LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
LM2770 High Efficiency Switched Capacitor Step-Down DC/DC Regulator with Sleep Mode
Check for Samples: LM2770
FEATURES
APPLICATIONS
•
•
•
•
•
1
2
•
•
•
•
•
•
•
•
•
•
•
High Efficiency Multi-Gain Architecture: Peak
Power Efficiency >85%
Output Voltage Pairs: 1.2V/1.5V and
1.2V/1.575V
Dynamic Output Voltage Selection
±3% Output Voltage Accuracy
Output Currents up to 250mA
2.7V to 5.5V Input Range
Low-Supply-Current Sleep Mode
55µA Quiescent Supply Current in Full-Power
Mode
Soft-Start
Short-Circuit Protection in Full-Power Mode
Current-Limit Protection in Sleep Mode
WSON-10 Package (3mm × 3mm × 0.8mm)
DSP Power Supplies
Baseband Power Supplies
Mobile Phones and Pagers
Portable Electronic Equipment
DESCRIPTION
The LM2770 is a switched capacitor step-down
regulator that is ideal for powering low-voltage
applications in portable systems. The LM2770 can
supply load currents up to 250mA and operates over
an input voltage range of 2.7V to 5.5V. This makes
the LM2770 a great choice for systems powered by
1-cell Li-Ion batteries and chargers. The output
voltage of the LM2770 can be dynamically switched
between two output levels with a logic input pin.
Output voltage pairs currently available include
1.2V/1.5V and 1.2V/1.575V. Other pairs of voltage
options can be developed upon request.
Typical Application Circuit
100%
VOUT :1.2V/1.5V
or 1.2V/1.575V
LM2770
LM2770
90%
Dynamic scaling w/ VSEL
VIN = 2.7V to
5.5V
80%
IOUT up to 250 mA
VIN
VOUT
70%
6
CIN
10 PF
COUT
10 PF
8
C1+
VSEL
C1
1 PF
7
C1-
EN
SLEEP
C2
1 PF
5
C2-
GND
60%
50%
40%
LDO
H: VOUT-H
30%
1
L: VOUT-L
20%
10%
2
H: ON
L: Shutdown
10
H: Sleep
L: Full-power
C2+
3
EFFICIENCY
9
VOUT = 1.5V
IOUT = 100 mA
0%
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
4
Capacitors: 1 PF - TDK C1005X5R0J105K
10 PF - TDK C2012X5R0J106M
or equivalent
Figure 1.
Figure 2. LM2770 Efficiency vs.
Low-Dropout Linear Regulator (LDO) Efficiency
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
DESCRIPTION (CONTINUED)
LM2770 efficiency is superior to both fixed-gain switched capacitor buck regulators and low-dropout linear
regulators (LDO's). Multiple fractional gains maximize power efficiency over the entire input voltage and output
current ranges. The LM2770 can also be switched into a low-power sleep mode when load currents are light (≤
20mA). In sleep mode, the charge pump is off, and the output is driven with a low-noise, low-power linear
regulator.
Soft-start, short-circuit protection, current-limit protection, and thermal-shutdown protection are also included. The
LM2770 is available in TI’s small 10-pin Leadless Leadframe Package (WSON-10).
Connection Diagram
VSEL
1
EN
2
C2+
3
GND
4
C2-
5
10 SLEEP SLEEP 10
Die-Attach
Pad (DAP)
GND
9
VIN
VIN 9
8
C1+
C1+ 8
7
C1-
C1- 7
6
VOUT
Die-Attach
Pad (DAP)
GND
VOUT 6
1
VSEL
2
EN
3
C2+
4
GND
5
C2-
Bottom View
Top View
Figure 3. 10-Pin Non-Pullback Leadless Frame Package (WSON-10)
See Package Number DSC0010A
Pin Description
Pin #
Name
1
VSEL
Description
Output Voltage Select Logic Input. If VSEL is high, VOUT = high voltage. If VSEL is low, VOUT = low voltage. (See
Order Information for available voltage options)
2
EN
Enable Pin Logic Input. If high, part is enabled. If low, part is in shutdown.
