LTC1514-3.3/LTC1514-5 Step-Up/Step-Down Switched Capacitor DC/DC Converters with Low-Battery Comparator U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1514-3.3/LTC1514-5 are micropower switched capacitor DC/DC converters that produce a regulated output voltage by either stepping up or stepping down the input voltage. Output voltage is fixed at either 3.3V (LTC1514-3.3) or 5V (LTC1514-5) by an internal resistor divider. 3.3V or 5V Output Voltages 2V to 10V Input Voltage Range Up to 50mA Output Current Only Three External Capacitors Required Soft Start Limits Inrush Current at Turn-On Low Operating Current: 60µA Low Shutdown Current: 10µA Shutdown Disconnects Load from VIN Short-Circuit and Overtemperature Protected 650kHz Switching Frequency Low-Battery Comparator Active in Shutdown Available in SO-8 Package A unique architecture allows the parts to accommodate a wide input voltage range (2V to 10V) while maintaining ±4% regulation. Additional circuitry prevents excessive inrush current and output voltage ripple when large VIN to VOUT differentials are present. An internal uncommitted comparator is kept active in shutdown. The comparator has an open-drain output for flexible interfacing. U APPLICATIONS ■ ■ ■ ■ ■ Battery-Operated Equipment Smart Card Readers Local Power Supplies Handheld Instruments Battery Backup Supplies The parts are short-circuit and overtemperature protected. Battery life is maximized by very low operating currents (ICC = 60µA typ, 10µA in shutdown). Both parts are available in an SO-8 package. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION LTC1514-5 Output Voltage vs Input Voltage 5V Step-Up/Step-Down Power Supply with Low-Battery Detect 5.2 IOUT = 10mA 100k 1.33M 1% ON OFF 2 LOW BAT 3 499k 1% 4 SHDN VOUT 8 7 LBO VIN LBI C1+ 6 – 5 GND C1 VOUT = 5V IOUT = 50mA + 10µF 0.22µF + 10µF 1514 TA01 VIN 4-CELL NiCd OUTPUT VOLTAGE (V) LTC1514-5 1 5.1 5.0 4.9 4.8 2 3 4 5 8 6 7 INPUT VOLTAGE (V) 9 10 LT1514 • TA02 1 LTC1514-3.3/LTC1514-5 W U U W W U W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) VIN to GND ................................................ – 0.3V to 12V VOUT to GND ............................................. – 0.3V to 12V SHDN, LBI, LBO to GND ........................... – 0.3V to 12V VOUT Short-Circuit Duration ............................. Indefinite Operating Temperature Range Commercial ............................................. 0°C to 70°C Industrial ........................................... – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW SHDN 1 LTC1514CS8-3.3 LTC1514CS8-5 LTC1514IS8-3.3 LTC1514IS8-5 8 VOUT LBO 2 7 VIN LBI 3 6 C1+ GND 4 5 C1– S8 PACKAGE 8-LEAD PLASTIC SO S8 PART MARKING TJMAX = 125°C, θJA = 110°C/ W 15143 15145 1514I3 1514I5 Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS VIN = 2V to 10V, SHDN = 3V, C1 = 0.22µF, CIN = COUT = 10µF, unless otherwise noted (Note 2). PARAMETER CONDITIONS VIN Operating Voltage LTC1514-3.3 LTC1514-5 ● ● 2.0 2.7 VOUT (LTC1514-3.3) 2V ≤ VIN ≤ 8V, IOUT ≤ 15mA 3V ≤ VIN ≤ 8V, IOUT ≤ 50mA ● ● 3.17 3.17 VOUT (LTC1514-5) 2.7V ≤ VIN ≤ 10V, IOUT ≤ 15mA 3.3V ≤ VIN ≤ 10V, IOUT ≤ 50mA ● ● 4.8 4.8 VIN Operating Current VIN ≤ 5V, IOUT = 0, SHDN = 3V VIN > 5V, IOUT = 0, SHDN = 3V VIN Shutdown Current SHDN = 0V, VIN ≤ 5V SHDN = 0V, VIN > 5V Output Ripple Full Load (Note 2) Switching Frequency MIN TYP MAX UNITS 8 10 V V 3.3 3.3 3.43 3.43 V V 5 5 5.2 5.2 V V ● ● 60 75 100 120 µA µA ● 10 20 35 µA µA 100 mVP-P ● 500 650 800 LBI Ramping Negative ● 1.110 1.145 1.180 V LBI Input Current LBI = 1.145V ● – 50 50 nA LBO VOL ISINK = 100µA, VIN = 3V ● 0.4 V LBO Leakage Current VLBO = 5V, LBI = VIN ● –1 1 µA SHDN Input Threshold VIL VIH ● ● 0.4 1.6 V V SHDN Input Current SHDN = VIN SHDN = 0V ● ● –1 –1 1 1 µA µA IOUT Short-Circuit Current VOUT = 0V ● 40 mA tON Soft Start Turn-On Time LBI Trip Point LBI Trip Point Hysteresis 1 The ● denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. 