DESCRIPTION FEATURES. LTC1550/LTC1551 Low Noise, Switched Capacitor Regulated Voltage Inverters APPLICATIONS TYPICAL APPLICATION

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LTC55/LTC55 Low Noise, Switched Capacitor Regulated Voltage Inverters FEATRES Regulated Negative Voltage from a Single Positive Supply Low Output Ripple: Less Than mv P-P Typ High Charge Pump

1 LTC55/LTC55 Low Noise, Switched Capacitor Regulated Voltage Inverters FEATRES Regulated Negative Voltage from a Single Positive Supply Low Output Ripple: Less Than mv P-P Typ High Charge Pump Frequency: 9kHz Typ Small Charge Pump Capacitors:.µF Requires Only Four External Capacitors Fixed.V or Adjustable Output Shutdown Mode Drops Supply Current to < µa High Output Current: p to ma, Output Regulation: 5% Available in SO- and -Lead SSOP APPLICATIONS GaAs FET Bias Generators Negative Supply Generators Battery-Powered Systems Single Supply Applications, LTC and LT are registered trademarks of Linear Technology Corporation. DESCRIPTION The LTC 55/LTC55 are switched capacitor charge pump voltage inverters which include internal linear postregulators to minimize output ripple. Output voltages are fixed at.v, with ripple voltages typically below mv P-P. The LTC55 is also available in an adjustable output voltage version. The LTC55/LTC55 are ideal for use as bias voltage generators for GaAs transmitter FETs in portable RF and cellular telephone applications. The LTC55/LTC55 operate from single.5v to.5v supplies and draw typical quiescent currents of.5ma with a 5V supply. Each device includes a TTL compatible Shutdown pin which drops supply current to.µa typically. The LTC55 Shutdown pin is active low (SHDN), while the LTC55 Shutdown pin is active high (SHDN). Only four external components are required: an input bypass capacitor, two.µf charge pump capacitors and a filter capacitor at the linear regulator output. The adjustable LTC55 requires two additional resistors to set the output voltage. The LTC55/LTC55 will supply up to ma output current with a 5V supply, while maintaining guaranteed output regulation of ±5%. The fixed voltage LTC55/LTC55 are available in S- plastic packages. The adjustable LTC55 is available in a -pin SSOP. TYPICAL APPLICATION.V Generator with mv P-P Noise Output Noise and Ripple V CC.µF C IN SHDN SENSE V CC CP OT LTC55 C GND C 5 C.µF FERRITE BEAD C OT µf C CP.µF =.V I LOAD = 5mA C L.µF 55/5 F AC COPLED mv/div µs/div 55/5 TA

2 LTC55/LTC55 ABSOLTE MAXIMM RATINGS W W W Supply Voltage... V Output Voltage....V to (V CC V) Total Voltage, V CC to CP OT... V Input Voltage (SHDN Pin)....V to (V CC.V) Input Voltage (REG Pin)....V to V Output Short-Circuit Duration... sec (Note ) Commercial Temperature Range... C to C Extended Commercial Operating Temperature Range (Note )... C to 5 C Industrial Temperature Range... C to 5 C Storage Temperature Range... 5 C to 5 C Lead Temperature (Soldering, sec)... C PACKAGE/ORDER INFORMATION SHDN* V CC C TOP VIEW S PACKAGE -LEAD PLASTIC SO SENSE CP OT GND 5 C *SHDN FOR LTC55, SHDN FOR LTC55 T JMAX = 5 C, θ JA = 5 C/ W W ORDER PART NMBER LTC55CS-. LTC55CS-. NC C NC C 5 PGND AGND NC TOP VIEW V CC 5 SHDN REG SENSE ADJ CP OT NC 9 NC GN PACKAGE -LEAD PLASTIC SSOP T JMAX = 5 C, θ JA = 5 C/ W ORDER PART NMBER LTC55CGN LTC55IGN GN PART MARKING 55 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS V CC =.5V to.5v, C = C =.µf, C OT = µf, T A = 5 C unless otherwise specified. (Note ) SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS V CC Supply Voltage (LTC55CGN/LTC55IGN)..5 V (LTC55CS-./LTC55CS-.).5.5 V V REF Reference Voltage. V I S Supply Current, V SHDN = V CC (LTC55) or GND (LTC55).5 ma, V SHDN = GND (LTC55) or V CC (LTC55). µa f OSC Internal Oscillator Frequency 9 khz V OL REG Output Low Voltage I REG = ma,.. V I REG REG Sink Current V REG =.V, 5 ma V IH SHDN Input High Voltage V V IL SHDN Input Low Voltage. V I IN SHDN Input Current V SHDN = V CC. µa t ON Turn-On Time I OT = ma ms Output Regulation.V V CC.5V, I OT 5mA V (LTC55CGN/LTC55IGN).V V CC.5V, I OT ma V.5V V CC.5V, I OT ma V Output Regulation.V V CC.5V, I OT 5mA...9 V (LTC55CGN/LTC55IGN).V V CC.5V, I OT ma...9 V.5V V CC.5V, I OT ma...9 V

