LM27761 [TI]
具有集成 LDO 的低噪声稳压逆变器;
| 型号： | LM27761 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 具有集成 LDO 的低噪声稳压逆变器 |
| 文件： | 总27页 (文件大小：2760K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
LM27761 低噪声稳压开关电容器电压逆变器
1 特性
3 说明
1
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对输入电源电压进行反相和稳压
LM27761 低噪声稳压开关电容器电压逆变器可针对
2.7V 到 5.5V 范围内的输入电压，提供可调节的超低
噪声输出。在应用解决方案中使用四个低成本电容器，
可以提供高达 250mA 的输出电流。该器件的稳压输出
可在 −5V 到 −1.5V 范围内进行调节。LM27761 以
2MHz（典型值）开关频率运行，以减小输出电阻和电
压波纹。LM27761 的工作电流仅为 370µA（对于大多
数负载，电荷泵功率效率均高于 80%）并且关断电流
典型值为 7µA，因此在驱动功率放大器、DAC 偏置电
源轨以及其他大电流、低噪声电压应用时， 可提供理
想的性能。
低输出波纹
关断时可使静态电流降至 7µA（典型值）
输出电流高达 250mA
2.5Ω 逆变器输出阻抗，VIN = 5V
峰值负载时的稳定度为 ±4%
370µA 静态电流
2MHz（典型值）固定频率、低噪声运行
2MHz 频率时的低压降稳压器 (LDO) 电源抑制比
(PSRR) 为 35dB（典型值），
负载电流为 80mA
•
100mA 电流时的 LDO 压降电压为 30mV，
VOUT = –5V
器件信息(1)
器件型号
LM27761
封装
WSON (8)
封装尺寸（标称值）
•
•
限流和热保护
使用 LM27761 并借助 WEBENCH® 电源设计器创
建定制设计
2.00mm x 2.00mm
(1) 如需了解所有可用封装，请参阅数据表末尾的可订购产品附
录。
2 应用
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运算放大器电源
无线通信系统
手机功率放大器偏置
接口电源
手持式仪表
高保真 (Hi-Fi) 耳机放大器
为数据转换器供电
典型应用
LM27761
VIN
EN
VOUT
C2
4.7 µF
R1
R2
C4
2.2 µF
VFB
C1+
C1-
CPOUT
C3
4.7 µF
C1
1 µF
GND
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
English Data Sheet: SNVSA85
LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
目录
7.4 Device Functional Modes........................................ 10
Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Application - Regulated Voltage Inverter.... 11
Power Supply Recommendations...................... 16
1
2
3
4
5
6
特性.......................................................................... 1
应用.......................................................................... 1
说明.......................................................................... 1
修订历史记录 ........................................................... 2
Pin Configuration and Functions......................... 3
Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings.............................................................. 4
6.3 Recommended Operating Conditions....................... 4
6.4 Thermal Information.................................................. 4
6.5 Electrical Characteristics........................................... 5
6.6 Typical Characteristics.............................................. 6
Detailed Description .............................................. 9
7.1 Overview ................................................................... 9
7.2 Functional Block Diagram ......................................... 9
7.3 Feature Description................................................. 10
8
9
10 Layout................................................................... 16
10.1 Layout Guidelines ................................................. 16
10.2 Layout Example .................................................... 17
11 器件和文档支持 ..................................................... 18
11.1 器件支持................................................................ 18
11.2 接收文档更新通知 ................................................. 18
11.3 社区资源................................................................ 18
11.4 商标....................................................................... 18
11.5 静电放电警告......................................................... 18
11.6 Glossary................................................................ 18
12 机械、封装和可订购信息....................................... 18
7
4 修订历史记录
Changes from Revision B (February 2016) to Revision C
Page
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已添加 WEBENCH 链接 ......................................................................................................................................................... 1
Changes from Revision A (December 2015) to Revision B
Page
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已更改 典型应用图中位置颠倒的“C1”和“C2” .......................................................................................................................... 1
Deleted footnote 3 to Abs Max table ..................................................................................................................................... 4
updated Specifications tables................................................................................................................................................. 4
已添加 Condition statement for Typical Charcteristics ........................................................................................................... 6
已更改 Figures 3 and 4; added Figures 16 through 18 ......................................................................................................... 8
已更改 "... reducing the quiescent current to 1 µA" to "...reducing the quiescent current to 7 µA"...................................... 10
已更改 "1-µA typical shutdown current" to "7-µA typical shutdown current" ........................................................................ 11
已更改 "C2 is charging C3" to "C1 is charging C3".............................................................................................................. 12
已更改 "VOUT" to "CPOUT" on Figure 20............................................................................................................................ 12
已更改 "C2" to "C1" ............................................................................................................................................................. 13
已更改 "RSW" to "(2 × RSW)" .................................................................................................................................................. 13
已更改 equation 1 ................................................................................................................................................................ 13
已更改 "–1.2 V" to "–1.22 V" ................................................................................................................................................ 13
Changes from Original (October 2015) to Revision A
Page
•
已更改 器件文档形式，从单页产品预览改为完整的超前信息数据表 ...................................................................................... 1
2
Copyright © 2015–2017, Texas Instruments Incorporated
LM27761
www.ti.com.cn
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
5 Pin Configuration and Functions
DSG Package
8-Pin WSON With Thermal Pad
Top View
1
8
7
6
5
2
3
4
Pin Functions
PIN
TYPE(1)
DESCRIPTION
NUMBER
NAME
VIN
1
2
3
4
P
G
P
P
P
Positive power supply input.
