LTC3221/ LTC3221-3.3/LTC3221-5 Micropower, Regulated Charge Pump in 2 × 2 DFN U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Ultralow Power: 8µA Quiescent Current Regulated Output Voltages: 3.3V ±4%, 5V ±4%, ADJ VIN Range: 1.8V to 4.4V (LTC3221-3.3) 2.7V to 5.5V (LTC3221-5) Output Current: Up to 60mA No Inductors Needed Very Low Shutdown Current: <1µA Shutdown Disconnects Load from VIN Burst Mode Control Short-Circuit Protected Solution Profile < 1mm Tiny 2mm × 2mm 6-Pin DFN Package U APPLICATIO S ■ ■ ■ ■ ■ Low Power 2 AA Cell to 3.3V Supply Memory Backup Supplies Tire Pressure Sensors General Purpose Low Power Li-Ion to 5V Supply RF Transmitters Glucose Meters The LTC3221 family includes fixed 5V and 3.3V output versions plus an adjustable version. All parts operate as Burst Mode® switched capacitor voltage doublers to achieve ultralow quiescent current. The chips use a controlled current to supply the output and will survive a continuous short-circuit from VOUT to GND. The FB pin of the adjustable LTC3221 can be used to program the desired output voltage. The LTC3221 family is available in a low profile (0.75mm) 2mm × 2mm 6-pin DFN package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. U ■ The LTC®3221 family are micropower charge pump DC/DC converters that produce a regulated output at up to 60mA. The input voltage range is 1.8V to 5.5V. Extremely low operating current (8µA typical at no load) and low external parts count (one flying capacitor and two small bypass capacitors at VIN and VOUT) make them ideally suited for small, battery-powered applications. TYPICAL APPLICATIO No-Load Input Current vs Supply Voltage 1µF 16 VIN 5 2.2µF 4,7 OFF ON 3 C– VIN 1 C+ 6 VOUT VOUT 4.7µF LTC3221-X GND SHDN 3221 TA01 REGULATED 3.3V OUTPUT FROM 1.8V TO 4.4V INPUT VOUT = 3.3V ±4% IOUT = OmA TO 25mA; VIN >1.8V IOUT = OmA TO 60mA; VIN >2V REGULATED 5V OUTPUT FROM 2.7V TO 5.5V INPUT VOUT = 5V ±4% IOUT = OmA TO 25mA; VIN >2.7V IOUT = OmA TO 60mA; VIN >3V NO-LOAD INPUT CURRENT (µA) 2 14 12 10 8 6 TA = 90°C TA = 25°C TA = –45°C 4 2 0 1.5 2.0 2.5 3.0 3.5 SUPPLY VOLTAGE (V) 4.0 4.5 3221 TA01b 3221f 1 LTC3221/ LTC3221-3.3/LTC3221-5 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW VIN, ⎯S⎯H⎯D⎯N, FB ............................................. – 0.3V to 6V VOUT to GND............................................. – 0.3V to 5.5V VOUT Short-Circuit Duration ............................ Indefinite Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range.................. – 65°C to 125°C Maximum Junction Temperature .......................... 125°C C+ 1 C– 2 6 VOUT 7 SHDN/FB* 3 5 VIN 4 GND TJMAX = 125°C, θJA = 80°C/W EXPOSED PAD IS GND (PIN 7) MUST BE SOLDERED TO PCB *⎯S⎯H⎯D⎯N ON LTC3221-3.3;LTC3221-5 FB ON LTC3221 ORDER PART NUMBER DC PART MARKING LTC3221EDC LTC3221EDC-3.3 LTC3221EDC-5 LCCP LBQP LCCN Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 2.5V (LTC3221-3.3/LTC3221) or 3V (LTC3221-5), ⎯S⎯H⎯D⎯N = VIN, CFLY = 1µF, CIN = 2.2µF, COUT = 2.2µF, unless otherwise specified. SYMBOL LTC3221-3.3 PARAMETER CONDITIONS VIN Input Supply Voltage VOUT Output Voltage ICC Operating Supply Current VR Output Ripple VIN = 2V, IOUT = 60mA, COUT = 4.7µF (Note 3) 35 mVP-P η Efficiency VIN = 2V, IOUT = 60mA (Note 3) 82 % ISC Output Short-Circuit Current VOUT = 0V 1.8V ≤ VIN ≤ 4.4V, IOUT ≤ 25mA 2V ≤ VIN < 4.4V, IOUT ≤ 60mA IOUT = 0mA MIN ● 1.8 ● 3.168 ● ● TYP 3.3 8 120 MAX UNITS 4.4 V 