LTC1550L/LTC1551L Low Noise, Switched Capacitor Regulated Voltage Inverters U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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: 0.1µF 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 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 U APPLICATIO S ■ ■ ■ ■ GaAs FET Bias Generators Negative Supply Generators Battery-Powered Systems Single Supply Applications , LTC and LT are registered trademarks of Linear Technology Corporation. The LTC®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 0.2µA 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 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. U TYPICAL APPLICATIO 1 2 + 2.2µF CIN SHDN VCC REG CPOUT R1 10k POWER VALID 7 CCP 0.1µF LTC1550L-2 3 4 + C1 GND VOUT C1 – C1 0.1µF 6 VOUT AC COUPLED 2mV/DIV 5 + 3.6V 8 VOUT Output Noise and Ripple COUT 10µF VOUT = –2V ILOAD = 5mA CL 0.1µF 1550L/51L TA01 Figure 1. – 2V Generator with 1mVP-P Noise 5µs/DIV 1550L/51L TA01a 1 LTC1550L/LTC1551L U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) 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 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 TOP VIEW TOP VIEW SHDN* VCC C1+ VOUT 1 2 3 4 8 7 6 5 REG (ADJ*) CPOUT GND C1 – SHDN* 1 MS8 PACKAGE 8-LEAD PLASTIC MSOP CPOUT 6 GND 5 C1 C1+ – MS8 PART MARKING LTFQ LTFT 14 REG VOUT 4 13 NC C1– 5 12 ADJ PGND 6 11 CPOUT AGND 7 10 NC 9 NC 8 TJMAX = 150°C, θJA = 135°C/W LTC1551LCMS8 LTC1551LCMS8-4.1 15 SHDN 2 NC 3 *SHDN FOR LTC1550L, SHDN FOR LTC1551L *FOR ADJUSTABLE VERSION ORDER PART NUMBER LTEG LTGR LTFV LTEH 7 C1+ 3 16 VCC NC 1 REG (ADJ*) S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150°C, θJA = 200°C/W LTC1550LCMS8 LTC1550LCMS8-2 LTC1550LCMS8-2.5 LTC1550LCMS8-4.1 8 VCC 2 VOUT 4 *SHDN FOR LTC1550L, SHDN FOR LTC1551L *FOR ADJUSTABLE VERSION TOP VIEW NC GN PACKAGE 16-LEAD PLASTIC SSOP ORDER PART NUMBER TJMAX = 150°C, θJA = 150°C/W LTC1550LCS8 LTC1550LCS8-2 LTC1550LCS8-2.5 LTC1550LCS8-4.1 LTC1551LCS8 LTC1551LCS8-4.1 ORDER PART NUMBER LTC1550LCGN LTC1550LIGN GN PART MARKING 1550L 1550LI Consult factory for Military grade parts and additional voltage options. ELECTRICAL CHARACTERISTICS 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) SYMBOL VCC 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 2 CONDITIONS MIN ● ● ● VCC = 5V, ADJ = GND, VREF = –VOUT IOUT = 0mA, 2.7V ≤ VCC ≤ 5.25V VCC = 5V, VSHDN = VCC (LTC1550L) or GND (LTC1551L) ● VCC = 5V, VSHDN = GND (LTC1550L) or VCC (LTC1551L) ● TYP 2.7 3.05 4.5 MAX UNITS 5.25 5.25 5.25 V V V V mV/V 1.225 2.5 3.65 0.2 7 10 mA µA LTC1550L/LTC1551L ELECTRICAL CHARACTERISTICS 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) SYMBOL PARAMETER fOSC VOL IREG VIH VIL IIN Internal Oscillator Frequency REG Output Low Voltage REG Sink Current SHDN Input High Voltage SHDN Input Low Voltage SHDN Input Current tON Turn-On Time VOUT Output Regulation (LTC1550L/LTC1551L) VOUT Output Regulation (LTC1550L/LTC1550L-2/ LTC1551L) Output Regulation (LTC1550L/LTC1550L-2.5/ LTC1551L) Output Regulation (LTC1550L/LTC1551L) VOUT VOUT VOUT Output Regulation (LTC1550L/LTC1551L) VOUT