1
LTC1550L/LTC1551L
Low Noise, Switched
Capacitor Regulated
Voltage Inverters
The LTC
®
1550L/LTC1551L are switched capacitor charge
pump voltage inverters which include internal linear post-
regulators to minimize output ripple. The LTC1550L fixed
output voltage versions include –4.1V, –2.5V and –2V with
ripple voltages typically below 1mV
P-P
. The LTC1550L is
also available in an adjustable output voltage version. The
LTC1550L/LTC1551L are ideal for use as bias voltage
generators for GaAs transmitter FETs in portable RF and
cellular telephone applications.
The LTC1550L/LTC1551L operate from single 2.7V to
5.5V supplies and draw typical quiescent currents of
3.5mA with a 5V supply. Each device includes a TTL
compatible Shutdown pin which drops supply current to
0.2µA typically. The LTC1550L Shutdown pin is active low
(SHDN), while the LTC1551L 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 LTC1550L/LTC1551L require two additional re-
sistors to set the output voltage. The LTC1550L/LTC1551L
will supply up to 20mA (depending on V
CC
to V
OUT
range),
while maintaining guaranteed output regulation of ±2.5%.
Both fixed voltage and adjustable LTC1550L/LTC1551L
are available in 8-lead MSOP and SO plastic packages: the
adjustable LTC1550L is also available in a 16-pin SSOP
with the REG pin.
, LTC and LT are registered trademarks of Linear Technology Corporation.
5µs/DIV 1550L/51L TA01a
■
Regulated Negative Voltage from a Single
Positive Supply
■
Low Output Ripple: Less Than 1mV
P-P
Typ
■
High Charge Pump Frequency: 900kHz
■
Small Charge Pump Capacitors: 0.1µF
■
Requires Only Four External Capacitors
■
Fixed –4.1V, –2.5V, –2V or Adjustable Output
■
Shutdown Mode Drops Supply Current to <1µA
■
High Output Current: Up to 20mA (Depending on
V
CC
to V
OUT
Range)
■
Output Regulation: 2.5% Over Line, Load and
Temperature
■
Available in 8-Lead MSOP, 8-Lead Narrow SO and
16-Lead Narrow SSOP
■
GaAs FET Bias Generators
■
Negative Supply Generators
■
Battery-Powered Systems
■
Single Supply Applications
V
OUT
AC COUPLED
2mV/DIV
VOUT Output Noise and Ripple
Figure 1. –2V Generator with 1mVP-P Noise
1
2
3.6V 8
7
REG
CPOUT
SHDN
VCC
C1+
VOUT
LTC1550L-2
GND
C1–
COUT
10µF
1550L/51L TA01
VOUT = –2V
ILOAD = 5mA
CCP
0.1µF
R1
10k
POWER VALID
C1
0.1µF
2.2µF
CIN 3
4
6
5
CL
0.1µF
+
+
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
2
LTC1550L/LTC1551L
ABSOLUTE MAXIMUM RATINGS
W
WW
U
(Note 1)
Supply Voltage ...................................................... 5.5V
Output Voltage............................. 0.3V to (V
CC
– 10.5V)
Total Voltage, V
CC
to CP
OUT ..........................................
10.8V
Input Voltage (SHDN Pin) ........... –0.3V to (V
CC
+ 0.3V)
Input Voltage (REG Pin) ............................. – 0.3V to 6V
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
PACKAGE/ORDER INFORMATION
W
UU
ORDER PART NUMBER
LTC1550LCGN
LTC1550LIGN
TOP VIEW
GN PACKAGE
16-LEAD PLASTIC SSOP
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
NC
C1
+
NC
V
OUT
C1
–
PGND
AGND
NC
V
CC
SHDN
REG
NC
ADJ
CP
OUT
NC
NC
T
JMAX
= 150°C, θ
JA
= 150°C/W
GN PART MARKING
T
JMAX
= 150°C, θ
JA
= 200°C/W
*SHDN FOR LTC1550L, SHDN FOR LTC1551L
*FOR ADJUSTABLE VERSION
ORDER PART NUMBER
MS8 PART MARKING
LTC1550LCMS8
LTC1550LCMS8-2
LTC1550LCMS8-2.5
LTC1550LCMS8-4.1
LTC1551LCMS8
LTC1551LCMS8-4.1
LTFQ
LTFT
LTEG
LTGR
LTFV
LTEH
T
JMAX
= 150°C, θ
JA
= 135°C/W
*SHDN FOR LTC1550L, SHDN FOR LTC1551L
*FOR ADJUSTABLE VERSION
1
2
3
4
8
7
6
5
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
REG (ADJ*)
CP
OUT
GND
C1
–
SHDN*
V
CC
C1
+
V
OUT
1
2
3
4
8
7
6
5
TOP VIEW
REG (ADJ*)
CP
OUT
GND
C1
–
SHDN*
V
CC
C1
+
V
OUT
S8 PACKAGE
8-LEAD PLASTIC SO
ORDER PART NUMBER
LTC1550LCS8
LTC1550LCS8-2
LTC1550LCS8-2.5
LTC1550LCS8-4.1
LTC1551LCS8
LTC1551LCS8-4.1
Consult factory for Military grade parts and additional voltage options.