3.432 15 V µA 240 mA 5.5 V 5.2 15 V µA LTC3221-5 VIN Input Supply Voltage VOUT Output Voltage ICC Operating Supply Current 2.7V ≤ VIN ≤ 5.5V, IOUT < 25mA 3V ≤ VIN ≤ 5.5V, IOUT < 60mA IOUT = 0mA VR Output Ripple VIN = 3V, IOUT = 60mA, COUT = 4.7µF (Note 3) η Efficiency VIN = 3V, IOUT = 60mA (Note 3) ISC Output Short-Circuit Current VOUT = 0V ● 2.7 ● 4.8 ● 5 8 45 mVP-P 82 ● 120 % 240 mA 5.5 V LTC3221 ● 1.8 ● 1.181 VIN Input Supply Voltage VFB Feedback Voltage ROL Open-Loop Impedance VIN = 1.8V, VOUT = 3V (Note 4) ● ICC Operating Supply Current IOUT = 0mA ● IFB FB Input Current FB = 1.33V, VIN = 2V ● 1.23 1.279 V 10 20 Ω 12 µA 100 nA 5 –100 3221f 2 LTC3221/ LTC3221-3.3/LTC3221-5 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C. V = 2.5V (LTC3221-3.3/LTC3221) or 3V (LTC3221-5), ⎯S⎯H⎯D⎯N = V , A IN IN CFLY = 1µF, CIN = 2.2µF, COUT = 2.2µF, unless otherwise specified. SYMBOL PARAMETER LTC3221-3.3/LTC3221-5 Shutdown Supply Current I⎯S⎯H⎯D⎯N ⎯S⎯H⎯D⎯N Input Threshold (High) VIH ⎯S⎯H⎯D⎯N Input Threshold (Low) VIL ⎯S⎯H⎯D⎯N Input Current (High) IIH ⎯S⎯H⎯D⎯N Input Current (Low) IIL LTC3221/LTC3221-3.3/LTC3221-5 Switching Frequency fOSC UVLO Threshold VUVLO CONDITIONS MIN VOUT = 0V, ⎯S⎯H⎯D⎯N = 0V TYP ● µA V V µA µA 1.3 ● ⎯S⎯H⎯D⎯N = VIN ⎯SH ⎯ D ⎯ N ⎯ = 0V UNITS 1 ● ● 0.4 1 1 –1 –1 ● VOUT = 2.5V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3221EDC-X is guaranteed to meet performance specifications from 0°C to 70°C. Specificaiton over the –40°C to 85°C MAX 600 1 kHz V operating temperature range are assured by design, characterization and correlation with statisitical process controls. Note 3: Guaranteed by design, not subject to test. Note 4: ROL = (2VIN – VOUT)/IOUT. U W TYPICAL PERFOR A CE CHARACTERISTICS 800 750 750 700 700 650 600 550 600 VIN = 2.5V 450 450 4.0 400 –50 4.5 VIN = 1.8V 550 500 2.5 3.0 3.5 SUPPLY VOLTAGE (V) VIN = 4.5V 650 500 2.0 0.9 THRESHOLD VOLTAGE (V) 800 400 1.5 ⎯S⎯H⎯D⎯N Threshold Voltage vs Supply Voltage Oscillator Frequency vs Temperature FREQUENCY (kHz) FREQUENCY (kHz) Oscillator Frequency vs Supply Voltage –25 0 25 50 75 TEMPERATURE (°C) 100 ⎯S⎯H⎯D⎯N LO-to-HI Threshold vs Temperature VIN = 1.8V 0.5 0 25 50 75 TEMPERATURE (°C) 0.5 100 125 3221 G04 2.0 2.5 3.0 3.5 SUPPLY VOLTAGE (V) 4.5 Short-Circuit Current vs Supply Voltage 150 VIN = 3.2V 0.8 0.7 4.0 3221 G03 SHORT-CIRCUIT CURRENT (mA) 0.6 SHDN HI-TO-LO THRESHOLD (V) SHDN LO-TO-HI THRESHOLD (V) VIN = 3.2V –25 0.6 0.4 1.5 125 0.9 VIN = 2.5V 0.4 –50 HIGH-TO-LOW THRESHOLD ⎯S⎯H⎯D⎯N HI-to-LO Threshold vs Temperature 0.9 0.7 0.7 3221 G02 3221 G01 0.8 LOW-TO-HIGH THRESHOLD 0.8 VIN = 2.5V 0.6 VIN = 1.8V 0.5 0.4 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3221 G05 TA = –45°C 130 TA = 90°C 110 TA = 25°C 90 70 50 1.5 2.0 2.5 3.0 3.5 SUPPLY VOLTAGE (V) 4.0 4.5 3221 G06 3221f 3 LTC3221/ LTC3221-3.3/LTC3221-5 U W TYPICAL PERFOR A CE CHARACTERISTICS 3.36 120 3.34 110 LOAD CURRENT (mA) OUTPUT VOLTAGE (V) VOUT = 3.168V TA = –45°C VIN = 3.2V 3.32 3.30 VIN = 2.5V 3.26 3.24 VIN = 1.8V 3.22 Effective Open-Loop Output Resistance vs Temperature 100 90 TA = 90°C 80 TA = 25°C 70 60 3.20 50 3.18 3.16 0 20 40 60 80 LOAD CURRENT (mA) 100 40 1.5 120 2.0 2.5 3.0 SUPPLY VOLTAGE (V) 3.5 EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω) Output Load Capability at 4% Below Regulation Load Regulation 3.28 (LTC3221-3.3 only) 15 VIN = 1.8V 14 VOUT = 3V 13 12 11 10 9 8 7 6 5 –50 –25 0 25 50 TEMPERATURE (°C) 75 3221 G08 