LINER LTC1550IGN

LTC1550/LTC1551
Low Noise, Switched
Capacitor Regulated
Voltage Inverters
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DESCRIPTION
FEATURES
The LTC®1550/LTC1551 are switched capacitor charge
pump voltage inverters which include internal linear postregulators to minimize output ripple. Output voltages are
fixed at – 4.1V, with ripple voltages typically below 1mVP-P.
The LTC1550 is also available in an adjustable output
voltage version. The LTC1550/LTC1551 are ideal for use
as bias voltage generators for GaAs transmitter FETs in
portable RF and cellular telephone applications.
Regulated Negative Voltage from a Single
Positive Supply
Low Output Ripple: Less Than 1mVP-P Typ
High Charge Pump Frequency: 900kHz Typ
Small Charge Pump Capacitors: 0.1µF
Requires Only Four External Capacitors
Fixed – 4.1V or Adjustable Output
Shutdown Mode Drops Supply Current to < 1µA
High Output Current: Up to 10mA, VCC = 5V
Output Regulation: 5%
Available in SO-8 and 16-Lead SSOP
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The LTC1550/LTC1551 operate from single 4.5V to 6.5V
supplies and draw typical quiescent currents of 4.25mA
with a 5V supply. Each device includes a TTL compatible
Shutdown pin which drops supply current to 0.2µA typically. The LTC1550 Shutdown pin is active low (SHDN),
while the LTC1551 Shutdown pin is active high (SHDN).
Only four external components are required: an input bypass
capacitor, two 0.1µF charge pump capacitors and a filter
capacitor at the linear regulator output. The adjustable LTC1550
requires two additional resistors to set the output voltage. The
LTC1550/LTC1551 will supply up to 10mA output current
with a 5V supply, while maintaining guaranteed output
regulation of ±5%.
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APPLICATIONS
GaAs FET Bias Generators
Negative Supply Generators
Battery-Powered Systems
Single Supply Applications
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The fixed voltage LTC1550/LTC1551 are available in S0-8
plastic packages. The adjustable LTC1550 is available in a
16-pin SSOP.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
– 4.1V Generator with 1mVP-P Noise
1
2
+
4.7µF
CIN
SHDN
SENSE
VCC
CPOUT
8
7
CCP
0.1µF
LTC1551
3
4
C1+
GND
VOUT
C1 –
6
FERRITE BEAD
C1
0.1µF
VOUT
AC COUPLED
2mV/DIV
5
+
VCC
VOUT Output Noise and Ripple
COUT
10µF
VOUT = –4.1V
ILOAD = 5mA
CL
0.1µF
1550/51 F01
10µs/DIV
1550/51 TA02
1
LTC1550/LTC1551
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ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage ......................................................... 7V
Output Voltage ................................ 0.3V to (VCC – 14V)
Total Voltage, VCC to CPOUT ............................................. 14V
Input Voltage (SHDN Pin) ........... – 0.3V to (VCC + 0.3V)
Input Voltage (REG Pin)............................ – 0.3V to 12V
Output Short-Circuit Duration .............................. 30 sec
Commercial Temperature Range ................. 0°C to 70°C
Extended Commercial Operating
Temperature Range (Note 3) .............. – 40°C to 85°C
Industrial Temperature Range ................ – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
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PACKAGE/ORDER INFORMATION
ORDER
PART NUMBER
TOP VIEW
TOP VIEW
NC 1
C1+ 2
SHDN* 1
8
SENSE
VCC 2
7
CPOUT
C1+ 3
6
GND
VOUT 4
5
C1 –
LTC1550CS8-4.1
LTC1551CS8-4.1
S8 PACKAGE
8-LEAD PLASTIC SO
NC 3
VOUT 4
C1– 5
15 SHDN
LTC1550CGN
LTC1550IGN
14 REG
13 SENSE
12 ADJ
PGND 6
11 CPOUT
AGND 7
10 NC
NC 8
ORDER
PART NUMBER
16 VCC
9
GN PART MARKING
NC
1550
*SHDN FOR LTC1550, SHDN FOR LTC1551
GN PACKAGE
16-LEAD PLASTIC SSOP
TJMAX = 150°C, θJA = 150°C/ W
TJMAX = 150°C, θJA = 150°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