3
C2+
Flying Capacitor 2: Positive Terminal
4
GND
Ground
5
C2-
10
SLEEP
Flying Capacitor 2: Negative terminal
9
VIN
Input Voltage. Recommended VIN operating range: 2.7V to 5.5V
8
C1+
Flying Capacitor 1: Positive Terminal
7
C1-
Flying Capacitor 1: Negative Terminal
6
VOUT
Sleep Mode Logic Input. If high, the part operates in sleep mode, and the output is driven by a low power linear
regulator. If low, the part operates in full-power mode, and the output is driven by the switched capacitor regulator
Output Voltage
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.
2
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
Absolute Maximum Ratings (1) (2) (3)
VIN Pin Voltage
-0.3V to 6.0V
EN, SLEEP, and VSEL Pin Voltages
-0.3V to (VIN+0.3V) w/ 6.0V max
Continuous Power Dissipation (4)
Internally Limited
VOUT Short to GND Duration (5)
Infinite
Junction Temperature (TJ-MAX)
150ºC
Storage Temperature Range
-65ºC to +150º C
Maximum Lead Temperature (6)
ESD Rating (7)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
265ºC
Human Body Model
2.0kV
Machine Model
200V
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is specified. Operating Ratings do not imply specified performance limits. For specified performance limits
and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pin.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150ºC (typ.) and
disengages at TJ=140ºC (typ.).
Short circuit protection circuitry protects the part from immediate destructive failure when VOUT is shorted to GND. Applying a continuous
GND short to the output may shorten the lifetime of the device.
For detailed information on soldering requirements and recommendations, please refer to Texas Instruments' Application Note 1187
(Literature Number SNOA401): Leadless Leadframe Package (LLP).
The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF
capacitor discharged directly into each pin. MIL-STD-883 3015.7
Operating Ratings (1) (2)
Input Voltage Range
2.7V to 5.5V
Recommended Load Current Range
0mA to 250mA
Junction Temperature (TJ) Range
-30°C to +105°C
Ambient Temperature (TA) Range (3)
(1)
(2)
(3)
-30°C to +85°C
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is specified. Operating Ratings do not imply specified performance limits. For specified performance limits
and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pin.
Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 105ºC), the
maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package
in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Thermal Properties
Juntion-to-Ambient Thermal Resistance (θJA), WSON10 Package (1)
(1)
55°C/W
Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power
dissipation exists, special care must be paid to thermal dissipation issues.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
3
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
Electrical Characteristics (1) (2)
Limits in standard typeface are for TJ = 25ºC. Limits in boldface type apply over the full operating junction temperature range
(-30°C ≤ TJ ≤ +105°C) . Unless otherwise noted, specifications apply to the LM2770 Typical Application Circuit (pg. 1) with:
VIN = 3.6V; V(EN) = VSEL = 1.8V, V(SLEEP) = 0V, CIN = COUT = 10µF, C1 = C2 = 1.0µF. (3)
Symbol
Parameter
Condition
Min
Typ
Max
VIN = 3.5V, IOUT = 150mA,
VSEL = 1.8V
1.443
1.495
1.547
3.0V ≤ VIN ≤ 4.5V
IOUT = 150mA, VSEL = 1.8V
1.420
1.495
1.570
4.5V < VIN ≤ 5.5V,
