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LTC1550L/LTC1551L Low Noise, Switched Capacitor Regulated Voltage Inverters
FEATURES
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DESCRIPTIO
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Regulated Negative Voltage from a Single Positive Supply Low Output Ripple: Less Than 1mVP-P Typ High Charge Pump Frequency: 900kHz Small Charge Pump Capacitors: 0.1F Requires Only Four External Capacitors Fixed - 4.1V, -2.5V, -2V or Adjustable Output Shutdown Mode Drops Supply Current to <1A High Output Current: Up to 20mA (Depending on VCC to VOUT Range) Output Regulation: 2.5% Over Line, Load and Temperature Available in 8-Lead MSOP, 8-Lead Narrow SO and 16-Lead Narrow SSOP
The LTC(R)1550L/LTC1551L are switched capacitor charge pump voltage inverters which include internal linear postregulators to minimize output ripple. The LTC1550L fixed output voltage versions include -4.1V, -2.5V and -2V with ripple voltages typically below 1mVP-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 0.2A 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 0.1F charge pump capacitors and a filter capacitor at the linear regulator output. The adjustable LTC1550L/LTC1551L require two additional resistors to set the output voltage. The LTC1550L/LTC1551L will supply up to 20mA (depending on VCC to VOUT 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.
VOUT Output Noise and Ripple
APPLICATIO 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 APPLICATIO
3.6V 1 2 SHDN VCC
+
REG CPOUT
8 7
R1 10k POWER VALID
+
2.2F CIN
LTC1550L-2 3 4 C1 GND C1 - 6 5
CCP 0.1F
VOUT AC COUPLED 2mV/DIV
VOUT
C1 0.1F
COUT 10F
VOUT = -2V ILOAD = 5mA CL 0.1F
1550L/51L TA01
Figure 1. - 2V Generator with 1mVP-P Noise
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5s/DIV
1550L/51L TA01a
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LTC1550L/LTC1551L
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ...................................................... 5.5V Output Voltage ............................. 0.3V to (VCC - 10.5V) Total Voltage, VCC to CPOUT .......................................... 10.8V Input Voltage (SHDN Pin) ........... - 0.3V to (VCC + 0.3V) Input Voltage (REG Pin) ............................. - 0.3V to 6V Output Short-Circuit Duration .............................. 30 sec
PACKAGE/ORDER INFORMATION
TOP VIEW SHDN* VCC C1+ VOUT 1 2 3 4 8 7 6 5 REG (ADJ*) CPOUT GND C1 -
SHDN* 1 VCC 2 C1+ 3 VOUT 4
MS8 PACKAGE 8-LEAD PLASTIC MSOP *SHDN FOR LTC1550L, SHDN FOR LTC1551L *FOR ADJUSTABLE VERSION TJMAX = 150C, JA = 200C/W
ORDER PART NUMBER LTC1550LCMS8 LTC1550LCMS8-2 LTC1550LCMS8-2.5 LTC1550LCMS8-4.1 LTC1551LCMS8 LTC1551LCMS8-4.1
*SHDN FOR LTC1550L, SHDN FOR LTC1551L *FOR ADJUSTABLE VERSION TJMAX = 150C, JA = 135C/W
MS8 PART MARKING LTEG LTGR LTFV LTEH LTFQ LTFT
Consult factory for Military grade parts and additional voltage options.