1550L
1550LI
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
Supply Voltage
(Adjustable, Fixed –2V) ●2.7 5.25 V
(Fixed –2.5V) ●3.05 5.25 V
(Fixed –4.1V) ●4.5 5.25 V
V
REF
Reference Voltage V
CC
= 5V, ADJ = GND, V
REF
= –V
OUT
1.225 V
∆V
REF
Reference Voltage I
OUT
= 0mA, 2.7V ≤ V
CC
≤ 5.25V 2.5 mV/V
∆(V
CC
– V
OUT)
Line Regulation
I
S
Supply Current V
CC
= 5V, V
SHDN
= V
CC
(LTC1550L) or GND (LTC1551L) ● 3.65 7 mA
V
CC
= 5V, V
SHDN
= GND (LTC1550L) or V
CC
(LTC1551L) ●0.2 10 µA
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VCC = 2.7V to 5.25V, C1 = CCP = 0.1µF, COUT = 10µF, TA = 25°C unless otherwise specified. (Note 3)
ELECTRICAL CHARACTERISTICS
3
LTC1550L/LTC1551L
f
OSC
Internal Oscillator Frequency 900 kHz
V
OL
REG Output Low Voltage I
REG
= 1mA, V
CC
= 5V ●0.1 0.8 V
I
REG
REG Sink Current V
REG
= 0.8V, V
CC
= 5V ●410 mA
V
IH
SHDN Input High Voltage V
CC
= 5V ●2V
V
IL
SHDN Input Low Voltage V
CC
= 5V ●0.8 V
I
IN
SHDN Input Current V
SHDN
= V
CC
(All LTC1550L Versions) ●0.1 1 µA
V
SHDN
= V
CC
(All LTC1551L Versions) ●520 µA
t
ON
Turn-On Time V
CC
= 5V, I
OUT
= 10mA, –1.5V ≤ V
OUT
≤ 4.1V ●15ms
(LTC1550L/LTC1551L)
V
CC
= 5V, I
OUT
= 5mA, V
OUT
= –4.5V ●15ms
(LTC1550L/LTC1551L)
V
CC
= 5V, I
OUT
= 10mA, V
OUT
= –2V ●15ms
(LTC1550L-2)
V
CC
= 5V, I
OUT
= 10mA, V
OUT
= –2.5V ●15ms
(LTC1550L-2.5)
V
CC
= 5V, I
OUT
= 10mA, V
OUT
= –4.1V ●15ms
(LTC1550L-4.1/LTC1551L-4.1)
V
OUT
Output Regulation 2.7V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–1.537 –1.5 –1.463 V
(LTC1550L/LTC1551L) 2.8V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–1.537 –1.5 –1.463 V
3.5V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 20mA ●–1.537 –1.5 –1.463 V
V
OUT
Output Regulation 2.7V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–2.05 –2.0 –1.95 V
(LTC1550L/LTC1550L-2/ 3.1V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–2.05 –2.0 –1.95 V
LTC1551L) 3.75V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 20mA ●–2.05 –2.0 –1.95 V
V
OUT
Output Regulation 3.05V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–2.562 –2.5 –2.438 V
(LTC1550L/LTC1550L-2.5/ 3.45V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–2.562 –2.5 –2.438 V
LTC1551L) 4.1V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 20mA ●–2.562 –2.5 –2.438 V
V
OUT
Output Regulation 3.45V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–3.075 –3.0 –2.925 V
(LTC1550L/LTC1551L) 3.85V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–3.075 –3.0 –2.925 V
4.5V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 20mA ●–3.075 –3.0 –2.925 V
V
OUT
Output Regulation 3.9V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–3.587 –3.5 –3.413 V
(LTC1550L/LTC1551L) 4.2V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–3.587 –3.5 –3.413 V
4.85V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 20mA ●–3.587 –3.5 –3.413 V
V
OUT
Output Regulation 4.5V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–4.203 –4.1 –3.998 V
