LM2687
Low Noise Regulated Switched Capacitor Voltage
Inverter
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 output for the LM2687 is
adjustable between -1.5V and -5.2V. The LM2687 operates
at 100 kHz (typical) switching frequency to reduce output
resistance and voltage ripple. With an operating current of
only 500 A (charge pump power efficiency greater than
90% with most loads) and 0.05 A typical shutdown current,
the LM2687 provides ideal performance for cellular phone
power amplifier bias and other low current, low noise nega-
tive voltage needs. The device comes in a small 8-pin MSOP
or LLP package.
Features
n
Inverts and regulates the input supply voltage
n
Small MSOP-8 or LLP-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 A (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
Typical Application Circuit
10118001
Connection Diagrams
8-Pin MSOP
8-Pin LLP
10118002
10118025
April 2003
LM2687
Low
Noise
Regulated
Switched
Capacitor
V
oltage
Inverter
2003 National Semiconductor Corporation
DS101180
www.national.com
Ordering Information for MSOP Package
Device Order Number
Package Number
Package Marking
*
Supplies As
LM2687MM
MUA08A
S12A
Tape and Reel (1000 units/reel)
LM2687MMX
MUA08A
S12A
Tape and Reel (3500 units/reel)
Ordering Information for LLP Package
Device Order Number
Package Number
Package Marking
*
Supplies As
LM2687LD
LDA08A
L050B
Tape and Reel (1000 units/reel)
LM2687LDX
LDA08A
L050B
Tape and Reel (3500 units/reel)
Note: * The small physical sizes of the MSOP-8 and LLP-8 packages do not
allow for the full part number marking. Devices will be marked with the
designation shown in the column Package Marking.
Pin Description
Pin No.
Name
Function
1
Cap+
Positive terminal for C
1
.
2
GND
Ground.
3
Cap-
Negative terminal for C
1
.
4
SD
Active low, logic-level shutdown input.
5
V
NEG
Negative unregulated output voltage.
6
V
FB
Feedback input. Connect V
FB
to an external resistor divider between V
OUT
and a positive
adjust voltage V
ADJ
(0
V
ADJ
V
IN
). DO NOT leave unconnected.
7
V
OUT
Regulated negative output voltage.
8
V
IN
Positive power supply input.
DAP
Die Attach Pad
LLP package only. Connect this pad to V
NEG
.
LM2687
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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
IN
to GND or GND
to OUT)
+ 5.8V
SD
(GND - 0.3V) to
(V
IN
+ 0.3V)
V
NEG
and V
OUT
Continuous Output
Current
10mA
V
OUT
Short-Circuit Duration to GND
(Note 2)
1 sec.
Continuous Power Dissipation (T
A
=
25C) (Note 3)
600mW
T
JMAX
(Note 3)
150C
JA
(Note 3)
250C/W
Operating Input Voltage Range
2.7V to 5.5V
Operating Output Current Range
0mA to 10mA
Operating Ambient
-40C to 85C
Temp. Range
Operating Junction Temp. Range
-40C to 110C
Storage Temperature
-65C to 150C
Lead Temp. (Soldering, 10 sec.)
300C
ESD Rating (Note 4)
2kV
Electrical Characteristics
Limits with standard typeface apply for T
J
= 25C, and limits in boldface type apply over the full temperature range. Unless
otherwise specified V
IN
= 3.6V, C
1
= C
2
= 1F, C
3
= 10F.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
I
Q
Supply Current
Open Circuit, No Load
500
950
A
I
SD
Shutdown Supply Current
0.05
1
A
F
SW
Switching Frequency
(Note 5)
2.7V
V
IN
.5.5V
V
IN
= 3.6V
50
60
110
105
180
170
kHz
POWER
Power Efficiency at V
NEG
I
L
= 3.6mA
I
L
= 10mA
94
91
%
T
START
Start Up time
(Note 6)
120
600
s
R
NEG
Output Resistance to V
NEG
(Note 7)
30
V
R
Output Voltage Ripple
(Note 8)
I
L
=2.5mA, V
OUT
= -2.7V
I
L
= 10mA, V
OUT
= -3.8V
1
2
mV
V
FB
Feedback Pin Reference
Voltage
I
L
= 2.5mA (Note 9)
-1.25
-1.20
-1.15
V
V
OUT
Adjustable Output Voltage
5.5V
V
IN
2.7V, 2.5mA I
L
5.5V
V
IN
3.0V, 10mA I
L
0mA
- (V
IN
-0.3V)
- (V
IN
-1.2V)
V
Load Regulation
0 to 10mA, V
OUT
= - 2.4V
5
mV/mA
Line Regulation
5.5V
V
IN
2.7V, I
L
= 2.5mA
1
mV/V
V
IH
Shutdown Pin Input Voltage
High
5.5V
V
IN
2.7V
2.2
V
V
IL
Shutdown Pin Input Voltage
Low
5.5V
V
IN
2.7V
0.5
V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V
IN
may damage the device and must be avoided. Also, for
temperatures above T
A
= 85C, OUT must not be shorted to GND or V
IN
or device may be damaged.
Note 3: The maximum power dissipation must be de-rated at elevated temperatures and is limited by T
JMAX
(maximum junction temperature), T
A
(ambient
temperature) and
JA
(junction-to-ambient thermal resistance). The maximum power dissipation at any temperature is:
PDiss
MAX
= (T
JMAX
-- T
A
)/
JA
up to the value listed in the Absolute Maximum Ratings.
Note 4: Rating is for the human body model, a 100pF capacitor discharged through a 1.5 k
resistor into each pin.
Note 5: The output switches operate at one half the oscillator frequency, f
OSC
= 2f
SW
.
Note 6: All capacitors are 1F.
Note 7: Current drawn from V
NEG
pin decreases power efficiency and will increase output voltage ripple.
Note 8: In the test circuit, capacitors C
1
and C
2
are 1F, C
3
= 10F, 0.30
maximum ESR capacitors. Capacitors with higher ESR will increase output resistance,
increase output voltage ripple, and reduce efficiency.
Note 9: The feedback resistors R1 and R2 are 200k
resistors.
LM2687
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3
Typical Performance Characteristics
Unless otherwise specified, T
A
= 25C, V
OUT
= -2.5V.
Output Voltage vs. Output Current
Figure 2
Output Voltage vs. Output Current
Figure 1
10118004
10118005
Output Voltage vs. Input Voltage
Maximum Output Current vs. Input Voltage
10118006
10118007
Maximum V
NEG
Current vs. Input Voltage
No Load Supply Current vs. Input Voltage
10118008
10118009
LM2687
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