LTC1429
Clock-Synchronized
Switched Capacitor
Regulated Voltage Inverter
FEATURES
s
s
DESCRIPTION
The LTC
®
1429 is a switched-capacitor voltage inverter de-
signed to provide a regulated negative voltage from a single
positive supply and permits clock synchronization in noise
sensitive systems. The LTC1429CS operates from a single 3V
to 8V supply and provides an adjustable output voltage from
– 1.25V to – 8V. An on-chip resistor string allows the
LTC1429CS to be configured for output voltages of – 3.5V,
–4V, –4.5V or – 5V. The LTC1429CS8 is optimized for
applications which require a fixed –4V output from a 5V
supply and requires only a single external 0.1µF flying
capacitor. The LTC1429CS requires one or two external
0.1µF capacitors, depending on input voltage. Both versions
require additional external 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 LTC1429 guarantees output regulation of
5%. The LTC1429 includes an open-drain REG output which
pulls low when the output is within 5% of the set value. Output
ripple is typically as low as 5mV. The LTC1429 requires an
external clock applied to the SYNC/SD for normal operation
and consumes a typical quiescent current of 600µA. Holding
the SYNC/SD either high or low brings the device into
shutdown and the supply current drops to 0.2µA. For appli-
cations which don’t have a clock signal available, the LTC1261
provides the same functionality with an internal oscillator. For
applications which require output ripple below 1mV, see the
LTC1550/LTC1551. The LTC1429CS is available in a 14-pin
SO package and the LTC1429CS8 is available in an 8-pin SO
package.
s
s
s
s
s
s
s
s
s
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Regulated Negative Voltage from a Single
Positive Supply
External Clock for Synchronization in Noise
Sensitive Systems
REG Output Indicates Output is in Regulation
Low Output Ripple: 5mV Typ
Can Provide Regulated – 5V from a 3V Supply
Supply Current: 600µA Typ
Shutdown Mode Drops Supply Current to 0.2µA
Up to 12mA Output Current
Adjustable or Fixed Output Voltages
Requires Only Three or Four External Caps
Output Regulation: 5%
Available in SO-8 Packages
APPLICATIONS
s
s
s
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GaAs FET Bias Generators
Negative Supply Generators
Battery Powered Systems
Single Supply Applications
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
– 4V Generator with Power Valid
5V
1
2
C1
0.1µF
C2
0.1µF
3
4
V
CC
SYNC/SD
8
7
6
5
*C3
0.001µF
10k
5V
POWER VALID
V
OUT
= –4V AT 10mA
C4
3.3µF
LTC1429 • TA01
Waveforms for –4V Generator with Power Valid
0V
V
OUT
– 4V
POWER VALID
SYNC/SD
5V
0V
5V
0V
0.2ms/DIV
LTC1429 • TA02
C1
+
REG
LTC1429-4CS8
C1
–
GND
OUT
COMP
*OPTIONAL
U
+
U
U
1
LTC1429
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Supply Voltage (Note 2)............................................. 9V
Output Voltage .............................................0.3V to – 9V
Total Voltage, V
CC
to V
OUT
(Note 2) ......................... 12V
Input Voltage (SYNC/SD Pin) ...... – 0.3V to (V
CC
+ 0.3V)
Input Voltage (REG Pin).............................– 0.3V to 12V
PACKAGE/ORDER INFORMATION
TOP VIEW
V
CC
1
C1
+
2
C1
–
3
8
7
6
5
SYNC/SD
REG
OUT
COMP
ORDER PART
NUMBER
LTC1429CS8-4*
GND 4
S8 PART MARKING
14294
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 150°C/ W
Consult factory for Industrial and Military grade parts. *Contact factory for other output voltages or 8-pin adjustable parts.
V
CC
= 3V to 6.5V. C1 = C2 = 0.1µF (Note 4), C
OUT
= 3.3µF, F
SYNC
= 700kHz with 50% duty cycle square wave, unless otherwise noted.
