NSC LM2798MMX-1.8, LM2798MMX-1.5, LM2798MM-2.0, LM2798MM-1.8, LM2798MM-1.5 Datasheet
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April 2003
LM2797/LM2798
120mA High Efficiency Step-Down Switched Capacitor
Voltage Converter with Voltage Monitoring
LM2797/LM2798 120mA High Efficiency Step-Down Switched Capacitor Voltage Converter with
Voltage Monitoring
General Description
The LM2797/98 switched capacitor step-down DC/DC converters efficiently produce 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 LM2797/98 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 LM2797/98: 35µA operating unloaded and 0.1µA in shutdown.
Features of the LM2797/98 include input voltage and output
voltage monitoring. Pin BATOK provides battery monitoring
by indicating when the input voltage is above 2.85V (typ.).
Pin POK verifies that the output voltage is not more than 5%
(typ.) below the nominal output voltage of the part.
The optimal external component requirements of the
LM2797/98 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
is required, and no inductors are needed.
The LM2797/98 also features short-circuit protection overtemperature protection, and soft-start circuitry to prevent
excessive inrush currents. The LM2798 has a 400µs turn-on
time. The turn-on time of the LM2797 is 100µs.
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 Input and Output Voltage Monitoring (BATOK and POK)
n Low operating supply current: 35µA
n Shutdown supply current: 0.1µA
n Thermal and short circuit protection
n LM2798 turn-on time: 400µs
n Available in an 10-Pin MSOP Package
±
5%, 1.8V±5%, and 1.5V±6%
2.0V
Efficiency - up to 90% Efficient
LM2797 turn-on time: 100µs
Applications
n Cellular Phones
n Pagers
n H/PC and P/PC Devices
n Portable Electronic Equipment
n Handheld Instrumentation
20044501
© 2003 National Semiconductor Corporation DS200445 www.national.com
Connection Diagram
LM2797/LM2798
LM2797/98
Mini SO-10 (MSOP-10) Package
NS Package #: MUB10A
Pin Description
Pin Name Description
1V
OUT
2 C1- First Flying Capacitor: Negative Terminal
3 C1+ First Flying Capicitor: Positive terminal
4V
IN
5 POK Power-OK Indicator: Output voltage sense. Open-drain NFET output. With an
6 BATOK Battery-OK Indicator: Input voltage sense. Open-drain NFET output. With an
7 EN Enable Logic Input. High voltage = ON, Low voltage = SHUTDOWN
8 C2+ Second Flying Capacitor: Positive Terminal
9 GND Ground Connection
10 C2- Second Flying Capacitor: Negative Terminal
Ordering Information
Top View
20044502
Regulated Output Voltage
Input Voltage. Recommended VINRange: 2.6V to 5.5V
external pull-up resistor tied to POK, V(POK) will be high when V
regulating correctly. When V
falls out of regulation, the internal open-drain
OUT
OUT
FET pulls the POK voltage low.
external pull-up resistor tied to BATOK, V(BATOK) will be high when V
2.85V (typ). LM2797/98 pulls V(BATOK) low when V
<
2.65V (typ.) , and/or
IN
when the part is in shutdown [V(EN) = 0].
