LM2776DBVR [TI]
开关电容器逆变器 | DBV | 6 | -40 to 85;
| 型号： | LM2776DBVR |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 开关电容器逆变器 | DBV | 6 | -40 to 85 开关 控制器 开关式稳压器 开关式控制器 光电二极管 电源电路 电容器 开关式稳压器或控制器 |
| 文件： | 总23页 (文件大小：1733K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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LM2776
SNVSA56 –MAY 2015
LM2776 Switched Capacitor Inverter
1 Features
3 Description
The LM2776 CMOS charge-pump voltage converter
inverts a positive voltage in the range of 2.7 V to 5.5
V to the corresponding negative voltage. The LM2776
uses three low-cost capacitors to provide 200 mA of
output current without the cost, size, and
electromagnetic interference (EMI) related to
inductor-based converters.
1
•
•
•
•
•
•
•
•
Input Voltage: 2.7 V to 5.5 V
200-mA Output Current
Inverts Input Supply Voltage
Low-Current PFM Mode Operation
2-MHz Switching Frequency
Greater than 90% Efficiency
Current Limit and Thermal Protection
No Inductors
With an operating current of only 100 μA and
operating efficiency greater than 90% at most loads,
the LM2776 provides ideal performance for battery-
powered systems requiring a high power negative
power supply.
2 Applications
•
•
•
•
•
Operational Amplifier Power Supplies
Interface Power Supplies
The LM2776 has been placed in TI's 6-pin SOT-23 to
maintain a small form factor.
Data Converter Supplies
Device Information(1)
Audio Amplifier Power Supplies
Portable Electronic Devices
PART NUMBER
LM2776
PACKAGE
BODY SIZE (NOM)
SOT (6)
2.90 mm x 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
space
space
space
Typical Application
Output Impedance vs Input Voltage
IOUT = 100 mA
LM2776
2.7 V to 5.5 V
-VIN @ up to 200mA
2.2 PF
5.0
VIN
EN
VOUT
C1+
TA = -40°C
TA = 25°C
4.5
2.2 PF
TA = 85°C
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1 PF
GND
C1-
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
D005
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.
LM2776
SNVSA56 –MAY 2015
www.ti.com
Table of Contents
7.3 Feature Description................................................... 9
7.4 Device Functional Modes........................................ 10
Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Application - Voltage Inverter ..................... 11
Power Supply Recommendations...................... 15
1
2
3
4
5
6
Features.................................................................. 1
Applications ........................................................... 1
Description ............................................................. 1
Revision History..................................................... 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 Switching Characteristics.......................................... 5
6.7 Typical Characteristics ............................................. 5
Detailed Description .............................................. 9
7.1 Overview ................................................................... 9
7.2 Functional Block Diagram ......................................... 9
8
9
10 Layout................................................................... 15
10.1 Layout Guidelines ................................................. 15
10.2 Layout Example .................................................... 15
11 Device and Documentation Support ................. 16
11.1 Device Support...................................................... 16
11.2 Community Resources.......................................... 16
11.3 Trademarks........................................................... 16
11.4 Electrostatic Discharge Caution............................ 16
11.5 Glossary................................................................ 16
7
12 Mechanical, Packaging, and Orderable
Information ........................................................... 16
4 Revision History
DATE
REVISION
NOTES
May 2015
*
Initial release.
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5 Pin Configuration and Functions
DBV Package
6 Pin SOT
Top View
1
2
6
5
LM2776
3
4
Pin Functions
PIN
TYPE
DESCRIPTION
NUMBER
NAME
VOUT
GND
VIN
1
2
3
Output/Power
Ground
Negative voltage output.
Power supply ground input.
Input/Power
Power supply positive voltage input.
Enable control pin, tie this pin high (EN = '1') for normal operation, and to GND
(EN = '0') for shutdown.
4
EN
Input
5
6
C1+
C1-
Power
Power
Connect this pin to the positive terminal of the charge-pump capacitor.
Connect this pin to the negative terminal of the charge-pump capacitor.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN
MAX
6
UNIT
V
Supply voltage (VIN to GND, or GND to VOUT)
EN
(GND − 0.3)
(VIN + 0.3)
250
V
VOUT continuous output current
mA
°C
(3)
Operating junction temperature, TJMax
125
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 Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) The maximum allowable power dissipation is calculated by using PDMax = (TJMax − TA)/RθJA, where TJMax is the maximum junction
temperature, TA is the ambient temperature, and RθJA is the junction-to-ambient thermal resistance of the specified package.