VCC = 4.5V to 6.5V, C1 = C2 = 0.1µF, COUT = 10µF, TA = 25°C unless otherwise specified. (Note 3)
SYMBOL
VCC
VREF
IS
PARAMETER
Supply Voltage
(LTC1550CGN/LTC1550IGN)
(LTC1550CS8-4.1/LTC1551CS8-4.1)
Reference Voltage
Supply Current
fOSC
VOL
IREG
VIH
VIL
IIN
tON
VOUT
Internal Oscillator Frequency
REG Output Low Voltage
REG Sink Current
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current
Turn-On Time
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CGN/LTC1550IGN)
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CONDITIONS
MIN
●
●
2.7
4.5
●
VCC = 5V, VSHDN = VCC (LTC1550) or GND (LTC1551)
VCC = 5V, VSHDN = GND (LTC1550) or VCC (LTC1551)
●
●
IREG = 1mA, VCC = 5V
VREG = 0.8V, VCC = 5V
VCC = 5V
VCC = 5V
VSHDN = VCC
IOUT = 10mA
2.7V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
2.8V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
3.5V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
2.7V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
3.1V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
3.75V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
●
●
●
TYP
7
2
6.5
6.5
1.24
4.25
0.2
900
0.1
15
●
●
●
●
●
●
●
●
– 1.575
– 1.575
– 1.575
– 2.1
– 2.1
– 2.1
MAX
0.1
1
– 1.5
– 1.5
– 1.5
– 2.0
– 2.0
– 2.0
7
10
0.8
0.8
1
– 1.425
– 1.425
– 1.425
– 1.9
– 1.9
– 1.9
UNITS
V
V
V
mA
µA
kHz
V
mA
V
V
µA
ms
V
V
V
V
V
V
LTC1550/LTC1551
ELECTRICAL CHARACTERISTICS
VCC = 4.5V to 6.5V, C1 = C2 = 0.1µF, COUT = 10µF, TA = 25°C unless otherwise specified. (Note 3)
SYMBOL
VOUT
PARAMETER
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CGN/LTC1550IGN)
VOUT
Output Regulation
(LTC1550CS8-4.1/LTC1551CS8-4.1)
ISC
Output Short-Circuit Current
VRIPPLE
Output Ripple Voltage
CONDITIONS
3.05V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
3.45V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
4.1V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
3.45V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
3.85V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
4.5V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
3.9V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
4.2V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
4.85V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
4.5V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
4.75V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
5.35V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
4.8V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
5.1V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
5.7V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
4.5V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 5mA
4.75V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 10mA
5.35V ≤ VCC ≤ 6.5V, 0 ≤ IOUT ≤ 20mA
VOUT = 0V, VCC = 5V
VOUT = 0V, VCC = 6.5V
The ● denotes specifications which apply over the specified
temperature range.
Note 1: 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. All typicals are given at TA = 25°C.
MIN
– 2.625
– 2.625
– 2.625
– 3.15
– 3.15
– 3.15
– 3.675
– 3.675
– 3.675
– 4.3
– 4.3
– 4.3
– 4.725
– 4.725
– 4.725
– 4.3
– 4.3
– 4.3
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
TYP
– 2.5
– 2.5
– 2.5
– 3.0
– 3.0
– 3.0
– 3.5
– 3.5
– 3.5
– 4.1
– 4.1
– 4.1
– 4.5
– 4.5
– 4.5
– 4.1
– 4.1
– 4.1
50
80
1
MAX
– 2.375
– 2.375
– 2.375
– 2.85
– 2.85
– 2.85
– 3.325
– 3.325
– 3.325
– 3.9
– 3.9
– 3.9
– 4.275
– 4.275
– 4.275
– 3.9
– 3.9
– 3.9
150
200
UNITS
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
mA
mA
mV
Note 3: C-grade device specifications are guaranteed over the 0°C to 70°C
temperature range. In addition, C-grade device specifications are assured
over the – 40°C to 85°C temperature range by design or correlation, but
are not production tested.