IOUT = 150mA, VSEL = 1.8V
1.428
1.495
1.562
VIN = 3.5V, IOUT = 150mA,
VSEL = 0V
1.157
1.205
1.253
3.0V ≤ VIN ≤ 4.5V
IOUT - 150mA, VSEL =0V
1.140
1.205
1.270
4.5V < VIN ≤ 5.5V,
IOUT = 150mA, VSEL = 0V
1.135
1.205
1.275
VIN = 3.5V, IOUT = 150mA,
VSEL = 1.8V
1.528
1.575
1.622
3.1V ≤ VIN ≤ 4.5V
IOUT = 150mA, VSEL = 1.8V
1.500
1.575
1.650
4.5V < VIN ≤ 5.5V,
IOUT = 150mA, VSEL = 1.8V
1.504
1.575
1.646
VIN = 3.5V, IOUT = 150mA,
VSEL = 0V
1.162
1.210
1.258
3.0V ≤ VIN ≤ 4.5V
IOUT - 150mA, VSEL =0V
1.145
1.210
1.275
4.5V < VIN ≤ 5.5V,
IOUT = 150mA, VSEL = 0V
1.145
1.210
1.275
Units
Output Voltage Specifications: Specific to Individual LM2770 Options
LM2770-1215:
1.5V Output Voltage Regulation
VOUT-1215
LM2770-1215:
1.2V Output Voltage Regulation
LM2770-12157:
1.575V Output Voltage Regulation
VOUT-12157
LM2770-12157:
1.2V Output Voltage Regulation
VOUT/IOUT
VLDO-1215
VLDO-12157
(1)
(2)
(3)
4
V
V
Load Regulation
IOUT = 1mA to 250mA
LM2770-1215:
1.5V Output Voltage Regulation SLEEP Mode
3.0V ≤ VIN ≤ 5.5V,
0mA ≤ IOUT ≤ 20mA,
VSEL= 0V, V(SLEEP) = 1.8V
0.18
1.435
LM2770-1215:
1.2V Output Voltage Regulation SLEEP Mode
3.0V ≤ VIN ≤ 5.5V,
0mA ≤ IOUT ≤ 20mA,
VSEL = 0V, V(SLEEP) = 1.8V
1.145
1.205
1.265
LM2770-12157:
1.575V Output Voltage Regulation
- SLEEP Mode
3.0V ≤ VIN ≤ 5.5V,
0mA ≤ IOUT ≤ 20mA,
VSEL= 0V, V(SLEEP) = 1.8V
1.520
1.575
1.630
LM2770-12157:
1.2V Output Voltage Regulation SLEEP Mode
3.0V ≤ VIN ≤ 5.5V,
0mA ≤ IOUT ≤ 20mA,
VSEL = 0V, V(SLEEP) = 1.8V
1.150
1.495
mV/mA
1.555
V
V
1.210
1.270
All voltages are with respect to the potential at the GND pin.
Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most
likely norm.
CIN, COUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
Electrical Characteristics(1)(2) (continued)
Limits in standard typeface are for TJ = 25ºC. Limits in boldface type apply over the full operating junction temperature range
(-30°C ≤ TJ ≤ +105°C) . Unless otherwise noted, specifications apply to the LM2770 Typical Application Circuit (pg. 1) with:
VIN = 3.6V; V(EN) = VSEL = 1.8V, V(SLEEP) = 0V, CIN = COUT = 10µF, C1 = C2 = 1.0µF.(3)
Symbol
Parameter
Condition
Min
Typ
Max
Units
Specifications Below Apply to All LM2770 Options
VIN = 3.6V, IOUT = 150mA
VOUT =1.5V
E
Power Efficiency
82
%
EAVG
Average Eficiency over Li-Ion Input 3.0V ≤ VIN ≤ 4.2V
Voltage Range (4)
IOUT = 200mA, VOUT = 1.5V
73
%
IQ
Quiescent Supply Current: Fullpower Mode
2.7V ≤ VIN ≤ 5.5V
IOUT = 0mA
V(SLEEP) = 0V
55
75
µA
ISLEEP
Quiescent Supply Current: Sleep
Mode
2.7V ≤ VIN ≤ 5.5V
IOUT = 0mA
V(SLEEP) = 1.8V
50
65
µA
ISD
Shutdown Current
2.7V ≤ VIN ≤ 5.5V
V(EN) = 0V
0.1
0.5
µA
ICL
Current Limit - Sleep Mode
0V ≤ VOUT ≤ 0.2V
V(SLEEP) = 1.8V
60
tON
Turn-on Time
VIN = 3.6V, COUT = 10µF
FSW
Switching Frequency
2.7V ≤ VIN ≤ 5.5V
mA
200
475
700
µs
925
kHz
Logic Pin Specifications: EN, ENA, ENB
VIL
Logic-low Input Voltage
2.7V ≤ VIN ≤ 5.5V
0
0.4
V
VIH
Logic-high Input Voltage
2.7V ≤ VIN ≤ 5.5V
1.0
VIN
V
IIH
Logic-high Input Current: SLEEP
and VSEL pins
(5)
IIH-EN
Logic-high Input Current: EN pin
IIL
Logic-low Input Current: All Logic
Pins
(4)
(5)
Logic Input = 3.0V
0.1
µA
V(EN) = 1.8V
6
µA
Logic Input = 0V
0
µA
Efficiency is measured versus VIN, with VIN being swept in small increments from 3.0V to 4.2V. The average is calculated from these
measurement results. Weighting to account for battery voltage discharge characteristics (VBAT vs. Time) is not done in computing the
average.
