LTC1261L
Switched Capacitor
Regulated Voltage Inverter
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Regulated Negative Voltage from a
Single Positive Supply
REG Pin Indicates Output is in Regulation
Adjustable or Fixed Output Voltages
Output Regulation:
±3.5%
Supply Current: 650µA Typ
Shutdown Mode Drops Supply Current to 5µA
Up to 20mA Output Current
Requires Only Three or Four External Capacitors
Available in MS8 and SO-8 Packages
The LTC
®
1261L is a switched-capacitor voltage inverter
designed to provide a regulated negative voltage from a
single positive supply. The LTC1261L operates from a
single 2.7V to 5.25V supply and provides an adjustable
output voltage from –1.23V to – 5V. The LTC1261L-4/
LTC1261L-4.5 needs a single 4.5V to 5.25V supply and
provides a fixed output voltage of – 4V to – 4.5V respec-
tively. Three external capacitors are required: a 0.1µF
flying capacitor and an input and output bypass capaci-
tors. An optional compensation capacitor at ADJ (COMP)
can be used to reduce the output voltage ripple.
Each version of the LTC1261L will supply up to 20mA
output current with guaranteed output regulation of
±3.5%.
The LTC1261L includes an open-drain REG output that
pulls low when the output is within 5% of the set value.
Quiescent current is typically 650µA when operating and
5µA in shutdown.
The LTC1261L is available in 8-pin MSOP and SO pack-
ages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
GaAs FET Bias Generators
Negative Supply Generators
Battery-Powered Systems
Single Supply Applications
TYPICAL APPLICATION
Waveforms for – 4V Generator with Power Valid
– 4V Generator with Power Valid
0V
5V
5V
C1
1µF
C2
0.1µF
1
2
V
CC
SHDN
8
10k
POWER VALID
V
OUT
= –4V
AT 10mA
OUT
– 4V
5V
SHDN
0V
5V
POWER VALID
0V
1261L TA01
7
REG
C1
+
LTC1261L-4
3
6
OUT
C1
–
4
C3*
100pF
*OPTIONAL
+
GND
COMP
5
C4
3.3µF
U
0.1ms/DIV
1261L TAO2
U
U
1
LTC1261L
ABSOLUTE
(Note 1)
AXI U
RATI GS
Output Short-Circuit Duration ......................... Indefinite
Commercial Temperature Range ................ 0°C to 70°C
Extended Commercial Operating
Temperature Range (Note 4) ................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage (Note 2) ........................................ 5.5V
Output Voltage (Note 3) ........................... 0.3V to – 5.3V
Total Voltage, V
CC
to V
OUT
(Note 2) ..................... 10.8V
SHDN Pin .................................. – 0.3V to (V
CC
+ 0.3V)
REG Pin ..................................................... – 0.3V to 6V
ADJ Pin ........................... (V
OUT
– 0.3V) to (V
CC
+ 0.3V)
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
CC
C1
+
C1
–
GND
1
2
3
4
8
7
6
5
SHDN
REG
OUT
ADJ (COMP)
ORDER PART
NUMBER
LTC1261LCMS8
LTC1261LCMS8-4
LTC1261LCMS8-4.5
MS8 PART MARKING
LTFM
LTFN
LTFP
V
CC
1
C1
+
2
C1
–
3
GND 4
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 150°C,
θ
JA
= 200°C/W
Consult factory for Industrial or Military grade parts or additional fixed voltage parts.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, C1 = 0.1µF, C
OUT
= 3.3µF unless otherwise noted. (Notes 2, 4)
SYMBOL
V
CC
PARAMETER
CONDITIONS
q
q
q
ELECTRICAL CHARACTERISTICS
Supply Voltage
(LTC1261LCMS8/LTC1261LCS8)
(LTC1261LCMS8-4/LTC1261LCS8-4)
(Note 5)
(LTC1261LCMS8-4.5/LTC1261LCS8-4.5) (Note 5)
Reference Voltage
Supply Current
Internal Oscillator Frequency
REG Output Low Voltage
REG Sink Current
Adjust Pin Current
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
Turn-On Time
V
REF
I
CC
f
OSC
V
OL
I
REG
I
ADJ
V
IH
V
IL
I
IN
t
ON
V
CC
= 5.25V, No Load, SHDN Floating
V
CC
= 5.25V, No Load, V
SHDN
= V
CC
V
CC
= 5V, V
OUT
= – 4V
I
REG
= 1mA, V
CC
= 5V, V
OUT
= – 4V
V
REG
= 0.8V, V
CC
= 3.3V
V
REG
= 0.8V, V
CC
= 5V
V
ADJ
= 1.23V
V
CC
= 5V
V
CC
= 5V
V
SHDN
= V
CC
V
CC
= 5V, I
OUT
= 10mA, –1.5V
≤V
OUT
≤
– 4V (LTC1261L)
V
CC
= 5V, I
OUT
= 5mA, V
OUT
= – 4.5V (LTC1261L)
V
CC
= 5V, I
OUT
= 10mA, V
OUT
= – 4V (LTC1261L-4)
V
CC
= 5V, I
OUT
= 5mA, V
OUT
= – 4.5V (LTC1261L-4.5)
2
U
U
W
W W
U
W
TOP VIEW
8
7
6
5
SHDN
REG
OUT
ADJ (COMP)
ORDER PART
NUMBER
LTC1261LCS8
LTC1261LCS8-4
LTC1261LCS8-4.5