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TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency
vs Temperature
–3.0
6.0
VOUT = – 4.1V
VCC = 5V
TA = 25°C
VOUT = – 4.1V
5.5
875
825
775
–3.2
OUTPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
OSCILLATOR FREQUENCY (kHz)
975
925
Output Voltage vs Output Current
(LTC1550CS8-4.1/LTC1551CS8-4.1)
Supply Current vs Temperature
5.0
4.5
VCC = 5V
4.0
–3.4
VCC = 4.5V
–3.6
VCC = 5V
–3.8
725
3.5
–4.0
675
–45 –25
3.0
–45 –25
–4.2
VCC = 6.5V
35
15
55
–5
TEMPERATURE (˚C)
75
95
LTC1550/51 G01
55
–5
35
15
TEMPERATURE (°C)
75
95
LTC1550/51 G02
0
5
25
10
15
20
OUTPUT CURRENT (mA)
30
LTC1550/51 G03
3
LTC1550/LTC1551
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TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Output Current
vs Supply Voltage
Start-Up Time vs Supply Voltage
45
Startup Time (LTC1550 Shown)
2.0
TA = 25°C
VOUT = – 4.1V
RL = 390Ω
TA = 25°C
1.8
40
35
30
25
20
15
5V
1.6
START-UP TIME (ms)
MAXIMUM OUTPUT CURRENT (mA)
50
SHDN
1.4
0V
1.2
0V
VOUT
1.0
– 4.1V
0.8
10
0.2ms/DIV
5
0.6
0
4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50
SUPPLY VOLTAGE (V)
0.4
4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50
SUPPLY VOLTAGE (V)
LTC1550/51 • TPC04
LTC1550/51 • G06
LTC1550/51 G05
Load Transient Response
(See Figure 2, VCC = 5V)
Line Transient Response
(See Figure 2, IL = 10mA)
Minimum Required VCC vs
VOUT and IOUT
6.0
5.6
VOUT
POSITIVE SUPPLY VOLTAGE (V)
5mV/DIV
5mV/DIV
VOUT
AC COUPLED
AC COUPLED
10mA
IOUT
VCC 5.5V
5V
0mA
1ms/DIV
2ms/DIV
LTC1550/51 • G07
5.2
4.8
IOUT = 20mA
4.4
4.0
3.6
3.2
IOUT = 5mA
IOUT = 10mA
2.8
2.4
LTC1550/51 • G08
2.0
–5
–4
–2
–1
–3
OUTPUT VOLTAGE (V)
0
LTC1550/51 • G08.5
Output Spectrum
(*See Typical Application)
Spot Noise
(*See Typical Application)
90
80
70
70
50
40
30
20
60
1
NOISE (dBµV)
NOISE (µV/√Hz)
NOISE (dBµV)
90
10
80
60
0.1
40
30
20
10
0
0
1M
FREQUENCY (Hz)
10M
LT1550/51 • G09
* On first page of data sheet.