100 3221 G09 3221 G07 No-Load Input Current vs Supply Voltage Extra Input Current vs Load Current (IIN-2 ILOAD) 10 16 Efficiency vs Supply Voltage 100 VIN = 2.5V 90 12 TA = 90°C 10 8 TA = 25°C TA = –45°C 6 4 1 0.1 70 60 IOUT = 30mA IOUT = 1mA 50 40 30 0.01 20 2 0 1.5 THEORETICAL MAX 80 EFFICIENCY (%) EXCESS INPUT CURRENT (mA) NO-LOAD INPUT CURRENT (µA) 14 10 2.0 2.5 3.0 3.5 SUPPLY VOLTAGE (V) 4.0 4.5 0.001 0.01 0 0.1 1 10 LOAD CURRENT (mA) 100 1.8 2.0 2.2 2.4 2.6 2.8 SUPPLY VOLTAGE (V) 3221 G10 3.2 3221 G12 3221 G11 Output Ripple vs Load Current 3.0 Output Ripple Load Transient Response 70 VOUT 20mV/DIV (AC-COUPLED) OUTPUT RIPPLE (mVP-P) 60 COUT = 2.2µF VOUT 20mV/DIV (AC-COUPLED) 50 40 60mA IOUT 0mA COUT = 4.7µF 30 20 10 0 0 20 40 60 80 LOAD CURRENT (mA) 100 1µs/DIV VIN = 2V ILOAD = 60mA COUT = 4.7µF, 6.3V, SIZE 0603 3221 G14 5µs/DIV VIN = 2V ILOAD = 0mA TO 60mA STEP COUT = 4.7µF, 6.3V, SIZE 0603 3221 G15 3221 G13 3221f 4 LTC3221/ LTC3221-3.3/LTC3221-5 U W TYPICAL PERFOR A CE CHARACTERISTICS 120 5.10 TA = –45°C 110 5.05 VIN = 4.2V LOAD CURRENT (mA) OUTPUT VOLTAGE (V) VOUT = 4.8V Effective Open-Loop Output Resistance vs Temperature 5.00 VIN = 3.6V 4.95 VIN = 2.7V 4.90 4.85 100 TA = 90°C 90 TA = 25°C 80 70 60 50 0 20 40 60 80 LOAD CURRENT (mA) 40 2.7 120 100 3.0 3.3 3.6 3.9 SUPPLY VOLTAGE (V) 4.2 EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω) Output Load Capability at 4% Below Regulation Load Regulation 4.80 (LTC3221-5 only) 15 VIN = 2.7V 14 VOUT = 4.5V 13 12 11 10 9 8 7 6 5 –50 –25 0 25 50 TEMPERATURE (°C) 75 3221 G17 100 3221 G18 3221 G16 No-Load Input Current vs Supply Voltage Extra Input Current vs Load Current (IIN-2 ILOAD) 10 16 Efficiency vs Supply Voltage 100 VIN = 3V 90 12 10 TA = 90°C 8 TA = –45°C 6 TA = 25°C 4 80 1 EFFICIENCY (%) EXCESS INPUT CURRENT (mA) NO-LOAD INPUT CURRENT (µA) 14 0.1 THEORETICAL MAX 70 IOUT = 1mA 60 IOUT = 30mA 50 40 30 0.01 20 2 10 0 2.7 3.0 3.3 3.6 3.9 SUPPLY VOLTAGE (V) 4.2 4.5 0.001 0.01 0 0.1 1 10 LOAD CURRENT (mA) 100 2.7 3.0 3.3 3.6 3.9 SUPPLY VOLTAGE (V) 3221 G19 Output Ripple vs Load Current Output Ripple Load Transient Response VIN = 3V VOUT 50mV/DIV (AC-COUPLED) OUTPUT RIPPLE (mVP-P) 80 COUT = 2.2µF 70 4.5 3221 G21 3221 G20 90 4.2 VOUT 50mV/DIV (AC-COUPLED) 60 50 60mA IOUT 0mA 40 COUT = 4.7µF 30 20 10 0 0 20 60 80 40 LOAD CURRENT (mA) 100 1µs/DIV VIN = 3V ILOAD = 60mA COUT = 4.7µF, 6.3V, SIZE 0603 3221 G23 5µs/DIV VIN = 3V ILOAD = 0mA TO 60mA STEP COUT = 4.7µF, 6.3V, SIZE 0603 3221 G24 3221 G13 3221f 5 LTC3221/ LTC3221-3.3/LTC3221-5 U U U PI FU CTIO S C+ (Pin 1): Flying Capacitor Positive Terminal. GND (Pin 4): Ground. Should be tied to a ground plane for best performance. C– (Pin 2): Flying Capacitor Negative Terminal. ⎯ SH ⎯ D ⎯ N ⎯ (Pin 3) (LTC3221-3.3/LTC3221-5): Active Low ⎯ D ⎯ N ⎯ disables the LTC3221-3.3/ Shutdown Input. A low on S⎯ H ⎯ D ⎯ N ⎯ must not be allowed to float. LTC3221-5. S⎯ H FB (Pin 3) (LTC3221): Feedback. The voltage on this pin is compared to the internal reference voltage (1.23V) by the error comparator to keep the output in regulation. An external resistor divider is required between VOUT and FB to program the output voltage. VIN (Pin 5): Input Supply Voltage. VIN should be bypassed with a 2.2µF low ESR capacitor. VOUT (Pin 6): Regulated Output Voltage. For best performance, VOUT should be bypassed with a 2.2µF or higher low ESR capacitor as close as possible to the pin. Exposed Pad (Pin 