(LTC1550L/LTC1550L-4.1) 4.75V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–4.203 –4.1 –3.998 V
(LTC1551L/LTC1551L-4.1)
V
OUT
Output Regulation 4.8V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 5mA ●–4.613 –4.5 –4.388 V
(LTC1550L/LTC1551L)) 5.1V ≤ V
CC
≤ 5.25V, 0 ≤ I
OUT
≤ 10mA ●–4.613 –4.5 –4.388 V
I
SC
Output Short-Circuit Current V
OUT
= 0V, V
CC
= 5.25V ●80 200 mA
V
RIPPLE
Output Ripple Voltage 1mV
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VCC = 2.7V to 5.25V, C1 = CCP = 0.1µF, COUT = 10µF, TA = 25°C unless otherwise specified. (Note 3)
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
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 T
A
= 25°C.
Note 3: The LTC1550LC/LTC1551LC are guaranteed to meet specified
performance from 0°C to 70°C and are designed, characterized and
expected to meet these extended temperature limits, but are not tested at
–40°C and 85°C. The LTC1550LI is guaranteed to meet the extended
temperature limits.
4
LTC1550L/LTC1551L
TYPICAL PERFORMANCE CHARACTERISTICS
UW
Supply Current vs Temperature
Oscillator Frequency vs
Temperature
OUTPUT VOLTAGE (V)
–5
POSITIVE SUPPLY VOLTAGE (V)
6.0
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0 –1
1550L/51L G03
–4 –3 –2 0
I
OUT
= 20mA
I
OUT
= 10mA
I
OUT
= 5mA
Minimum Required VCC
vs VOUT and IOUT
TEMPERATURE (˚C)
–55 –35 –15 5 25 45 65 85 105 125
OSCILLATOR FREQUENCY (kHz)
875
925
975
1550L/51L G01
825
775
725
675
V
CC
= 5V
V
OUT
= –4.1V
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
1550L/51L G02
V
CC
= 5V
V
OUT
= –4.1V
–55 –35 –15 5 25 45 65 85 105 125
5.0
4.5
4.0
3.5
3.0
2.5
Reference Voltage vs VCC + |VOUT|Start-Up Time vs Supply Voltage
Maximum Output Current
vs Supply Voltage
Load Transient Response
(See Figure 3, VCC = 5V)
Line Transient Response
(See Figure 3, IL = 10mA)
5V
0V
–4.1V
V
OUT
SHDN
0.2ms/DIV 1550/51 G07
Startup Time (LTC1550L Shown)
0V
5V
0V
POWER VALID 0mA
1ms/DIV 1550/51 G08
10mA
V
OUT
5mV/DIV
AC
COUPLED
I
OUT
4.75V
2ms/DIV 1550/51 G09
V
OUT
5mV/DIV
AC
COUPLED
5.25V
V
CC
SUPPLY VOLTAGE (V)
2.25 2.75 3.25 3.75 4.25 4.75 5.25
MAXIMUM OUTPUT CURRENT (mA)
1550L/51L G04
80
70
60
50
40
30
20
10
0
T
A
= 25°C
V
OUT
= –2V V
OUT
= –2.5V
V
OUT
= –4.1V
SUPPLY VOLTAGE (V)
2.25 2.75 3.25 3.75 4.25 4.75 5.25
START-UP TIME (ms)
1550L/51L G05
2.5
2.0
1.5
1.0
0.5
0
T
A
= 25°C
V
OUT
= –2V
R
L
= 390Ω
V
OUT
= –4.1V
R
L
= 820Ω
1.24
1.238
1.236
1.234
1.232
1.230
1.228
1.226
1.224
1.222
1.220
1.218
V
CC
+ |V
OUT
| (V)
456789104.5 5.5 6.5 7.5 8.5 9.5
REFERENCE VOLTAGE (V)
1550L/51L G06
T
A
= 25°C
5
LTC1550L/LTC1551L
TYPICAL PERFORMANCE CHARACTERISTICS
UW
FREQUENCY (Hz)
100k
NOISE (dBµV)
90
80
70
60
50
40
30
20
10
0
–10 1M 10M
1550L/51L G10
FREQUENCY (kHz)
1
0.01
NOISE (µV/√Hz)
1
0.1
10
10 100
1550 /51L G11
Spot Noise (*See Figure 1) Output Spectrum (See Figure 3)
FREQUENCY (Hz)
100k
NOISE (dBµV)
90
80
70
60
50
40
30
20
10
0
–10 1M 10M
1550L/51L G12
V
CC
= 5V
I
L
= 5mA
C
IN
= 2.2µF
C
OUT
= 4.7µF
C
L
= 0.1µF
Output Spectrum (*See Figure 1)
* On first page of data sheet.