S8 PART MARKING
1261L
1261L4
261L45
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 135°C/W
MIN
2.7
4.35
4.75
TYP
MAX
5.25
5.25
5.25
UNITS
V
V
V
V
µA
µA
kHz
V
mA
mA
1.23
q
q
650
5
650
0.1
4
5
2
8
12
±0.01
1500
20
0.8
q
q
q
q
q
q
q
q
q
q
q
±1
0.8
µA
V
V
µA
µs
µs
µs
µs
2.5
250
250
250
250
25
1500
1500
1500
1500
LTC1261L
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, C1 = 0.1µF, C
OUT
= 3.3µF unless otherwise noted. (Notes 2, 4)
SYMBOL
V
OUT
PARAMETER
Output Regulation (LTC1261L)
CONDITIONS
2.70V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
3.25V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
2.70V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
2.95V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
3.50V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
2.95V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
3.30V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
3.85V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
3.40V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
3.70V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
4.25V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
3.85V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
4.10V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
4.60V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
Output Regulation
(LTC1261L/LTC1261L-4)
Output Regulation
(LTC1261L/LTC1261L-4.5)
I
SC
Output Short-Circuit Current
4.35V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
4.60V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
5.10V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
20mA
4.75V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
5mA
5.05V
≤
V
CC
≤
5.25V, 0mA
≤
I
OUT
≤
10mA
V
OUT
= 0V, V
CC
= 5.25V
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
– 1.552
– 1.552
– 2.070
– 2.070
– 2.070
– 2.587
– 2.587
– 2.587
– 3.105
– 3.105
– 3.105
– 3.622
– 3.622
– 3.622
– 4.140
– 4.140
– 4.140
– 4.657
– 4.657
TYP
– 1.5
– 1.5
– 2.0
– 2.0
– 2.0
– 2.5
– 2.5
– 2.5
– 3.0
– 3.0
– 3.0
– 3.5
– 3.5
– 3.5
– 4.0
– 4.0
– 4.0
– 4.5
– 4.5
100
MAX
– 1.448
– 1.448
– 1.930
– 1.930
– 1.930
– 2.413
– 2.413
– 2.413
– 2.895
– 2.895
– 2.895
– 3.378
– 3.378
– 3.378
– 3.860
– 3.860
– 3.860
– 4.343
– 4.343
220
UNITS
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
mA
Note 1:
The Absolute Maximum Ratings are those values beyond which
the life of a device may be impaired.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 3:
The output should never be set to exceed V
CC
– 10.8V.
Note 4:
The LTC1261L is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet these
extended commercial temperature limits, but is not tested at – 40°C and
85°C. Guaranteed I grade parts are available, consult factory.
Note 5:
The LTC1261L-4 and LTC1261L-4.5 will operate with less than the
minimum V
CC
specified in the electrical characteristics table, but they are
not guaranteed to meet the
±3.5%
V
OUT
specification.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Output Current
0
– 0.25
– 0.50
OUTPUT VOLTAGE (V)
T
A
= 25°C
V
OUT
= – 2V
OUTPUT VOLTAGE (V)
– 0.75
–1.00
–1.25
–1.50
–1.75
V
CC
= 3V
– 2.00
– 2.25
0
5
10
15
25
20
OUTPUT CURRENT (mA)
30
V
CC
= 2.7V
– 3.4
– 3.5
– 3.6
– 3.7
– 3.8
– 3.9
– 4.0
– 4.1
– 4.2
0
5
V
CC
= 4.5V
OUTPUT VOLTAGE (V)
U W
(See Test Circuits)
Output Voltage vs Output Current
– 3.0
– 3.1
– 3.2
– 3.3
T
A
= 25°C
V
OUT
= – 4V
–1.90
Output Voltage vs Supply Voltage
V
OUT
= – 2V
–1.95
T
A
= – 40°C
–2.00
T
A
= 85°C
–2.05
T
A
= 25°C
V
CC
= 5V
10
15
20
25
OUTPUT CURRENT (mA)
30
–2.10
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
1261L G03
1261L G01
1261L G02
3
LTC1261L
TYPICAL PERFORMANCE CHARACTERISTICS
Output Voltage vs Supply Voltage
– 3.85
– 3.90
OUTPUT VOLTAGE (V)
V
OUT
= – 4V
POSITIVE SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
– 3.95
T
A
= – 40°C
– 4.00
T
A
= 85°C
– 4.05
– 4.10
– 4.15
4.5
T
A
= 25°C
4.6
4.7 4.8 4.9 5.0 5.1
SUPPLY VOLTAGE (V)
Supply Current vs Supply Voltage
3.0
2.5
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
V
OUT
= – 2V
I
OUT
= 0
REFERENCE VOLTAGE (V)
