LTC1550/LTC1551 Low Noise, Switched Capacitor Regulated Voltage Inverters U 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 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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%. U APPLICATIONS GaAs FET Bias Generators Negative Supply Generators Battery-Powered Systems Single Supply Applications ■ ■ ■ ■ 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. U 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 U W W W 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 U W U 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) 2 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. U W 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 U W 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 U W 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 U U U 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. 5 LTC1550/LTC1551 U U U 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 W 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 U W U U 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 U W U U 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 7 LTC1550/LTC1551 U U W U 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 100mA Switched-Capacitor Converter LTC1261 Switched-Capacitor Regulated Voltage Inverter Selectable Fixed Output Voltages LTC1429 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