7) Ground. The exposed pad must be soldered to PCB ground to provide electrical contact and optimum thermal performance. W BLOCK DIAGRA LTC3221-3.3/LTC3221-5 VOUT LTC3221 VOUT 6 2 1 CMP + CONTROL – 1 C+ 5 VIN 2 C– 6 2 1 ISW CMP FB 3 CONTROL 5 VIN 2 C– 4 GND 2 – 1 C+ ISW + 2 1 1 VREF 4 SHDN GND VREF 3 3221 BD U OPERATIO (Refer to Block Diagrams) The LTC3221 family uses a switched capacitor charge pump to boost VIN to a regulated output voltage. Regulation is achieved by monitoring the output voltage, VOUT using a comparator (CMP in the Block Diagram) and keeping it within a hysteresis window. If VOUT drops below the lower trip point of CMP, VOUT is charged by the controlled current, ISW in series with the flying capacitor CFLY. Once VOUT goes above the upper trip point of CMP, or if the upper trip point is not reached after 0.8µs, CFLY is disconnected from VOUT. The bottom plate of CFLY is then connected to GND to allow ISW to replenish the charge on CFLY for 0.8µs. After which, ISW is turned off to keep the operating supply current low. CMP continues to monitor VOUT and turns on ISW if the lower threshold is reached again. 6 Shutdown Mode The ⎯S⎯H⎯D⎯N pin is a CMOS input with a threshold voltage of approximately 0.8V. The LTC3221-3.3/ LTC3221-5 are in shutdown when a logic low is applied to the ⎯S⎯H⎯D⎯N pin. In shutdown mode, all circuitry is turned off and the LTC3221-3.3/ LTC3221-5 draw only leakage current from the VIN supply. Furthermore, VOUT is disconnected from VIN. Since the ⎯S⎯H⎯D⎯N pin is a very high impedance CMOS input, it should never be allowed to float. When ⎯S⎯H⎯D⎯N is asserted low, the charge pump is first disabled, but the LTC3221-3.3/LTC3221-5 continue to draw 5µA of supply current. This current will drop to zero when the output voltage (VOUT) is fully discharged to 0V. 3221f LTC3221/ LTC3221-3.3/LTC3221-5 U OPERATIO (Refer to Block Diagrams) The LTC3221 has a FB pin in place of the ⎯S⎯H⎯D⎯N pin. This allows the output voltage to be programmed using an external resistive divider. VOUT stays above this lower threshold for a long period of time, this result in a very low average input current. Soft-Start and Short-Circuit Protection Burst Mode Operation The LTC3221 family regulates the output voltage throughout the full 60mA load range using Burst Mode control. This keeps the quiescent current low at light load and improves the efficiency at full load by reducing the switching losses. All the internal circuitry except the comparator is kept off if the output voltage is high and the flying capacitor has been fully charged. These circuits are turned on only if VOUT drops below the comparator lower threshold. At light load, The LTC3221 family uses a controlled current, ISW to deliver current to the output. This helps to limit the input and output current during start-up and output short-circuit condition. During start up ISW is used to charge up the flying capacitor and output capacitor, this limits the input current to approximately 240mA. During short-circuit condition, the output current is delivered through ISW and this limits the output current to approximately 120mA. This prevents excessive self-heating that causes damage to the part. U W U U APPLICATIO S I FOR ATIO Power Efficiency The input current of a doubling charge pump like the LTC3221 family is always twice that of the output current. This is true regardless of whether the output voltage is