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LM2776
SNVSA56B – MAY 2015 – REVISED FEBRUARY 2017
LM2776 Switched Capacitor Inverter
1 Features
3 Description
•
•
•
•
•
•
•
•
The LM2776 CMOS charge-pump voltage converter
inverts a positive voltage in the range from 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 batterypowered systems requiring a high power negative
power supply.
2 Applications
•
•
•
•
•
Operational Amplifier Power Supplies
Interface Power Supplies
Data Converter Supplies
Audio Amplifier Power Supplies
Portable Electronic Devices
The LM2776 has been placed in TI's 6-pin SOT-23 to
maintain a small form factor.
Device Information(1)
PART NUMBER
LM2776
PACKAGE
BODY SIZE (NOM)
SOT-23 (6)
2.90 mm × 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
space
space
space
Typical Application
Output Impedance vs Input Voltage
IOUT = 100 mA
LM2776
2.7 V to 5.5 V
VIN
VOUT
-VIN @ up to 200mA
5.0
TA = -40°C
TA = 25°C
TA = 85°C
4.5
EN
GND
2.2 PF
C1+
1 PF
C1-
4.0
Output Impedance (:)
2.2 PF
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
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
SNVSA56B – MAY 2015 – REVISED FEBRUARY 2017
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
5
5
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Switching Characteristics ..........................................
Typical Characteristics .............................................
Detailed Description .............................................. 9
7.1 Overview ................................................................... 9
7.2 Functional Block Diagram ......................................... 9
7.3 Feature Description................................................... 9
7.4 Device Functional Modes........................................ 10
8
Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Application - Voltage Inverter ..................... 11
9 Power Supply Recommendations...................... 15
10 Layout................................................................... 15
10.1 Layout Guidelines ................................................. 15
10.2 Layout Example .................................................... 15
11 Device and Documentation Support ................. 16
11.1
11.2
11.3
11.4
11.5
11.6
Device Support......................................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
16
16
16
16
16
16
12 Mechanical, Packaging, and Orderable
Information ........................................................... 16
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision A (February 2016) to Revision B
•
Added link for TIDA-01063 reference design ......................................................................................................................... 1
Changes from Original (May 2015) to Revision A
•
2
Page
Page
Changed Equation 1 from "ROUT = RSW..." to "ROUT = (2 × RSW)..."....................................................................................... 12
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5 Pin Configuration and Functions
DBV Package
6-Pin SOT
Top View
1
2
6
LM2776
3
5
4
Pin Functions
PIN
TYPE
DESCRIPTION
NUMBER
NAME
1
VOUT
Output/Power
2
GND
Ground
3
VIN
Input/Power
4
EN
Input
Enable control pin, tie this pin high (EN = 1) for normal operation, and to GND (EN
= 0) for shutdown.
5
C1+
Power
Connect this pin to the positive terminal of the charge-pump capacitor.
6
C1-
Power
Connect this pin to the negative terminal of the charge-pump capacitor.
Negative voltage output.
Power supply ground input.
Power supply positive voltage input.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
MIN
MAX
UNIT
6
V
Supply voltage (VIN to GND, or GND to VOUT)
(GND − 0.3)
EN
(VIN + 0.3)
V
VOUT continuous output current
250
mA
Operating junction temperature, TJMax (3)
125
°C
150
°C
Storage temperature, Tstg
(1)
(2)
(3)
–65
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.
