NSC LM2687MMX Datasheet

LM2687
Low Noise Regulated Switched Capacitor Voltage
Inverter

LM2687 Low Noise Regulated Switched Capacitor Voltage Inverter

August 1999

General Description

The LM2687 CMOS Negative Regulated Switched Capacitor
Voltage Inverter delivers a very low noise adjustable output
for an input voltage in the range of +2.7V to +5.5V. Four low
cost capacitors are used in this circuit to provide up to 10mA
of output current. The regulated outputfor the LM2687 is ad­justable between −1.5V and −5.2V. The LM2687operates at
100 kHz (typical) switching frequencyto reduce output resis­tance and voltage ripple. With an operating current of only
500 µA (charge pump power efficiency greater than 90
with most loads) and 0.05 µA typical shutdown current, the
LM2687 provides ideal performance for cellular phone power
amplifier bias and other low current, low noise negative volt­age needs. The device comes in a small 8-pin MSOP pack­age.

Typical Application Circuit

Features

n Inverts and regulates the input supply voltage
n Small MSOP-8 package
n 91%typical charge pump power efficiency at 10mA
n Low output ripple (1mV typical)
n Shutdown lowers Quiescent current to 0.05 µA (typical)

Applications

n Wireless Communication Systems

%

n Cellular Phone Power Amplifier Biasing
n Interface Power Supplies
n Handheld Instrumentation
n Laptop Computers and PDA’s

DS101180-1

Connection Diagram

8-Pin MSOP

DS101180-2

© 1999 National Semiconductor Corporation DS101180 www.national.com

Ordering Information

Device Order Number Package Number Package Marking

LM2687MM MUA08A S12A Tape and Reel (1000 units/reel)

LM2687MMX MUA08A S12A Tape and Reel (3500 units/reel)

Note:*The small physical size of the MSOP-8 package does not allow for the full part number marking. Devices will be marked with the designation shown in the

column Package Marking.

*

Supplies As

Pin Description

Pin No. Name Function

1 Cap+ Positive terminal for C
2 GND Ground.
3 Cap− Negative terminal for C
4SD
5V
6

7V
8V

NEG

V

FB

OUT

IN

Active low, logic-level shutdown input.
Negative unregulated output voltage.
Feedback input. Connect VFBto an external resistor divider between V

adjust voltage V
Regulated negative output voltage.
Positive power supply input.

ADJ

1

(0≤V

.

.

1

). DO NOT leave unconnected.

ADJ≤VIN

and a positive

OUT

www.national.com 2

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage (V
GND to OUT) + 5.8V

SD

V

and V

NEG

Current 10mA

Short-Circuit Duration to GND

V

OUT

(Note 2) 1 sec.
Continuous Power Dissipation (T

=

25˚C) (Note 3) 600mW

to GND or

IN

Continuous Output

OUT

A

(GND − 0.3V) to

+ 0.3V)

(V

IN

T

(Note 3) 150˚C

JMAX

θ

(Note 3) 250˚C/W

JA

Operating Input Voltage Range 2.7V to 5.5V
Operating Output Current Range 0mA to 10mA
Operating Ambient −40˚C to 85˚C
Temp. Range
Operating Junction Temp. Range −40˚C to 110˚C
Storage Temperature −65˚C to 150˚C
Lead Temp. (Soldering, 10 sec.) 300˚C
ESD Rating (Note 4) 2kV

Electrical Characteristics

Limits with standard typeface apply for T
otherwise specified V

IN

=

3.6V, C

Symbol Parameter Conditions Min Typ Max Units

Supply Current Open Circuit, No Load 500 950 µA

Q

Shutdown Supply Current 0.05 1 µA

SD

Switching Frequency

SW

(Note 5)
Power Efficiency at V

Start Up time (Note 6) 120 600 µs
Output Resistance to V
Output Voltage Ripple

R

(Note 8)
Feedback Pin Reference

FB

Voltage
Adjustable Output Voltage 5.5V ≥ VIN≥ 2.7V, 2.5mA ≥ I

η

POWER

T

R

V

I

I

F

START

NEG

V

V

OUT

Load Regulation 0 to 10mA, V
Line Regulation 5.5V ≥ V

V

V

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications donotapplywhenoperatingthedevice
beyond its rated operating conditions.

Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V
peratures above T

Note 3: The maximum powerdissipationmust be de-rated at elevated temperatures and is limited by T
ture) and θ

Note 4: Rating is for the human body model, a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 5: The output switches operate at one half the oscillator frequency, f
Note 6: All capacitors are 1µF.
Note 7: Current drawn from V
Note 8: In the test circuit, capacitors C

increase output voltage ripple, and reduce efficiency.
Note 9: The feedback resistors R1 and R2 are 200kΩ resistors.

Shutdown Pin Input

IH

Voltage High
Shutdown Pin Input

IL

Voltage Low

=

85˚C, OUT must not be shorted to GND or V

A

(junction-to-ambient thermal resistance). The maximum power dissipation at any temperature is:

JA

PDiss

=

(T

MAX

pin decreases power efficiency and will increase output voltage ripple.

NEG

and C2are 1µF,C

1

=

25˚C, and limits in boldface type apply over the full temperature range. Unless

J

=

C

1

2

NEGIL

NEG

=

=

1µF, C

2.7V ≤ VIN≤.5.5V
V

I

L

IN

=

=
=

3

3.6V

3.6mA
10mA

10µF.

50
60

110
105

94
91

(Note 7) 30 Ω

=

I

2.5mA, V

L

=

10mA, V

I

L

=

I

2.5mA (Note 9) −1.25 −1.20 −1.15 V

L

5.5V ≥ VIN≥ 3.0V, 10mA ≥ IL≥
0mA

≥ 2.7V, I

IN

=

−2.7V

OUT

=

−3.8V

OUT

−0.3V)

−(V

L

=

− 2.4V 5 mV/mA

OUT

=

2.5mA 1 mV/V

L

−(V

IN
IN

−1.2V)

1
2

5.5V ≥ VIN≥ 2.7V 2.2 V

5.5V ≥ VIN≥ 2.7V 0.5 V

may damage the device and must be avoided. Also, for tem-

or device may be damaged.

IN

—TA)/θJAup to the value listed in the Absolute Maximum Ratings.

JMAX

=

.

2f

OSC

SW

=

10µF,0.30Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance,

3

IN

(maximum junction temperature), TA(ambient tempera-

JMAX

180
170

kHz

%

mV

V

www.national.com3