Output Regulation (LTC1550L/LTC1550L-4.1) (LTC1551L/LTC1551L-4.1) Output Regulation (LTC1550L/LTC1551L)) Output Short-Circuit Current Output Ripple Voltage VOUT ISC VRIPPLE CONDITIONS MIN UNITS ● 0.1 5 1 0.8 1 20 5 ● 1 5 ms ● 1 5 ms ● 1 5 ms ● 1 5 ms ● ● – 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 – 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 – 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 V V V V V V V V V V V V V V V V V ● ● – 4.613 – 4.613 – 4.5 – 4.5 80 1 – 4.388 – 4.388 200 V V mA mV ● 4.8V ≤ VCC ≤ 5.25V, 0 ≤ IOUT ≤ 5mA 5.1V ≤ VCC ≤ 5.25V, 0 ≤ IOUT ≤ 10mA VOUT = 0V, VCC = 5.25V ● ● 4 2 900 0.1 10 MAX kHz V mA V V µA µA ms 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 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. TYP ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0.8 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. 3 LTC1550L/LTC1551L U W TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency vs Temperature 5.0 6.0 VCC = 5V VOUT = –4.1V 925 VCC = 5V VOUT = – 4.1V SUPPLY CURRENT (mA) 4.5 875 825 775 5.6 POSITIVE SUPPLY VOLTAGE (V) 975 OSCILLATOR FREQUENCY (kHz) Minimum Required VCC vs VOUT and IOUT Supply Current vs Temperature 4.0 3.5 3.0 725 5.2 4.8 IOUT = 20mA 4.4 4.0 3.6 3.2 IOUT = 5mA IOUT = 10mA 2.8 2.4 675 –55 –35 –15 2.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (˚C) Maximum Output Current vs Supply Voltage TA = 25°C 1.236 30 VOUT = –2.5V 1.5 REFERENCE VOLTAGE (V) START-UP TIME (ms) 40 VOUT = –4.1V RL = 820Ω 1.0 VOUT = –2V RL = 390Ω 0.5 10 2.75 3.25 3.75 4.25 SUPPLY VOLTAGE (V) 1.234 1.232 1.230 1.228 1.226 1.224 1.222 VOUT = –4.1V 0 2.25 TA = 25°C 1.238 2.0 50 0 Reference Voltage vs VCC + |VOUT| TA = 25°C 60 20 –2 –1 –3 OUTPUT VOLTAGE (V) 1.24 2.5 VOUT = –2V –4 1550L/51L G03 Start-Up Time vs Supply Voltage 80 70 –5 1550L/51L G02 1550L/51L G01 MAXIMUM OUTPUT CURRENT (mA) 2.0 5 25 45 65 85 105 125 TEMPERATURE (°C) 1.220 4.75 5.25 0 2.25 1.218 2.75 3.25 3.75 4.25 SUPPLY VOLTAGE (V) 1550L/51L G04 4.75 5.25 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 VCC + |VOUT| (V) 1550L/51L G05 1550L/51L G06 Line Transient Response (See Figure 3, IL = 10mA) Load Transient Response (See Figure 3, VCC = 5V) Startup Time (LTC1550L Shown) 5V SHDN 0V VOUT – 4.1V POWER VALID 10mA VCC IOUT 5V 0V 5.25V 4.75V 0mA 0.2ms/DIV 4 VOUT 5mV/DIV AC COUPLED VOUT 5mV/DIV AC COUPLED 0V 1550/51 G07 1ms/DIV 1550/51 G08 2ms/DIV 1550/51 G09 LTC1550L/LTC1551L U W TYPICAL PERFORMANCE CHARACTERISTICS Output Spectrum (*See Figure 1) Spot Noise (*See Figure 1) 90 10 90 80 80 70 70 60 40 30 NOISE (dBµV) 50 0.1 20 50 40 30 20 10 10 0 0 –10 100k 1M FREQUENCY (Hz) 10M –10 100k 0.01 1 10 FREQUENCY (kHz) 1550L/51L G10 100 10 Spot Noise (See Figure 3) 10 90 70 60 NOISE (dBµV) VCC = 5V IL = 5mA CIN = 2.2µF COUT = 4.7µF CL = 0.1µF 0.1 10 FREQUENCY (kHz) 50 40 30 20 VCC = 5V IL = 5mA CIN = 2.2µF COUT = 10µF CL = 0.1µF 1 0.1 10 0 0.01 1 VCC = 5V IL = 5mA CIN 2.2µF COUT = 10µF CL = 0.1µF NOISE (µV/√Hz) 80 10M 1550L/51L G12 Output Spectrum (See Figure 3) 1 1M FREQUENCY (Hz) 1550 /51L G11 Spot Noise (See Figure 3) NOISE (µV/√Hz) VCC = 5V IL = 5mA CIN = 2.2µF COUT = 4.7µF CL = 0.1µF 60 1 NOISE (µV/√Hz) NOISE (dBµV) Output Spectrum (See Figure 3) 100 1550L/51L G13 –10 100k 1M FREQUENCY (Hz) 10M 1550L/51L G14 0.01 1 10 FREQUENCY (kHz) 100 1550L/51L G15 * On first page of data sheet. 