2 0.025 1 1 12 4 Note 2: For VIN ≥ 8V, COUT = 22µF. kHz % ms LTC1514-3.3/LTC1514-5 U W TYPICAL PERFORMANCE CHARACTERISTICS LTC1514-3.3 Efficiency vs Output Current LTC1514-5 Efficiency vs Output Current 100 100 VIN = 2.7V VIN = 2V 80 250 80 EFFICIENCY (%) VIN = 4.4V VIN = 2.7V 60 VIN = 6V OUTPUT VOLTAGE RIPPLE (mVP-P) VOUT = 3.3V TA = 25°C EFFICIENCY (%) LTC1514-3.3 Output Voltage Ripple vs Input Voltage VIN = 6V 40 20 VIN = 3.3V 60 VIN = 8V 40 20 VOUT = 5V TA = 25°C 0 0.01 0.1 1 10 OUTPUT CURRENT (mA) 0 0.01 100 COUT = 22µF 100 COUT = 47µF 3.30 0 2 6 4 INPUT VOLTAGE (V) 8 LTC1514-3.3 Efficiency vs Input Voltage 20 8 10 1514 G07 40 0 2 6 4 INPUT VOLTAGE (V) 8 SHDN = 0V 60 20 10 1514 G06 SHUTDOWN SUPPLY CURRENT (µA) EFFICIENCY (%) –40°C 25 VOUT = 5V IOUT = 10mA TA = 25°C 80 EFFICIENCY (%) 6 4 INPUT VOLTAGE (V) 85°C LTC1514-X Shutdown Supply Current vs Input Voltage 40 2 25°C 60 20 10 100 VOUT = 3.3V IOUT = 10mA TA = 25°C 0 80 LTC1514-5 Efficiency vs Input Voltage 100 10 100 1514 G05 1514 G04 40 8 VOUT = 5V IOUT = 0mA 3.35 10 60 6 4 INPUT VOLTAGE (V) 1514 G03 3.20 80 2 120 3.25 0 8 COUT = 47µF 0 OPERATING CURRENT (µA) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE RIPPLE (mVP-P) COUT = 10µF 6 4 INPUT VOLTAGE (V) 50 LTC1514-5 Operating Current vs Input Voltage VOUT = 3.3V COUT = 10µF TA = 25°C 3.40 150 COUT = 22µF 100 100 3.45 VOUT = 5V IOUT = 10mA TA = 25°C 2 COUT = 10µF LTC1514-3.3 Output Voltage vs Input Voltage 250 0 150 1514 G02 LTC1514-5 Output Voltage Ripple vs Input Voltage 50 200 0 0.1 1 10 OUTPUT CURRENT (mA) 1514 G01 200 VOUT = 3.3V IOUT = 10mA TA = 25°C 20 15 25°C 85°C 10 –40°C 5 0 2 4 8 6 INPUT VOLTAGE (V) 10 12 1514 G08 0 2 6 4 INPUT VOLTAGE (V) 8 10 1514 G09 3 LTC1514-3.3/LTC1514-5 U W TYPICAL PERFORMANCE CHARACTERISTICS LTC1514-5 Step-Down Mode Load Transient Response LTC1514-5 Step-Up Mode Load Transient Response VOUT AC COUPLED 100mV/DIV VOUT AC COUPLED 100mV/DIV 50mA IOUT 50mA/DIV IOUT 50mA/DIV 0mA VIN = 8V, VOUT = 5V, COUT = 10µF, TA = 25°C VIN = 3.3V, VOUT = 5V, COUT = 10µF, TA = 25°C 1514 G10 1514 G11 W BLOCK DIAGRAM C1 – VIN C1 + STEP-UP/STEP-DOWN CHARGE PUMP VOUT SHDN – 650kHz OSCILLATOR + LBO – LBI + 1.145V VREF GND 1514 BD U U U PIN FUNCTIONS SHDN (Pin 1): Shutdown Input. A logic low on the SHDN pin puts the part into shutdown mode. A logic high (VSHDN ≥ 1.6V) enables the charge pump regulator. At high VIN voltages, the SHDN pin may still be controlled with 3V logic without causing a large rise in VIN quiescent current. The SHDN pin may not float; connect to VIN if unused. 4 LBO (Pin 2): Open-Drain, Low-Battery Comparator Output. This pin will pull low whenever the voltage on the LBI pin is less than the internal reference voltage (1.145V typ). LBI (Pin 3): Low-Battery Comparator Input. The voltage on this pin is compared to the internal reference voltage (1.145V). The LBO output will sink current when the voltage on the LBI pin is less than 1.145V typ. The low- LTC1514-3.3/LTC1514-5 U U U PIN FUNCTIONS battery comparator and 1.145V reference are kept alive in shutdown. GND (Pin 4): Ground. Should be tied to a ground plane for best performance. C1 – (Pin 5): Charge Pump Flying Capacitor, Negative Terminal. C1 + (Pin 6): Charge Pump Flying Capacitor, Positive Terminal. VIN (Pin 7): Charge Pump Input Voltage. May be between 2V and 8V (LTC1514-3.3) or between 2.7V and 10V (LTC1514-5). VIN should be bypassed with a ≥ 10µF low ESR capacitor as close as possible to the pin for best performance. VOUT (Pin 8): Regulated Output Voltage. The output voltage is internally set to either 3.3V (LTC1514-3.3) or to 5V (LTC1514-5) using an internal resistor divider. VOUT should be bypassed with a ≥ 10µF low ESR capacitor as close as possible to the pin for best performance. U W U U APPLICATIONS INFORMATION Regulator