There is a 300kΩ pull-down resistor connected internally between the EN pin and GND.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
5
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
Block Diagram
LM2770
VIN
720k
C1+
320k
GAIN
CONTROL
SWITCH
ARRAY
SWITCH
CONTROL
C1-
1 1 2
420k
G = 3 ,2 , 3
540k
C2+
C2-
GND
VOUT
Short-Circuit
Protection
165 mV
Ref.
700 kHz
OSC.
VIN
SD
SLEEP
SLEEP-MODE
LDO
ON/
OFF
1.2V/
FB 1.5V
1.2
PUMP/
SKIP
1.5
EN
Enable/
Shutdown
Control
VSEL
Soft-Start
Ramp
0.61V
Reference
1.2
HOP
1.5
6
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
Typical Performance Characteristics
Unless otherwise specified: CIN = 10µF, C1 = 1.0µF, C2 = 1.0µF, COUT = 10µF, TA = 25ºC. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's).
Output Voltage vs. Input Voltage: VOUT = 1.2V
Efficiency vs. Input Voltage: VOUT = 1.2V
1.30
90
85
I OUT = 100 mA
IOUT = 100 mA
80
I OUT = 1 mA
EFFICIENCY (%)
VOUT (V)
1.25
1.20
75
70
65
1.15
I OUT = 200 mA
60
I OUT = 250 mA
I OUT = 250 mA
55
I OUT = 200 mA
1.10
3.0
3.5
4.0
G=1/2
4.5
5.0
G=1/3
50
5.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
Figure 4.
Figure 5.
Output Voltage vs. Input Voltage: VOUT = 1.5V
Efficiency vs. Input Voltage: VOUT = 1.5V
1.60
90
I OUT = 100 mA
85
80
I OUT = 1 mA
I OUT = 100 mA
EFFICIENCY (%)
VOUT (V)
1.55
1.50
1.45
75
70
65
60
I OUT = 200 mA
I OUT = 250 mA
I OUT = 200 mA, 250 mA
55
G=2/3
1.40
3.0
3.5
4.0
4.5
5.0
G=1/2
G=1/3
50
5.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
Figure 6.
Figure 7.
Output Voltage vs. Input Voltage: VOUT = 1.575V
Efficiency vs. Input Voltage: VOUT = 1.575V
90
1.70
IOUT = 1 mA
1.65
85
IOUT = 100 mA
EFFICIENCY (%)
VOUT (V)
1.55
IOUT = 200 mA
IOUT = 100 mA
80
1.60
IOUT = 250 mA
1.50
75
70
65
60
IOUT = 200 mA, 250 mA
1.45
1.40
3.0
55
3.5
4.0
4.5
5.0
5.5
G=2/3
50
3.0
3.5
G=1/2
4.0
4.5
G=1/3
5.0
5.5
VIN (V)
VIN (V)
Figure 8.
Figure 9.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
7
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
Typical Performance Characteristics (continued)
Unless otherwise specified: CIN = 10µF, C1 = 1.0µF, C2 = 1.0µF, COUT = 10µF, TA = 25ºC. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's).
Load Regulation: VOUT = 1.2V
1.560
1.240
1.540
1.220
1.520
-30oC
VOUT (V)
VOUT (V)
Load Regulation: VOUT = 1.5V
1.260
1.200
25oC
1.180
-30oC
1.500
25oC
1.480
85oC
85oC
1.460
1.160
1.440
1.140
0
50
100
150
200
250
0
50
100
150
200
250
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
Figure 10.