3 LTC55/LTC55 ELECTRICAL CHARACTERISTICS V CC =.5V to.5v, C = C =.µf, C OT = µf, T A = 5 C unless otherwise specified. (Note ) SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS Output Regulation.5V V CC.5V, I OT 5mA V (LTC55CGN/LTC55IGN).5V V CC.5V, I OT ma V.V V CC.5V, I OT ma V Output Regulation.5V V CC.5V, I OT 5mA.5..5 V (LTC55CGN/LTC55IGN).5V V CC.5V, I OT ma.5..5 V.5V V CC.5V, I OT ma.5..5 V Output Regulation.9V V CC.5V, I OT 5mA V (LTC55CGN/LTC55IGN).V V CC.5V, I OT ma V.5V V CC.5V, I OT ma V Output Regulation.5V V CC.5V, I OT 5mA...9 V (LTC55CGN/LTC55IGN).5V V CC.5V, I OT ma...9 V 5.5V V CC.5V, I OT ma...9 V Output Regulation.V V CC.5V, I OT 5mA V (LTC55CGN/LTC55IGN) 5.V V CC.5V, I OT ma V 5.V V CC.5V, I OT ma V Output Regulation.5V V CC.5V, I OT 5mA...9 V (LTC55CS-./LTC55CS-.).5V V CC.5V, I OT ma...9 V 5.5V V CC.5V, I OT ma...9 V I SC Output Short-Circuit Current = V, 5 5 ma = V, V CC =.5V ma V RIPPLE Output Ripple Voltage mv The denotes specifications which apply over the specified temperature range. Note : Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note : 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 = 5 C. Note : C-grade device specifications are guaranteed over the C to C temperature range. In addition, C-grade device specifications are assured over the C to 5 C temperature range by design or correlation, but are not production tested. TYPICAL PERFORMANCE CHARACTERISTICS W OSCILLATOR FREQENCY (khz) Oscillator Frequency vs Temperature =.V TEMPERATRE ( C) LTC55/5 G SPPLY CRRENT (ma) Supply Current vs Temperature =.V TEMPERATRE ( C) LTC55/5 G OTPT VOLTAGE (V) Output Voltage vs Output Current (LTC55CS-./LTC55CS-.) T A = 5 C V CC =.5V 5 5 OTPT CRRENT (ma) V CC =.5V 5 LTC55/5 G

LTC55/LTC55 TYPICAL PERFORMANCE CHARACTERISTICS W MAXIMM OTPT CRRENT (ma) 5 5 5 5 5 5 Maximum Output Current vs Supply Voltage T A = 5 C START-P TIME (ms).

C =.V R L = 9Ω Startup Time (LTC55 Shown) 5V SHDN V V.V.ms/DIV LTC55/5 G.5.5 5. 5.5 5.5 5.5..5.5 SPPLY VOLTAGE (V)..5.5 5. 5.5 5.5 5.5..5.5 SPPLY VOLTAGE (V) LTC55/5 TPC LTC55/5 G5 Load Transient Response (See Figure, ) Line Transient Response (See Figure, I L = ma).

....... I OT = 5mA I OT = ma I OT = ma. 5 OTPT VOLTAGE (V) LTC55/5 G.5 NOISE (dbµv) 9 5 k Output Spectrum (*See Typical Application) * On first page of data sheet.