6.2 ESD Ratings
VALUE
±1000
±250
UNIT
V
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
–40
-40
2.7
0
NOM
MAX
125
85
UNIT
°C
Junction temperature
Ambient temperature
Input voltage
°C
5.5
V
Output current
200
mA
6.4 Thermal Information
LM2776
THERMAL METRIC(1)
DBV (SOT)
6 PINS
187
UNIT
RθJA
RθJC(top)
RθJB
ψJT
Junction-to-ambient thermal resistance
Junction-to-case (top) thermal resistance
Junction-to-board thermal resistance
158.2
33.3
°C/W
Junction-to-top characterization parameter
Junction-to-board characterization parameter
37.8
ψJB
32.8
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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6.5 Electrical Characteristics
Typical limits tested at TA = 25°C. Minimum and maximum limits apply over the full operating ambient temperature range
(−40°C ≤ TA ≤ 85°C). VIN = 3.6 V, CIN = COUT = 2.2 µF, C1 = 1 µF
PARAMETER
Supply current
TEST CONDITIONS
EN = '1'. No load
MIN
TYP
100
0.1
MAX UNIT
IQ
200
1
µA
µA
ISD
Shutdown supply current
EN = '0'
Normal operation
Shutdown mode
1.2
VEN
Enable pin input threshold voltage
V
0.4
ROUT
ICL
Output resistance
Output current limit
2.5
400
2.4
2.6
Ω
mA
VIN Falling
VIN Rising
UVLO
Undervoltage lockout
V
6.6 Switching Characteristics
over operating free-air temperature range (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
1.7
TYP
MAX
2.3
UNIT
ƒSW
Switching frequency
2
MHz
6.7 Typical Characteristics
(Circuit of Typical Application , VIN = 3.6 V unless otherwise specified.)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.035
TA = -40°C
TA = 25°C
TA = 85°C
0.030
0.025
0.020
0.015
0.010
0.005
0.000
TA = -40°C
TA = 25°C
TA = 85°C
0.0001
0.001
0.01
0.1
1
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Output Current (A)
Input Voltage (V)
D001
D002
VIN = 5.5 V
Figure 1. Output Ripple vs Output Current
IOUT = 100 mA
Figure 2. Output Ripple vs Input Voltage
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Typical Characteristics (continued)
(Circuit of Typical Application , VIN = 3.6 V unless otherwise specified.)
0.000002
0.0000015
0.000001
0.0000005
0
0.00012
TA = -40°C
TA = 25°C
TA = 85°C
0.0001
0.00008
0.00006
0.00004
0.00002
0
TA = -40°C
TA = 25°C
TA = 85°C
-0.0000005
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
VIN (V)
VIN (V)
D003
D004
No load
Figure 3. Shutdown Current vs Input Voltage
Figure 4. Quiescent Current vs Input Voltage
1000
500
100
90
80
70
60
50
40
30
20
10
TA = -40°C
TA = 25°C
TA = 85°C
300
200
100
50
30
20
10
5
TA = -40°C
TA = 25°C
TA = 85°C
3
2
1
0
0.0001
0.001
0.010.02 0.05 0.1 0.2 0.5
Output Current (A)
1
10P
100P
1m
IOUT (A)
10m
100m
D0056
D00567
VIN = 5.5 V
VIN = 5.5 V
Figure 5. Output Impedance vs Output Current
Figure 6. Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
10
0
-4.7
-4.8
-4.9
-5.0
-5.1
-5.2
-5.3
TA = -40°C
TA = 25°C
TA = 85°C
TA = -40°C
TA = 25°C
TA = 85°C
-5.4
10P
100P
1m
IOUT (A)
10m
100m
10P
100P
1m
IOUT (A)
10m
100m
D00567
D009
VIN = 3.6 V
Figure 7. Efficiency vs Output Current
VIN = 5.5 V
Figure 8. Output Voltage vs Output Current
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Typical Characteristics (continued)
(Circuit of Typical Application , VIN = 3.6 V unless otherwise specified.)