Ground
GND
CPOUT
VOUT
Negative unregulated output voltage.
Regulated negative output voltage.
Feedback input. Connect VFB to an external resistor divider between VOUT and
GND. DO NOT leave unconnected.
5
VFB
6
EN
C1–
I
Active high enable input.
7
P
P
G
Negative terminal for C1.
8
C1+
Positive terminal for C1.
—
Thermal Pad
Ground. DO NOT leave unconnected.
(1) P: Power; G: Ground; I: Input.
Copyright © 2015–2017, Texas Instruments Incorporated
3
LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN
MAX
5.8
UNIT
Ground voltage, VIN to GND or GND to VOUT
EN
V
(GND − 0.3 V)
(VIN + 0.3 V)
300
Continuous output current, CPOUT and VOUT
mA
°C
(3)
TJMAX
150
Storage temperature, Tstg
–65
150
°C
(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under . Exposure to
absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, contact the TI Sales Office/Distributors for availability and specifications.
(3) The maximum power dissipation must be de-rated at elevated temperatures and is limited by TJMAX (maximum junction temperature), TA
(ambient temperature) and RθJA (junction-to-ambient thermal resistance). The maximum power dissipation at any temperature is:
PDissMAX = (TJMAX – TA)/RθJA up to the value listed in the Absolute Maximum Ratings.
6.2 ESD Ratings
VALUE
±1000
±250
UNIT
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)
Charged-device model (CDM), per JEDEC specification JESD22-C101(2)
Electrostatic
discharge
V(ESD)
V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
85
UNIT
Operating ambient temperature, TA
Operating junction temperature, TJ
Operating input voltage, VIN
–40
–40
2.7
0
°C
°C
V
125
5.5
Operating output current, IOUT
250
mA
6.4 Thermal Information
LM27761
THERMAL METRIC(1)
WSON (DSG)
UNIT
8 PINS
67.7
89.9
37.6
2.4
RθJA
Junction-to-ambient thermal resistance
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
RθJC(top)
RθJB
Junction-to-case (top) thermal resistance
Junction-to-board thermal resistance
ψJT
Junction-to-top characterization parameter
Junction-to-board characterization parameter
Junction-to-case (bottom) thermal resistance
ψJB
38
RθJC(bot)
9.4
(1) For more information about traditional and new thermal metrics, see Semiconductor and IC Package Thermal Metrics.
4
Copyright © 2015–2017, Texas Instruments Incorporated
LM27761
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ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
6.5 Electrical Characteristics
Typical limits apply for TA = 25°C, and minimum and maximum limits apply over the full temperature range. Unless otherwise
specified, VIN = 5 V and values for C1 to C4 are as shown in the 典型应用.
PARAMETER
Supply current
TEST CONDITIONS
Open circuit, no load
MIN
TYP
370
7
MAX
600
12
UNIT
µA
Iq
ISD
Shutdown supply current
Switching frequency
µA
ƒSW
RNEG
VDO
PSRR
VN
VIN = 3.6 V
1.7
2
2.3
MHz
Ω
Output resistance to CPOUT
LDO dropout voltage
VIN = 5.5 V
2
ILOAD = 100 mA, VOUT = −5 V
ILOAD = 80 mA, VCPOUT = −5 V
ILOAD = 80 mA, 10 Hz to 100 kHz
30
35
20
1.22
mV
dB
Power supply rejection ratio
Output noise voltage
µVRMS
V
VFB
VOUT
Feedback pin reference voltage
Adjustable output voltage
Load regulation
1.202
–5
1.238
–1.5
5.5 V ≥ VIN ≥ 2.7 V
0 to 250 mA, VOUT = −1.8 V
5.5 V ≥ VIN ≥ 2.7 V, ILOAD = 50 mA
5.5 V ≥ VIN ≥ 2.7 V
5.5 V ≥ VIN ≥ 2.7 V
VIN falling
V
4.6
1.5
µV/mA
mV/V
V
Line regulation
VIH
VIL
Enable pin input voltage high
Enable pin input voltage low
1.2
0.4
V
2.6
2.4
UVLO
Undervoltage lockout
V
VIN rising
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6.6 Typical Characteristics
Unless otherwise specified, TA = 25°C, VIN = 5 V, and values for C1 to C4 are as shown in the 典型应用.