4 LTC55/LTC55 TYPICAL PERFORMANCE CHARACTERISTICS W MAXIMM OTPT CRRENT (ma) Maximum Output Current vs Supply Voltage T A = 5 C START-P TIME (ms) Start-p Time vs Supply Voltage T A = 5 C =.V R L = 9Ω Startup Time (LTC55 Shown) 5V SHDN V V.V.ms/DIV LTC55/5 G SPPLY VOLTAGE (V) SPPLY VOLTAGE (V) LTC55/5 TPC LTC55/5 G5 Load Transient Response (See Figure, ) Line Transient Response (See Figure, I L = ma). Minimum Required V CC vs and I OT 5mV/DIV 5mV/DIV 5. AC COPLED I OT ma ma ms/div LTC55/5 G AC COPLED V 5.5V CC 5V ms/div LTC55/5 G POSITIVE SPPLY VOLTAGE (V) I OT = 5mA I OT = ma I OT = ma. 5 OTPT VOLTAGE (V) LTC55/5 G.5 NOISE (dbµv) 9 5 k Output Spectrum (*See Typical Application) * On first page of data sheet. M FREQENCY (Hz) LT55/5 G9 M NOISE (µv/ Hz).. Spot Noise (*See Typical Application) FREQENCY (khz) LTC55/5 G NOISE (dbµv) 9 5 k Output Spectrum (See Figure, C OT = µf) I L = 5mA C IN =.µf C OT = µf C L =.µf M FREQENCY (Hz) LT55/5 G M

5 LTC55/LTC55 TYPICAL PERFORMANCE CHARACTERISTICS NOISE (µv/ Hz).. W Spot Noise (See Figure, C OT = µf) I L = 5mA C IN =.µf C OT = µf C L =.µf FREQENCY (khz) LTC55/5 G NOISE (dbµv) 9 5 k Output Spectrum (See Figure, C OT = µf) I L = 5mA C IN.µF C OT = µf C L =.µf M FREQENCY (Hz) LT55/5 G M NOISE (µv/ Hz).. Spot Noise (See Figure, C OT = µf) I L = 5mA C IN =.µf C OT = µf C L =.µf FREQENCY (khz) LTC55/5 G PIN FNCTIONS SHDN: Shutdown (TTL Compatible). This pin is active low (SHDN) for the LTC55 and active high (SHDN) for the LTC55. When this pin is at V CC (GND for LTC55), the LTC55 operates normally. When SHDN is pulled low (high for LTC55), the LTC55 enters shutdown mode. In shutdown, the charge pump stops, the output collapses to V, and the quiescent current drops typically to.µa. V CC : Power Supply. V CC requires an input voltage between.5v and.5v for the fixed voltage LTC55CS-./ LTC55CS-.. The adjustable voltage LTC55CGN/ LTC55IGN operates with a VCC range of.v to.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 V or damage to the chip may occur. V CC must be bypassed to PGND (GND for -pin packages) with at least a.µf capacitor placed in close proximity to the chip. A.µF or larger bypass capacitor is recommended to minimize noise and ripple at the output. C : C Positive Input. Connect a.µf capacitor between C and C. : Negative Voltage Output. This pin must be bypassed to ground with a.µf or larger capacitor to ensure regulator loop stability. At least µf is recommended to provide specified output ripple. An additional.µf low ESR capacitor is recommended to minimize high frequency spikes at the output. C : C Negative Input. Connect a.µf capacitor from C to C. GND: Ground. Connect to a low impedance ground. A ground plane will help minimize regulation errors. CP OT : Negative Charge Pump Output. This pin requires a.µf storage capacitor to ground. SENSE: Connect to. The LTC55/LTC55 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

6 LTC55/LTC55 PIN FNCTIONS REG: This is an open-drain output that pulls low when the output voltage is within 5% of the set value. It will sink ma 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 V above ground without damage. ADJ: For adjustable versions only, this is the feedback point for the external resistor divider string. Connect a divider string from AGND to 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. BLOCK DIAGRAM W C CP C OT V CC CPOT S S LINEAR REGLATOR CLK 9kHz S C C C ** S CHARGE PMP ** ADJ *SHDN.V mv.v COMP REG *SHDN FOR LTC55, SHDN FOR LTC55 ** FIXED OTPT VERSIONS ONLY SENSE 55/5 BD APPLICATIONS INFORMATION OVERVIEW W The LTC55/LTC55 are switched capacitor, inverting charge pumps with internal linear post-regulators. The LTC55CS/LTC55CS provide a regulated, low ripple.v output at up to ma load current from a single 5V supply. The LTC55CGN provides a regulated, low ripple adjustable output. Output load current for the adjustable version 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 LTC55/LTC55 are ideal for use as bias voltage generators for GaAs transmitter FETs in portable RF and cellular telephone applications. The LTC55 features an active-low Shutdown pin (SHDN) that drops quiescent current to below µa. The LTC55 is identical to the LTC55,