unregulated or regulated or of the regulation method used. In an ideal unregulated doubling charge pump, conservation of energy implies that the input current has to be twice that of the output current in order to obtain an output voltage twice that of the input voltage. In a regulated charge pump like the LTC3221, the regulation of VOUT is similar to that of a linear regulator, with the voltage difference between 2 • VIN (Input voltage plus the voltage across a fully charged flying capacitor) and VOUT being absorbed in an internal pass transistor. In the LTC3221, the controlled current ISW acts as a pass transistor. So the input current of an ideal regulated doubling charge pump is the same as an unregulated one, which is equal to twice the output current. The efficiency (n) of an ideal regulated doubler is therefore given by: η= the theoretical 83.3% calculation. The LTC3221 product family continues to maintain good efficiency even at fairly light loads because of its inherently low power design. Maximum Available Output Current For the adjustable LTC3221, the maximum available output current and voltage can be calculated from the effective open-loop output resistance, ROL, and effective output voltage, 2VIN(MIN). From Figure 1 the available current is given by: IOUT = 2VIN – VOUT ROL Effective Open-Loop Output Resistance (ROL) The effective open-loop output resistance(ROL) of a charge pump is a very important parameter which determines the strength of the charge pump. The value of this parameter POUT VOUT • IOUT VOUT = = 2VIN PIN VIN • 2IOUT At moderate to high output power, the switching losses and quiescent current of the LTC3221 family are negligible and the expression is valid. For example, an LTC3221-5 with VIN = 3V, IOUT = 60mA and VOUT regulating to 5V, has a measured efficiency of 82% which is in close agreement with ROL + – + 2VIN IOUT VOUT – 3221 F01 Figure 1. Equivalent Open-Loop Circuit 3221f 7 LTC3221/ LTC3221-3.3/LTC3221-5 U W U U APPLICATIO S I FOR ATIO depends on many factors such as the oscillator frequency (fOSC), value of the flying capacitor (CFLY), the nonoverlap time, the internal switch resistances (RS) and the ESR of the external capacitors. A first order approximation for ROL is given below: ROL ≅ 2 ∑ S = 1 TO 4 RS + 1 fOSC • C FLY EFFECTIVE OPEN-LOOP OUTPUT RESISTANCE (Ω) Typical ROL values as a function of temperature are shown in Figure 2. 15 VIN = 1.8V 14 VOUT = 3V 13 12 11 ESR of the output capacitor. It is proportional to the input voltage, the value of the flying capacitor and the ESR of the output capacitor. A smaller output capacitor and/ or larger output current load will result in higher ripple due to higher output voltage slew rates. There are several ways to reduce output voltage ripple. For applications requiring lower peak-to-peak ripple, a larger COUT capacitor (4.7µF or greater) is recommended. A larger capacitor will reduce both the low and high frequency ripple due to the lower charging and discharging slew rates, as well as the lower ESR typically found with higher value (larger case size) capacitors. A low ESR ceramic output capacitor will minimize the high frequency ripple, but will not reduce the low frequency ripple unless a high capacitance value is used. 10 VIN, VOUT Capacitor Selection 9 8 7 6 5 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 3221 F02 Figure 2. Effective Open-Loop Output Resistance vs Temperature