Spot Noise (See Figure 3)
FREQUENCY (kHz)
1
0.01
NOISE (µV/√Hz)
1
0.1
10
10 100
1550L/51L G13
V
CC
= 5V
I
L
= 5mA
C
IN
= 2.2µF
C
OUT
= 4.7µF
C
L
= 0.1µF
FREQUENCY (Hz)
100k
NOISE (dBµV)
90
80
70
60
50
40
30
20
10
0
–10 1M 10M
1550L/51L G14
V
CC
= 5V
I
L
= 5mA
C
IN
2.2µF
C
OUT
= 10µF
C
L
= 0.1µF
Spot Noise (See Figure 3)
FREQUENCY (kHz)
1
0.01
NOISE (µV/√Hz)
1
0.1
10
10 100
1550L/51L G15
VCC = 5V
IL = 5mA
CIN = 2.2µF
COUT = 10µF
CL = 0.1µF
Output Spectrum (See Figure 3)
6
LTC1550L/LTC1551L
PIN FUNCTIONS
UUU
SHDN: Shutdown (TTL Compatible). This pin is active low
(SHDN) for the LTC1550L and active high (SHDN) for the
LTC1551L. When this pin is at V
CC
(GND for LTC1551L),
the LTC1550L operates normally. When SHDN is pulled
low (SHDN pulled high for LTC1551L), the LTC1550L
enters shutdown mode. In shutdown, the charge pump
stops, the output collapses to 0V, and the quiescent
current drops typically to 0.2µA. The SHDN pin for the
LTC1550L is a high impedance input and has no internal
pull-up. The user must supply a resistor or current source
pull-up to default the LTC1550L into normal operation.
The SHDN pin for the LTC1551L has an internal 5µA
typical pull-down that defaults the LTC1551L into normal
operation.
V
CC
: Power Supply. V
CC
requires an input voltage between
2.7V and 5.25V. Certain combinations of output voltage
and output load current may place additional restrictions
on the required input voltage. Consult the Electrical Char-
acteristics table and Typical Performance Characteristics
for guaranteed test points. The difference between the
input voltage and output should not exceed 10.5V or
damage to the chip may occur. V
CC
must be bypassed
directly to PGND (GND for 8-pin packages) with at least a
0.1µF capacitor placed in close proximity to the chip. A 1µF
or larger low ESR bypass capacitor is recommended to
minimize noise and ripple at the output. A surface mount
ceramic capacitor is recommended.
C1
+
: C1 Positive Input. Connect a 0.1µF capacitor between
C1
+
and C1
–
.
V
OUT
: Negative Voltage Output. This pin must be bypassed
with a 4.7µF or larger capacitor to ensure regulator loop
stability. LTC recommends at least 10µF to achieve the
specified output ripple. The output capacitor should be a
moderate ESR capacitor, and not a very low ESR capaci-
tor, as the zero in the feedback loop (formed by the ESR
and the output capacitor) provides phase lead to the linear
regulator feedback loop. Using very low ESR output ca-
pacitors will result in the output oscillating. A low ESR
0.1µF capacitor is recommended in parallel with the main
output capacitor to minimize high frequency spikes at the
output. The ground connection for the output capacitor
should connect directly to the V
CC
and CP
OUT
bypass
capacitors, as well as to the GND of the LTC1550L/
LTC1551L. LTC recommends a separate trace for the V
OUT
capacitor ground connection to minimize noise.
