NCT3705U-25 [NUVOTON]
500mA Linear Regulator;
| 型号： | NCT3705U-25 |
| 厂家： | 
NUVOTON |
| 描述： | 500mA Linear Regulator |
| 文件： | 总23页 (文件大小：376K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Nuvoton
500mA Linear Regulator
NCT3705U Series
NCT3705U
-Table of Content-
1. GENERAL DESCRIPTION .............................................................................................................. 1
2. FEATURES ...................................................................................................................................... 1
3. BLOCK DIAGRAM ........................................................................................................................... 2
4. PIN CONFIGURATION AND TYPICAL APPLICATION CIRCUIT .................................................. 4
5. PIN DESCRIPTION.......................................................................................................................... 5
6. FUNCTIONAL DESCRIPTION ........................................................................................................ 6
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
OUTPUT VOLTAGE AND DROPOUT VOLTAGE ................................................................... 6
NOISE....................................................................................................................................... 6
PSRR ........................................................................................................................................ 6
LOAD REGULATION CONSIDERATION ................................................................................ 7
CURRENT LIMIT PROTECTION ............................................................................................. 8
VIN & VOUT CAPACITOR SELECTION ...................................................................................... 8
OVER TEMPERATURE PROTECTION................................................................................... 8
LAYOUT NOTE......................................................................................................................... 9
THERMAL CONSIDERATION.................................................................................................. 9
7. ELECTRICAL CHARACTERISTIC ................................................................................................ 10
7.1
7.2
7.3
7.4
ABSOLUTE MAXIMUM RATINGS ......................................................................................... 10
THERMAL INFORMATION .................................................................................................... 11
RECOMMENDED OPERATING CONDITIONS..................................................................... 11
ELECTRICAL CHARACTERISTICS....................................................................................... 11
8. TYPICAL OPERATING WAVEFORMS ......................................................................................... 13
9. PACKAGE DIMENSION ................................................................................................................ 17
ꢀ
TAPING SPECIFICATION.......................................................................................................... 17
ORDERING INFORMATION...................................................................................................... 18
TOP MARKING SPECIFICATION.............................................................................................. 18
REVISION HISTORY ................................................................................................................. 19
10.
11.
12.
Publication Date: Dec., 2008
-I-
Revision A1
NCT3705U
1. GENERAL DESCRIPTION
The NCT3705U is a low supply current and low dropout linear regulator which provides
500mA power for battery-powered application such as notebook computers, cellular phones,
and handheld devices. An over current protection and an over-temperature protection circuit
were built-in the chip to prevent current and thermal overload. Featured low noise, high PSRR
and low dropout make it ideal for audio codec and handheld devices. It comes in a space
saving SOT-23-5 package and suitable for handheld applications.
The NCT3705U has two versions for different operation circuits. In fixed mode, the SET pin is
connected to ground. The output voltage is a preset value. There is no external component
required. When an output other than the preset value is needed, two external resistors should
be used as an output voltage divider and operates in adjustable mode. The output voltage can
be adjusted by the resistor ratio and regulates from 1.25V to 5.0V.