3.5
3
2
1.8
1.6
1.4
1.2
1
2.5
2
1.5
1
0.8
0.6
0.4
0.2
0
0.5
0
VIN = 3 V, VOUT = -1.8 V
VIN = 5.5 V, VOUT = -5 V
0
50
100
150
200
250
2.7
3.2
3.7
4.2
4.7
5.2
5.5
Output Current (mA)
VIN (V)
D001
D002
VOUT = –1.8 V
IOUT = 100 mA
图 1. Output Voltage Ripple vs Output Current
图 2. Output Voltage Ripple vs Input Voltage
500
450
400
350
300
250
200
150
100
50
10
9
8
7
6
5
4
3
2
1
0
25°C
85°C
-40°C
25èC
85èC
-40èC
0
2.7
3.2
3.7
4.2
4.7
5.2
5.5
2.7
3.2
3.7
4.2
4.7
5.2
5.7
VIN (V)
VIN (V)
D015
D016
EN = 1
ILOAD = 0 mA
EN = 0
图 3. Quiescent Current
图 4. Shutdown Current
-1.75
-4.8
-4.85
-4.9
25°C
85°C
-40°C
-1.77
-1.79
-1.81
-1.83
-1.85
-4.95
-5
-5.05
-5.1
25°C
85°C
-40°C
-5.15
-5.2
0.001
0.01
0.1
0.25
0.001
0.01
0.1
1
IOUT (A)
IOUT (A)
D006
D007
VIN = 3 V
R1 = 237 kΩ
VOUT = –1.8 V
VIN = 5.5 V
R1 = 1.54 MΩ
VOUT = –5 V
R2 = 500 kΩ
R2 = 500 kΩ
图 5. Load Regulation
图 6. Load Regulation
6
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LM27761
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ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
Typical Characteristics (接下页)
Unless otherwise specified, TA = 25°C, VIN = 5 V, and values for C1 to C4 are as shown in the 典型应用.
-3.2
-3.25
-3.3
-3.35
-3.4
0.001
VIN = 5 V
0.01
IOUT (A)
0.1
0.25
D011
VIN = 3 V
VOUT = –1.8 V
IOUT = 250 mA
VOUT = –3.3 V
R1 = 856 kΩ
R2 = 500 kΩ
图 8. Output Voltage Ripple
图 7. Load Regulation
VIN = 5.5 V
VOUT = –5 V
IOUT = 250 mA
图 9. Output Voltage Ripple
图 10. Enable High
100
90
80
70
60
50
40
30
20
10
0
VOUT = -5 V
VOUT = -3 V
VOUT = -3.3 V
VOUT = -4.5 V
0
50
100
150
200
250
IOUT (mA)
D008
图 12. LDO Dropout Voltage vs IOUT
图 11. Enable Low
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LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
Typical Characteristics (接下页)
Unless otherwise specified, TA = 25°C, VIN = 5 V, and values for C1 to C4 are as shown in the 典型应用.
-1.77
-1.78
-1.79
-1.8
-1.77
-1.78
-1.79
-1.8
25°C
85°C
-40°C
25°C
85°C
-40°C
-1.81
-1.82
-1.83
-1.81
-1.82
-1.83
2.7
3.2
3.7
4.2
4.7
5.2
5.5
2.7
3.2
3.7
4.2
4.7
5.2
5.5
VIN (V)
VIN (V)
D012
D013
VOUT = –1.8 V
IOUT = 50 mA
VOUT = –1.8 V
IOUT = 100 mA
R1 = 237 kΩ
R2 = 500 kΩ
R1 = 237 kΩ
R2 = 500 kΩ
图 13. Line Regulation
图 14. Line Regulation
-1.78
25°C
85°C
-40°C
-1.79
-1.8
-1.81
-1.82
-1.83
2.7
3.2
3.7
4.2
4.7
5.2
5.5
VIN (V)
D014
VOUT = –1.8
IOUT = 250 mA
R1 = 237 kΩ
R2 = 500 kΩ
图 15. Line Regulation
8
版权 © 2015–2017, Texas Instruments Incorporated
LM27761
www.ti.com.cn
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
7 Detailed Description
7.1 Overview
The LM27761 regulated charge-pump voltage converter inverts a positive voltage in the range of 2.7 V to 5.5 V
to a negative voltage in the range of –1.5 V to –5 V. The negative LDO (low drop-out regulator), at the output of
the charge-pump voltage converter, allows the device to provide a very low noise output, low output-voltage
ripple, high PSRR, and low line and load transient responses. The output is externally configurable with gain-
setting resistors. The LM27761 uses four low-cost capacitors to deliver up to 250 mA of output current.