Figure 11.
Load Regulation: VOUT = 1.575V
Output Voltage Ripple
1.630
1.610
-30ºC
VOUT (V)
1.590
25ºC
1.570
1.550
85ºC
1.530
1.510
0
50
100
150
200
250
OUTPUT CURRENT (mA)
Figure 12.
VIN = 3.6V, VOUT = 1.5V, IOUT = 200mA
CH1: CIN = COUT = 2×10µF; C1 = C2 = 1µF; Scale: 50mV/Div
CH2: CIN = COUT = 10µF; C1 = C2 = 1µF; Scale: 50mV/Div
Time scale: 4µs/Div
Figure 13.
Input Voltage Ripple
Start-up Behavior
VIN = 3.6V, VOUT = 1.5V, IOUT = 200mA
CH1: CIN = COUT = 2×10µF; C1 = C2 = 1µF; Scale: 50mV/Div
CH2: CIN = COUT = 10µF; C1 = C2 = 1µF; Scale: 50mV/Div
Time scale: 4µs/Div
Figure 14.
8
VIN = 3.6V, VOUT = 1.5V, Load = 7.5Ω (200mA)
CH1: EN pin; Scale: 1V/Div
CH2: VOUT; Scale: 500mV/Div
Time scale: 40µs/Div
Figure 15.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
Typical Performance Characteristics (continued)
Unless otherwise specified: CIN = 10µF, C1 = 1.0µF, C2 = 1.0µF, COUT = 10µF, TA = 25ºC. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's).
Load Step
Active-to-Sleep Mode Transitions
VIN = 3.6V, VOUT = 1.5V, Load = 10mA - 150mA step
CH1 (top): Output Current; Scale: 100mA/Div
CH2: VOUT; Scale: 100mV/Div
Time scale: 40µs/Div
Figure 16.
VIN = 3.6V, VOUT = 1.5V, Load = 20mA
CH1: SLEEP pin; Scale: 2V/Div
CH2: VOUT; Scale: 200mV/Div
Time scale: 200µs/Div
Figure 17.
Dynamic Output Voltage Switching: 1.5V to 1.2V
VIN = 3.6V, VOUT = 1.5V, Load = 10mA - 150mA step
CH1: VSEL pin; Scale: 2V/Div
CH2: VOUT; Scale: 500mV/Div
Time scale: 40µs/Div
Figure 18.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
9
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
OPERATION DESCRIPTION
OVERVIEW
The LM2770 is a switched capacitor converter that produces a regulated low voltage output. The core of the part
is a highly efficient charge pump that utilizes multiple fractional gains and pulse-frequency-modulated (PFM)
switching to minimize power losses over wide input voltage and output current ranges. A description of the
principal operational characteristics of the LM2770 is broken up into the following sections: PFM REGULATION,
FRACTIONAL MULTI-GAIN CHARGE PUMP, and MULTI-GAIN EFFICIENCY PERFORMANCE . Each of these
sections refers to the Block Diagram.
PFM REGULATION
The LM2770 achieves tightly regulated output voltages with pulse-frequency-modulated (PFM) regulation. PFM
simply means the part only pumps when charge needs to be delivered to the output in order to keep the output
voltage in regulation. When the output voltage is above the target regulation voltage, the part idles and
consumes minimal supply-current. In this state, the load current is supplied solely by the charge stored on the
output capacitor. As this capacitor discharges and the output voltage falls below the target regulation voltage, the
charge pump activates, and charge is delivered to the output. This charge supplies the load current and boosts
the voltage on the output capacitor.
The primary benefit of PFM regulation is when output currents are light and the part is predominantly in the lowsupply-current idle state. Net supply current is minimal because the part only occasionally needs to recharge the
output capacitor by activating the charge pump. With PFM regulation, input and output ripple frequencies vary
significantly, and are dependent on output current, input voltage, and, to a lesser degree, other factors such as
temperature and internal switch characteristics.
