LM2788
120mA High Efficiency Step-Down Switched Capacitor
Voltage Converter
General Description
The LM2788 switched capacitor step-down DC/DC con-
verter 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 mul-
tiple 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: 32A operating
unloaded and 0.1A 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 1F
flying capacitors and two 10F 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.
Features
n
Output voltage options:
2.0V
5%, 1.8V
5%, 1.5V
6%
n
120mA output current capability
n
Multi-Gain and Gain Hopping for Highest Possible
Efficiency - up to 90% Efficient
n
2.6V to 5.5V input range
n
Low operating supply current: 32A
n
Shutdown supply current: 0.1A
n
Thermal and short circuit protection
n
Available in an 8-Pin MSOP Package
Applications
n
Cellular Phones
n
Pagers
n
H/PC and P/PC Devices
n
Portable Electronic Equipment
n
Handheld Instrumentation
Typical Application Circuit
20044401
October 2002
LM2788
120mA
High
Efficiency
Step-Down
Switched
Capacitor
V
oltage
Converter
2002 National Semiconductor Corporation
DS200444
www.national.com
Connection Diagram
LM2788
Mini SO-8 (MSOP-8) Package
NS Package #: MUA08A
20044402
Top View
Pin Description
Pin
Name
Description
1
V
OUT
Regulated Output Voltage
2
C1-
First Flying Capacitor: Negative Terminal
3
C1+
First Flying Capicitor: Positive terminal
4
V
IN
Input voltage. Recommended V
IN
Range: 2.6V to 5.5V
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
Ordering Information
Output
Voltage
Ordering
Information
Package Type
Package Marking
Supplied as
1.50V
LM2788MM-1.5
MSOP-8
S30B
1000 units on Tape-and Reel
LM2788MMX-1.5
S30B
3500 units onTape-and-Reel
1.80V
LM2788MM-1.8
S23B
1000 units on Tape-and Reel
LM2788MMX-1.8
S23B
3500 units on Tape-and Reel
2.00V
LM2788MM-2.0
S24B
1000 units on Tape-and Reel
LM2788MMX-2.0
S24B
3500 units on Tape-and Reel
LM2788
www.national.com
2
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.
V
IN
, EN pins: Voltage to Ground
(Note 3)
-0.3V to 5.6V
Junction Temperature (T
J-MAX-ABS
)
150C
Continuous Power Dissipation
(Note 4)
Internally Limited
V
OUT
Short-Circuit to GND Duration
(Note 4)
Unlimited
Storage Temperature Range
-65C to 150C
Lead Temperature
(Soldering, 5 Sec.)
260C
ESD Rating (Note 5)
Human-body model:
Machine model
2 kV
200V
Operating Ratings
(Notes 1, 2)
Input Voltage Range
2.6V to 5.5V
Recommended Output Current
Range
0mA to 120mA
Junction Temperature Range
-40C to 125C
Ambient Temperature Range
(Note 6)
-40C to 85C
Thermal Information
Junction-to-Ambient Thermal
220C/W
Resistance, MSOP-8 Package
(
JA
) (Note 7)
Electrical Characteristics
(Notes 2, 8) Limits in standard typeface and typical values apply for T
J
=
25
o
C. Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: 2.6
V
IN
5.5V, V(EN) = V
IN
, C
1
= C
2
= 1F, C
IN
= C
OUT
= 10F. (Note 9)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
LM2788-1.8, LM2788-2.0
V
OUT
Output Voltage Tolerance
2.8V
V
IN
4.2V
0mA
I
OUT
120mA
-5
+5
% of
V
OUT (nom)
(Note 10)
4.2V
V
IN
5.5V
0mA
I
OUT
120 mA
-6
+6
LM2788-1.5
V
OUT
Output Voltage Tolerance
2.8V
V
IN
4.2V
0mA
I
OUT
120 mA
-6
+6
% of
V
OUT (nom)
(Note 10)
4.2V
V
IN
5.5V
0mA
I
OUT
120mA
-6
+6
All Output Voltage Options
I
Q
Operating Supply Current
I
OUT
= 0mA
32
50
A
I
SD
Shutdown Supply Current
V(EN) = 0V
0.1
2
A
V
R
Output Voltage Ripple
LM2788-1.8: V
IN
= 3.6V, I
OUT
= 120mA
20
mV
p-p
E
PEAK
Peak Efficiency
LM2788-1.8: V
IN
= 3.0V, I
OUT
= 60mA
90
%
E
AVG
Average Efficiency over
Li-Ion Input Voltage Range
(Note 11)
LM2788-1.5: 3.0
V
IN
4.2V, I
OUT
= 60mA
76
%
LM2788-1.8: 3.0
V
IN
4.2V, I
OUT
= 60mA
82
LM2788-2.0: 3.0
V
IN
4.2V, I
OUT
= 60mA
75
t
ON
Turn-On Time
V
IN
= 3.6V, I
OUT
= 120mA (Note 12)
0.4
ms
f
SW
Switching Frequency
500
kHz
I
SC
Short-Circuit Current
V
IN
= 3.6, V
OUT
= 0V
25
mA
Enable Pin (EN) Characteristics
V
IH
EN pin Logic-High Input
0.9
V
IN
V
V
IL
EN pin Logic-Low Input
0
0.4
V
I
EN
EN pin input current
V
EN
= 0V
0
nA
V
EN
= 5.5V
30
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
IN
+ 0.3V.
LM2788
www.national.com
3
Electrical Characteristics
(Notes 2, 8) Limits in standard typeface and typical values apply for T
J
= 25
o
C.
Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: 2.6
V
IN
5.5V,
V(EN) = V
IN
, C
1
= C
2
= 1F, C
IN
= C
OUT
= 10F. (Note 9) (Continued)
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 k
resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 6: Maximum ambient temperature (T
A-MAX
) is dependent on the maximum operating junction temperature (T
J-MAX-OP
= 125
o
C), the maximum power
dissipation of the device in the application (P
D-MAX
), and the junction-to ambient thermal resistance of the part/package in the application (
JA
), as given by the
following equation: T
A-MAX
= T
J-MAX-OP
- (
JA
x P
D-MAX
). The ambient temperature operating rating is provided merely for convenience. This part may be operated
outside the listed T
A
rating, so long as the junction temperature of the device does not exceed the maximum operating rating of 125
o
C.
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
FLY
, C
IN
, and C
OUT
: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
Note 10: Nominal output voltage (V
OUT
(nom) ) is the target output voltage of the part, as given by the output-voltage-option identifier. See Ordering Information
table for available options.
Note 11: Efficiency is measured versus V
IN
, with V
IN
being swept in small increments from 3.0V to 4.2V. The average is calculated from these measurements
results. Weighting to account for battery voltage discharge characteristics (V
BAT
vs. Time) is not done in computing the average.
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.
Block Diagram
20044403
LM2788
www.national.com
4
Typical Performance Characteristics
Unless otherwise specified: C
IN
= 10F, C1 = 1.0F, C2 = 1.0F C
OUT
= 10F, T
A
= 25
o
C. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's).
Output Voltage vs. Input Voltage:
LM2788-1.5 (1mA)
Output Voltage vs. Input Voltage:
LM2788-1.5 (120mA)
20044407
20044408
Output Voltage vs. Input Voltage:
LM2788-1.8 (1mA)
Output Voltage vs. Input Voltage:
LM2788-1.8 (120mA)
20044409
20044410
Output Voltage vs. Input Voltage:
LM2788-2.0 (1mA)
Output Voltage vs. Input Voltage:
LM2788-2.0 (120mA)
20044411
20044412
LM2788
www.national.com
5
PDF 
ZIP