7.2 Functional Block Diagram
VIN
Current Limit
C1+
Switch Array Switch
2-MHz
Oscillator
Drivers
C1-
CPOUT
EN
GND
Reference
LPF
VOUT
Negative
Bandgap
LPF
VFB
LDO
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7.3 Feature Description
7.3.1 Undervoltage Lockout
The LM27761 has an internal comparator that monitors the voltage at VIN and forces the device into shutdown if
the input voltage drops to 2.4 V. If the input voltage rises above 2.6 V, the LM27761 resumes normal operation.
7.3.2 Input Current Limit
The LM27761 contains current limit circuitry that protects the device in the event of excessive input current
and/or output shorts to ground. The input current is limited to 500 mA (typical) when the output is shorted directly
to ground. When the LM27761 is current limiting, power dissipation in the device is likely to be quite high. In this
event, thermal cycling is expected.
7.3.3 PFM Operation
To minimize quiescent current during light load operation, the LM27761 allows PFM or pulse-skipping operation.
By allowing the charge pump to switch less when the output current is low, the quiescent current drawn from the
power source is minimized. The frequency of pulsed operation is not limited and can drop into the sub-2-kHz
range when unloaded. As the load increases, the frequency of pulsing increases until it transitions to constant
frequency. The fundamental switching frequency in the LM27761 is 2 MHz.
7.3.4 Output Discharge
In shutdown, the LM27761 actively pulls down on the output of the device until the output voltage reaches GND.
In this mode, the current drawn from the output is approximately 1.85 mA.
7.3.5 Thermal Shutdown
The LM27761 implements a thermal shutdown mechanism to protect the device from damage due to
overheating. When the junction temperature rises to 150°C (typical), the device switches into shutdown mode.
The LM27761 releases thermal shutdown when the junction temperature is reduced to 130°C (typical).
Thermal shutdown is most often triggered by self-heating, which occurs when there is excessive power
dissipation in the device and/or insufficient thermal dissipation. The LM27761 device power dissipation increases
with increased output current and input voltage. When self-heating brings on thermal shutdown, thermal cycling
is the typical result. Thermal cycling is the repeating process where the part self-heats, enters thermal shutdown
(where internal power dissipation is practically zero), cools, turns on, and then heats up again to the thermal
shutdown threshold. Thermal cycling is recognized by a pulsing output voltage and can be stopped by reducing
the internal power dissipation (reduce input voltage and/or output current) or the ambient temperature. If thermal
cycling occurs under desired operating conditions, thermal dissipation performance must be improved to
accommodate the power dissipation of the device.
7.4 Device Functional Modes
7.4.1 Shutdown Mode
An enable pin (EN) pin is available to disable the device and place the LM27761 into shutdown mode reducing
the quiescent current to 7 µA. In shutdown, the output of the LM27761 is pulled to ground by an internal pullup
current source (approximately 1.85 mA).
7.4.2 Enable Mode
Applying a voltage greater than 1.2 V to the EN pin brings the device into enable mode. When unloaded, the
input current during operation is 370 µA. As the load current increases, so does the quiescent current. When
enabled, the output voltage is equal to the inverse of the input voltage minus the voltage drop across the charge
pump.
10
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ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
8 Application and Implementation
注
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM27761 low-noise charge-pump voltage converter inverts a positive voltage in the range of 2.7 V to 5.5 V
to a negative output voltage configurable with external gain setting resistors. The device uses four low-cost
capacitors to provide up to 250 mA of output current. The LM27761 operates at a 2-MHz oscillator frequency to
reduce charge-pump output resistance and voltage ripple under heavy loads. With an operating current of only
370 µA and 7-µA typical shutdown current, the LM27761 provides ideal performance for battery-powered
systems.
8.2 Typical Application - Regulated Voltage Inverter
LM27761
VIN
EN
VOUT
C2
4.7 µF
R1
R2
C4
2.2 µF
VFB
C1+
C1-
CPOUT
C3
4.7 µF
C1
1 µF
GND
图 16. LM27761 Typical Application
8.2.1 Design Requirements
Example requirements for typical applications using the LM27761 device are listed in 表 1:
表 1. Design Parameters
DESIGN PARAMETER
Input voltage
EXAMPLE VALUE
2.7 V to 5.5 V
–1.5 V to –5 V
0 mA to 250 mA
2 MHz
Output voltage
Output current
Boost switching frequency
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8.2.2 Detailed Design Procedure
8.2.2.1 Custom Design With WEBENCH® Tools
Click here to create a custom design using the LM27761 device with the WEBENCH® Power Designer.
1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.
2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.
3. Compare the generated design with other possible solutions from Texas Instruments.
The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time
pricing and component availability.