2.06
-2.5
-2.6
-2.7
-2.8
-2.9
-3.0
-3.1
-3.2
-3.3
-3.4
-3.5
-3.6
TA = -40°C
TA = 25°C
TA = 85°C
TA = -40°C
TA = 25°C
TA = 85°C
2.04
2.02
2.00
1.98
1.96
1.94
1.92
1.90
2.7
3.1
3.5
3.9
VIN (V)
4.3
4.7
5.1
5.5
10P
100P
1m
IOUT (A)
10m
100m
D011
D010
IOUT = 150 mA
Figure 10. Frequency vs Input Voltage
VIN = 3.6 V
Figure 9. Output Voltage vs Output Current
IOUT = 0 mA
VIN = 5.5 V
IOUT = 200 mA
VIN = 5.5 V
Figure 11. Unloaded Output Voltage Ripple
Figure 12. Loaded Output Voltage Ripple
EN = 1
VIN = 5.5 V
IOUT = 100 mA
EN = 0
VIN = 5.5 V
IOUT = 100 mA
Figure 13. EN High
Figure 14. EN Low
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Typical Characteristics (continued)
(Circuit of Typical Application , VIN = 3.6 V unless otherwise specified.)
IOUT = 75 mA
VIN = 5.5 V
Figure 16. Load Step 10 mA to 100 mA
Figure 15. Line Step 5.5V to 5V
VIN = 5.5 V
Figure 17. Output Short
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7 Detailed Description
7.1 Overview
The LM2776 CMOS charge-pump voltage converter inverts a positive voltage in the range of 2.7 V to 5.5 V to
the corresponding negative voltage of −2.7 V to −5.5 V. The LM2776 uses three low-cost capacitors to provide
up to 200 mA of output current.
7.2 Functional Block Diagram
LM2776
Current
VIN
Limit
C1+
Switch Array
Switch
2 MHz
Drivers
C1-
Osc.
VOUT
GND
EN
Reference
7.3 Feature Description
7.3.1 Input Current Limit
The LM2776 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 400 mA (typical at VIN = 5.5 V) when the output is shorted
directly to ground. When the LM2776 is current limiting, power dissipation in the device is likely to be quite high.
In this event, thermal cycling should be expected.
7.3.2 PFM Operation
To minimize quiescent current during light load operation, the LM2776 allows PFM or pulse-skipping operation.
By allowing the charge pump to switch less when the output current is less than 40 mA, the quiescent current
drawn from the power source is minimized. The frequency of pulsed operation is not limited and can drop into the
sub-1-kHz range when unloaded. As the load increases, the frequency of pulsing increases until it transitions to
constant frequency. The fundamental switching frequency of the LM2776 is 2 MHz.
7.3.3 Output Discharge
In shutdown, the LM2776 will actively pull 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.
7.3.4 Thermal Shutdown
The LM2776 implements a thermal shutdown mechanism to protect the device from damage due to overheating.
When the junction temperature rises to 150°C (typical), the part switches into shutdown mode. The LM2776
releases thermal shutdown when the junction temperature of the part is reduced to 130°C (typical).
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Feature Description (continued)
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. LM2776 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 be 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 LM2776.
7.3.5 Undervoltage Lockout
The LM2776 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 LM2776 will resume normal operation.
7.4 Device Functional Modes
7.4.1 Shutdown Mode
An enable pin (EN) pin is available to disable the device and place the LM2776 into shutdown mode reducing the
quiescent current to 1 µA. In shutdown, the output of the LM2776 is pulled to ground by an internal pullup current
source (approx 1.85 mA).
7.4.2 Enable Mode
Applying a voltage greater than 1.2 V to the EN pin will bring the device into Enable mode. When unloaded, the
input current during operation is 120 µA. As the load current increases, so does the quiescent current. When
enabled, the output voltage will be equal to the inverse of the input voltage minus the voltage drop across the
charge pump.
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM2776 CMOS charge-pump voltage converter inverts a positive voltage in the range of 2.7 V to 5.5 V to
the corresponding negative voltage of −2.7 V to −5.5 V. The device uses three low-cost capacitors to provide up
to 200 mA of output current. The LM2776 operates at 2-MHz oscillator frequency to reduce output resistance and
voltage ripple under heavy loads. With an operating current of only 100 µA (operating efficiency greater than
91% with most loads) and 1-µA typical shutdown current, the LM2776 provides ideal performance for battery-
powered systems.