2. FEATURES
2.1. General
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Guaranteed 500mA Output Current
Low Ground Current 90uA @ No Load (Typical)
70dB PSRR @ 10mA, 100Hz
Low Dropout Voltage 145mV @ 150mA (VOUT = 5V)
Low Output Noise 28u Vrms @ 1mA with Bypass Capacitor
Excellent Load Regulation & Line Regulation
Short Circuit Protection & Over Current Protection
Over Temperature Protection
Stable with Low ESR Capacitor
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0℃ to 70℃ Ambient Operating Temperature Range
2.2. Package
SOT23-5 Green Package (Lead Free and Halogen Free)
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NCT3705U
2.3. Application
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Desktop PCs, Notebooks, and Workstations
Graphics Card or Add-on Card Low Power Applications
Set Top Boxes, Digital TVs and Printers
Digital Still Camera and Camcorders
Mobile or handheld Devices
3. BLOCK DIAGRAM
IN
Short Circuit Protection
Over Current Protection
VREF
Over Temperature
Protection
Shut Down
SHDN#
OUT
SET
VCOMP
GND
Figure1. Adjustable Mode
Publication Date: Nov., 2008
Revision A1
-2-
NCT3705U
IN
Short Circuit Protection
Over Current Protection
VREF
Over Temperature
Protection
SHDN#
Shut Down
OUT
BYP
GND
Figure2. Fixed Mode
Publication Date: Dec., 2008
Revision A1
-3-
NCT3705U
4. PIN CONFIGURATION AND TYPICAL APPLICATION CIRCUIT
IN
GND
1
2
3
5 OUT
4 BYP
IN
GND
1
2
3
5 OUT
SHDN#
SHDN#
4 SET
Fixed Mode
Adjustable Mode
NCT3705U -XXX
(Top View)
NCT3705U -A
(Top View)
Figure3. Pin Configuration
VOUT
VOUT
COUT
IN
OUT
BYP
IN
OUT
SET
+
+
COUT
4.7uF
R1
R2
4.7uF
CIN
CIN
-
-
SHDN#
SHDN#
1uF
1uF
CBYP
GND
GND
10nF
Fixed Mode
Adjustable Mode
NCT3705U -A
(Top View)
NCT3705U -XXX
(Top View)
Figure4. Typical Application Circuits
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Revision A1
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NCT3705U
5. PIN DESCRIPTION
PIN
NAME
I/O
FUNCTION
NCT3705 NCT3705
U-A U-XXX
Regulator input voltage.
IN
1
2
I
Supply voltage can range from 2.5V to 6.0V.
GND
Ground
Active-Low shutdown input pin.
3
I
SHDN#
BYP
A logic low reduces the supply current to 1uA. Connect to IN
for normal operation.
This is a reference bypass pin. It should connect an external
capacitor to GND to reduce output noise.
4
O
Feedback input for setting the output voltage.
Connect to GND to set the output voltage to the preset
output voltage. Connect to an external resistor divider for
adjustable-output operation.
4
I
SET
OUT
Regulator output.
5
Fixed or adjustable from 1.25V to 5.0V with sourcing current
which up to 500mA.
Publication Date: Dec., 2008
-5-
Revision A1
NCT3705U
6. FUNCTIONAL DESCRIPTION
6.1 Output Voltage and Dropout voltage
The output voltage of NCT3705U-A can be adjusted by the resistive divider between OUT,
SET and GND pins. The internal VREF is 1.25V and the output voltage is given by the following
equation:
VOUT = VREF (1+R1/R2) =1.25(1+R1/R2)
For the reasons of reducing power dissipation and loop stability, R2 is chosen to be 120KΩ.
Alternatively, the relationship between R1 and R2 is given by:
R1 = R2 (VOUT /1.25 - 1)
A regulator's minimum input-output voltage differential (or dropout voltage) determines the
lowest usable supply voltage. NCT3705U uses a P-channel MOSFET pass transistor, it’s
dropout voltage is a function of RDS(ON) multiplied by the load current. Dropout voltage is
defined as the input-output voltage differential at which output 100mV below the standard of
output voltage. The NCT3705U has a very low dropout voltage 280 mV (typical at VOUT = 5V)
with 500mA of output current.
6.2
Noise
Noise is specified in two–spot noise or output noise density is the RMS (root means square)
sum of all noise source, measured at the regulator output , at a specific frequency from
10Hz~100KHz,this type of frequency. Total output noise or Broad-Band Noise is the RMS sum
of spot noise over specified bandwidth, usually several decades of frequencies. Total output
noise is measured in μV (rms).
With the 10nF capacitor at the BYP pin can reduce the noise significantly and is required for
loop stability. The bandgap is noise source in the NCT3705U LDO that will generates
32uVrms in the 10HZ to 100KHZ bandwidth. It will be increased following the loop gain as
below equation:
Vnoise = 32uVrms *(VO/VREF) μV
6.3 PSRR
PSRR (Power Supply Rejection Ratio) can be improved by CBYP capacitor selection. It’s the
key of LDO anti-interference capability. With the increasing value of CBYP, the PSRR will be
better.