In most cases, these actions are available:
•
•
•
•
Run electrical simulations to see important waveforms and circuit performance
Run thermal simulations to understand board thermal performance
Export customized schematic and layout into popular CAD formats
Print PDF reports for the design, and share the design with colleagues
Get more information about WEBENCH tools at www.ti.com/WEBENCH.
8.2.2.2 Charge-Pump Voltage Inverter
The main application of the LM27761 is to generate a regulated negative supply voltage. The voltage inverter
circuit uses only three external capacitors, and the LDO regulator circuit uses one additional output capacitor.
The voltage inverter portion of the LM27761 contains four large CMOS switches which are switched in sequence
to invert the input supply voltage. Energy transfer and storage are provided by external capacitors. 图 17 shows
the voltage switches S2 and S4 are open. In the second time interval, S1 and S3 are open; at the same time, S2
and S4 are closed, and C1 is charging C3. After a number of cycles, the voltage across C3 is pumped into VIN.
Because the anode of C3 is connected to ground, the output at the cathode of C3 equals –(VIN) when there is no
load current. When a load is added the output voltage dropis determined by the parasitic resistance (RDSON of the
MOSFET switches and the equivalent series resistance (ESR) of the capacitors) and the charge transfer loss
between the capacitors.
S1
C1+
S2
VIN
CIN
GND
C1
COUT
GND
S3
S4
C1-
CPOUT
OSC.
2 MHz
+
PFM COMP
VIN
图 17. Voltage Inverting Principle
12
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LM27761
www.ti.com.cn
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
The output characteristic of this circuit can be approximated by an ideal voltage source in series with a
resistance. The voltage source equals –(VIN). The output resistance ROUT is a function of the ON resistance of
the internal MOSFET switches, the oscillator frequency, the capacitance, and the ESR of C1 and C3. Because
the switching current charging and discharging C1 is approximately twice as the output current, the effect of the
ESR of the pumping capacitor C1 is multiplied by four in the output resistance. The charge-pump output
capacitor C3 is charging and discharging at a current approximately equal to the output current; therefore, its
ESR only counts once in the output resistance. A good approximation of charge-pump ROUT is shown in 公式 1:
ROUT = (2 × RSW) + [1 / (ƒSW × C)] + (4 × ESRC1) + ESRCOUT
where
•
RSW is the sum of the ON resistance of the internal MOSFET switches shown in 图 17.
(1)
High capacitance and low-ESR ceramic capacitors reduce the output resistance.
8.2.2.3 Negative Low-Dropout Linear Regulator
At the output of the inverting charge-pump the LM27761 features a low-dropout, linear negative voltage regulator
(LDO). The LDO output is rated for a current of 250 mA. This negative LDO allows the device to provide a very
low noise output, low output voltage ripple, high PSRR, and low line or load transient response.
8.2.2.4 Power Dissipation
The allowed power dissipation for any package is a measure of the ability of the device to pass heat from the
junctions of the device to the heatsink and the ambient environment. Thus, the power dissipation is dependent
on the ambient temperature and the thermal resistance across the various interfaces between the die junction
and ambient air.
The maximum allowable power dissipation can be calculated by 公式 2:
PD-MAX = (TJ-MAX – TA) / RθJA
(2)
The actual power being dissipated in the device can be represented by 公式 3:
PD = PIN – POUT = [VIN × (–IOUT + IQ) – (VOUT × IOUT)]
(3)
公式 2 and 公式 3 establish the relationship between the maximum power dissipation allowed due to thermal
consideration, the voltage drop across the device, and the continuous current capability of the device. These
equations must be used to determine the optimum operating conditions for the device in a given application.
In lower power dissipation applications the maximum ambient temperature (TA-MAX) may be increased. In higher
power dissipation applications the maximum ambient temperature(TA-MAX) may have to be derated. TA-MAX can be
calculated using 公式 4:
TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX
)
where
•
•
•
TJ-MAX-OP = maximum operating junction temperature (125°C)
PD-MAX = the maximum allowable power dissipation
RθJA = junction-to-ambient thermal resistance of the package
(4)
Alternately, if TA-MAX cannot be derated, the power dissipation value must be reduced. This can be accomplished
by reducing the input voltage as long as the minimum VIN is not violated, or by reducing the output current, or
some combination of the two.
8.2.2.5 Output Voltage Setting
The output voltage of the LM27761 is externally configurable. The value of R1 and R2 determines the output
voltage setting. The output voltage can be calculated using 公式 5:
VOUT = –1.22 V × (R1 + R2) / R2
(5)
The value for R2 must be no less than 50 kΩ.
版权 © 2015–2017, Texas Instruments Incorporated
13
LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
8.2.2.6 External Capacitor Selection
The LM27761 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive, and have very low ESR (≤ 15 mΩ typical). Tantalum
capacitors, OS-CON capacitors, and aluminum electrolytic capacitors generally are not recommended for use
with the LM27761 due to their high ESR compared to ceramic capacitors.