FRACTIONAL MULTI-GAIN CHARGE PUMP
The core of the LM2770 is a two-phase charge pump controlled by an internally generated non-overlapping
clock. The charge pump operates by using the external flying capacitors, C1 and C2, to transfer charge from the
input to the output.
The two phases of the switching cycle will be referred to as the "charge phase" and the "hold/rest phase". During
the charge phase, the flying capacitors are charged by the input supply. After charging the flying capacitors for
half of a switching cycle [ t = 1/(2×FSW) ], the LM2770 switches to the hold/rest phase. In this configuration, the
charge that was stored on the flying capacitors in the charge phase is transferred to the output. If the voltage on
the output is below the target regulation voltage at completion of the switching cycle, the charge pump will switch
back to the charge phase. But if the output voltage is above the target regulation voltage at the end of the
switching cycle, the charge pump will remain in the hold/rest state. It will idle in this mode until the output voltage
drops below the target regulation voltage. When this finally occurs, the LM2770 will switch back to the charge
phase.
Input, output, and intermediary connections of the flying capacitors are made with internal MOS switches. The
LM2770 utilizes two flying capacitors and a versatile switch network to achieve three distinct fractional voltage
gains: ⅓, ½, and ⅔. With this gain-switching ability, it is as if the LM2770 is three-charge-pumps-in-one. The
"active" charge pump at any given time is the one that yields the highest efficiency based on the input and output
conditions present.
MULTI-GAIN EFFICIENCY PERFORMANCE
The ability to switch gains based on input and output conditions results in optimal efficiency throughout the
operating ranges of the LM2770. Charge-pump efficiency is derived in the following two ideal equations (supply
current and other losses are neglected for simplicity):
IIN = G x IOUT E = (VOUT x IOUT) ÷ (VIN x IIN) = VOUT ÷ (G X VIN)
(1)
In the equations, G represents the charge pump gain. Efficiency is at its highest as G×VIN approaches VOUT.
Refer to the efficiency graphs in the Typical Performance Characteristics section for detailed efficiency data. The
gain regions are clearly distinguished by the sharp discontinuities in the efficiency curves and are identified at the
bottom of each graph (G = ⅔, G = ½, and G = ⅓).
10
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
DYNAMIC OUTPUT VOLTAGE SELECTION
The output voltage of the LM2770 can be dynamically adjusted for the purpose of improving system efficiency.
Each LM2770 version contains two built-in output voltage options: a high level and a low level (1.5V and 1.2V, for
example). With the simple VSEL logic input pin, the output voltage can be switched between these two voltages.
Dynamic voltage selection can be used to improve overall system efficiency. When comparing system efficiency
between two different output voltages, evaluating power consumption often lends more insight than actually
comparing converter efficiencies. An application powered with a Li-Ion battery is a good example to illustrate this.
Referring to the LM2770 efficiency curves (see Typical Performance Characteristics), all LM2770 output voltage
options operate with G = ½ over the core Li-Ion battery voltage range (3.5V - 3.9V). Thus, the LM2770 circuit will
draw an input current that is approximately half the output current in the core Li-Ion voltage range, regardless of
the output voltage (IIN = G × IOUT).
While varying the LM2770 output voltage does not directly improve system efficiency, it can have a secondary
effect. Different output voltages often will result in different LM2770 load currents. This is where system efficiency
can benefit from dynamic output voltage selection: the LM2770 load circuit can run at lower currents. This
reduces LM2770 input current and improves overall system efficiency.
SLEEP MODE BYPASS LDO
The LM2770 offers a bypass low-dropout linear regulator (LDO) for low-noise performance under light loads.
Capable of delivering up to 20mA of output current, this LDO has low ground pin current and is ideal for stand-by
operation. The LDO is activated with the SLEEP logic input pin. When SLEEP is active, the charge pump is
disabled and the LDO supplies all load current.
SHUTDOWN
The LM2770 is in shutdown mode when the voltage on the enable pin (EN) is logic-low. In shutdown, the
LM2770 draws virtually no supply current. When in shutdown, the output of the LM2770 is completely
disconnected from the input. The internal feedback resistors will pull the output voltage down to 0V (unless the
output is driven by an outside source).