Publication Date: Nov., 2008
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Revision A1
NCT3705U
Figure5. Select a CBYP for NCT3705 Circuits
6.4 Load Regulation Consideration
Load regulation will be affected by the length of trace. The impendence of the trace (RLine1 &
RLine2) will have influence on the VOUT. The output voltage is given by the following equation:
VOUT = VOUT -[ ILoad * (RLine1 +RLine2) ] (Figure 6)
The best method/layout is making terminals of VOUT & R1, R2 & GND as close as possible to
reduce the trace impedance. It will have the better load regulation of the circuits. (Figure7)
RLine1
R1
VOUT
RLine1
R1
VOUT
IN
OUT
SET
IN
OUT
SET
COUT
COUT
4.7uF
4.7uF
CIN
CIN
SHDN#
SHDN#
1uF
1uF
R2
R2
GND
GND
RLine2
Figure7. Recommended Circuits
RLine2
Figure6. Equivalent Trace Impedance Circuits
Publication Date: Dec., 2008
Revision A1
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NCT3705U
6.5
Current Limit Protection
The NCT3705U uses a current sense-resistor to monitor the output current. Once the output
current exceeds limit threshold, NCT3705U would be protected with a limited output current.
Further more, when the output is short to ground (<0.7V), the output current would be folded-
back to a less limit and less thermal accumulation.
6.6
VIN & VOUT Capacitor Selection
When operating from batteries, or in applications with long line length (> 10 inches) between
the input source and the LDO, some input capacitance is recommended. A minimum of 1.0μF
to 4.7μF is recommended for most applications.
For applications that have output step load requirements, the input capacitance of the LDO is
very important. The input capacitance provides the LDO with a good local low-impedance
source to pull the transient currents from in order to respond quickly to the output load step.
For good step response performance, the output capacitor value should be equivalent or
higher than the input capacitor. The capacitor should be placed as close to the LDO as
possible.
Larger input capacitors will also help reduce any high-frequency noise on the input and output
of the LDO and reduce the effects of any inductance that exists between the input source
voltage and the input capacitance of the LDO. The recommended value of output capacitor is
at least 1uF with low ESR.
6.7
Over Temperature Protection
The NCT3705U LDO has temperature-sensing circuitry to prevent the junction temperature
from exceeding approximately 150°C. If the LDO junction temperature does reach 150°C, the
LDO output will be turned off until the junction temperature cools to approximately 110°C, at
which point the LDO output will automatically resume normal operation. If the internal power
dissipation continues to be excessive, the device will again shut off. The junction temperature
of the die is a function of power dissipation, ambient temperature and package thermal
resistance.
Publication Date: Nov., 2008
-8-
Revision A1
NCT3705U
6.8
Layout note
Dropout and load regulation will be deteriorated when COUT, CIN and NCT3705U distance is
too far. The capacitor must be located a distance of not more than 1 inch from the input and
return to a clean analog ground.
By putting CBYP close to the NCT3705U, the transient and PSRR will be improved and
performs less output noise.
Figure8. Fixed Mode Recommended Layout
Figure9. Adjustable Mode Recommended Layout
6.9
Thermal Consideration
Different (VIN-VOUT) combinations and ambient temperature play important roles in the
thermal dissipation. The maximum power dissipation can be calculated by following formula:
PD(MAX) = ( TJ-TA ) / θJA
Where TJ is the maximum junction temperature.TA is the ambient temperature. θJA is the
junction to ambient thermal resistance.
For example: NCT3705U at the TA =25℃.it can calculate PD(MAX) = 520mW = (150℃ -25℃) /
240℃/W
Differential voltage can to explain below：
( VIN – VOUT ) = PD(MAX) / IOUT
NCT3705U occurs Over Temperature Protection if differential voltage surpasses below
Figure10 & Figure11 safe operation range.