VCC = 5V
IL = 5mA
CIN = 4.7µF
COUT = 10µF
CL = 0.1µF
50
10
–10
100k
4
Output Spectrum
(See Figure 2, COUT = 10µF)
0.01
1
10
FREQUENCY (kHz)
100
LTC1550/51 • G10
–10
100k
1M
FREQUENCY (Hz)
10M
LT1550/51 • G11
LTC1550/LTC1551
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TYPICAL PERFORMANCE CHARACTERISTICS
Spot Noise
(See Figure 2, COUT = 10µF)
Output Spectrum
(See Figure 2, COUT = 22µF)
90
VCC = 5V
IL = 5mA
CIN = 4.7µF
COUT = 10µF
CL = 0.1µF
70
60
NOISE (dBµV)
1
80
0.1
10
VCC = 5V
IL = 5mA
CIN 4.7µF
COUT = 22µF
CL = 0.1µF
NOISE (µV/√Hz)
10
NOISE (µV/√Hz)
Spot Noise
(See Figure 2, COUT = 22µF)
50
40
30
20
VCC = 5V
IL = 5mA
CIN = 4.7µF
COUT = 22µF
CL = 0.1µF
1
0.1
10
0
0.01
1
10
FREQUENCY (kHz)
100
–10
100k
LTC1550/51 • G12
1M
FREQUENCY (Hz)
10M
LT1550/51 • G13
0.01
1
10
FREQUENCY (kHz)
100
LTC1550/51 • G14
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PIN FUNCTIONS
SHDN: Shutdown (TTL Compatible). This pin is active low
(SHDN) for the LTC1550 and active high (SHDN) for the
LTC1551. When this pin is at VCC (GND for LTC1551), the
LTC1550 operates normally. When SHDN is pulled low
(high for LTC1551), the LTC1550 enters shutdown mode.
In shutdown, the charge pump stops, the output collapses
to 0V, and the quiescent current drops typically to 0.2µA.
VCC: Power Supply. VCC requires an input voltage between
4.5V and 6.5V for the fixed voltage LTC1550CS8-4.1/
LTC1551CS8-4.1. The adjustable voltage LTC1550CGN/
LTC1550IGN operates with a VCC range of 2.7V to 6.5V.
Output voltage and output load current conditions depend
on the VCC supply voltage. Consult the Electrical Characteristics table and Typical Performance Characteristics for
guaranteed test points. The difference between the input
voltage and output should never be set to exceed 14V or
damage to the chip may occur. VCC must be bypassed to
PGND (GND for 8-pin packages) with at least a 0.1µF
capacitor placed in close proximity to the chip. A 4.7µF or
larger bypass capacitor is recommended to minimize
noise and ripple at the output.
C1 +: C1 Positive Input. Connect a 0.1µF capacitor between
C1 + and C1 –.
VOUT: Negative Voltage Output. This pin must be bypassed
to ground with a 4.7µF or larger capacitor to ensure
regulator loop stability. At least 10µF is recommended to
provide specified output ripple. An additional 0.1µF low
ESR capacitor is recommended to minimize high frequency spikes at the output.
C1 –: C1 Negative Input. Connect a 0.1µF capacitor from
C1 + to C1 –.
GND: Ground. Connect to a low impedance ground. A
ground plane will help minimize regulation errors.
CPOUT: Negative Charge Pump Output. This pin requires a
0.1µF storage capacitor to ground.
SENSE: Connect to VOUT. The LTC1550/LTC1551 internal
regulator uses this pin to sense the output voltage. For
optimum regulation, SENSE should be connected close to
the output load.
SSOP PACKAGE ONLY
PGND: Power Ground. Connect to a low impedance ground.
PGND should be connected to the same potential as
AGND.
AGND: Analog Ground. Connect to a low impedance
ground. AGND should be connected to a ground plane to
minimize regulation errors.
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LTC1550/LTC1551
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PIN FUNCTIONS
REG: This is an open-drain output that pulls low when the
output voltage is within 5% of the set value. It will sink 7mA
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 VCC and can be pulled up to 12V above
ground without damage.
divider string from AGND to VOUT with the divided tap
connected to ADJ. Note that the resistor string needs to be
connected “upside-down” from a traditional negative regulator. See the Applications Information section for hookup details.
NC: No Internal Connection.