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.
CP
OUT
: Negative Charge Pump Output. This pin requires a
0.1µF storage capacitor to ground. In order to achieve
ripple on the output voltage of less than 1mV, the ground
connection for the CP
OUT
capacitor must tie directly to the
bottom of the V
CC
bypass capacitor and at the GND pin of
the LTC1550L/LTC1551L. This minimizes the AC current
path for the charge pump.
REG: This is an open-drain output that pulls low when the
output voltage is within 5% of the set value. It will sink 4mA
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. For the LTC1550L adjustable
voltage version, the REG pin is only available in the 16-lead
GN package.
ADJ (for adjustable versions): This is the feedback point
for the external resistor divider string. Connect a divider
string from GND to V
OUT
with the divided tap connected to
ADJ. Note that the resistor string needs to be connected
“upside-down” from a negative regulator. See the Applica-
tions Information section for hook-up details.
GN 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.
NC: No Internal Connection.
7
LTC1550L/LTC1551L
BLOCK DIAGRAM
W
–
+
–+
S2
S3
S1
S4
CCP
VCC CPOUT
C1+
C1–
C1
CLK
900kHz
CHARGE
PUMP
LINEAR
REGULATOR
1550L/51L BD
VOUT
ADJ
REG
COUT
58mV
1.167V
*SHDN
*SHDN FOR LTC1550L, SHDN FOR LTC1551L
** FIXED OUTPUT VERSIONS ONLY
COMP2
**
**
+
1.225V
APPLICATIONS INFORMATION
WUUU
OVERVIEW
The LTC1550L/LTC1551L are switched capacitor, inverting
charge pumps with internal linear post-regulators. The
LTC1550L/LTC1551L provide a regulated, low ripple output
at up to 20mA load current with the appropriate input
voltage as output load current depends on the input/
output voltage combination. Consult the graph provided in
the Typical Performance Characteristics section and the
Electrical Characteristics table for guaranteed test points.
The LTC1550L/LTC1551L are ideal for use as bias voltage
generators for GaAs transmitter FETs in portable RF and
cellular telephone applications. The LTC1550L features an
active-low Shutdown pin (SHDN) that drops quiescent
current to below 1µA. The LTC1551L is identical to the
LTC1550L, except that the Shutdown pin is active-high
(SHDN). All members of the LTC1550L/LTC1551L family
feature a 900kHz charge pump frequency. The LTC1550L/
LTC1551L come standard with fixed –4.1V, –2.5V, –2V
and adjustable output voltages. The LTC1550L/LTC1551L
can be configured for other fixed output voltages; contact
Linear Technology for more information.
8
LTC1550L/LTC1551L
The LTC1550L/LTC1551L consist 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 C
CP
to generate a negative
voltage at CP
OUT
. It operates by charging and discharging
C1 on alternate phases of the internal 900kHz clock. C1 is
initially charged to V
CC
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 C
CP
through S4. As this cycle
repeats, the magnitude of the negative voltage approaches
V
CC
. The 900kHz internal clock frequency helps keep noise
out of the 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 C
CP
.
Increasing C1 and C
CP
beyond 0.1µF has little effect on the
output ripple or the output current capacity of the
LTC1550L/LTC1551L.
The negative voltage at CP
OUT
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
V
OUT
pin. The regulation loop is optimized for fast tran-
sient response, enabling it to remove most of the switch-
ing artifacts present at the CP
OUT
pin. Output ripple is
typically below 1mV
P-P
with output loads between 0mA
and 10mA. The output voltage is set by a pair of internal
divider resistors for the fixed voltage versions. The N-
channel pass device minimizes dropout, allowing the
output to remain in regulation with supply voltages as low
as 2.7V for an output voltage of –2V. An output capacitor
of at least 4.7µF from V
OUT
to ground is required to keep
the regulator loop stable; for optimum stability and mini-
mum output ripple, at least 10µF is recommended.
Adjustable Hook-Up
For the adjustable LTC1550L/LTC1551L, the output volt-
age is set with a resistor divider from GND to V
OUT
(Figure␣ 2). Note that the internal reference and the internal
feedback amplifier are set up as a positive-output regula-
tor referenced to the V
OUT
pin, not as a negative regulator
APPLICATIONS INFORMATION
WUUU
Figure 2. External Resistor Connections
referenced to ground. The output resistor divider must be
set to provide 1.225V at the ADJ pin with respect to V
OUT
.