SYMBOL
V
REF
I
S
PARAMETER
Reference Voltage
Supply Current
CONDITIONS
q
ELECTRICAL CHARACTERISTICS
F
SYNC
P
EFF
V
OL
I
REG
I
ADJ
V
IH
V
IL
I
IN
T
ON
Synchronous Clock Frequency (Note 8)
Power Efficiency
REG Output Low Voltage
REG Sink Current
Adjust Pin Current
SYNC/SD Input High Voltage
SYNC/SD Input Low Voltage
SYNC/SD Input Current
Turn On Time
V
CC
= 3.3V
V
CC
= 5V
V
SYNC/SD
= V
CC
or GND
V
CC
≤
5V
V
CC
= 6.5V
I
REG
= 1mA
V
REG
= 0.8V, V
CC
= 3.3V
V
REG
= 0.8V, V
CC
= 5V
V
ADJ
= 1.24V (Note 5)
V
CC
= 5V
V
CC
= 5V
V
SYNC/SD
= V
CC
or GND
I
OUT
= 10mA
2
U
U
W
W W
U
W
Input Voltage (ADJ, RO-1, R
ADJ
)
.....................................(V
OUT
– 0.3V) to (V
CC
+ 0.3V)
Output Short Circuit Duration .......................... Indefinite
Operating Temperature Range ..................... 0°C to 70°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
NC 1
C1
+
2
C1
–
C2
–
3
C2
+
4
5
14 V
CC
13 SYNC/SD
12 REG
11 OUT
10 ADJ
9
8
R
ADJ
R1
ORDER PART
NUMBER
LTC1429CS
GND 6
R0 7
S PACKAGE
14-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 110°C/ W
q
q
q
q
q
q
q
q
q
q
LTC1429CS8/LTC1429CS
MIN
TYP
MAX
1.20
1.24
1.28
600
1500
600
1500
0.2
5
60
700
2000
100
700
2000
65
0.1
0.8
5
8
8
15
0.01
1
2.0
0.8
±1
200
UNITS
V
µA
µA
µA
kHz
kHz
%
V
mA
mA
µA
V
V
µA
µs
LTC1429
Tripler Mode,V
CC
= 3.3V, C1 = C2 = 0.1µF (Note 4), C
OUT
= 3.3µF,
F
SYNC
= 700kHz with 50% duty cycle square wave, unless otherwise noted.
SYMBOL
∆V
OUT
I
SC
V
RIP
PARAMETER
Output Regulation
Output Short Circuit Current
Output Ripple Voltage
CONDITIONS
– 1.24V
≥
V
OUT
≥
– 4V, 0
≤
I
OUT
≤
12mA
– 4V
≥
V
OUT
≥
– 5V, 0
≤
I
OUT
≤
8mA
V
OUT
= 0V
I
OUT
= 5mA, V
OUT
= – 4V
MIN
q
q
q
ELECTRICAL CHARACTERISTICS
LTC1429CS
TYP
1
2
35
5
MAX
5
5
75
UNITS
%
%
mA
mV
Doubler Mode, V
CC
= 5V, C1 = 0.1µF, C2 = 0 (Note 4), C
OUT
= 3.3µF, F
SYNC
=700kHz with 50% duty cycle, unless otherwise noted.
SYMBOL
∆V
OUT
V
OUT
I
SC
V
RIP
PARAMETER
Output Regulation
Output Voltage
Output Short Circuit Current
Output Ripple Voltage
CONDITIONS
– 1.24V
≥
V
OUT
≥
– 4V, 0
≤
I
OUT
≤
10mA
– 4V
≥
V
OUT
≥
– 4.5V, 0
≤
I
OUT
≤
10mA (Note 6)
V
OUT
Set to – 4V, 0
≤
I
OUT
≤
10mA
V
OUT
= 0V
I
OUT
= 5mA, V
OUT
= – 4V
LTC1429CS8/LTC1429CS
MIN
TYP
MAX
1
5
2
5
– 3.80
– 4.00
– 4.20
80
125
10
UNITS
%
%
V
mA
mV
q
q
q
q
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
Setting output to < – 7V will exceed the total voltage maximum
rating with a 5V supply. With supplies higher than 4V the output should
never be set to exceed (V
CC
– 12V).
Note 3:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground, unless otherwise
specified. All typicals are given at T
A
= 25°C.