ADJ: For adjustable versions only, this is the feedback
point for the external resistor divider string. Connect a
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BLOCK DIAGRAM
+
CCP
VCC
COUT
CPOUT
S1
LINEAR
REGULATOR
S4
VOUT
C1 +
CLK
900kHz
C1
S2
C1 –
–
+
**
S3
ADJ
CHARGE
PUMP
**
*SHDN
+
60mV
REG
COMP2
–
1.24V
1.18V
*SHDN FOR LTC1550, SHDN FOR LTC1551
** FIXED OUTPUT VERSIONS ONLY
SENSE
1550/51 BD
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APPLICATIONS INFORMATION
OVERVIEW
The LTC1550/LTC1551 are switched capacitor, inverting
charge pumps with internal linear post-regulators. The
LTC1550CS8/LTC1551CS8 provide a regulated, low ripple
– 4.1V output at up to 10mA load current from a single 5V
supply. The LTC1550CGN provides a regulated, low ripple
adjustable output. Output load current for the adjustable
version depends on the input/output voltage combination.
6
Consult the graph provided in the Typical Performance
Characteristics section and the Electrical Characteristics
table for guaranteed test points. The LTC1550/LTC1551
are ideal for use as bias voltage generators for GaAs
transmitter FETs in portable RF and cellular telephone
applications. The LTC1550 features an active-low
Shutdown pin (SHDN) that drops quiescent current to
below 1µA. The LTC1551 is identical to the LTC1550,
LTC1550/LTC1551
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APPLICATIONS INFORMATION
except that the Shutdown pin is active-high (SHDN). All
members of the LTC1550 family feature a 900kHz charge
pump frequency. The LTC1550/ LTC1551 come standard
with fixed – 4.1V output voltages and the LTC1550 is
available with an adjustable output voltage. Both devices
can be configured with other fixed output voltages; contact
Linear Technology for more information.
The LTC1550 consists of two major blocks (see Block
Diagram): an inverting charge pump and a negative linear
regulator. The charge pump uses two external capacitors,
C1 and CCP to generate a negative voltage at CPOUT. It
operates by charging and discharging C1 on alternate
phases of the internal 900kHz clock. C1 is initially charged
to VCC through switches S1 and S3. When the internal
clock changes phase, S1 and S3 open and S2 and S4 close,
shorting the positive side of C1 to ground. This forces the
negative side of C1 below ground, and charge is transferred
to CCP through S4. As this cycle repeats, the magnitude of
the negative voltage approaches VCC. The 900kHz internal
clock frequency helps keep noise out of 400kHz to 600kHz
IF bands commonly used by portable radio frequency
systems and reduces the size of the external capacitors
required. Most applications can use standard 0.1µF ceramic
capacitors for C1 and CCP. Increasing C1 and CCP beyond
0.1µF has little effect on the output ripple or the output
current capacity of the LTC1550/LTC1551.
The negative voltage at CPOUT supplies the input to the
negative regulator block. This block consists of an
N-channel MOSFET pass device and a feedback amplifier
that monitors the output voltage and compares it to the
internal reference. The regulated output appears at the
VOUT pin. The regulation loop is optimized for fast transient response, enabling it to remove most of the switching artifacts present at the CPOUT pin. Output ripple is
typically below 1mVP-P with output loads between 0mA
and 10mA. The output voltage is set to – 4.1V by a pair of
internal divider resistors. The N-channel pass device minimizes dropout, allowing the output to remain in regulation
with supply voltages as low as 4.5V. An output capacitor
of at least 4.7µF from VOUT to ground is required to keep
the regulator loop stable; for optimum stability and minimum output ripple, at least 10µF is recommended.