In some applications, it may be desired to disable the LM2770 and drive the output pin with another voltage
source. This can be done, but the voltage on the output pin of the LM2770 must not be brought above the input
voltage. The output pin will draw a small amount of current when driven externally due the internal feedback
resistor divider connected between VOUT and GND.
SOFT START
The LM2770 employs soft start circuitry to prevent excessive input inrush currents during startup. At startup, the
output voltage gradually rises from 0V to the nominal output voltage. This occurs in 200µs (typ.). Soft-start is
engaged when the part is enabled, including situations where voltage is established simultaneously on the VIN
and EN pins.
THERMAL SHUTDOWN
Protection from overheating-related damage is achieved with a thermal shutdown feature. When the junction
temperature rises to 150ºC (typ.), the part switches into shutdown mode. The LM2770 disengages thermal
shutdown when the junction temperature of the part is reduced to 140ºC (typ.). Due to the high efficiency of the
LM2770, thermal shutdown and/or thermal cycling should not be encountered when the part is operated within
specified input voltage, output current, and ambient temperature operating ratings. If thermal cycling is seen
under these conditions, the most likely cause is an inadequate PCB layout that does not allow heat to be
sufficiently dissipated out of the WSON package.
SHORT-CIRCUIT AND CURRENT LIMIT PROTECTION
The LM2770 charge pump contains circuitry that protects the device from destructive failure in the event of a
direct short to ground on the output. This short-circuit protection circuit limits the output current to 400mA (typ.)
when the output voltage is below 165mV (typ.). The sleep-mode LDO contains a 60mA (typ.) current limit circuit.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
11
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
RECOMMENDED CAPACITOR TYPES
The LM2770 requires 4 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, ≤ 15mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors generally
are not recommended for use with the LM2770 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 LM2770. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over
temperature (X7R: ±15% over -55ºC to 125ºC; X5R: ±15% over -55ºC to 85ºC).
Capacitors with a Y5V or Z5U temperature characteristic are generally not recommended for use with the
LM2770. These types of capacitors typically have wide capacitance tolerance (+80%, -20%) and vary
significantly over temperature (Y5V: +22%, -82% over -30ºC to +85ºC range; Z5U: +22%, -56% over +10ºC to
+85ºC range). Under some conditions, a 1µF-rated Y5V or Z5U capacitor could have a capacitance as low as
0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum
capacitance requirements of the LM2770.
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 LM2770 circuit be thoroughly evaluated early in the
design-in process with the mass-production capacitors of choice. This will help to ensure that any such variability
in capacitance does not negatively impact circuit performance.
The table below lists some leading ceramic capacitor manufacturers.
Manufacturer
Contact Information
AVX
www.avx.com
Murata
www.murata.com
Taiyo-Yuden
www.t-yuden.com
TDK
www.component.tdk.com
Vishay-Vitramon
www.vishay.com
OUTPUT CAPACITOR AND OUTPUT VOLTAGE RIPPLE
The output capacitor in the LM2770 circuit (COUT) directly impacts the magnitude of output voltage ripple. Other
prominent factors also affecting output voltage ripple include input voltage, output current and flying capacitance.
Due to the complexity of multi-gain and PFM switching, providing equations or models to approximate the
magnitude of the ripple can not be easily accomplished. But one important generalization can be made:
increasing (decreasing) the output capacitance will result in a proportional decrease (increase) in output voltage
ripple. This can be observed in the output voltage ripple waveforms in the Typical Performance Characteristics
section.
In typical high-current applications, a 10µF 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 capacitors and/or input capacitor to maintain
good overall circuit performance. Performance of the LM2770 with different capacitor setups in discussed in the
section RECOMMENDED CAPACITOR CONFIGURATIONS.
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 vey 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.
12
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
Due to the PFM nature of the LM2770, output voltage ripple is highest at light loads. To eliminate this ripple,
consider running the LM2770 in sleep mode when load currents are 20mA or less. Sleep mode disables the
charge pump and enables the internal low-noise bypass linear regulator (LDO).