For most applications, ceramic capacitors with an X7R or X5R temperature characteristic are preferable for use
with the LM27761. These capacitors have tight capacitance tolerances (as good as ±10%) and hold their value
over temperature (X7R: ±15% over –55°C to +125°C; X5R ±15% over –55°C to +85°C).
Using capacitors with a Y5V or Z5U temperature characteristic is generally not recommended for the LM27761.
These capacitors typically have wide capacitance tolerance (80%, ….20%) and vary significantly over
temperature (Y5V: 22%, –82% over –30°C to +85°C range; Z5U: 22%, –56% over 10°C to 85°C range). Under
some conditions a 1-µF-rated Y5V or Z5U capacitor could have a capacitance as low as 0.1 µF. Such
detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capacitance
requirements of the LM27761.
Net capacitance of a ceramic capacitor decreases with increased DC bias. This degradation can result in lower-
than-expected capacitance on the input and/or output, resulting in higher ripple voltages and currents. Using
capacitors at DC bias voltages significantly below the capacitor voltage rating usually minimizes DC bias effects.
Consult capacitor manufacturers for information on capacitor DC bias characteristics.
Capacitance characteristics can vary quite dramatically with different application conditions, capacitor types, and
capacitor manufacturers. TI strongly recommends that the LM27761 circuit be evaluated thoroughly early in the
design-in process with the mass-production capacitor of choice. This helps ensure that any such variability in
capacitance does not negatively impact circuit performance.
8.2.2.6.1 Charge-Pump Output Capacitor
In typical applications, a 4.7-µF low-ESR ceramic charge-pump output capacitor (C3) is recommended. Different
output capacitance values can be used to reduce charge pump ripple, shrink the solution size, and/or cut the
cost of the solution. However, changing the output capacitor may also require changing the flying capacitor or
input capacitor to maintain good overall circuit performance.
In higher-current applications, a 10-µF, 10-V low-ESR ceramic output capacitor is recommended. If a small
output capacitor is used, the output ripple can become large during the transition between PFM mode and
constant switching. To prevent toggling, a 2-µF capacitance is recommended. For example, 10-µF, 10-V output
capacitor in a 0402 case size typically has only 2-µF capacitance when biased to 5 V.
8.2.2.6.2 Input Capacitor
The input capacitor (C2) is a reservoir of charge that aids in a quick transfer of charge from the supply to the
flying capacitors during the charge phase of operation. The input capacitor helps to keep the input voltage from
drooping at the start of the charge phase when the flying capacitors are connected to the input. It also filters
noise on the input pin, keeping this noise out of the sensitive internal analog circuitry that is biased off the input
line.
Input capacitance has a dominant and first-order effect on the input ripple magnitude. Increasing (decreasing) the
input capacitance results in a proportional decrease (increase) in input voltage ripple. Input voltage, output
current, and flying capacitance also affects input ripple levels to some degree.
In typical applications, a 4.7-µF low-ESR ceramic capacitor is recommended on the input. When operating near
the maximum load of 250 mA, after taking into the DC bias derating, a minimum recommended input capacitance
is 2 µF or larger. Different input capacitance values can be used to reduce ripple, shrink the solution size, and/or
cut the cost of the solution.
8.2.2.6.3 Flying Capacitor
The flying capacitor (C1) transfers charge from the input to the output. Flying capacitance can impact both output
current capability and ripple magnitudes. If flying capacitance is too small, the LM27761 may not be able to
regulate the output voltage when load currents are high. On the other hand, if the flying capacitance is too large,
the flying capacitor might overwhelm the input and charge pump output capacitors, resulting in increased input
and output ripple.
14
版权 © 2015–2017, Texas Instruments Incorporated
LM27761
www.ti.com.cn
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
In typical high-current applications, 0.47-µF or 1-µF 10-V low-ESR ceramic capacitors are recommended for the
flying capacitors. Polarized capacitors (tantalum, aluminum, electrolytic, etc.) must not be used for the flying
capacitor, as they could become reverse-biased during LM27761 operation.
8.2.2.6.4 LDO Output Capacitor
The LDO output capacitor (C4) value and the ESR affect stability, output ripple, output noise, PSRR and
transient response. The LM27761 only requires the use of a 2.2-µF ceramic output capacitor for stable operation.
For typical applications, a 2.2-µF ceramic output capacitor located close to the output is sufficient.
