National LM2788MM-1.5, LM2788MM-1.8, LM2788MM-2.0 Schematic [ru]
October 2002
LM2788
120mA High Efficiency Step-Down Switched Capacitor
Voltage Converter
LM2788 120mA High Efficiency Step-Down Switched Capacitor Voltage Converter
General Description
The LM2788 switched capacitor step-down DC/DC converter efficiently produces a 120mA regulated low-voltage
rail from a 2.6V to 5.5V input. Fixed output voltage options of
1.5V, 1.8V, and 2.0V are available. The LM2788 uses multiple fractional gain configurations to maximize conversion
efficiency over the entire input voltage and output current
ranges. Also contributing to high overall efficiency is the
extremely low supply current of the LM2788: 32µA operating
unloaded and 0.1µA in shutdown.
The optimal external component requirements of the
LM2788 solution minimize size and cost, making the part
ideal for Li-Ion and other battery powered designs. Two 1µF
flying capacitors and two 10µF bypass capacitors are all that
are required, and no inductors are needed.
The LM2788 also features noise-reducing soft-start circuitry,
short-circuit protection and over-temperature protection.
Typical Application Circuit
Features
n Output voltage options:
n 120mA output current capability
n Multi-Gain and Gain Hopping for Highest Possible
n 2.6V to 5.5V input range
n Low operating supply current: 32µA
n Shutdown supply current: 0.1µA
n Thermal and short circuit protection
n Available in an 8-Pin MSOP Package
±
5%, 1.8V±5%, 1.5V±6%
2.0V
Efficiency - up to 90% Efficient
Applications
n Cellular Phones
n Pagers
n H/PC and P/PC Devices
n Portable Electronic Equipment
n Handheld Instrumentation
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© 2002 National Semiconductor Corporation DS200444 www.national.com
Connection Diagram
LM2788
LM2788
Mini SO-8 (MSOP-8) Package
NS Package #: MUA08A
Pin Description
Pin Name Description
1V
2 C1- First Flying Capacitor: Negative Terminal
3 C1+ First Flying Capicitor: Positive terminal
4V
5 EN Enable. Logic Input. High voltage = ON, Low voltage = SHUTDOWN
6 C2+ Second Flying-Capacitor: Positive Terminal
7 GND Ground Connection
8 C2- Second Flying Capacitor: Negative Terminal
OUT
IN
Ordering Information
Output
Voltage
1.50V LM2788MM-1.5
1.80V LM2788MM-1.8 S23B 1000 units on Tape-and Reel
2.00V LM2788MM-2.0 S24B 1000 units on Tape-and Reel
Ordering
Information
LM2788MMX-1.5 S30B 3500 units onTape-and-Reel
LM2788MMX-1.8 S23B 3500 units on Tape-and Reel
LM2788MMX-2.0 S24B 3500 units on Tape-and Reel
Top View
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Regulated Output Voltage
Input voltage. Recommended VINRange: 2.6V to 5.5V
Package Type Package Marking Supplied as
S30B 1000 units on Tape-and Reel
MSOP-8
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Absolute Maximum Ratings (Notes 1,
2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
, EN pins: Voltage to Ground
V
IN
(Note 3) −0.3V to 5.6V
Junction Temperature (T
J-MAX-ABS
Continuous Power Dissipation
(Note 4) Internally Limited
V
Short-Circuit to GND Duration
OUT
(Note 4) Unlimited
Storage Temperature Range −65˚C to 150˚C
Lead Temperature
(Soldering, 5 Sec.) 260˚C
ESD Rating (Note 5)
Human-body model:
Machine model
) 150˚C
2kV
200V
Operating Ratings (Notes 1, 2)
Input Voltage Range 2.6V to 5.5V
Recommended Output Current
Range 0mA to 120mA
Junction Temperature Range -40˚C to 125˚C
Ambient Temperature Range
-40˚C to 85˚C
(Note 6)
Thermal Information
Junction-to-Ambient Thermal 220˚C/W
Resistance, MSOP-8 Package
(θJA) (Note 7)
LM2788
Electrical Characteristics (Notes 2, 8) Limits in standard typeface and typical values apply for T
o
C. Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: 2.6 ≤ VIN≤
25
5.5V, V(EN) = V
IN,C1=C2
= 1µF, CIN=C
= 10µF. (Note 9)
OUT
=
J
Symbol Parameter Conditions Min Typ Max Units