8.2 Typical Application - Voltage Inverter
VS+
+
Boost or Battery
VS-
2.2 PF
LM2776
VIN
EN
VOUT
C1+
1 PF
2.2 PF
PP / PC
GND
C1-
Figure 18. Voltage Inverter
8.2.1 Design Requirements
Example requirements for typical voltage inverter applications:
DESIGN PARAMETER
Input voltage range
Output current
EXAMPLE VALUE
2.7 V to 5.5 V
0 mA to 200 mA
2 MHz
Boost switching frequency
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8.2.2 Detailed Design Requirements
The main application of LM2776 is to generate a negative supply voltage. The voltage inverter circuit uses only
three external capacitors with an range of the input supply voltage from 2.7 V to 5.5 V.
The LM2776 contains four large CMOS switches which are switched in a sequence to invert the input supply
voltage. Energy transfer and storage are provided by external capacitors. Figure 19 illustrates the voltage
conversion scheme. When S1 and S3 are closed, C1 charges to the supply voltage VIN. During this time interval,
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, C1 is charging C2. After a number of cycles, the voltage across C2 will be pumped to VIN. Since the
anode of C2 is connected to ground, the output at the cathode of C2 equals −(VIN) when there is no load current.
The output voltage drop when a load is added is determined by the parasitic resistance (Rds(on) of the MOSFET
switches and the equivalent series resistance (ESR) of the capacitors) and the charge transfer loss between
capacitors.
S1
C1+
S2
VIN
CIN
GND
C1
COUT
GND
S3
S4
C1-
VOUT
OSC.
2 MHz
+
PFM COMP
Figure 19. Voltage Inverting Principle
The output characteristics 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 ESR of C1 and C2. Since the
switching current charging and discharging C1 is approximately twice as the output current, the effect of the ESR
of the pumping capacitor C1 will be multiplied by four in the output resistance. The output capacitor C2 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 ROUT is:
ROUT = RSW + [1 / (ƒSW × C)] + (4 × ESRC1) + ESRCOUT
where
•
RSW is the sum of the ON resistance of the internal MOSFET switches shown in Figure 19.
(1)
High capacitance, low ESR ceramic capacitors will reduce the output resistance.
8.2.2.1 Efficiency
Charge-pump efficiency is defined as
Efficiency = [(VOUT × IOUT) / {VIN × (IIN + IQ)}]
where
•
IQ(VIN) is the quiescent power loss of the device.
(2)
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8.2.2.2 Power Dissipation
LM2776 power dissipation (PD) is calculated simply by subtracting output power from input power:
PD = PIN - POUT = [VIN × ( -IOUT + IQ)] – [VOUT × IOUT
]
(3)
Power dissipation increases with increased input voltage and output current. Internal power dissipation self-heats
the device. Dissipating this amount power/heat so the LM2776 does not overheat is a demanding thermal
requirement for a small surface-mount package. When soldered to a PCB with layout conducive to power
dissipation, the thermal properties of the SOT package enable this power to be dissipated from the LM2776 with
little or no derating, even when the circuit is placed in elevated ambient temperatures when the output current is
200 mA or less.
8.2.2.3 Capacitor Selection
The LM2776 requires 3 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive, and have very low equivalent series resistance
(ESR, ≤ 15 mΩ typical). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors
generally are not recommended for use with the LM2776 due to their high ESR, as compared to ceramic
capacitors.
For most applications, ceramic capacitors with an X7R or X5R temperature characteristic are preferred for use
with the LM2776. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over
temperature (X7R: ±15% over –55ºC to 125°C; X5R: ±15% over –55°C to 85°C).
Capacitors with a Y5V or Z5U temperature characteristic are generally not recommended for use with the
LM2776. These types of 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 LM2776.
Net capacitance of a ceramic capacitor decreases with increased DC bias. This degradation can result in lower
capacitance than expected 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 will usually minimize 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. It is strongly recommended that the LM2776 circuit be thoroughly evaluated early in the
design-in process with the mass-production capacitors of choice. This will help ensure that any such variability in
capacitance does not negatively impact circuit performance.
The voltage rating of the output capacitor should be 10 V or more. For example, a 10-V 0603 1-µF is acceptable
for use with the LM2776, as long as the capacitance does not fall below a minimum of 0.5 µF in the intended
application. All other capacitors should have a voltage rating at or above the maximum input voltage of the
application. The capacitors should be selected such that the capacitance on the input does not fall below 0.7 µF,
and the capacitance of the flying capacitor does not fall below 0.2 µF.