8.2.3 Application Curves
100
10
1
200
100
25°C
85°C
-40°C
25°C
85°C
-40°C
10
1
0.001
0.001
0.01
IOUT (A)
0.1
0.25
0.01
IOUT (A)
0.1
0.25
D003
D004
VIN = 3 V
VOUT = –1.8 V
VIN = 5.5 V
VOUT = –5 V
图 18. Charge-Pump Output Impedance vs
图 19. Charge-Pump Output Impedance vs
Output Current
Output Current
VIN = 3 V
VOUT = –1.8 V
VIN = 4V to 4.5 V
VOUT = –1.8 V
IOUT = 100 mA
图 21. Load Step
图 20. Line Step
版权 © 2015–2017, Texas Instruments Incorporated
15
LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
25°C
85°C
-40°C
0
0.0001
0.001
0.01
0.1
1
Output Current (A)
D005
VIN = 5.5 V
VOUT = –5 V
R1 = 1.54 MΩ
R2 = 500 kΩ
图 22. Efficiency vs Output Current
9 Power Supply Recommendations
The LM27761 is designed to operate from an input voltage supply range between 2.7 V and 5.5 V. This input
supply must be well regulated and capable of supplying the required input current. If the input supply is located
far form the LM27761, additional bulk capacitance may be required in addition to the ceramic bypass capacitors.
10 Layout
10.1 Layout Guidelines
The high switching frequency and large switching currents of the LM27761 make the choice of layout important.
Use the following steps as a reference to ensure the device is stable and maintains proper LED current
regulation across its intended operating voltage and current range:
•
Place CIN on the top layer (same layer as the LM27761) and as close to the device as possible. Connecting
the input capacitor through short, wide traces to both the VIN and GND pins reduces the inductive voltage
spikes that occur during switching which can corrupt the VIN line.
•
Place CCPOUT on the top layer (same layer as the LM27761) and as close to the VOUT and GND pins as
possible. The returns for both CIN and CCPOUT must come together at one point, as close to the GND pin
as possible. Connecting CCPOUT through short, wide traces reduces the series inductance on the VCPOUT
and GND pins that can corrupt the VCPOUT and GND lines and cause excessive noise in the device and
surrounding circuitry.
•
•
Place C1 on top layer (same layer as the LM27761) and as close to the device as possible. Connect the
flying capacitor through short, wide traces to both the C1+ and C1– pins.
Place COUT on the top layer (same layer as the LM27761) and as close to the VOUT pin as possible. For
best performance the ground connection for COUT must connect back to the GND connection at the thermal
pad of the device.
•
Place R1 and R2 on the top layer (same layer as LM27761) and as close to the VFB pin as possible. For best
performance the ground connection of R2 must connect back to the GND connection at the thermal pad of
the device.
Connections using long trace lengths, narrow trace widths, or connections through vias must be avoided. These
add parasitic inductance and resistance that results in inferior performance, especially during transient
conditions.
16
版权 © 2015–2017, Texas Instruments Incorporated
LM27761
www.ti.com.cn
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
10.2 Layout Example
C1
R1
R2
COUT
To Supply
CIN
CCPOUT
To GND Plane
图 23. LM27761 Layout Example
版权 © 2015–2017, Texas Instruments Incorporated
17
LM27761
ZHCSEO7C –OCTOBER 2015–REVISED JANUARY 2017
www.ti.com.cn
11 器件和文档支持
11.1 器件支持
11.1.1 开发支持
11.1.1.1 使用 WEBENCH® 工具创建定制设计
请单击此处，使用 LM27761 器件并借助 WEBENCH® 电源设计器创建定制设计。
1. 在开始阶段键入输出电压 (VIN)、输出电压 (VOUT) 和输出电流 (IOUT) 要求。
2. 使用优化器拨盘优化关键设计参数，如效率、封装和成本。
3. 将生成的设计与德州仪器 (TI) 的其他解决方案进行比较。
WEBENCH Power Designer 提供一份定制原理图以及罗列实时价格和组件可用性的物料清单。
在多数情况下，可执行以下操作：
•
•
•
•
运行电气仿真，观察重要波形以及电路性能
运行热性能仿真，了解电路板热性能
将定制原理图和布局方案导出至常用 CAD 格式
打印设计方案的 PDF 报告并与同事共享
有关 WEBENCH 工具的详细信息，请访问 www.ti.com/WEBENCH。
11.2 接收文档更新通知
要接收文档更新通知，请导航至德州仪器 TI.com.cn 上的器件产品文件夹。请单击右上角的通知我 进行注册，即可
收到任意产品信息更改每周摘要。有关更改的详细信息，请查看任意已修订文档中包含的修订历史记录。
11.3 社区资源
下列链接提供到 TI 社区资源的连接。链接的内容由各个分销商“按照原样”提供。这些内容并不构成 TI 技术规范，
并且不一定反映 TI 的观点；请参阅 TI 的 《使用条款》。
TI E2E™ 在线社区 TI 的工程师对工程师 (E2E) 社区。此社区的创建目的在于促进工程师之间的协作。在
e2e.ti.com 中，您可以咨询问题、分享知识、拓展思路并与同行工程师一道帮助解决问题。
设计支持
TI 参考设计支持 可帮助您快速查找有帮助的 E2E 论坛、设计支持工具以及技术支持的联系信息。
11.4 商标
E2E is a trademark of Texas Instruments.
