NSC LM2798MMX-1.8, LM2798MMX-1.5, LM2798MM-2.0, LM2798MM-1.8, LM2798MM-1.5 Datasheet

April 2003

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.

Features

n Output voltage options:

2.0V ± 5%, 1.8V ± 5%, and 1.5V ± 6%

n120mA output current capability

nMulti-Gain and Gain Hopping for Highest Possible Efficiency - up to 90% Efficient

n2.6V to 5.5V input range

nInput and Output Voltage Monitoring (BATOK and POK)

nLow operating supply current: 35µA

nShutdown supply current: 0.1µA

nThermal and short circuit protection

nLM2798 turn-on time: 400µs LM2797 turn-on time: 100µs

nAvailable in an 10-Pin MSOP Package

Applications

nCellular Phones

nPagers

nH/PC and P/PC Devices

nPortable Electronic Equipment

nHandheld Instrumentation

Typical Application Circuit

20044501

with Converter Voltage Capacitor Switched Down-Step Efficiency High 120mA LM2797/LM2798

Monitoring Voltage

© 2003 National Semiconductor Corporation

DS200445

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LM2797/LM2798

Connection Diagram

LM2797/98

Mini SO-10 (MSOP-10) Package

NS Package #: MUB10A

20044502

Top View

Pin Description

Pin

Name

Description

1

VOUT

Regulated Output Voltage

2

C1-

First Flying Capacitor: Negative Terminal

3

C1+

First Flying Capicitor: Positive terminal

4

VIN

Input Voltage. Recommended VIN Range: 2.6V to 5.5V

5

POK

Power-OK Indicator: Output voltage sense. Open-drain NFET output. With an

external pull-up resistor tied to POK, V(POK) will be high when VOUT is

regulating correctly. When VOUT falls out of regulation, the internal open-drain

FET pulls the POK voltage low.

6

BATOK

Battery-OK Indicator: Input voltage sense. Open-drain NFET output. With an

external pull-up resistor tied to BATOK, V(BATOK) will be high when VIN >

2.85V (typ). LM2797/98 pulls V(BATOK) low when VIN < 2.65V (typ.) , and/or

when the part is in shutdown [V(EN) = 0].

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

Nominal

Output

Turn-on

Order Number

Package Marking

Supplied As:

Voltage

Time

VOUT(NOM)

1.80V

100µs

LM2797MM-1.8

S80B

1000 units on Tape-and Reel

LM2797MMX-1.8

3500 units on Tape-and-Reel

1.50V

400µs

LM2798MM-1.5

S56B

1000 units on Tape-and Reel

LM2798MMX-1.5

3500 units on Tape-and-Reel

1.80V

400µs

LM2798MM-1.8

S57B

1000 units on Tape-and Reel

LM2798MMX-1.8

3500 units on Tape-and-Reel

2.00V

400µs

LM2798MM-2.0

S58B

1000 units on Tape-and Reel

LM2798MMX-2.0

3500 units on Tape-and-Reel

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Electrical Characteristics

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.

VIN, EN, POK, BATOK pins: Voltage
to Ground (Note 3)	−0.3V to 5.6V
Junction Temperature (TJ-MAX-ABS)	150˚C
Continuous Power Dissipation
(Note 4)	Internally Limited
VOUT Short-Circuit to GND Duration
(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:	2 kV
Machine model	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
Thermal Resistance, MSOP-8	220˚C/W
Resistance, MSOP-8 Package
(θJA) (Note 7)

(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 ≤ VIN ≤ 5.5V, V(EN) = VIN, C1 = C2 = 1µF, CIN = COUT = 10µF. (Note 9)

Symbol	Parameter	Conditions	Min	Typ	Max	Units
LM2797-1.8, LM2798-1.8, LM2798-2.0
		2.8V ≤ VIN ≤ 4.2V	-5		+5	% of
		0mA ≤ IOUT ≤ 120mA
VOUT	Output Voltage Tolerance					VOUT(nom)
		4.2V < VIN ≤ 5.5V	-6		+6
						(Note 10)
		0mA ≤ IOUT ≤ 120mA
LM2798-1.5
		2.8V ≤ VIN ≤ 4.2V	-6		+6	% of
		0mA ≤ IOUT ≤ 120mA
VOUT	Output Voltage Tolerance					VOUT(nom)
		4.2V < VIN ≤ 5.5V	-6		+6
						(Note 10)
		0mA ≤ IOUT ≤ 120mA
All Output Voltage Options
IQ	Operating Supply Current	IOUT = 0mA		35	50	µA
I SD	Shutdown Supply Current	V(EN) = 0V		0.1	2	µA
VR	Output Voltage Ripple	LM2798-1.8: VIN = 3.6V, IOUT = 120mA		20		mVp-p
EPEAK	Peak Efficiency	LM2798-1.8: VIN = 3.0V, IOUT = 60mA		90		%
	Average Efficiency over	LM2798-1.5: 3.0 ≤ VIN ≤ 4.2V, IOUT = 60mA		76		%
EAVG	Li-Ion Input Voltage Range	LM2798-1.8: 3.0 ≤ VIN ≤ 4.2V, IOUT = 60mA		82
	(Note 11)	LM2798-2.0: 3.0 ≤ VIN ≤ 4.2V, IOUT = 60mA		75
tON	Turn-On Time	LM2798, VIN=2.6V, IOUT=100mA, (Note 12)		400		µs
		LM2797, VIN=2.6V, IOUT=100mA, (Note 12)		100
fSW	Switching Frequency			500		kHz
ISC	Short-Circuit Current	VIN = 3.6, VOUT = 0V		25		mA
Enable Pin (EN) Characteristics
VIH	EN pin Logic-High Input		0.9		VIN	V
VIL	EN pin Logic-Low Input		0		0.4	V
IEN	EN pin input current	VEN = 0V		0		nA
		VEN = 5.5V		30

LM2797/LM2798

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LM2797/LM2798

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 ≤ VIN ≤ 5.5V, V(EN) = VIN, C1 = C2 = 1µF, CIN = COUT = 10µF. (Note 9)

Symbol	Parameter	Conditions	Min	Typ	Max	Units
POK Characteristics
VT-POK	Threshold of output voltage	POK transition L to H		95	99	% of
	for POK transition	POK transition H to L	83	92		VOUT-NOM
		Hysterisis		3		(Note 10)
IPOK-H	POK-high leakage current	V(POK) = 3.6V		1	5	µA
VPOK-L	POL-low pull-down voltage	I(POK) = -100µA		200	300	mV
BATOK Characteristics
VT-BATOK	Input voltage threshold for	BATOK transition L to H		2.85	3.0	V
	BATOK transition	BATOK transition H to L	2.4	2.65
		Hysterisis		0.20
IBATOK-H	BATOK-high leakage	V(BATOK) = 3.6V		1	5	µA
	current
VBATOK-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 VIN + 0.3V.

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 (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125oC), 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 x PD-MAX). The ambient temperature operating rating is provided merely for convenience. This part may be operated outside the listed TA rating so long as the junction temperature of the device does not exceed the maximum operating rating of 125oC.

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: CIN, COUT, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics Note 10: VOUT (NOM) is the nominal output voltage of the part. An example: VOUT-NOM of LM2798MM-1.8 is 1.8V.

Note 11: 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.

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 IOUT = 100mA when the output voltage is fully established.

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Block Diagram

LM2797/LM2798

20044503

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