5 LTC1550L/LTC1551L U U U 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 0.2µA. 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. 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 0.1µF 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 –. VOUT: 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 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 0.1µF 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 6 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 0.1µF 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. 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. LTC1550L/LTC1551L W BLOCK DIAGRAM + CCP VCC COUT CPOUT S1 LINEAR REGULATOR S4 VOUT C1 + CLK 900kHz C1 S2 C1 – + – ** S3 ADJ CHARGE PUMP ** *SHDN + 58mV REG COMP2 – 1.225V 1.167V 1550L/51L BD *SHDN FOR LTC1550L, SHDN FOR LTC1551L ** FIXED OUTPUT VERSIONS ONLY U W U U 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 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. 7 LTC1550L/LTC1551L U W U U 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 0.1µF 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 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 4.7µF from VOUT to ground is required to keep the regulator loop stable; for optimum stability and minimum output ripple, at least 10µF is recommended. 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 8 PGND, AGND R1 LTC1550L ADJ R2 VOUT VOUT = –1.225V ( ) 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 0.1µF 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 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 = 2.2µF 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 0.1µF ceramic capacitor. As a general rule, larger output capacitors provide lower output ripple. To keep output voltage ripple below 1mVP–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. LTC1550L/LTC1551L U U W U APPLICATIONS INFORMATION 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 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 0.1µF 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. 8 VCC = 5V TA = 25°C CIN = 2.2µF 1 VCC 2 + CIN 2.2µF SHDN VCC REG CPOUT 8 R1 10k 7 CCP 0.1µF LTC1551L 3 4 + GND VOUT C1 – C1 OUTPUT RIPPLE (mVP-P) 7 6 6 5 WITHOUT 0.1µF 4 3 2 5 WITH 0.1µF 1 VOUT – 4.1V + C1 0.1µF COUT 10µF 0 1 CL 0.1µF 10 OUTPUT CAPACITANCE (µF) 100 1550L/51L F04 1550L/51L F03 Figure 4. Output Ripple vs Output Capacitance Figure 3. Output Ripple Test Circuit VOUT AC COUPLE 2mV/DIV VOUT AC COUPLE 5mV/DIV 5µs/DIV 1550L/51L F05 Figure 5. Output Ripple with 10µF Tantalum Capacitor 10µs/DIV 1550L/51L F06 Figure 6. Output Ripple with 10µF Tantalum Capacitor Paralleled with 0.1µF Ceramic Capacitor 9 LTC1550L/LTC1551L U U W U 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 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 10µF in parallel with a 0.1µF ceramic capacitor. A 2.2µF surface mount ceramic capacitor at VCC generally provides adequate output ripple performance for most applications. 