PGND, AGND
6, 7
R1
LTC1550 ADJ
10
R2
VOUT, SENSE
4, 11
VOUT = –1.24V
(
)
R1 + R2
R2
LTC1550/51 • F02
Figure 1. External Resistor Connections
Adjustable Hook-Up
The LTC1550CGN is available in an adjustable output
version in a 16-pin SSOP package. The output voltage is
set with a resistor divider from GND to SENSE/VOUT
(Figure 1). Note that the internal reference and the internal
feedback amplifier are set up as a positive-output regulator referenced to the SENSE pin, not a negative regulator
referenced to ground. The output resistor divider must be
set to provide a 1.24V at the ADJ pin with respect to VOUT.
For example, a – 3V output would require a 13k resistor
from GND to ADJ, and a 9.1k resistor to SENSE/VOUT. If,
after connecting the divider resistors, the output voltage is
not what you expected, try swapping them.
CAPACITOR SELECTION
The LTC1550/LTC1551 requires four external capacitors:
an input bypass capacitor, two 0.1µF charge pump capacitors and an output filter capacitor. The overall behavior of
the LTC1550/LTC1551 is strongly affected by the capacitors used. In particular, the output capacitor has a significant effect on the output ripple and noise performance.
Proper capacitor selection is critical for optimum performance of the LTC1550/LTC1551.
Output Ripple vs Output Capacitor
Figure 3 shows the effect of using different output capacitor values on LTC1550/LTC1551 output ripple. These
curves are taken using the circuit in Figure 2, with
CIN = 4.7µF and ILOAD = 5mA. The upper curve shows the
performance with a standard tantalum capacitor alone and
the lower curve shows the tantalum capacitor in parallel
with a 0.1µF ceramic capacitor. As a general rule, larger
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LTC1550/LTC1551
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APPLICATIONS INFORMATION
output capacitors provide lower output ripple. To keep
ripple below 1mVP-P, 10µF or greater, with a 0.1µF ceramic
capacitor in parallel, is required. At least 4.7µF is required
at the output under all conditions to guarantee loop
stability.
Figure 3 shows a marked decrease in peak-to-peak output
ripple when a 0.1µF ceramic capacitor added in parallel
with the tantalum output capacitor. The additional ripple
with the tantalum output capacitor alone is mostly very
high order harmonics of the 900kHz clock, which appear
as sharp "spikes" at the output. The energy in these spikes
is very small and they do not contribute to the RMS output
voltage, but their peak-to-peak amplitude can be several
millivolts under some conditions. A garden variety 0.1µF
ceramic capacitor has significantly lower impedance at the
spike frequency than even a large tantalum capacitor, and
helps eliminate most of these left-over switching spikes
that the tantalum capacitor leaves behind. Figure 4 and 5
show scope photos of the output of Figure 3 with and
without the additional ceramic capacitor at the output.
A series RC or LC filter can reduce high frequency output
noise even further. Due to the high 900kHz switching
frequency, not much R or L is required; a ferrite bead or a
relatively long PC board trace in series with 0.1µF ceramic
capacitor will usually keep the output ripple well below
1mVP-P. The cover page shows an example of an ultralow
8
7
1
VCC
2
+
CIN
4.7µF
SHDN
SENSE
VCC
CPOUT
8
7
CCP
0.1µF
LTC1551
3
4
C1+
GND
VOUT
C1 –
OUTPUT RIPPLE (mVP-P)
WITHOUT 0.1µF
6
5
4
3
2
WITH 0.1µF
1
+
C1
0.1µF
COUT
10µF
0
1
CL
0.1µF*
10
OUTPUT CAPACITANCE (µF)
100
LTC1550/51 • F04
1550/51 F03
Figure 2. Output Ripple Test Circuit
Figure 3. Output Ripple vs Output Capacitance
VOUT
AC COUPLE
2mV/DIV
VOUT
AC COUPLE
5mV/DIV
5µs/DIV
LTC1550/51 • F03
Figure 4. Output Ripple with 10µF Tantalum Capacitor
8
6
5
VOUT
– 4.1V
*CL IS OPTIONAL
VCC = 6V
TA = 25°C
CIN = 4.7µF
10µs/DIV
LTC1550/51 • F04
Figure 5. Output Ripple with 10µF Tantalum
Capacitor Paralleled with 0.1µF Ceramic Capacitor
LTC1550/LTC1551
U
U
W
U
APPLICATIONS INFORMATION
noise – 4.1V generator which uses a ferrite bead output
filter to achieve better than 1mVP-P noise and output
ripple. The corresponding spectrum and spot noise plots
for this circuit are shown in the Typical Performance
Characteristics section.