Note 4:
C1 = C2 = 0.1µF means the specifications apply to tripler mode
where V
CC
– V
OUT
= 3.3V
CC
(LTC1429CS only; the LTC1429CS8 cannot be
connected in tripler mode), with C1 connected between C1
+
and C1
–
and
C2 connected between C2
+
and C2
–
. C2 = 0 implies doubler mode where
V
CC
– V
OUT
= 2V
CC
; for the LTC1429CS, this means C1 connects from C1
+
to C2
–
with C1
–
and C2
+
floating. For the LTC1429CS8 in doubler mode,
C1 connects from C1
+
to C1
–
; there are no C2 pins.
Note 5:
Adjustable output parts only; does not apply to fixed output parts.
Note 6:
For output voltages below – 4.5V, the LTC1429 may reach 50%
duty cycle and fall out of regulation with heavy load or low input voltages.
Beyond this point, the output will follow the input with no regulation.
Note 7:
LTC1429 will operate with square wave of 40% to 60% duty cycle.
For best performance, use a square wave with 50% duty cycle.
Note 8:
Maximum frequency is not tested. Typical part can be used
beyond 2MHz.
TYPICAL PERFORMANCE CHARACTERISTICS
(See Test Circuits; Figure 1 for Doubler Mode, Figure 2 for Tripler Mode)
Output Voltage vs Output Current
–4.10
–4.08
–4.06
T
A
= 25°C
OUTPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
–4.04
–4.02
–4.00
–3.98
–3.96
– 3.94
–3.92
–3.90
0
1
2
3 4 5 6 7 8
OUTPUT CURRENT (mA)
9
10
V
CC
= 3.3V
TRIPLER MODE
V
CC
= 5V
DOUBLER MODE
U W
LTC1429 • TPC01
Output Voltage vs Supply Voltage
–4.08
–4.07
–4.06
–4.05
–4.04
–4.03
–4.02
–4.01
–4.00
3.0
3.5
4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
6.5 7.0
TRIPLER MODE
I
L
= 5mA
DOUBLER MODE
I
L
= 5mA
T
A
= 25°C
45
40
35
30
25
20
15
10
5
0
Maximum Output Current vs
Supply Voltage
V
OUT
= –4V
±
5%
T
A
= 25°C
DOUBLER MODE
TRIPLER MODE
3.0
3.5
4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
6.5
7.0
LTC1429 • TPC02
LTC1429 • TPC03
3
LTC1429
TYPICAL PERFORMANCE CHARACTERISTICS
(See Test Circuits: Figure 1 for Doubler Mode, Figure 2 for Tripler Mode)
Supply Current vs Supply Voltage
1000
900
800
V
OUT
= –4V
T
A
= 25°C
TRIPLER MODE
SUPPLY CURRENT (µA)
700
600
500
400
300
200
100
0
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
SUPPLY VOLTAGE (V)
LTC1429 • TPC04
DOUBLER MODE
500
400
300
200
100
0
0
10
20
V
OUT
= –4V
V
CC
= 3.3V
TRIPLER MODE
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
PIN FUNCTIONS
Pin numbers are shown as (LTC1429CS/LTC1429CS8).
NC (Pin 1/NA):
No Internal Connection.
C1
+
(Pin 2/Pin 2):
C1 Positive Input. Connect an 0.1µF
capacitor between C1
+
and C1
–
. With the LTC1429CS in
doubler mode, connect a 0.1µF capacitor from C1
+
to C2
–
.
(Pin 3/Pin 3):
C1 Negative Input. Connect a 0.1µF
capacitor from C1
+
to C1
–
. With the LTC1429CS in doubler
mode only, C1
–
should float.
C2
+
(Pin 4/NA):
C2 Positive Input. In tripler mode, connect
a 0.1µF capacitor from C2
+
to C2
–
. This pin is used with
the LTC1429CS in tripler mode only; in doubler mode, this
pin should float.
C2
–
(Pin 5/NA):
C2 Negative Input. In tripler mode, con-
nect a 0.1µF capacitor from C2
+
to C2
–
. In doubler mode,
connect a 0.1µF capacitor from C1
+
to C2
–
.
GND (Pin 6/Pin 4):
Ground. Connect to a low-impedance
ground. A ground plane will help to minimize regulation
errors.
R0 (Pin 7/NA):
Internal Resistor String-1st Tap. See Table
3 in the Applications Information section for information
on internal resistor string pin connections vs output
voltage.
R1 (Pin 8/NA):
Internal Resistor String-2nd Tap.