7 LTC55/LTC55 APPLICATIONS INFORMATION W except that the Shutdown pin is active-high (SHDN). All members of the LTC55 family feature a 9kHz charge pump frequency. The LTC55/ LTC55 come standard with fixed.v output voltages and the LTC55 is available with an adjustable output voltage. Both devices can be configured with other fixed output voltages; contact Linear Technology for more information. The LTC55 consists of two major blocks (see Block Diagram): an inverting charge pump and a negative linear regulator. The charge pump uses two external capacitors, C and C CP to generate a negative voltage at CP OT. It operates by charging and discharging C on alternate phases of the internal 9kHz clock. C is initially charged to V CC through switches S and S. When the internal clock changes phase, S and S open and S and S close, shorting the positive side of C to ground. This forces the negative side of C below ground, and charge is transferred to C CP through S. As this cycle repeats, the magnitude of the negative voltage approaches V CC. The 9kHz internal clock frequency helps keep noise out of khz to khz IF bands commonly used by portable radio frequency systems and reduces the size of the external capacitors required. Most applications can use standard.µf ceramic capacitors for C and C CP. Increasing C and C CP beyond.µf has little effect on the output ripple or the output current capacity of the LTC55/LTC55. The negative voltage at CP OT 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 pin. The regulation loop is optimized for fast transient response, enabling it to remove most of the switching artifacts present at the CP OT pin. Output ripple is typically below mv P-P with output loads between ma and ma. The output voltage is set to.v 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.5v. An output capacitor of at least.µf from to ground is required to keep the regulator loop stable; for optimum stability and minimum output ripple, at least µf is recommended. PGND, AGND LTC55 ADJ, SENSE,, R R =.V Figure. External Resistor Connections R R ( R ) LTC55/5 F Adjustable Hook-p The LTC55CGN is available in an adjustable output version in a -pin SSOP package. The output voltage is set with a resistor divider from GND to SENSE/ (Figure ). 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.v at the ADJ pin with respect to. For example, a V output would require a k resistor from GND to ADJ, and a 9.k resistor to SENSE/. If, after connecting the divider resistors, the output voltage is not what you expected, try swapping them. CAPACITOR SELECTION The LTC55/LTC55 requires four external capacitors: an input bypass capacitor, two.µf charge pump capacitors and an output filter capacitor. The overall behavior of the LTC55/LTC55 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 LTC55/LTC55. Output Ripple vs Output Capacitor Figure shows the effect of using different output capacitor values on LTC55/LTC55 output ripple. These curves are taken using the circuit in Figure, with C IN =.µf and I LOAD = 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.µf ceramic capacitor. As a general rule, larger

LTC55/LTC55 APPLICATIONS INFORMATION W output capacitors provide lower output ripple. To keep ripple below mv P-P, µf or greater, with a.µf ceramic capacitor in parallel, is required. At least.

µf ceramic capacitor added in parallel with the tantalum output capacitor.

8 LTC55/LTC55 APPLICATIONS INFORMATION W output capacitors provide lower output ripple. To keep ripple below mv P-P, µf or greater, with a.µf ceramic capacitor in parallel, is required. At least.µf is required at the output under all conditions to guarantee loop stability. Figure shows a marked decrease in peak-to-peak output ripple when a.µf 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 9kHz 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.µf 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 and 5 show scope photos of the output of Figure 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 9kHz switching frequency, not much R or L is required; a ferrite bead or a relatively long PC board trace in series with.µf ceramic capacitor will usually keep the output ripple well below mv P-P. The cover page shows an example of an ultralow V CC C IN.µF *C L IS OPTIONAL SHDN SENSE V CC CP OT LTC55 C GND C 5 C.µF C OT µf Figure. Output Ripple Test Circuit C CP.µF C L.µF*.V 55/5 F OTPT RIPPLE (mv P-P ) 5 WITHOT.µF WITH.µF V CC = V T A = 5 C C IN =.µf OTPT CAPACITANCE (µf) LTC55/5 F Figure. Output Ripple vs Output Capacitance AC COPLE 5mV/DIV AC COPLE mv/div 5µs/DIV LTC55/5 F Figure. Output Ripple with µf Tantalum Capacitor µs/div LTC55/5 F Figure 5. Output Ripple with µf Tantalum Capacitor Paralleled with.µf Ceramic Capacitor