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
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
Electrostatic
discharge
V(ESD)
(1)
(2)
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001
VALUE
UNIT
±1000
V
±250
V
(1)
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
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
UNIT
125
°C
–40
85
°C
2.7
5.5
V
0
200
mA
Junction temperature
–40
Ambient temperature
Input voltage
Output current
NOM
6.4 Thermal Information
LM2776
THERMAL METRIC (1)
DBV (SOT)
UNIT
6 PINS
RθJA
Junction-to-ambient thermal resistance
187
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
158.2
°C/W
RθJB
Junction-to-board thermal resistance
33.3
°C/W
ψJT
Junction-to-top characterization parameter
37.8
°C/W
ψJB
Junction-to-board characterization parameter
32.8
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and 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
TEST CONDITIONS
IQ
Supply current
EN = 1. No load
ISD
Shutdown supply current
EN = 0
VEN
Enable pin input threshold voltage
ROUT
Output resistance
ICL
Output current limit
UVLO
Undervoltage lockout
MIN
Normal operation
TYP
MAX
UNIT
100
200
µA
0.1
1
µA
1.2
Shutdown mode
V
0.4
2.5
Ω
400
mA
VIN Falling
2.4
VIN Rising
2.6
V
6.6 Switching Characteristics
over operating free-air temperature range (unless otherwise noted)
PARAMETER
ƒSW
TEST CONDITIONS
Switching frequency
MIN
TYP
MAX
UNIT
1.7
2
2.3
MHz
6.7 Typical Characteristics
(Typical Application circuit, VIN = 3.6 V unless otherwise specified.)
0.14
0.035
TA = -40°C
TA = 25°C
TA = 85°C
0.12
0.030
0.025
Ripple (V)
Ripple (V)
0.10
0.08
0.06
0.020
0.015
0.04
0.010
0.02
0.005
0.00
0.0001
0.001
0.01
Output Current (A)
0.1
1
0.000
2.7
TA = -40°C
TA = 25°C
TA = 85°C
3.1
D001
VIN = 5.5 V
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.5
D002
IOUT = 100 mA
Figure 1. Output Ripple vs Output Current
Figure 2. Output Ripple vs Input Voltage
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Typical Characteristics (continued)
(Typical Application circuit, VIN = 3.6 V unless otherwise specified.)
0.000002
0.00012
TA = -40°C
TA = 25°C
TA = 85°C
0.0000015
0.0001
Current (A)
Current (A)
0.00008
0.000001
0.0000005
0.00006
0.00004
0
TA = -40°C
TA = 25°C
TA = 85°C
0.00002
-0.0000005
2.7
3.1
3.5
3.9
4.3
VIN (V)
4.7
5.1
0
2.7
5.5
3.1
D003
3.5
3.9
4.3
VIN (V)
4.7
5.1
5.5
D004
No load
Figure 3. Shutdown Current vs Input Voltage
Figure 4. Quiescent Current vs Input Voltage
100
TA = -40°C
TA = 25°C
TA = 85°C
500
300
200
90
80
70
100
Efficiency (%)
Output Impedance (:)
1000
50
30
20
10
60
50
40
30
5
3
2
20
TA = -40°C
TA = 25°C
TA = 85°C
10
1
0.0001
0.001
0.010.02 0.05 0.1 0.2
Output Current (A)
0.5
0
10P
1
VIN = 5.5 V
10m
100m
D005
D006
D007
Figure 6. Efficiency vs Output Current
100
-4.7
90
TA = -40°C
TA = 25°C
TA = 85°C
-4.8
80
-4.9
70
60
VOUT (V)
Efficiency (%)
1m
IOUT (A)
VIN = 5.5 V
Figure 5. Output Impedance vs Output Current
50
40
30
-5.0
-5.1
-5.2
20
TA = -40°C
TA = 25°C
TA = 85°C
10
0
10P
100P
1m
IOUT (A)
10m
-5.3
-5.4
10P
100m
100P
D005
D006
D007
VIN = 3.6 V
1m
IOUT (A)
10m
100m
D009
VIN = 5.5 V
Figure 7. Efficiency vs Output Current
6
100P
D006
D005
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Figure 8. Output Voltage vs Output Current
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Typical Characteristics (continued)
(Typical Application circuit, VIN = 3.6 V unless otherwise specified.)