Output Ripple Low frequency regulation mode ripple exists due to the hysteresis in the comparator CMP and propagation delay in the charge pump control circuit. The amplitude and frequency of this ripple are heavily dependent on the load current, the input voltage and the output capacitor size. The LTC3221 family uses a controlled current, ISW to deliver current to the output. This helps to keep the output ripple fairly constant over the full input voltage range. Typical combined output ripple for the LTC3221-3.3 with VIN = 2V under maximum load is 35mVP-P using a 4.7µF 6.3V X5R case size 0603 output capacitor. A high frequency ripple component may also be present on the output capacitor due to the charge transfer action of the charge pump. In this case the output can display a voltage pulse during the charging phase. This pulse results from the product of the charging current and the The style and value of capacitors used with the LTC3221 family determine several important parameters such as output ripple, charge pump strength and minimum startup time. To reduce noise and ripple, it is recommended that low ESR (< 0.1Ω) capacitors be used for both CIN and COUT. These capacitors should be either ceramic or tantalum and should be 2.2µF or greater. Aluminum capacitors are not recommended because of their high ESR. Flying Capacitor Selection Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitor since its voltage can reverse upon start-up of the LTC3221. Low ESR ceramic capacitors should always be used for the flying capacitor. The flying capacitor controls the strength of the charge pump. In order to achieve the rated output current, it is necessary to have at least 0.6µF of capacitance for the flying capacitor. For very light load applications, the flying capacitor may be reduced to save space or cost.From the first order approximation of ROL in the section “Effective Open-Loop Output Resistance,” the theoretical minimum output resistance of a voltage doubling charge pump can 3221f 8 LTC3221/ LTC3221-3.3/LTC3221-5 U W U U APPLICATIO S I FOR ATIO be expressed by the following equation: ROL(MIN) ≡ 2VIN – VOUT 1 ≅ IOUT fOSC • C FLY where fOSC is the switching frequency (600kHz) and CFLY is the value of the flying capacitor. The charge pump will typically be weaker than the theoretical limit due to additional switch resistance. However, for very light load applications, the above expression can be used as a guideline in determining a starting capacitor value. Programming the LTC3221 Output Voltage (FB Pin) While the LTC3221-3.3/LTC3221-5 versions have internal resistive dividers to program the output voltage, the programmable LTC3221 may be set to an arbitrary voltage via an external resistive divider. Figure 3 shows the required voltage divider connection. VOUT 6 R1 LTC3221 FB C1 COUT 3 Ceramic Capacitors R2 Capacitors of different materials lose their capacitance with higher temperature and voltage at different rates. For example, a ceramic capacitor made of X7R material will retain most of its capacitance from –40°C to 85°C, whereas, a Z5U or Y5V style capacitor will lose considerable capacitance over that range. Z5U and Y5V capacitors may also have a very strong voltage coefficient causing them to lose 50% or more of their capacitance when the rated voltage is applied. Therefore when comparing different capacitors, it is often more appropriate to compare the amount