9 LTC55/LTC55 APPLICATIONS INFORMATION W noise.v generator which uses a ferrite bead output filter to achieve better than mv P-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 (C IN ) can also have a fairly significant impact on the output ripple. C IN provides most of the LTC55/LTC55 s supply current while it is charging the flying capacitor (C). Inadequate input bypass 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 LTC55/LTC55 as possible and its value should be significantly larger than C. Tantalum capacitors with low ESR generally provide adequate performance. Figure shows the LTC55/LTC55 peak-to-peak output ripple vs C IN, taken using the test circuit in Figure with I LOAD set at 5mA. C OT is a µf in parallel with a.µf ceramic capacitor. A.µF tantalum capacitor at V CC generally provides adequate output ripple performance for most applications. OTPT RIPPLE (mv P-P ) 5 V CC = V T A = 5 C C OT = µf. INPT CAPACITANCE (µf) LTC55/5 F Figure. Output Ripple vs Input Bypass Capacitance TYPICAL APPLICATION.V Output GaAs FET Bias Generator.5V V CC.5V C IN.µF SHDN SENSE V CC CP OT LTC55 C GND C 5 C CP.µF.V BIAS C.µF C OT µf C L.µF GaAs TRANSMITTER 55/5 TA 9

10 LTC55/LTC55 PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. GN Package -Lead Plastic SSOP (Narrow.5) (LTC DWG # 5--).9.9* (..9) (5..9).5.5** (..9) (.9.9).5 ±. 5 (. ±.) TYP.5.9 (.5.)..9 (..9)..5 (..) * DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED." (.5mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED." (.5mm) PER SIDE.. (..5).5 (.5) BSC GN (SSOP) 95

11 LTC55/LTC55 PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S Package -Lead Plastic Small Outline (Narrow.5) (LTC DWG # 5--).9.9* (. 5.) 5.. (5.9.9).5.5** (..9).. (..5).. (.5.5) 5 TYP.5.9 (..5).. (..5)..5.. *DIMENSION DOES NOT INCLDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED." (.5mm) PER SIDE ** DIMENSION DOES NOT INCLDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED." (.5mm) PER SIDE..9 (.55.).5 (.) TYP SO 99 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.

12 LTC55/LTC55 TYPICAL APPLICATION < mv P-P Ripple,.V Output GaAs FET Bias Generator.5V V CC.5V C IN.µF SHDN V CC SENSE CP OT LTC55 C GND C 5 C CP.µF FERRITE BEAD.V C.µF C OT µf C L.µF GaAs TRANSMITTER 55/5 TA RELATED PARTS PART NMBER DESCRIPTION COMMENTS LT 5 Switched-Capacitor Voltage Converter with Regulator ma Switched-Capacitor Converter LTC Switched-Capacitor Regulated Voltage Inverter Selectable Fixed Output Voltages LTC9 Clock-Synchronized Switched-Capacitor Voltage Inverter Synchronizable p to MHz System Clock Linear Technology Corporation McCarthy Blvd., Milpitas, CA 955- () -9 FAX: () -5 TELEX: fa LT/TP 9 REV A K PRINTED IN SA LINEAR TECHNOLOGY CORPORATION 99

DESCRIPTIO FEATURES TYPICAL APPLICATIO. LTC1550L/LTC1551L Low Noise, Switched Capacitor Regulated Voltage Inverters APPLICATIO S

DESCRIPTIO FEATURES TYPICAL APPLICATIO. LTC1550L/LTC1551L Low Noise, Switched Capacitor Regulated Voltage Inverters APPLICATIO S FEATRES Regulated Negative Voltage from a Single Positive Supply Low Output Ripple: Less Than mv P-P Typ High Charge Pump Frequency: 9kHz Small Charge Pump Capacitors:.µF Requires Only Four External Capacitors