Publication Date: Dec., 2008
-9-
Revision A1
NCT3705U
Thermal Consideration Area @ Iout=500mA
500
Thermal Consideration Area @ Iout=300mA
500
450
400
350
300
250
200
150
100
50
450
400
350
300
250
200
150
100
50
50
℃
25
℃
50℃
25℃
100℃
100
℃
75
℃
75℃
0
0
0.1 0.4 0.7
1
1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7
4
4.3 4.6
0.1 0.4 0.7
1
1.3 1.6 1.9 2.2 2.5 2.8 3.1 3.4 3.7
4
4.3 4.6
Vin - Vout Differential Voltage (V)
Vin - Vout Differential Voltage (V)
Figure11. Safe Operating Area (IOUT=500mA)
Figure10. Safe Operating Area (IOUT=300mA)
7. ELECTRICAL CHARACTERISTIC
7.1 Absolute Maximum Ratings
ITEM
SYMBOL
RATING
UNIT
Input Voltage
VIN
-0.3 to 7
V
Output Voltage to Ground
VOUT
-0.3 to 7
V
Output Current
IOUT
Topt
Internally limited
Operating Temperature Range
0 to 70
±2
℃
kV
V
Human Body Mode
Machine Mode
Latch-Up
Electrostatic discharge protection
±200
±100
mA
Note: Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to
the device and exposure to absolute maximum rating conditions for extended periods may affect device
reliability.
Publication Date: Nov., 2008
-10-
Revision A1
NCT3705U
7.2 Thermal Information
ITEM
RATING
Internal Limited
240
UNIT
W
Power Dissipation, PD @ TA=25℃
Package Thermal Resistance, SOT23-5, θ
℃/W
JA
7.3 Recommended operating conditions
ITEM SYMBOL
MIN MAX UNIT
Input Voltage
VIN
2.5
0
6.0
500
800
70
V
Continuous Output Current
Peak Output Current
IOUT
IPEAK
mA
0
Operating Temperature Range
0
℃
℃
Junction Temperature Range
0
125
7.4 Electrical Characteristics
PARAMETER
SYMBOL
VIN
CONDITION
MIN
TYP
MAX
UNIT
Input Voltage
2.5
-2
---
6.0
V
Variation from specified VOUT,
IOUT=1mA
Output Voltage Accuracy
VOUT
---
2
%
Output Voltage range
Maximum Output Current
Current Limit
1.25
500
500
---
---
5.0
---
V
mA
mA
mA
µA
ILIM
Isc
IQ
750
280
90
Shot Circuit Current
Ground Pin Current
---
120
VOUT =1.25V
VOUT =1.80V
VOUT =2.50V
---
---
---
---
---
---
---
1.5
0.9
1.8
1.2
1.0
1.0
0.9
0.75
0.7
0.7
VOUT =2.80V
VOUT =3.30V
VOUT =4.75V
VOUT =5.00V
0.7
Dropout Voltage
VDROP
IOUT = 500mA
V
0.6
0.45
0.40
VIN=V(STD)+0.1V to 6.2V,
OUT=10mA
Line Regulation
Load Regulation
ΔVLNR
---
---
0.05
---
0.1
%/V
I
ΔVLDR
IOUT=10mA to 500mA
0.02
%/mA
Ripple Rejection
PSRR
Freq. =100Hz, IOUT=10mA
---
---
70
32
---
---
dB
µVRMS
Output Voltage Noise
VOUT =1.25V
COUT=4.7µF,
en
Publication Date: Dec., 2008
Revision A1
-11-
NCT3705U
CBYP=10nF,
OUT=1mA
(10Hz to 100kHz)
V
OUT =1.80V
---
---
---
46
64
72
---
---
---
I
VOUT =2.50V
VOUT =2.80V
VOUT =3.30V
VOUT =4.75V
VOUT =5.00V
---
---
84
---
122
128
---
---
---
---
V
OUT =0V,TA=+25℃
Shutdown Supply Current
Stable COUT ESR Range
SHUTDOWN
I SHDN
---
1
µA
IOUT =500mA
5m
---
500m
Ω
VIH
VIL
Regulator enabled
Regulator shutdown
1.5
---
---
---
---
SHDN# Input Threshold
V
0.4
V
SHDN# = VIN, TA=+25℃
ISHDN#
---
---
---
---
0.1
0.1
SHDN# Input Bias Current
SET INPUT
µA
VSHDN# = GND, TA=+25℃
IQSHDN#
VIN=2.5V to
5.5V ,
TA=+25℃
1.225
---
1.25
1.25
1.275
---
SET Reference Voltage
VSET
V
TA=TMIN to TMAX
IOUT=1mA
SET
current
Input
Leakage
TA=+25℃
ISET
VSET = 1.3V
---
5
30
nA
THERMAL PROTECTION
Thermal Shutdown
Temperature
℃
℃
TSHDN
---
---
150
40
---
Thermal Shutdown
Hysteresis