2.06
-2.5
TA = -40°C
TA = 25°C
TA = 85°C
-2.6
-2.7
2.02
Frequency (MHz)
-2.8
-2.9
VOUT (V)
TA = -40°C
TA = 25°C
TA = 85°C
2.04
-3.0
-3.1
-3.2
-3.3
2.00
1.98
1.96
1.94
-3.4
1.92
-3.5
-3.6
10P
100P
1m
IOUT (A)
10m
1.90
2.7
100m
3.9
4.3
VIN (V)
4.7
5.1
5.5
D011
Figure 10. Frequency vs Input Voltage
Figure 9. Output Voltage vs Output Current
VIN = 5.5 V
IOUT = 200 mA
Figure 11. Unloaded Output Voltage Ripple
EN = 1
3.5
IOUT = 150 mA
VIN = 3.6 V
IOUT = 0 mA
3.1
D010
VIN = 5.5 V
IOUT = 100 mA
Figure 13. EN High
VIN = 5.5 V
Figure 12. Loaded Output Voltage Ripple
EN = 0
VIN = 5.5 V
IOUT = 100 mA
Figure 14. EN Low
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Typical Characteristics (continued)
(Typical Application circuit, VIN = 3.6 V unless otherwise specified.)
IOUT = 75 mA
VIN = 5.5 V
Figure 15. Line Step 5.5 V to 5 V
Figure 16. Load Step 10 mA to 100 mA
VIN = 5.5 V
Figure 17. Output Short
8
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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
Limit
VIN
Switch Array
Switch
Drivers
2 MHz
Osc.
C1+
C1VOUT
EN
GND
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 is 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 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.
7.3.4 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 resumes 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 places 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 is equal to the inverse of the input voltage minus the voltage drop across the charge
pump.
10
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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 batterypowered systems.
8.2 Typical Application - Voltage Inverter
VS+
+
Boost or Battery
VS-
2.2 PF
LM2776
PP / PC
VIN
VOUT
EN
C1+
GND
C1-
1 PF
2.2 PF
Figure 18. Voltage Inverter
8.2.1 Design Requirements
Example requirements for typical voltage inverter applications:
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
2.7 V to 5.5 V
Output current
0 mA to 200 mA
Boost switching frequency
2 MHz
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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 shows 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 is pumped to VIN. Because 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
VIN
C1+
S2
GND
CIN
C1
COUT
GND
S3
S4
C1-
VOUT
OSC.
2 MHz
+
PFM COMP
VIN
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. 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 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 = (2 × 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 reduce the output resistance.
8.2.2.1 Efficiency
Charge-pump efficiency is defined as
Efficiency = [(VOUT × IOUT) / {VIN × (IIN + IQ)}]
where
•
12
IQ (VIN) is the quiescent power loss of the device.
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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. TI recommends surface-mount multi-layer
ceramic capacitors. 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 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 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. 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 helps ensure that any such variability in
capacitance does not negatively impact circuit performance.
The voltage rating of the output capacitor must 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 must have a voltage rating at or above the maximum input voltage of the
application. Select the capacitors 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, TI recommends a 10-µF, 10-V low-ESR ceramic output
capacitor. 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 typically only has 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 is 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 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 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, TI recommends 0.47-µF or 1-µF 10 V low-ESR ceramic capacitors 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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8.2.3 Application Curve
5.0
TA = -40°C
TA = 25°C
TA = 85°C
4.5
Output Load (:)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
4.7
5.1
5.4
D005
Figure 20. Output Impedance vs Input Voltage
9 Power Supply Recommendations
The LM2776 is designed to operate from an input voltage supply range from 2.7 V to 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.
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 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 to the VOUT and GND pins as
possible. The returns for both CIN and COUT must 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
C1-
COUT
To GND Plane
CIN
C1
GND
C1+
VIN
EN
To Supply
Figure 21. LM2776 Layout Example
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SNVSA56B – MAY 2015 – REVISED FEBRUARY 2017
www.ti.com
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 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.3 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.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 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.
11.6 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.
16
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM2776DBVR
ACTIVE
SOT-23
DBV
6
3000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
2776
LM2776DBVT
ACTIVE
SOT-23
DBV
6
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
2776
(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
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