of achievable capacitance for a given case size rather than discussing the specified capacitance value. For example, over rated voltage and temperature conditions, a 1µF 10V Y5V ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22µF 10V X7R capacitor available in the same 0603 case. In fact, for most LTC3221-3.3/LTC3221-5/LTC3221 applications, these capacitors can be considered roughly equivalent. The capacitor manufacturer’s data sheet should be consulted to determine what value of capacitor is needed to ensure 0.6µF at all temperatures and voltages. Table 1 shows a list of ceramic capacitor manufacturers and how to contact them. Table 1. Ceramic Capacitor Manufacturers AVX Kemet Murata Taiyo Yuden Vishay VOUT = 1.23V (1 + R1 ) R2 www.avxcorp.com www.kemet.com www.murata.com www.t-yuden.com www.vishay.com GND 4 3221 F03 Figure 3. Programming the Adjustable LTC3221 The voltage divider ratio is given by the expression: R1 VOUT = –1 R2 1.23V Since the LTC3221 employs a voltage doubling charge pump, it is not possible to achieve output voltages greater than twice the available input voltage. The VIN supply range required for regulation is given by the following expression: Maximum VIN < VOUT + 0.6 Minimum VIN = ( VOUT + IOUT • ROL ) or 1.8V; 2 whichever is higher Where ROL is the effective open-loop output resistance and IOUT is the maximum load current. VIN cannot be higher than VOUT by more than 0.6V, or else the line regulation is poor. Also, VIN has to be higher than the minimum operating voltage of 1.8V. The sum of the voltage divider resistors can be made large to keep the quiescent current to a minimum. Any standing current in the output divider (given by 1.23/R2) will be reflected by a factor of 2 in the input current. A reasonable resistance value should be such that the standing current is in the range of 10µA to 100µA when VOUT is regulated. 3221f 9 LTC3221/ LTC3221-3.3/LTC3221-5 U U W U APPLICATIO S I FOR ATIO If the standing current is too low, the FB pin becomes very sensitive to the switching noise and will result in errors in the programmed VOUT. The compensation capacitor (C1) helps to improve the response time of the comparator and to keep the output ripple within an acceptable range. For best results, C1 should be between 22pF to 220pF. Layout Considerations Due to high switching frequency and high transient currents produced by the LTC3221 product family, careful board layout is necessary. A true ground plane and short 2.2µF 1µF 2 3 R1 VOUT VIN 5 4 To prevent an overtemperature condition in high power applications, Figure 5 should be used to determine the maximum combination of ambient temperature and power dissipation. The power dissipated in the LTC3221 family should always fall under the line shown for a given ambient temperature. The power dissipation is given by the expression: PD = (2V IN– VOUT )• IOUT VOUT 6 PIN 7 Derating Power at High Temperatures 2.2µF GND R2 3221 F04 Figure 4. Recommended Layout connections to all capacitors will improve performance and ensure proper regulation under all conditions. Figure 4 shows the recommended layout configuration. The flying capacitor pins C+ and C– will have very high edge rate waveforms. The large dv/dt on these pins can couple energy capacitively to adjacent printed circuit board runs. Magnetic fields can also be generated if the flying capacitors are not close to the LTC3221 (i.e. the loop area