ELECTRICAL CHARACTERISTICS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.7V to 5.25V, C1 = CCP = 0.1F, COUT = 10F, TA = 25C unless otherwise specified. (Note 3)
PARAMETER Supply Voltage (Adjustable, Fixed -2V) (Fixed -2.5V) (Fixed - 4.1V) VREF Reference Voltage VREF Reference Voltage (VCC - VOUT) Line Regulation IS Supply Current SYMBOL VCC CONDITIONS
q q q
VCC = 5V, ADJ = GND, VREF = -VOUT IOUT = 0mA, 2.7V VCC 5.25V VCC = 5V, VSHDN = VCC (LTC1550L) or GND (LTC1551L) q VCC = 5V, VSHDN = GND (LTC1550L) or VCC (LTC1551L) q
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(Note 1)
Commercial Temperature Range ................. 0C to 70C Extended Commercial Operating Temperature Range (Note 3) .............. - 40C to 85C Industrial Temperature Range ................ - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
TOP VIEW 8 7 6 5 REG (ADJ*) CPOUT GND C1
-
TOP VIEW NC 1 C1+ 2 16 VCC 15 SHDN 14 REG 13 NC 12 ADJ 11 CPOUT 10 NC 9 NC
NC 3 VOUT 4 C1- 5
S8 PACKAGE 8-LEAD PLASTIC SO
PGND 6 AGND 7 NC 8
GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 150C, JA = 150C/W
ORDER PART NUMBER LTC1550LCS8 LTC1550LCS8-2 LTC1550LCS8-2.5 LTC1550LCS8-4.1 LTC1551LCS8 LTC1551LCS8-4.1
ORDER PART NUMBER LTC1550LCGN LTC1550LIGN GN PART MARKING 1550L 1550LI
MIN 2.7 3.05 4.5
TYP
MAX 5.25 5.25 5.25
UNITS V V V V mV/V mA A
1.225 2.5 3.65 0.2 7 10
LTC1550L/LTC1551L
ELECTRICAL CHARACTERISTICS
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 2.7V to 5.25V, C1 = CCP = 0.1F, COUT = 10F, TA = 25C unless otherwise specified. (Note 3)
SYMBOL fOSC VOL IREG VIH VIL IIN tON PARAMETER Internal Oscillator Frequency REG Output Low Voltage REG Sink Current SHDN Input High Voltage SHDN Input Low Voltage SHDN Input Current Turn-On Time CONDITIONS IREG = 1mA, VCC = 5V VREG = 0.8V, VCC = 5V VCC = 5V VCC = 5V VSHDN = VCC (All LTC1550L Versions) VSHDN = VCC (All LTC1551L Versions) VCC = 5V, IOUT = 10mA, -1.5V VOUT 4.1V (LTC1550L/LTC1551L) VCC = 5V, IOUT = 5mA, VOUT = - 4.5V (LTC1550L/LTC1551L) VCC = 5V, IOUT = 10mA, VOUT = - 2V (LTC1550L-2) VCC = 5V, IOUT = 10mA, VOUT = - 2.5V (LTC1550L-2.5) VCC = 5V, IOUT = 10mA, VOUT = - 4.1V (LTC1550L-4.1/LTC1551L-4.1) 2.7V VCC 5.25V, 0 IOUT 5mA 2.8V VCC 5.25V, 0 IOUT 10mA 3.5V VCC 5.25V, 0 IOUT 20mA 2.7V VCC 5.25V, 0 IOUT 5mA 3.1V VCC 5.25V, 0 IOUT 10mA 3.75V VCC 5.25V, 0 IOUT 20mA 3.05V VCC 5.25V, 0 IOUT 5mA 3.45V VCC 5.25V, 0 IOUT 10mA 4.1V VCC 5.25V, 0 IOUT 20mA 3.45V VCC 5.25V, 0 IOUT 5mA 3.85V VCC 5.25V, 0 IOUT 10mA 4.5V VCC 5.25V, 0 IOUT 20mA 3.9V VCC 5.25V, 0 IOUT 5mA 4.2V VCC 5.25V, 0 IOUT 10mA 4.85V VCC 5.25V, 0 IOUT 20mA 4.5V VCC 5.25V, 0 IOUT 5mA 4.75V VCC 5.25V, 0 IOUT 10mA 4.8V VCC 5.25V, 0 IOUT 5mA 5.1V VCC 5.25V, 0 IOUT 10mA VOUT = 0V, VCC = 5.25V
q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q
MIN
TYP 900 0.1 10
MAX 0.8
UNITS kHz V mA V V A A ms ms ms ms ms V V V V V V V V V V V V V V V V V V V mA mV
4 2
0.1 5 1 1 1 1 1 - 1.537 - 1.537 - 1.537 - 2.05 - 2.05 - 2.05 - 2.562 - 2.562 - 2.562 - 3.075 - 3.075 - 3.075 - 3.587 - 3.587 - 3.587 - 4.203 - 4.203 - 4.613 - 4.613 - 1.5 - 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 - 4.1 - 4.1 - 4.5 - 4.5 80 1