For example, a –3V output would require a 17.4k resistor
from GND to ADJ, and a 12.1k resistor to V
OUT
.
CAPACITOR SELECTION
The LTC1550L/LTC1551L requires four external capaci-
tors: an input bypass capacitor, two 0.1µF charge pump
capacitors and an output filter capacitor. The overall
behavior of the LTC1550L/LTC1551L is strongly affected
by how the capacitors are used, and by how the capacitors
are laid out on the printed circuit board (PCB). In particu-
lar, the output capacitor’s value and ESR have a significant
effect on the output ripple and noise performance. In
addition, the ground connections for the V
CC
bypass
capacitor, the CP
OUT
capacitor and the V
OUT
bypass ca-
pacitor must employ star-ground techniques at the GND
pin of the LTC1550L/LTC1551L. Proper capacitor selec-
tion is critical for optimum performance of the LTC1550L/
LTC1551L.
Output Ripple vs Output Capacitor
Figure 4 shows the effect of using different output capaci-
tor values on the LTC1550L/LTC1551L output ripple.
These curves are taken using the LTC1551L circuit in
Figure 3, with C
IN
= 2.2µF and I
LOAD
= 5mA. The upper
curve shows the performance with a standard tantalum
capacitor alone and the lower curve shows that of the
tantalum capacitor in parallel with a 0.1µF ceramic capaci-
tor. As a general rule, larger output capacitors provide
lower output ripple. To keep output voltage ripple below
1mV
P–P
, 10µF, or greater, in parallel with a 0.1µF ceramic
capacitor is required. To guarantee loop stability under all
conditions, a minimum of 4.7µF is required at the output.
PGND, AGND
LTC1550L
V
OUT
ADJ
R1
R2
V
OUT
= –1.225V R1 + R2
R2
()
1550L/51L • F02
9
LTC1550L/LTC1551L
APPLICATIONS INFORMATION
WUUU
Figure 4 shows a marked decrease in peak-to-peak output
ripple when a 0.1µF ceramic capacitor is 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 0.1µF ceramic capaci-
tor has significantly lower impedance at the spike fre-
quency than a large tantalum capacitor, and eliminates
most of these left-over switching spikes that the tantalum
capacitor leaves behind. Figure 5 and 6 show scope photos
of the output of Figure 4 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
1mV
P-P
. Figure 1 shows an example of an ultralow noise
–2V generator. The corresponding spectrum and spot
noise plots for this circuit are shown in the Typical Perfor-
mance Characteristics section.
5µs/DIV 1550L/51L F05
Figure 5. Output Ripple with 10µF Tantalum Capacitor
V
OUT
AC COUPLE
5mV/DIV
Figure 3. Output Ripple Test Circuit Figure 4. Output Ripple vs Output Capacitance
OUTPUT CAPACITANCE (µF)
8
7
6
5
4
3
2
1
010
1550L/51L F04
OUTPUT RIPPLE (mV
P-P
)
1100
V
CC
= 5V
T
A
= 25°C
C
IN
= 2.2µF
WITHOUT 0.1µF
WITH 0.1µF
1
2
V
CC
8
7
REG
CP
OUT
SHDN
V
CC
C1
+
V
OUT
LTC1551L
GND
C1
–
C
OUT
10µF
1550L/51L F03
V
OUT
–4.1V
C
CP
0.1µF
C1
0.1µF
C
IN
2.2µF3
4
6
5
C
L
0.1µF
+
+
R1
10k
10µs/DIV 1550L/51L F06
V
OUT
AC COUPLE
2mV/DIV
Figure 6. Output Ripple with 10µF Tantalum
Capacitor Paralleled with 0.1µF Ceramic Capacitor
10
LTC1550L/LTC1551L
APPLICATIONS INFORMATION
WUUU
Figure 7. Output Ripple vs Input Bypass Capacitance
INPUT CAPACITANCE (µF)
0.1
OUTPUT RIPPLE (mV
P-P
)
8
7
6
5
4
3
2
1
01 10 100
1550L/51L F08
V
CC
= 5V
T
A
= 25°C
C
OUT
= 10µF
Output Ripple vs Input Bypass Capacitor
The input bypass capacitor (C
IN
) can also have a fairly
significant impact on the output ripple. C
IN
provides most
of the LTC1550L/LTC1551L’s supply current while it is
charging the flying capacitor (C1). Inadequate input
bypassing can cause the V
CC
supply to dip when the
charge pump switches, causing the output linear regulator
to momentarily stop regulating. C
IN
should be mounted as
close to the LTC1550L/LTC1551L V
CC
and GND pins as
possible and its value should be significantly larger than
C1. Surface mount tantalum or ceramic capacitors with
low ESR generally provide adequate performance. Figure␣ 7
shows the LTC1550L/LTC1551L peak-to-peak output ripple
vs C
IN
, taken using the test circuit in Figure 3 with I
LOAD
set
at 5mA. C
OUT
is a 10µF in parallel with a 0.1µF ceramic
capacitor.
