
Region of Instability
10
Region of Instability
1
0.1
1
0.1
Region of Stability
Region of Stability
0.01
0.01
0
25 50 75 100 125 150 175 200 225 250
(mA)
1
10 20 40 60 80 120 200 250
(mA)
I
I
OUT
OUT
Figure 20.
Figure 21.
8
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
APPLICATION INFORMATION
The TPS794xx family of low-dropout (LDO) regulators has been optimized for use in noise-sensitive equipment.
The device features extremely low dropout voltages, high PSRR, ultralow output noise, low quiescent current,
and enable input to reduce supply currents to less than 1 µA when the regulator is turned off.
A typical application circuit is shown in Figure 22.
VIN
VOUT
IN
OUT
NR
TPS794xx
EN
GND
µ
µ
F
0.1
F
2.2
µ
0.01
F
Figure 22. Typical Application Circuit
External Capacitor Requirements
A 0.1-µF or larger ceramic input bypass capacitor, connected between IN and GND and located close to the
TPS794xx, is required for stability. It improves transient response, noise rejection, and ripple rejection. A
higher-value input capacitor may be necessary if large, fast-rise-time load transients are anticipated or the device
is located several inches from the power source.
Like most low dropout regulators, the TPS794xx requires an output capacitor connected between OUT and GND
to stabilize the internal control loop. The minimum recommended capacitance is 2.2 µF. Any 2.2 µF or larger
ceramic capacitor is suitable.
The internal voltage reference is a key source of noise in an LDO regulator. The TPS794xx has an NR pin which
is connected to the voltage reference through a 250-kΩ internal resistor. The 250-kΩ internal resistor, in
conjunction with an external bypass capacitor connected to the NR pin, creates a low-pass filter to reduce the
voltage reference noise and, therefore, the noise at the regulator output. In order for the regulator to operate
properly, the current flow out of the NR pin must be at a minimum, because any leakage current creates an IR
drop across the internal resistor thus creating an output error. Therefore, the NR capacitor must have minimal
leakage current. The bypass capacitor should be no more than 0.1 µF to ensure that it is fully charged during the
quickstart time provided by the internal switch shown in the functional block diagram.
For example, the TPS79428 exhibits only 32 µVRMS of output voltage noise using a 0.1-µF ceramic NR capacitor
and a 2.2-µF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance
increases due to the RC time constant at the NR pin that is created by the internal 250-kΩ resistor and external
capacitor.
9
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
Board Layout Recommendation to Improve PSRR and Noise Performance
To improve ac measurements like PSRR, output noise, and transient response, it is recommended that the board
be designed with separate ground planes for VIN and VOUT, with each ground plane connected only at the ground
pin of the device. In addition, the ground connection for the bypass capacitor should connect directly to the
ground pin of the device.
THERMAL RESISTANCE
vs
PCB COPPER AREA
180
CIRCUIT BOARD COPPER AREA
Surface-Mount Package
1 oz. Copper
160
140
120
100
80
60
40
20
SOT223 Surface-Mount Package
0
0
1
2
3
4
5
PCB Copper Area − in
Figure 23. Thermal Resistance vs PCB Area for the SOT223-6.
Power and Dissipation and Junction Temperature
Specified regulator operation is assured to a junction temperature of 125°C; the maximum junction temperature
should be restricted to 125°C under normal operating conditions. This restriction limits the power dissipation the
regulator can handle in any given application. To ensure the junction temperature is within acceptable limits,
calculate the maximum allowable dissipation, PD(max), and the actual dissipation, PD, which must be less than or
equal to PD(max)
.
The maximum-power-dissipation limit is determined using the following equation:
T max
J
T
A
P
+
D(max)
R
θJA
(1)
where:
•
•
TJmax is the maximum allowable junction temperature.
RθJA is the thermal resistence juntion-to-ambient for the package. See the power dissipation table and
Figure 1
•
TA is the ambient temperature.