△TSHDN
----
Publication Date: Nov., 2008
Revision A1
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NCT3705U
8. TYPICAL OPERATING WAVEFORMS (VOUT=4.75V)
Turn – on time
Turn – off time
Line Transient
Load Transient
Publication Date: Dec., 2008
Revision A1
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NCT3705U
Short Circuit Protection
Over Current Protection
Output Voltage Noise
Power Supply Rejection Ratio
90
80
70
60
50
40
30
20
10
0
dB
NCT3705= 4.75V
NCT3705 =3.3V
NCT3705 =2.8V
NCT3705 =2.5V
NCT3705 =1.8V
Publication Date: Nov., 2008
Revision A1
10
100
1000
10000
100000 1000000
HZ
NCT3705U
Quiescent current VS Output Current
Dropout voltage VS Output Current
99
98
97
96
95
94
93
92
91
300
250
200
150
100
50
0
0
100
200
300
0
100
200
300
Iout(mA)
Iout(mA)
Line Regulation VS Output Current
PSRR VS Output Current
1
0.8
0.6
0.4
0.2
0
100
80
60
40
20
0
0
100
200
300
0
100
200
300
Iout(mA)
Iout(mA)
Publication Date: Dec., 2008
Revision A1
-15-
NCT3705U
Dropout VS Temperature
Output Voltage VS Temperature
4.75
4.7
350
300
250
200
150
100
50
4.65
4.6
4.55
4.5
0
-20
0
20 40 60 80 100 120
Temperature (℃)
-20
0
20 40 60 80 100 120
Temperature (℃)
P.S.R.R VS Temperature
Quiescent Current VS Temperature
80
70
60
50
40
30
20
10
0
120
100
80
60
40
20
0
-20
0
20 40 60 80 100 120
Temperature (℃)
-20
0
20 40 60 80 100 120
Temperature (℃)
Publication Date: Nov., 2008
Revision A1
-16-
NCT3705U
9. PACKAGE DIMENSION
5pin SOT23 Package
D
e1
HE
E
e
b
Y
L
L1
¾
TAPING SPECIFICATION
5pin SOT23 Package
Publication Date: Dec., 2008
Revision A1
-17-
NCT3705U
10. ORDERING INFORMATION
PRODUCTION
FLOW
PART NUMBER
NCT3705U-A
NCT3705U-12
MARKING
5A00
VOUT
ADJ
1.2V
SUPPLIED AS
PACKAGE TYPE
5120
NCT3705U-15
NCT3705U-18
NCT3705U-25
NCT3705U-28
5150
5180
5250
5250
1.5V
1.8V
2.5V
2.8V
Commercial,
T Shape:
5 PIN SOT23
3,000 units/T&R
(Green package)
0℃ to +70℃
NCT3705U-33
NCT3705U-475
NCT3705U-50
5330
5475
5500
3.3V
4.75V
5.0V
11. TOP MARKING SPECIFICATION
5 X X X
1st Line: 3XXX
z
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5: 500mA (NCT3705U)
XXX : Please check ordering information
Publication Date: Nov., 2008
Revision A1
-18-
NCT3705U
12. REVISION HISTORY
VERSION
DATE
PAGE
DESCRIPTION
A1
03/18/2009
All
New Create
Important Notice
Nuvoton products are not designed, intended, authorized or warranted for use as components
in systems or equipment intended for surgical implantation, atomic energy control
instruments, airplane or spaceship instruments, transportation instruments, traffic signal
instruments, combustion control instruments, or for other applications intended to support or
sustain life. Further more, Nuvoton products are not intended for applications wherein failure
of Nuvoton products could result or lead to a situation wherein personal injury, death or
severe property or environmental damage could occur.
Nuvoton customers using or selling these products for use in such applications do so at their
own risk and agree to fully indemnify Nuvoton for any damages resulting from such improper
use or sales.
Publication Date: Dec., 2008
-19-
Revision A1
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