C1
–
R
ADJ
(Pin 9/NA):
Internal Resistor String Output. Connect
this pin to ADJ to use the internal resistor divider. See
Table 3 in the Applications Information section for infor-
mation on internal resistor string pin connections vs
output voltage.
ADJ (COMP for fixed output versions) (Pin 10/Pin 5):
Output Adjust/Compensation. For adjustable parts, this
pin is used to set the output voltage. The output voltage
should be divided down with a resistor divider and fed
back to this pin to set the regulated output voltage. The
resistor divider can be external or the internal divider
string can be used if it can provide the required 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 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 adjustable and fixed
output voltage parts. See the Applications Information
section for more on compensation and output ripple.
OUT (Pin 11/Pin 6):
Negative Voltage Output. This pin
must be bypassed to ground with a 1.0µF or larger
capacitor; it must be at least 3.3µF to provide specified
output ripple. The size of the output capacitor has a strong
4
U W
Supply Current vs Temperature
800
700
600
V
CC
= 5V
DOUBLER MODE
Supply Current vs
Input Frequency
750
700
650
600
550
500
DOUBLER MODE
V
CC
= 5V
TRIPLER MODE
V
CC
= 3.3V
T
A
= 25°C
I
LOAD
= 0mA
40
50
30
TEMPERATURE (˚C)
60
70
450
100
1000
2000
INPUT FREQUENCY (kHz)
4000
LTC1429 • TPC05
LTC1429 • TPC06
U
U
U
LTC1429
PIN FUNCTIONS
effect on output ripple; see the Applications Information
section for more details.
REG (Pin 12/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 10mA 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
; it can be pulled up to
12V above ground without damage.
SYNC/SD (Pin 13/Pin 8):
Synchronous Clock Input. A
minimum input clock frequency (60kHz with V
CC
≤
5V and
100kHz with V
CC
= 6.5V) must be applied to this input to
keep the LTC1429 operating normally. An input clock
below the minimum frequency may cause the charge
pump to operate erratically or the device to shut down. A
logic high or low at the SYNC/SD pin will put the device
into SHUTDOWN and drop the supply current to 0.2µA.
The LTC1429 will operate with input square wave of 40%
to 60% duty cycle. For best performance, use a square
wave of 50% duty cycle.
V
CC
(Pin 14/Pin 1):
Power Supply. This requires an input
voltage between 3V and 6.5V. Certain combinations of
output voltage and operating mode may place additional
restrictions on the input voltage; see the Applications
Information section for details. V
CC
must be bypassed to
ground with at least a 0.1µF capacitor, placed in close
proximity to the chip; again, see the Applications Informa-
tion section.
TEST CIRCUITS
V
IN
= 3.3V
14
10µF
5V
1
2
10µF
0.1µF
3
4
V
CC
C1
+
REG
LTC1429-4CS8
OUT
COMP
C1
–
GND
0.001µF
Figure 1. Doubler Mode
Figure 2. Tripler Mode
APPLICATIONS INFORMATION
MODES OF OPERATION
The LTC1429 uses a charge pump to generate a negative
output voltage that can be regulated to a value either
higher or lower than the original input voltage. It has two
modes of operation: a doubler inverting mode, which can
provide a negative output equal to or less than the positive
power supply, and a tripler inverting mode, which can
provide negative output voltages either larger or smaller in
magnitude than the original positive supply. The tripler
offers greater versatility and wider input range but re-
quires four external capacitors and a 14-pin package; the
doubler offers the SO-8 package and requires only three
external capacitors. The optional compensation capacitor
at ADJ/COMP is used to reduce the ripple output voltage.
Doubler Mode
This mode allows the LTC1429 to generate negative
output voltage magnitudes up to that of the supply voltage,
+
U
+
W
U
U
U
U
U
+
10
9
8
0.001µF
F
SYNC
= 700kHz
2
V
CC
C1
+
C1
–
0.1µF
ADJ
R
ADJ
R1
SYNC/SD
8
3
7
6
5
V
OUT
= –4V
±
5%
3.3µF
0.1µF
NC
F
SYNC
= 700kHz
NC
V
OUT
= –4V
±
5%
3.3µF
4
5
LTC1429CS
13
SYNC/SD
C2
+
R0
C2
–
GND
6
7
OUT 11
LTC1429 • TC01
LTC1429 • TC02
5
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