2.0
1.5
1.0
0.5
0
2.5
T
A
= 85°C
T
A
= – 40°C
T
A
= 25°C
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
Oscillator Frequency
vs Temperature
725
OSCILLATOR FREQUENCY (kHz)
SHORT-CIRCUIT CURRENT (mA)
700
675
650
625
600
575
550
T
A
= 25°C
V
OUT
= – 4V
V
CC
= 5V
START-UP TIME (ms)
525
–40 –25 –10
5 20 35 50 65
TEMPERATURE (°C)
4
U W
5.2
(See Test Circuits)
Maximum Output Current
vs Supply Voltage
80
70
60
V
OUT
= – 2V
50
40
30
20
10
V
OUT
= – 3V
V
OUT
= – 4V
T
A
= 25°C
Minimum Required V
CC
vs V
OUT
and I
OUT
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
I
OUT
= 5mA
I
OUT
= 10mA
I
OUT
= 20mA
5.3
–5
–4
–3
–2
–1
OUTPUT VOLTAGE (V)
0
1261L G05
0
2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4
SUPPLY VOLTAGE (V)
1261L G06
1261L G04
Supply Current vs Supply Voltage
V
OUT
= – 4.5V
4.5 I
OUT
= 0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
T
A
= – 40°C
4.5 4.6
4.7 4.8 4.9 5.0 5.1
SUPPLY VOLTAGE (V)
5.2
5.3
T
A
= 25°C
T
A
= 85°C
5.0
1.25
Reference Voltage
vs Temperature
V
CC
= 5V
ADJ = 0V
1.24
1.23
1.22
5.0
1261L G07
1.21
– 55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
1261L G09
1261L G08
Start-Up Time vs Supply Voltage
0.7
0.6
0.5
V
OUT
= – 4V
0.4
0.3
V
OUT
= – 2V
0.2
0.1
0
2.5
3.0
3.5
4.5
4.0
SUPPLY VOLTAGE (V)
5.0
1261L G11
Output Short-Circuit Current
vs Temperature
160
140
120
100
V
CC
= 5V
80
60
V
CC
= 3V
40
20
V
CC
= 2.7V
5 20 35 50 65
TEMPERATURE (°C)
80
95
V
CC
= 5.25V
T
A
= 25°C
I
OUT
= 10mA
80
95
0
– 40 – 25 –10
1261L G10
1261L G12
LTC1261L
PIN FUNCTIONS
V
CC
(Pin 1):
Power Supply. This requires an input voltage
between 2.7V and 5.25V. V
CC
must be bypassed to
ground with at least a 1µF capacitor placed in close
proximity to the chip. See the Applications Information
section for details.
C1
+
(Pin 2):
C1 Positive Input. Connect a 0.1µF capacitor
between C1
+
and C1
–
.
C1
–
(Pin 3):
C1 Negative Input. Connect a 0.1µF capacitor
from C1
+
to C1
–
.
GND (Pin 4):
Ground. Connect to a low impedance
ground. A ground plane will help to minimize regulation
errors.
ADJ (COMP for fixed versions) (Pin 5):
Output Adjust/
Compensation Pin. For adjustable parts this pin is used
to set the output voltage. The output voltage is divided
down with an external resistor divider and fed back to this
pin to set the regulated output voltage. Typically the
resistor string should draw
≥
10µA from the output to
minimize errors due to the bias current at the adjust pin.
Fixed output voltage parts have the internal resistor
string connected to this pin inside the package. The pin
can be used to trim the output voltage if desired. It can
also be used as an optional feedback compensation pin to
reduce output ripple on both the adjustable and fixed
output voltage parts. See the Applications Information
section for more information on compensation and out-
put ripple.
OUT (Pin 6):
Negative Voltage Output. This pin must be
bypassed to ground with a 1µF or larger capacitor. The
value of the output capacitor and its ESR have a strong
effect on output ripple. See the Applications Information
section for more details.
REG (Pin 7):
This is an open-drain output that pulls low
when the output voltage is within 5% of the set value. It
will sink 5mA to ground with a 5V supply. The external
circuitry must provide a pull-up or REG will not swing
high. The voltage at REG may exceed V
CC
and can be
pulled up to 6V above ground without damage.
SHDN (Pin 8):
Shutdown. When this pin is at ground the
LTC1261L operates normally. An internal 5µA pull-down
keeps SHDN low if it is left floating. When SHDN is pulled
high, the LTC1261L enters shutdown mode. In shut-
down, the charge pump is disabled, the output collapses
to 0V and the quiescent current drops to 5µA typically.
TEST CIRCUITS
Fixed Output
1
V
CC
SHDN
8
V
CC
1
2
0.1µF
5V
+
10µF
0.1µF
2
7
REG
C1
+
LTC1261L-X
3
6
OUT
C1
–
4
1261L TCO1
+
+
GND
U
U
U
Adjustable Output
V
CC
SHDN
8
V
OUT
= – 4V (LTC1261L-4)
V
OUT
= – 4.5V (LTC1261L-4.5)
3.3µF
7
C1
+
REG
LTC1261L
3
6
OUT
C1
–
4
GND
ADJ
5
3.3µF
1261L TCO2
V
OUT
COMP
5
5
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