A 2.2µF surface mount ceramic capacitor at V
CC
generally
provides adequate output ripple performance for most
applications.
1
2
4.5V ≤ V
CC
≤ 5.25V
8
7
REG
CP
OUT
SHDN
V
CC
C1
+
V
OUT
LTC1550L-4.1
–4.1V BIAS
GND
C1
–
C
OUT
10µF
1550L/51L TA02
C
CP
0.1µF
GaAs
TRANSMITTER
C1
0.1µF
C
IN
2.2µF3
4
6
5
C
L
0.1µF
+
+
–4.1V Output GaAs FET Bias Generator
TYPICAL APPLICATION
U
11
LTC1550L/LTC1551L
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTION
U
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
GN16 (SSOP) 1098
* 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
12
345678
0.229 – 0.244
(5.817 – 6.198)
0.150 – 0.157**
(3.810 – 3.988)
16 15 14 13
0.189 – 0.196*
(4.801 – 4.978)
12 11 10 9
0.016 – 0.050
(0.406 – 1.270)
0.015 ± 0.004
(0.38 ± 0.10) × 45°
0° – 8° TYP
0.007 – 0.0098
(0.178 – 0.249)
0.053 – 0.068
(1.351 – 1.727)
0.008 – 0.012
(0.203 – 0.305)
0.004 – 0.0098
(0.102 – 0.249)
0.0250
(0.635)
BSC
0.009
(0.229)
REF
MS8 Package
8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
MSOP (MS8) 1098
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006"
(
0.152mm
)
PER SIDE
0.021 ± 0.006
(0.53 ± 0.015)
0° – 6° TYP
SEATING
PLANE
0.007
(0.18)
0.040 ± 0.006
(1.02 ± 0.15)
0.012
(0.30)
REF
0.006 ± 0.004
(0.15 ± 0.102)
0.034 ± 0.004
(0.86 ± 0.102)
0.0256
(0.65)
BSC 12
34
0.193 ± 0.006
(4.90 ± 0.15)
8765
0.118 ± 0.004*
(3.00 ± 0.102)
0.118 ± 0.004**
(3.00 ± 0.102)
12
LTC1550L/LTC1551L
15501lf LT/TP 0300 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1996
TYPICAL APPLICATION
U
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OUT
= 20mA (V
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OUT
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LTC1754-5 Micropower, Regulated 5V Charge Pump with Shutdown in SOT-23 I
CC
= 13µA, I
OUT
= 50mA (V
IN
≥ 3V), I
OUT
= 25mA (V
IN
≥ 2.7V)
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTION
U
1
2
2.7V ≤ V
CC
≤ 5.25V
8
7
REG
CP
OUT
SHDN
V
CC
C1
+
V
OUT
LTC1550L-2
–2V
GND
C1
–
C
OUT
10µF
1550L/51L TA03
C
CP
0.1µF
GaAs
TRANSMITTER
C1
0.1µF
C
IN
2.2µF3
4
6
5
C
L
0.1µF
+
+
10k
REG
1mVP-P Ripple, –2V Output GaAs FET Bias Generator
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear-tech.com
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.016 – 0.050
(0.406 – 1.270)
0.010 – 0.020
(0.254 – 0.508)× 45°
0°– 8° TYP
0.008 – 0.010
(0.203 – 0.254)
SO8 1298
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
1234
0.150 – 0.157**
(3.810 – 3.988)
8765
0.189 – 0.197*
(4.801 – 5.004)
0.228 – 0.244
(5.791 – 6.197)
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
*
**