The regulator dissipation is calculated using:
+ ǒVIN
Ǔ
P
* V
I
D
OUT
OUT
(2)
Power dissipation resulting from quiescent current is negligible. Excessive power dissipation triggers the thermal
protection circuit.
Regulator Mounting
The tab of the SOT223-6 package is electrically connected to ground. For best thermal performance, the tab of
the surface-mount version should be soldered directly to a circuit-board copper area. Increasing the copper area
improves heat dissipation. Solder pad footprint recommendations for the devices are presented in an application
bulletin Solder Pad Recommendations for Surface-Mount Devices, literature number AB-132, available from the
TI web site (www.ti.com).
10
TPS79401, TPS79418
TPS79425, TPS79428
TPS79430, TPS79433
www.ti.com
SLVS349D–NOVEMBER 2001–REVISED OCTOBER 2004
Programming the TPS79401 Adjustable LDO Regulator
The output voltage of the TPS79401 adjustable regulator is programmed using an external resistor divider as
shown in Figure 24. The output voltage is calculated using:
R1
R2
ǒ1 ) Ǔ
V
+ V
OUT
REF
(3)
where:
•
VREF = 1.2246 V typ (the internal reference voltage).
Resistors R1 and R2 should be chosen for approximately 40-µA divider current. Lower value resistors can be
used for improved noise performance, but the device wastes more power. Higher values should be avoided as
leakage current at FB increases the output voltage error. The recommended design procedure is to choose
R2 = 30.1 kΩ to set the divider current at 40 µA, C1 = 15 pF for stability, and then calculate R1 using:
V
OUT
R1 +
* 1 R2
ǒ Ǔ
V
REF
(4)
In order to improve the stability of the adjustable version, it is suggested that a small compensation capacitor be
placed between OUT and FB. For voltages < 1.8 V, the value of this capacitor should be 100 pF. For voltages
> 1.8 V, the approximate value of this capacitor can be calculated as:
–7
(3 x 10 ) x (R1 ) R2)
C1 +
(R1 x R2)
(5)
The suggested value of this capacitor for several resistor ratios is shown in the table below. If this capacitor is
not used (such as in a unity-gain configuration) or if an output voltage < 1.8 V is chosen, then the minimum
recommended output capacitor is 4.7 µF instead of 2.2 µF.
OUTPUT VOLTAGE
PROGRAMMING GUIDE
OUTPUT
VOLTAGE
VIN
VOUT
IN
OUT
FB
R1
R2
C1
TPS794xx
R1
R2
µ
C1
1
F
EN
NR
31.6 kΩ 30.1 kΩ 22 pF
49.9 kΩ 30.1 kΩ 15 pF
59 kΩ 30.1 kΩ 15 pF
2.5 V
3.3 V
3.6 V
µ
2.2
F
GND
µ
0.01
F
†
Not Available on the DCQ package.
Figure 24. TPS79401 Adjustable LDO Regulator Programming
Regulator Protection
The TPS794xx PMOS-pass transistor has a built-in back diode that conducts reverse current when the input
voltage drops below the output voltage (e.g., during power-down). Current is conducted from the output to the
input and is not internally limited. If extended reverse voltage operation is anticipated, external limiting might be
appropriate.
The TPS794xx features internal current limiting and thermal protection. During normal operation, the TPS794xx
limits output current to approximately 925 mA. When current limiting engages, the output voltage scales back
linearly until the overcurrent condition ends. While current limiting is designed to prevent gross device failure,
care should be taken not to exceed the power dissipation ratings of the package or the absolute maximum
voltage rating of the device. If the temperature of the device exceeds approximately 165°C, thermal-protection
circuitry shuts it down. Once the device has cooled down to below approximately 140°C, regulator operation
resumes.
11
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相关型号：
TPS79425DCQG4
Ultralow-Noise, High-PSRR, Fast, 250-mA Low-Dropout Linear Regulators 6-SOT-223 -40 to 85
TI
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