is large). To decouple capacitive energy transfer, a Faraday shield may be used. This is a grounded PC trace between the sensitive node and the LTC3221 pins. For a high quality AC ground it should be returned to a solid ground plane that extends all the way to the LTC3221. To reduce the maximum junction temperature due to power dissipation in the chip, a good thermal connection This derating curve assumes a maximum thermal resistance, θJA, of 80°C/W for 2mm × 2mm DFN package. This can be achieved from a printed circuit board layout with a solid ground plane and a good connection to the ground pins of the LTC3221 and the Exposed Pad of the DFN package. Operation out of this curve will cause the junction temperature to exceed 150°C which is the maximum junction temperature allowed. 3.0 θJA = 80°C/W TJ = 160°C 2.5 POWER DISSIPATION (W) (LTC3221) 1 to the PC board is recommended. Connecting the GND pin (Pin 4 and Pin 7 on the DFN package) to a ground plane, and maintaining a solid ground plane under the device can reduce the thermal resistance of the package and PC board considerably. 2.0 1.5 1.0 0.5 0 –50 –25 25 50 75 100 125 0 AMBIENT TEMPERATURE (°C) 150 3221 F05 Figure 5. Maximum Power Dissipation vs Ambient Temperature 3221f 10 LTC3221/ LTC3221-3.3/LTC3221-5 U PACKAGE DESCRIPTIO DC Package 6-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1703) R = 0.115 TYP 0.56 ± 0.05 (2 SIDES) 0.675 ±0.05 2.50 ±0.05 1.15 ±0.05 0.61 ±0.05 (2 SIDES) PIN 1 BAR PACKAGE TOP MARK OUTLINE (SEE NOTE 6) 0.38 ± 0.05 4 2.00 ±0.10 (4 SIDES) PIN 1 CHAMFER OF EXPOSED PAD 3 0.25 ± 0.05 0.50 BSC 1.42 ±0.05 (2 SIDES) 0.200 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WCCD-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 6 1 (DC6) DFN 1103 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 1.37 ±0.05 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3221f 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. 11 LTC3221/ LTC3221-3.3/LTC3221-5 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1262 12V, 30mA Flash Memory Program Supply Regulated 12V ±5% Output, IQ = 500µA LTC1514/LTC1515 Buck/Boost Charge Pumps with IQ = 60µA 50mA Output at 3.3V or 5V; 2V to 10V Input LTC1516 Micropower 5V Charge Pump IQ = 12µA, Up to 50mA Output, VIN = 2V to 5V LTC1517-5/LTC1517-3.3 Micropower 5V/3.3V Doubler Charge Pumps IQ = 6µA, Up to 20mA Output LTC1522 Micropower 5V Doubler Charge Pump IQ = 6µA, Up to 20mA Output LTC1555/LTC1556 SIM Card Interface Step-Up/Step-Down Charge Pump, VIN = 2.7V to 10V LTC1682 Low Noise Doubler Charge Pump Output Noise = 60µVRMS, 2.5V to 5.5V Output LTC1751-3.3/LTC1751-5 Micropower 5V/3.3V Doubler Charge Pumps IQ = 20µA, Up to 100mA Output, SOT-23 Package LTC1754-3.3/LTC1754-5 Micropower 5V/3.3V Doubler Charge Pumps IQ = 13µA, Up to 50mA Output, SOT-23 Package LTC1755 Smart Card Interface Buck/Boost Charge Pump, IQ = 60µA, VIN = 2.7V to 6V LTC3200 Constant Frequency Doubler Charge Pump Low Noise, 5V Output or Adjustable LTC3203/LTC3203B/ LTC3203B-1/LTC3203-1 500mA Low Noise High Efficiency Dual Mode Step Up Charge Pumps VIN: 2.7V to 5.5V, 3mm × 3mm DFN-10 Package LTC3204/LTC3204B-3.3/ LTC3204-5 Low Noise Regulated Charge Pumps Up to 150mA (LTC3204-5), Up to 50mA (LTC3204-3.3) LTC3240-3.3/LTC3240-2.5 Step-Up/Step-Down Regulated Charge Pumps Up to 150mA Output 3221f 12 Linear Technology Corporation LT 1006 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006