0.8 1 20 5 5 5 5 5 - 1.463 - 1.463 - 1.463 - 1.95 - 1.95 - 1.95 - 2.438 - 2.438 - 2.438 - 2.925 - 2.925 - 2.925 - 3.413 - 3.413 - 3.413 - 3.998 - 3.998 - 4.388 - 4.388 200
VOUT
Output Regulation (LTC1550L/LTC1551L) Output Regulation (LTC1550L/LTC1550L-2/ LTC1551L) Output Regulation (LTC1550L/LTC1550L-2.5/ LTC1551L) Output Regulation (LTC1550L/LTC1551L) Output Regulation (LTC1550L/LTC1551L) Output Regulation (LTC1550L/LTC1550L-4.1) (LTC1551L/LTC1551L-4.1) Output Regulation (LTC1550L/LTC1551L)) Output Short-Circuit Current Output Ripple Voltage
VOUT
VOUT
VOUT
VOUT
VOUT
VOUT ISC VRIPPLE
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 = 25C.
Note 3: The LTC1550LC/LTC1551LC are guaranteed to meet specified performance from 0C to 70C and are designed, characterized and expected to meet these extended temperature limits, but are not tested at - 40C and 85C. The LTC1550LI is guaranteed to meet the extended temperature limits.
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LTC1550L/LTC1551L TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency vs Temperature
975
4.5
SUPPLY CURRENT (mA)
POSITIVE SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
925 875 825 775 725
VCC = 5V VOUT = -4.1V
675 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1550L/51L G01
Maximum Output Current vs Supply Voltage
80
MAXIMUM OUTPUT CURRENT (mA)
70 60 50 40 30 20 10 0 2.25
TA = 25C 2.0
REFERENCE VOLTAGE (V)
START-UP TIME (ms)
VOUT = -2V
VOUT = -2.5V VOUT = -4.1V
2.75
3.25 3.75 4.25 SUPPLY VOLTAGE (V)
Startup Time (LTC1550L Shown)
5V SHDN 0V 0V VOUT - 4.1V POWER VALID 5V 0V 0.2ms/DIV
1550/51 G07
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UW
4.75
Supply Current vs Temperature
5.0 VCC = 5V VOUT = - 4.1V
6.0 5.6 5.2 4.8 4.4 4.0 3.6 3.2 2.8 2.4
Minimum Required VCC vs VOUT and IOUT
IOUT = 20mA
4.0
3.5
3.0
IOUT = 5mA
IOUT = 10mA
2.5 -55 -35 -15
5 25 45 65 85 105 125 TEMPERATURE (C)
1550L/51L G02
2.0
-5
-4
-2 -1 -3 OUTPUT VOLTAGE (V)
0
1550L/51L G03
Start-Up Time vs Supply Voltage
2.5 TA = 25C 1.24 1.238 1.236 1.234 1.232 1.230 1.228 1.226 1.224 1.222 1.220 5.25 0 2.25 1.218 2.75 3.25 3.75 4.25 SUPPLY VOLTAGE (V) 4.75 5.25
Reference Voltage vs VCC + |VOUT|
TA = 25C
1.5
VOUT = -4.1V RL = 820 VOUT = -2V RL = 390
1.0
0.5
4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 VCC + |VOUT| (V)
1550L/51L G06
1550L/51L G04
1550L/51L G05
Load Transient Response (See Figure 3, VCC = 5V)
Line Transient Response (See Figure 3, IL = 10mA)
VOUT 5mV/DIV AC COUPLED 10mA IOUT 0mA 1ms/DIV
1550/51 G08
VOUT 5mV/DIV AC COUPLED 5.25V 4.75V
VCC
2ms/DIV
1550/51 G09
LTC1550L/LTC1551L TYPICAL PERFORMANCE CHARACTERISTICS
Output Spectrum (*See Figure 1)
90 80 70 60
10
NOISE (V/Hz)
NOISE (dBV)
NOISE (dBV)
50 40 30 20 10 0 -10 100k 1M FREQUENCY (Hz) 10M
1550L/51L G10
Spot Noise (See Figure 3)
10
90 80 70
NOISE (V/Hz)
50 40 30 20 10 0
0.1
VCC = 5V IL = 5mA CIN = 2.2F COUT = 4.7F CL = 0.1F 1 10 FREQUENCY (kHz) 100
1550L/51L G13
NOISE (V/Hz)
NOISE (dBV)
1
0.01
* On first page of data sheet.