8.2.2.4 Output Capacitor and Output Voltage Ripple
The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the
output capacitor COUT
:
VRIPPLE = [(2 × ILOAD) / (ƒSW × COUT)] + (2 × ILOAD × ESRCOUT
)
(4)
In typical applications, a 1-µF low-ESR ceramic output capacitor is recommended. Different output capacitance
values can be used to reduce ripple shrink the solution size, and/or cut the cost of the solution. But changing the
output capacitor may also require changing the flying capacitor and/or input capacitor to maintain good overall
circuit performance.
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NOTE
In high-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, a 10- µF, 10-V output capacitor in a 0402
case size will typically only have 2-µF capacitance when biased to 5 V.
High ESR in the output capacitor increases output voltage ripple. If a ceramic capacitor is used at the output, this
is usually not a concern because the ESR of a ceramic capacitor is typically very low and has only a minimal
impact on ripple magnitudes. If a different capacitor type with higher ESR is used (tantalum, for example), the
ESR could result in high ripple. To eliminate this effect, the net output ESR can be significantly reduced by
placing a low-ESR ceramic capacitor in parallel with the primary output capacitor. The low ESR of the ceramic
capacitor will be in parallel with the higher ESR, resulting in a low net ESR based on the principles of parallel
resistance reduction.
8.2.2.5 Input Capacitor
The input capacitor (CIN) is a reservoir of charge that aids 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 sensitive internal analog circuitry that is biased off the input line.
Much like the relationship between the output capacitance and output voltage ripple, input capacitance has a
dominant and first-order effect on input ripple magnitude. Increasing (decreasing) the input capacitance will result
in a proportional decrease (increase) in input voltage ripple. Input voltage, output current, and flying capacitance
also will affect input ripple levels to some degree.
In typical applications, a 1-µF low-ESR ceramic capacitor is recommended on the input. When operating near the
maximum load of 200 mA, a minimum recommended input capacitance after taking into the DC Bias derating 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 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 LM2776 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 output capacitors, resulting in increased input and output
ripple.
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 LM2776 operation.
14
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Product Folder Links: LM2776
LM2776
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SNVSA56 –MAY 2015
8.2.3 Application Curve
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TA = -40°C
TA = 25°C
TA = 85°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.4
Input Voltage (V)
D005
Figure 20. Output Impedance vs Input Voltage
9 Power Supply Recommendations
The LM2776 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 to supply the required input current. If the input supply is located far
from the LM2776 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 LM2776 make the choice of layout important.
The following steps should be used 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 LM2776) 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 COUT on the top layer (same layer as the LM2776) and as close as possible to the VOUT and GND
pins. The returns for both CIN and COUT should come together at one point, as close to the GND pin as
possible. Connecting COUT through short, wide traces reduce the series inductance on the VOUT and GND
pins that can corrupt the VOUT and GND lines and cause excessive noise in the device and surrounding
circuitry.
•
Place C1 on the top layer (same layer as the LM2776) and as close to the device as possible. Connect the
flying capacitor through short, wide traces to both the C1+ and C1– pins.
10.2 Layout Example
LM2776
To Load
VOUT
GND
VIN
C1-
C1+
EN
COUT
C1
To GND Plane
CIN
To Supply
Figure 21. LM2776 Layout Example
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11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.3 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
9-Jul-2015
PACKAGING INFORMATION
Orderable Device
LM2776DBVR
LM2776DBVT
Status Package Type Package Pins Package
Eco Plan
Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-40 to 85
Device Marking
Samples
Drawing
Qty
(1)
(2)
(6)
(3)
(4/5)
ACTIVE
SOT-23
SOT-23
DBV
6
6
3000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
2776
2776
ACTIVE
DBV
250
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 85
(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.
(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/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
9-Jul-2015
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Jul-2015
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)
LM2776DBVR
LM2776DBVT
SOT-23
SOT-23
DBV
DBV
6
6
3000
250
178.0
178.0
9.0
9.0
3.23
3.23
3.17
3.17
1.37
1.37
4.0
4.0
8.0
8.0
Q3
Q3
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Jul-2015
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM2776DBVR
LM2776DBVT
SOT-23
SOT-23
DBV
DBV
6
6
3000
250
180.0
180.0
180.0
180.0
18.0
18.0
Pack Materials-Page 2
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相关型号：
LM2781TPX/NOPB
IC SWITCHED CAPACITOR CONVERTER, 400 kHz SWITCHING FREQ-MAX, PBGA8, CSP-8, Switching Regulator or Controller
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