8 VCC = 5V 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 1550L/51L F08 Figure 7. Output Ripple vs Input Bypass Capacitance U TYPICAL APPLICATION – 4.1V Output GaAs FET Bias Generator 1 4.5V ≤ VCC ≤ 5.25V + CIN 2.2µF 2 SHDN VCC REG CPOUT 8 7 LTC1550L-4.1 3 4 C1+ GND VOUT C1 6 CCP 0.1µF – 5 – 4.1V BIAS 10 + C1 0.1µF COUT 10µF CL 0.1µF GaAs TRANSMITTER 1550L/51L TA02 LTC1550L/LTC1551L 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) 0.009 (0.229) REF 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) 0.007 – 0.0098 (0.178 – 0.249) 2 3 4 5 6 7 0.053 – 0.068 (1.351 – 1.727) 8 0.004 – 0.0098 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.0250 (0.635) BSC 0.008 – 0.012 (0.203 – 0.305) * 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 GN16 (SSOP) 1098 MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.034 ± 0.004 (0.86 ± 0.102) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC 0.006 ± 0.004 (0.15 ± 0.102) 0.118 ± 0.004** (3.00 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) * 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. MSOP (MS8) 1098 1 2 3 4 11 LTC1550L/LTC1551L U TYPICAL APPLICATION 1mVP-P Ripple, – 2V Output GaAs FET Bias Generator 10k 1 2.7V ≤ VCC ≤ 5.25V + CIN 2.2µF 2 SHDN REG VCC CPOUT 8 REG 7 CCP 0.1µF LTC1550L-2 3 4 + GND VOUT C1 – C1 6 5 –2V + C1 0.1µF COUT 10µF CL 0.1µF GaAs TRANSMITTER 1550L/51L TA03 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) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 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) 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 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 2 3 4 SO8 1298 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 LTC1261L Switched-Capacitor Regulated Voltage Inverter Adjustable and Fixed Output Voltages, Up to 20mA IOUT, MSOP LTC1429 Clock-Synchronized Switched-Capacitor Voltage Inverter Synchronizable Up to 2MHz System Clock LTC1514/LTC1515 Step-Up/Step-Down Switched-Capacitor DC/DC Converters VIN 2V to 10V, Adjustable or Fixed VOUT, IOUT to 50mA LTC1516 Micropower Regulated 5V Charge Pump DC/DC Converter IOUT = 20mA (VIN ≥ 2V), IOUT = 50mA (VIN ≥ 3V) LTC1522 Micropower Regulated 5V Charge Pump DC/DC Converter IOUT = 10mA (VIN ≥ 2.7V), IOUT = 20mA (VIN ≥ 3V) LTC1550/LTC1551 Low Noise, Switched-Capacitor Regulated Voltage Inverters 900kHz Charge Pump, 1mVP-P Ripple LTC1555/LTC1556 SIM Power Supply and Level Translator Step-Up/Step-Down SIM Power Supply and Level Translators LT1611 1.4MHz Inverting Mode Switching Regulator – 5V at 150mA from a 5V Input, 5-Lead SOT-23 LT1614 Inverting 600kHz Switching Regulator with Low-Battery Detector – 5V at 200mA from a 5V Input, MSOP LTC1754-5 Micropower, Regulated 5V Charge Pump with Shutdown in SOT-23 ICC = 13µA, IOUT = 50mA (VIN ≥ 3V), IOUT = 25mA (VIN ≥ 2.7V) 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com 15501lf LT/TP 0300 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1996