UW
Spot Noise (*See Figure 1)
90 80 70
Output Spectrum (See Figure 3)
VCC = 5V IL = 5mA CIN = 2.2F COUT = 4.7F CL = 0.1F
1
60 50 40 30 20 10 0
0.1
0.01 1 10 FREQUENCY (kHz) 100
1550 /51L G11
-10 100k
1M FREQUENCY (Hz)
10M
1550L/51L G12
Output Spectrum (See Figure 3)
10
VCC = 5V IL = 5mA CIN 2.2F COUT = 10F CL = 0.1F
Spot Noise (See Figure 3)
VCC = 5V IL = 5mA CIN = 2.2F COUT = 10F CL = 0.1F
60
1
0.1
-10 100k
1M FREQUENCY (Hz)
10M
1550L/51L G14
0.01 1 10 FREQUENCY (kHz) 100
1550L/51L G15
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LTC1550L/LTC1551L
PIN FUNCTIONS
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 VCC (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 0.2A. 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 5A typical pull-down that defaults the LTC1551L into normal operation. VCC: Power Supply. VCC 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 Characteristics 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. VCC must be bypassed directly to PGND (GND for 8-pin packages) with at least a 0.1F capacitor placed in close proximity to the chip. A 1F 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 0.1F capacitor between C1 + and C1 -. VOUT: Negative Voltage Output. This pin must be bypassed with a 4.7F or larger capacitor to ensure regulator loop stability. LTC recommends at least 10F to achieve the specified output ripple. The output capacitor should be a moderate ESR capacitor, and not a very low ESR capacitor, 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 capacitors will result in the output oscillating. A low ESR 0.1F 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 VCC and CPOUT bypass capacitors, as well as to the GND of the LTC1550L/ LTC1551L. LTC recommends a separate trace for the VOUT capacitor ground connection to minimize noise. C1 -: C1 Negative Input. Connect a 0.1F 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 0.1F storage capacitor to ground. In order to achieve ripple on the output voltage of less than 1mV, the ground connection for the CPOUT capacitor must tie directly to the bottom of the VCC 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 VCC 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 VOUT with the divided tap connected to ADJ. Note that the resistor string needs to be connected "upside-down" from a negative regulator. See the Applications 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.
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LTC1550L/LTC1551L
BLOCK DIAGRAM W
CCP VCC CPOUT
+
COUT
S1 S4 CLK 900kHz S2 C1 + C1 C1 -
LINEAR REGULATOR
VOUT
+
-
**
S3 CHARGE PUMP **
ADJ
*SHDN
+
58mV 1.225V 1.167V COMP2
REG
-
*SHDN FOR LTC1550L, SHDN FOR LTC1551L ** FIXED OUTPUT VERSIONS ONLY
1550L/51L BD
APPLICATIONS INFORMATION
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 1A. 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.