Output Ripple vs Input Bypass Capacitor
The input bypass capacitor (CIN) can also have a fairly
significant impact on the output ripple. CIN provides most
of the LTC1550/LTC1551’s supply current while it is
charging the flying capacitor (C1). Inadequate input bypass
can cause the VCC supply to dip when the charge pump
switches, causing the output linear regulator to momentarily
stop regulating. CIN should be mounted as close to the
LTC1550/LTC1551 as possible and its value should be
significantly larger than C1. Tantalum capacitors with low
ESR generally provide adequate performance. Figure 6
shows the LTC1550/LTC1551 peak-to-peak output ripple
vs CIN, taken using the test circuit in Figure 2 with ILOAD set
at 5mA. COUT is a 10µF in parallel with a 0.1µF ceramic
capacitor.
A 4.7µF tantalum capacitor at VCC generally provides
adequate output ripple performance for most applications.
8
VCC = 6V
TA = 25°C
COUT = 10µF
OUTPUT RIPPLE (mVP-P)
7
6
5
4
3
2
1
0
0.1
1
10
INPUT CAPACITANCE (µF)
100
LTC1550/51 • F07
Figure 6. Output Ripple vs Input Bypass Capacitance
U
TYPICAL APPLICATION
– 4.1V Output GaAs FET Bias Generator
+
CIN
4.7µF
2
SHDN
SENSE
VCC
CPOUT
8
7
LTC1550
3
4
C1+
GND
VOUT
C1 –
6
CCP
0.1µF
5
– 4.1V BIAS
C1
0.1µF
+
1
4.5V ≤ VCC ≤ 6.5V
COUT
10µF
CL
0.1µF
GaAs
TRANSMITTER
1550/51 TA02
9
LTC1550/LTC1551
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 – 0.196*
(4.801 – 4.978)
16 15 14 13 12 11 10 9
0.229 – 0.244
(5.817 – 6.198)
0.150 – 0.157**
(3.810 – 3.988)
1
0.015 ± 0.004
× 45°
(0.38 ± 0.10)
0.0075 – 0.0098
(0.191 – 0.249)
4
5 6
7
8
0.004 – 0.009
(0.102 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
10
0.053 – 0.069
(1.351 – 1.748)
2 3
0.008 – 0.012
(0.203 – 0.305)
0.025
(0.635)
BSC
GN16 (SSOP) 0895
LTC1550/LTC1551
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8
7
6
5
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
2
3
4
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
SO8 0996
11
LTC1550/LTC1551
U
TYPICAL APPLICATION
< 1mVP-P Ripple, – 4.1V Output GaAs FET Bias Generator
1
4.5V ≤ VCC ≤ 6.5V
+
CIN
4.7µF
2
SHDN
SENSE
VCC
CPOUT
8
7
LTC1550
3
4
6
C1+
GND
VOUT
5
C1 –
CCP
0.1µF
FERRITE BEAD
+
C1
0.1µF
– 4.1V
COUT
10µF
CL
0.1µF
GaAs
TRANSMITTER
1550/51 TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT 1054
Switched-Capacitor Voltage Converter with Regulator
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LTC1261
Switched-Capacitor Regulated Voltage Inverter
Selectable Fixed Output Voltages
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Clock-Synchronized Switched-Capacitor Voltage Inverter
Synchronizable Up to 2MHz System Clock
®
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
15501fa LT/TP 0897 REV A 4K • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 1996