is
>
IN
Nominal
Output
Voltage
V
OUT(NOM)
1.80V 100µs
1.50V 400µs
1.80V 400µs
2.00V 400µs
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Turn-on
Time
Order Number Package Marking Supplied As:
LM2797MM-1.8
LM2797MMX-1.8 3500 units on Tape-and-Reel
LM2798MM-1.5
LM2798MMX-1.5 3500 units on Tape-and-Reel
LM2798MM-1.8
LM2798MMX-1.8 3500 units on Tape-and-Reel
LM2798MM-2.0
LM2798MMX-2.0 3500 units on Tape-and-Reel
S80B
S56B
S57B
S58B
1000 units on Tape-and Reel
1000 units on Tape-and Reel
1000 units on Tape-and Reel
1000 units on Tape-and Reel
LM2797/LM2798
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, POK, BATOK pins: Voltage
V
IN
to Ground (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
) 150˚C
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
Thermal Resistance, MSOP-8 220˚C/W
Resistance, MSOP-8 Package
) (Note 7)
(θ
JA
Lead Temperature
(Soldering, 5 Sec.) 260˚C
ESD Rating (Note 5)
Human-body model:
Machine model
2kV
200V
Electrical Characteristics (Notes 2, 8)
Limits in standard typeface and typical values apply for TJ=25oC. Limits in boldface type apply over the operating junction
temperature range. Unless otherwise specified: 2.6 ≤ V
≤ 5.5V, V(EN) = VIN,C1=C2= 1µF, CIN=C
IN
Symbol Parameter Conditions Min Typ Max Units
LM2797-1.8, LM2798-1.8, LM2798-2.0
2.8V ≤ V
V
OUT
Output Voltage Tolerance
0mA ≤ I
4.2V
0mA ≤ I
IN
OUT
<
VIN≤ 5.5V
OUT
≤ 4.2V
≤ 120mA
≤ 120mA
-5 +5
-6 +6
LM2798-1.5
2.8V ≤ V
V
OUT
Output Voltage Tolerance
0mA ≤ I
4.2V
0mA ≤ I
IN
OUT
<
VIN≤ 5.5V
OUT
≤ 4.2V
≤ 120mA
≤ 120mA
-6 +6
-6 +6
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 35 50 µA
OUT
Shutdown Supply Current V(EN) = 0V 0.1 2 µA
Output Voltage Ripple LM2798-1.8: VIN= 3.6V, I
Peak Efficiency LM2798-1.8: VIN= 3.0V, I
Average Efficiency over
Li-Ion Input Voltage Range
(Note 11)
Turn-On Time LM2798, VIN=2.6V, I
LM2798-1.5: 3.0 ≤ V
LM2798-1.8: 3.0 ≤ V
LM2798-2.0: 3.0 ≤ V
LM2797, V
=2.6V, I
IN
IN
IN
IN
OUT
OUT
= 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
=100mA, (Note 12) 400 µs
=100mA, (Note 12) 100
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
EN pin Logic-High Input 0.9 V
EN pin Logic-Low Input 0 0.4 V
=0V 0 nA
V
EN pin input current
EN
V
= 5.5V 30
EN
= 10µF. (Note 9)
OUT
IN
%of
V
OUT(nom)
(Note 10)
%of
V
OUT(nom)
(Note 10)
p-p
V
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Electrical Characteristics (Notes 2, 8) (Continued)
Limits in standard typeface and typical values apply for TJ=25oC. Limits in boldface type apply over the operating junction
temperature range. Unless otherwise specified: 2.6 ≤ V
≤ 5.5V, V(EN) = VIN,C1=C2= 1µF, CIN=C
IN
Symbol Parameter Conditions Min Typ Max Units
POK Characteristics
LM2797/LM2798
V
T-POK
Threshold of output voltage
for POK transition
POK transition L to H 95 99
POK transition H to L 83 92
Hysterisis 3
I
POK-H
V
POK-L
POK-high leakage current V(POK) = 3.6V 1 5 µA
POL-low pull-down voltage I(POK) = -100µA 200 300 mV
BATOK Characteristics
V
T-BATOK
Input voltage threshold for
BATOK transition
BATOK transition L to H 2.85 3.0 V
BATOK transition H to L 2.4 2.65
Hysterisis 0.20
I
BATOK-H
BATOK-high leakage
V(BATOK) = 3.6V 1 5 µA
current
V
BATOK-L
BATOK-low pull-down
I(BATOK) = - 100µA 200 300 mV
voltage
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
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 1.5kΩ 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 highly dependent on application conditions and PC board layout. In applications where high maximum power
dissipation exists, special care must be paid to thermal dissipation issues. For 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: V
Note 11: Efficiency is measured versus V
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. Resistive load used for startup
measurement, with value chosen to give I
A
IN,COUT,C1
OUT (NOM)
A-MAX=TJ-MAX-OP
rating so long as the junction temperature of the device does not exceed the maximum operating rating of 125oC.
, and C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
is the nominal output voltage of the part. An example: V
-(θJAxP
) 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
D-MAX
, with VINbeing swept in small increments from 3.0V to 4.2V. The average is calculated from these measurement results.
IN
= 100mA when the output voltage is fully established.
OUT
+ 0.3V.
IN
J-MAX-OP
). The ambient temperature operating rating is provided merely for convenience. This part may be operated
of LM2798MM-1.8 is 1.8V.
OUT-NOM
vs. Time) is not done in computing the average.
BAT
= 10µF. (Note 9)
OUT
= 125oC), the maximum power
%of
V
OUT-NOM
(Note 10)
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Block Diagram
LM2797/LM2798
20044503
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