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LTC1550L/LTC1551L
APPLICATIONS INFORMATION
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 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 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 0.1F ceramic capacitors for C1 and CCP. Increasing C1 and CCP beyond 0.1F has little effect on the output ripple or the output current capacity of the LTC1550L/LTC1551L. 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 by a pair of internal divider resistors for the fixed voltage versions. The Nchannel 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 4.7F from VOUT to ground is required to keep the regulator loop stable; for optimum stability and minimum output ripple, at least 10F is recommended. Adjustable Hook-Up For the adjustable LTC1550L/LTC1551L, the output voltage is set with a resistor divider from GND to VOUT (Figure 2). Note that the internal reference and the internal feedback amplifier are set up as a positive-output regulator referenced to the VOUT pin, not as a negative regulator
PGND, AGND R1 LTC1550L ADJ R2 VOUT VOUT = -1.225V
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(
R1 + R2 R2
)
1550L/51L * F02
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 VOUT. For example, a - 3V output would require a 17.4k resistor from GND to ADJ, and a 12.1k resistor to VOUT. CAPACITOR SELECTION The LTC1550L/LTC1551L requires four external capacitors: an input bypass capacitor, two 0.1F 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 particular, 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 VCC bypass capacitor, the CPOUT capacitor and the VOUT bypass capacitor must employ star-ground techniques at the GND pin of the LTC1550L/LTC1551L. Proper capacitor selection is critical for optimum performance of the LTC1550L/ LTC1551L. Output Ripple vs Output Capacitor Figure 4 shows the effect of using different output capacitor values on the LTC1550L/LTC1551L output ripple. These curves are taken using the LTC1551L circuit in Figure 3, with CIN = 2.2F and ILOAD = 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 0.1F ceramic capacitor. As a general rule, larger output capacitors provide lower output ripple. To keep output voltage ripple below 1mVP-P, 10F, or greater, in parallel with a 0.1F ceramic capacitor is required. To guarantee loop stability under all conditions, a minimum of 4.7F is required at the output.
LTC1550L/LTC1551L
APPLICATIONS INFORMATION
Figure 4 shows a marked decrease in peak-to-peak output ripple when a 0.1F 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 0.1F ceramic capacitor has significantly lower impedance at the spike frequency 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 0.1F ceramic capacitor will usually keep the output ripple well below 1mVP-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 Performance Characteristics section.
VCC
1 2
SHDN VCC
+
REG CPOUT
8 7
R1 10k
OUTPUT RIPPLE (mVP-P)
+
CIN 2.2F
LTC1551L 3 4 C1 GND C1 - 6 5
CCP 0.1F
VOUT
C1 0.1F
COUT 10F
CL 0.1F
1550L/51L F03
Figure 3. Output Ripple Test Circuit
VOUT AC COUPLE 5mV/DIV
5s/DIV
1550L/51L F05
Figure 5. Output Ripple with 10F Tantalum Capacitor
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8 7 6 5 WITHOUT 0.1F 4 3 2 WITH 0.1F 1 VCC = 5V TA = 25C CIN = 2.2F
VOUT - 4.1V
0 1 10 OUTPUT CAPACITANCE (F) 100
1550L/51L F04
Figure 4. Output Ripple vs Output Capacitance
VOUT AC COUPLE 2mV/DIV
10s/DIV
1550L/51L F06
Figure 6. Output Ripple with 10F Tantalum Capacitor Paralleled with 0.1F Ceramic Capacitor
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LTC1550L/LTC1551L
APPLICATIONS INFORMATION
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 LTC1550L/LTC1551L's supply current while it is charging the flying capacitor (C1). Inadequate input bypassing 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 LTC1550L/LTC1551L VCC and GND pins as possible and its value should be significantly larger than
8 7 VCC = 5V TA = 25C COUT = 10F
OUTPUT RIPPLE (mVP-P)
6 5 4 3 2 1 0 0.1
Figure 7. Output Ripple vs Input Bypass Capacitance
TYPICAL APPLICATION
- 4.1V Output GaAs FET Bias Generator
1 4.5V VCC 5.25V 2 SHDN VCC C1+ VOUT REG CPOUT 8 7 CCP 0.1F
+
CIN 2.2F
LTC1550L-4.1 3 4 GND C1 6
-5
C1 0.1F
10
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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 CIN, taken using the test circuit in Figure 3 with ILOAD set at 5mA. COUT is a 10F in parallel with a 0.1F ceramic capacitor. A 2.2F surface mount ceramic capacitor at VCC generally provides adequate output ripple performance for most applications.