INPUT CAPACITOR AND INPUT VOLTAGE RIPPLE
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 capacitor is 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. This can be observed in the input voltage ripple
waveforms in the Typical Performance Characteristics section. Input voltage, output current, and flying
capacitance also will affect input ripple levels to some degree.
In typical high-current applications, a 10µF low-ESR ceramic capacitor is recommended on the input. Different
input capacitance values can be used to reduce ripple, shrink the solution size, and/or cut the cost of the
solution. But changing the input capacitor may also require changing the flying capacitors and/or output capacitor
to maintain good overall circuit performance. Performance of the LM2770 with different capacitor setups is
discussed below in RECOMMENDED CAPACITOR CONFIGURATIONS.
FLYING CAPACITORS
The flying capacitors (C1 and C2) transfer 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 LM2770 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 capacitors might overwhelm the input and output capacitors, resulting in increased input and output
ripple.
The flying capacitors should be identical. As a general guideline, the capacitance value of each flying capacitor
should be 1/10th that of the output capacitor, up to a maximum of 1µF. This is a recommendation, not a
requirement. Polarized capacitors (tantalum, aluminum electrolytic, etc.) must not be used for the flying
capacitors, however, as they could become reverse-biased during LM2770 operation.
RECOMMENDED CAPACITOR CONFIGURATIONS
The data in Table 1 can be used to assist in the selection of a capacitor configuration that best balances solution
size and cost with the electrical requirements of the application (ripple voltages, output current capability, etc.).
As previously discussed, input and output ripple voltages and frequencies will vary considerably with output
current and input voltage. The numbers provided show expected ripple voltage when VIN = 3.6V and load
currents are between 100mA and 250mA. The table offers first look at approximate ripple levels and provides a
comparison for the different capacitor configurations presented, but is not intended to ensure performance.
The columns that provide minimum input voltage recommendations illustrate the effect that smaller flying
capacitors have on charge pump output current capability. Using smaller flying capacitors increases the output
resistance of the charge pump. As a result, the minimunm input voltage of an application using small flying
capacitance may need to be set slightly higher to prevent the output from falling out of regulation when loaded.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
13
LM2770
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
www.ti.com
Table 1. LM2770 Performance with Different Capacitor Configurations (1)
TYPICAL
OUTPUT RIPPLE
(VIN = 3.6V)
TYPICAL
INPUT RIPPLE
(VIN = 3.6V)
25mV
CIN = COUT = 10µF,
C1 = C2 = 1µF
CAPACITOR
CONFIGURATION
Recommended Minimum VIN for Different Output Currents
IOUT = 50mA
IOUT = 150mA
IOUT = 250mA
35mV
3.0V
3.0V
3.1V
50mV
70mV
3.0V
3.0V
3.1V
CIN = COUT = 4.7µF,
C1 = C2 = 0.47µF
130mV
150mV
3.0V
3.1V
3.2V
CIN = COUT = 2.2µF,
C1 = C2 = 0.22µF
200mV
260mV
3.0V
3.1V
3.2V
CIN = COUT = 2×10µF,
C1 = C2 = 1µF
(1)
Refer to the text in the Recommended Capacitor Configurations section for detailed information on the data in this table
Layout Guidelines
Proper board layout will help to ensure optimal performance of the LM2770 circuit. The following guidelines are
recommended:
• Place capacitors as close to the LM2770 as possible, and preferably on the same side of the board as the IC.
• Use short, wide traces to connect the external capacitors to the LM2770 to minimize trace resistance and
inductance.
• Use a low resistance connection between ground and the GND pin of the LM2770. Using wide traces and/or
multiple vias to connect GND to a ground plane on the board is most advantageous.
Unlabelled vias connect to an internal ground plane
Figure 19. Recommended Board Layout of a LM2770 Circuit
14
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
LM2770
www.ti.com
SNVS318E – NOVEMBER 2004 – REVISED MAY 2013
REVISION HISTORY
Changes from Revision D (May 2013) to Revision E
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM2770
15
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)
LM2770SD-1215/NOPB
ACTIVE
WSON
DSC
10
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-30 to 105
L162B
(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
工商网监
湘ICP备2023018690号