WEBENCH is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 静电放电警告
这些装置包含有限的内置 ESD 保护。 存储或装卸时，应将导线一起截短或将装置放置于导电泡棉中，以防止 MOS 门极遭受静电损
伤。
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 机械、封装和可订购信息
以下页面包括机械、封装和可订购信息。这些信息是指定器件的最新可用数据。这些数据发生变化时，我们可能不
会另行通知或修订此文档。如欲获取此产品说明书的浏览器版本，请参阅左侧的导航栏。
18
版权 © 2015–2017, Texas Instruments Incorporated
PACKAGE OPTION ADDENDUM
www.ti.com
18-Jul-2023
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
(6)
LM27761DSGR
LM27761DSGT
ACTIVE
ACTIVE
WSON
WSON
DSG
DSG
8
8
3000 RoHS & Green
250 RoHS & Green
NIPDAU
Level-1-260C-UNLIM
Level-1-260C-UNLIM
-40 to 85
-40 to 85
ZGLI
ZGLI
Samples
Samples
NIPDAU
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
18-Jul-2023
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Mar-2022
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LM27761DSGR
LM27761DSGR
LM27761DSGT
LM27761DSGT
WSON
WSON
WSON
WSON
DSG
DSG
DSG
DSG
8
8
8
8
3000
3000
250
180.0
180.0
180.0
180.0
8.4
8.4
8.4
8.4
2.3
2.3
2.3
2.3
2.3
2.3
2.3
2.3
1.15
1.15
1.15
1.15
4.0
4.0
4.0
4.0
8.0
8.0
8.0
8.0
Q2
Q2
Q2
Q2
250
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Mar-2022
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM27761DSGR
LM27761DSGR
LM27761DSGT
LM27761DSGT
WSON
WSON
WSON
WSON
DSG
DSG
DSG
DSG
8
8
8
8
3000
3000
250
210.0
210.0
210.0
210.0
185.0
185.0
185.0
185.0
35.0
35.0
35.0
35.0
250
Pack Materials-Page 2
GENERIC PACKAGE VIEW
DSG 8
2 x 2, 0.5 mm pitch
WSON - 0.8 mm max height
PLASTIC SMALL OUTLINE - NO LEAD
This image is a representation of the package family, actual package may vary.
Refer to the product data sheet for package details.
4224783/A
www.ti.com
PACKAGE OUTLINE
DSG0008A
WSON - 0.8 mm max height
SCALE 5.500
PLASTIC SMALL OUTLINE - NO LEAD
2.1
1.9
B
A
0.32
0.18
PIN 1 INDEX AREA
2.1
1.9
0.4
0.2
ALTERNATIVE TERMINAL SHAPE
TYPICAL
0.8
0.7
C
SEATING PLANE
0.05
0.00
SIDE WALL
0.08 C
METAL THICKNESS
DIM A
OPTION 1
0.1
OPTION 2
0.2
EXPOSED
THERMAL PAD
(DIM A) TYP
0.9 0.1
5
4
6X 0.5
2X
1.5
9
1.6 0.1
8
1
0.32
0.18
PIN 1 ID
(45 X 0.25)
8X
0.4
0.2
8X
0.1
C A B
C
0.05
4218900/E 08/2022
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.
www.ti.com
EXAMPLE BOARD LAYOUT
DSG0008A
WSON - 0.8 mm max height
PLASTIC SMALL OUTLINE - NO LEAD
(0.9)
(
0.2) VIA
8X (0.5)
TYP
1
8
8X (0.25)
(0.55)
SYMM
9
(1.6)
6X (0.5)
5
4
SYMM
(1.9)
(R0.05) TYP
LAND PATTERN EXAMPLE
SCALE:20X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
SOLDER MASK
OPENING
METAL
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
NON SOLDER MASK
DEFINED
SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK DETAILS
4218900/E 08/2022
NOTES: (continued)
4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
5. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown
on this view. It is recommended that vias under paste be filled, plugged or tented.
www.ti.com
EXAMPLE STENCIL DESIGN
DSG0008A
WSON - 0.8 mm max height
PLASTIC SMALL OUTLINE - NO LEAD
8X (0.5)
METAL
8
SYMM
1
8X (0.25)
(0.45)
SYMM
9
(0.7)
6X (0.5)
5
4
(R0.05) TYP
(0.9)
(1.9)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
EXPOSED PAD 9:
87% PRINTED SOLDER COVERAGE BY AREA UNDER PACKAGE
SCALE:25X
4218900/E 08/2022
NOTES: (continued)
6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
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