1 10 INPUT CAPACITANCE (F)
100
1550L/51L F08
- 4.1V BIAS COUT 10F CL 0.1F
GaAs TRANSMITTER
1550L/51L TA02
LTC1550L/LTC1551L
PACKAGE DESCRIPTION
0.007 - 0.0098 (0.178 - 0.249) 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
0.007 (0.18) 0.021 0.006 (0.53 0.015)
0 - 6 TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.193 0.006 (4.90 0.15) 0.118 0.004** (3.00 0.102)
* 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
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.
U
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
0.009 (0.229) REF
0.229 - 0.244 (5.817 - 6.198)
0.150 - 0.157** (3.810 - 3.988)
1 0.015 0.004 x 45 (0.38 0.10) 0 - 8 TYP 0.053 - 0.068 (1.351 - 1.727)
23
4
56
7
8 0.004 - 0.0098 (0.102 - 0.249)
0.008 - 0.012 (0.203 - 0.305)
0.0250 (0.635) BSC
GN16 (SSOP) 1098
MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102)
0.040 0.006 (1.02 0.15)
0.034 0.004 (0.86 0.102)
8
76
5
0.006 0.004 (0.15 0.102)
MSOP (MS8) 1098
1
23
4
11
LTC1550L/LTC1551L
TYPICAL APPLICATION
1mVP-P Ripple, - 2V Output GaAs FET Bias Generator
10k 1 2.7V VCC 5.25V 2 SHDN VCC
+
+
C1 0.1F
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) 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 7 6 5
0.014 - 0.019 (0.355 - 0.483) TYP *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
0.016 - 0.050 (0.406 - 1.270)
RELATED PARTS
PART NUMBER LT (R)1054 LTC1261 LTC1261L LTC1429 LTC1516 LTC1522 DESCRIPTION Switched-Capacitor Voltage Converter with Regulator Switched-Capacitor Regulated Voltage Inverter Switched-Capacitor Regulated Voltage Inverter Clock-Synchronized Switched-Capacitor Voltage Inverter Micropower Regulated 5V Charge Pump DC/DC Converter Micropower Regulated 5V Charge Pump DC/DC Converter COMMENTS 100mA Switched-Capacitor Converter Selectable Fixed Output Voltages Adjustable and Fixed Output Voltages, Up to 20mA IOUT, MSOP Synchronizable Up to 2MHz System Clock VIN 2V to 10V, Adjustable or Fixed VOUT, IOUT to 50mA IOUT = 20mA (VIN 2V), IOUT = 50mA (VIN 3V) IOUT = 10mA (VIN 2.7V), IOUT = 20mA (VIN 3V) 900kHz Charge Pump, 1mVP-P Ripple Step-Up/Step-Down SIM Power Supply and Level Translators - 5V at 150mA from a 5V Input, 5-Lead SOT-23 - 5V at 200mA from a 5V Input, MSOP
LTC1514/LTC1515 Step-Up/Step-Down Switched-Capacitor DC/DC Converters
LTC1550/LTC1551 Low Noise, Switched-Capacitor Regulated Voltage Inverters LTC1555/LTC1556 SIM Power Supply and Level Translator LT1611 LT1614 LTC1754-5 1.4MHz Inverting Mode Switching Regulator Inverting 600kHz Switching Regulator with Low-Battery Detector
Micropower, Regulated 5V Charge Pump with Shutdown in SOT-23 ICC = 13A, IOUT = 50mA (VIN 3V), IOUT = 25mA (VIN 2.7V)
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
+
U
U
REG CPOUT
8 7
REG CCP 0.1F
CIN 2.2F
LTC1550L-2 3 4 C1 GND C1 - 6 5
VOUT
-2V COUT 10F CL 0.1F
GaAs TRANSMITTER
1550L/51L TA03
0.050 (1.270) BSC
1
2
3
4
SO8 1298
15501lf LT/TP 0300 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1996

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