LM2788-1.8, LM2788-2.0
2.8V ≤ V
V
OUT
Output Voltage Tolerance
0mA ≤ I
4.2V ≤ VIN≤ 5.5V
0mA ≤ I
IN
OUT
OUT
≤ 4.2V
≤ 120mA
≤ 120 mA
-5 +5
-6 +6
%of
V
OUT (nom)
(Note 10)
LM2788-1.5
2.8V ≤ V
V
OUT
Output Voltage Tolerance
0mA ≤ I
4.2V ≤ VIN≤ 5.5V
0mA ≤ I
IN
OUT
OUT
≤ 4.2V
≤ 120 mA
≤ 120mA
-6 +6
-6 +6
%of
V
OUT (nom)
(Note 10)
All Output Voltage Options
I
I
V
E
E
t
f
I
Q
SD
R
PEAK
AVG
ON
SW
SC
Operating Supply Current I
= 0mA 32 50 µA
OUT
Shutdown Supply Current V(EN) = 0V 0.1 2 µA
Output Voltage Ripple LM2788-1.8: VIN= 3.6V, I
Peak Efficiency LM2788-1.8: VIN= 3.0V, I
Average Efficiency over
Li-Ion Input Voltage Range
(Note 11)
Turn-On Time VIN= 3.6V, I
LM2788-1.5: 3.0 ≤ V
LM2788-2.0: 3.0 ≤ V
= 120mA (Note 12) 0.4 ms
OUT
IN
IN
IN
= 120mA 20 mV
OUT
= 60mA 90 %
OUT
≤ 4.2V, I
≤ 4.2V, I
≤ 4.2V, I
= 60mA 76
OUT
= 60mA 82
OUT
= 60mA 75
OUT
Switching Frequency 500 kHz
Short-Circuit Current VIN= 3.6, V
=0V 25 mA
OUT
Enable Pin (EN) Characteristics
V
IH
V
IL
I
EN
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of
the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the
Electrical Characteristics tables.
Note 2: All voltages are with respect to the potential at the GND pin.
Note 3: Voltage on the EN pin must not be brought above V
EN pin Logic-High Input 0.9 V
IN
EN pin Logic-Low Input 0 0.4 V
=0V 0 nA
V
EN pin input current
EN
V
= 5.5V 30
EN
+ 0.3V.
IN
p-p
%LM2788-1.8: 3.0 ≤ V
V
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Electrical Characteristics (Notes 2, 8) Limits in standard typeface and typical values apply for T
Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: 2.6 ≤ V
LM2788
V(EN) = V
Note 4: Thermal shutdown circuitry protects the device from permanent damage.
Note 5: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 6: Maximum ambient temperature (T
dissipation of the device in the application (P
following equation: T
outside the listed T
Note 7: Junction-to-ambient thermal resistance is a highly application and board-layout dependent. In applications where high maximum power dissipation exists,
special care must be paid to thermal dissipation issues. Fore more information on these topics, please refer to the Power Dissipation section of this datasheet.
Note 8: All room temperature limits are 100% tested or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed by correlation
using standard Statistical Quality Control methods (SQC). All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are not
guaranteed, but do represent the most likely norm.
Note 9: C
Note 10: Nominal output voltage (V
table for available options.
Note 11: Efficiency is measured versus V
results. Weighting to account for battery voltage discharge characteristics (V
Note 12: Turn-on time is measured from when the EN signal is pulled high until the output voltage crosses 90% of its final value.
IN,C1=C2
FLY,CIN
= 1µF, CIN=C
A-MAX=TJ-MAX-OP
rating, so long as the junction temperature of the device does not exceed the maximum operating rating of 125oC.
A
, and C
OUT
-(θJAxP
: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
(nom) ) is the target output voltage of the part, as given by the output-voltage-option identifier. See Ordering Information
OUT
= 10µF. (Note 9) (Continued)
OUT
) is dependent on the maximum operating junction temperature (T
A-MAX
), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the
D-MAX
). The ambient temperature operating rating is provided merely for convenience. This part may be operated
D-MAX
, with VINbeing swept in small increments from 3.0V to 4.2V. The average is calculated from these measurements
IN
vs. Time) is not done in computing the average.
BAT
J-MAX-OP
= 125oC), the maximum power
Block Diagram
IN
=25oC.
J
≤ 5.5V,
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