Operation The regulator section of the LTC1514-3.3/LTC1514-5 consists of a charge pump, reference, comparator and some logic. The divided down output voltage is compared to the internal reference voltage. When the divided output drops below the reference voltage, the charge pump is enabled, which boosts the output back into regulation. Hysteresis in the comparator forces the regulator to burst on and off and causes approximately 100mV of peak-to-peak ripple to appear at the output. By enabling the charge pump only when needed, the LTC1514-3.3 and LTC1514-5 are able to achieve high efficiencies with low output load currents. Each part’s charge pump has a unique architecture that allows the input voltage to be either stepped up or stepped down to produce a regulated output. Internal circuitry senses the VIN to VOUT differential voltage and controls the charge pump operating mode. In addition, the effective output impedance of the charge pump is internally adjusted to prevent large inrush currents and allow for a wide input voltage range. When the input voltage is lower than the output voltage, the charge pump operates as a step-up voltage doubler. When the input voltage is greater than the output, the charge pump operates as a step-down gated switch. Capacitor Selection For best performance, low ESR capacitors are recommended for both CIN and COUT to reduce noise and ripple. The CIN and COUT capacitors should be either ceramic or tantalum and should be 10µF or greater. If the input source impedance is very low (< 0.5Ω), CIN may not be needed. Increasing the size of COUT to 22µF or greater will reduce output voltage ripple—particularly with high VIN voltages (8V or greater). A ceramic capacitor is recommended for the flying capacitor C1 with a value of 0.1µF or 0.22µF. Smaller value flying capacitors may be used in low output current applications. Output Ripple Normal LTC1514-3.3/LTC1514-5 operation produces voltage ripple on the VOUT pin. Output voltage ripple is required for the parts to regulate. Low frequency ripple exists due to the hysteresis in the sense comparator and propagation delays in the charge pump enable/disable circuits. High frequency ripple is also present mainly from the ESR (equivalent series resistance) in the output capacitor. Typical output ripple (VIN < 8V) under maximum load is 100mV peak-to-peak with a low ESR (< 0.5Ω) 10µF output capacitor. For applications requiring VIN to exceed 8V, a 22µF or larger COUT capacitor is recommended to maintain max ripple in the 100mV range. The magnitude of the ripple voltage depends on several factors. High input voltages increase the output ripple since more charge is delivered to COUT per charging cycle. A large C1 flying capacitor (> 0.22µF) also increases ripple in step-up mode for the same reason. Large output current load and/or a small output capacitor (< 10µF) results in higher ripple due to higher output voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the 5 LTC1514-3.3/LTC1514-5 U U W U APPLICATIONS INFORMATION output pin cause high frequency voltage spikes on VOUT with every clock cycle. There are several ways to reduce the output voltage ripple. A larger COUT capacitor (22µF or greater) will reduce both the low and high frequency ripple due to the lower COUT charging and discharging dV/dt and 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 chosen. A reasonable compromise is to use a 10µF to 22µF tantalum capacitor in parallel with a 1µF to 3.3µF ceramic capacitor on VOUT to reduce both the low and high frequency ripple. An RC or LC filter may also be used to reduce high frequency voltage spikes (see Figure 1). VOUT 8 + LTC1514-X VOUT LTC1514-X VOUT 1µF CERAMIC 15µF TANTALUM 2Ω 8 + 10µF TANTALUM + VOUT 10µF TANTALUM 1514 F01 Figure 1. Output Ripple Reduction Techniques Inrush Currents A common problem with switched capacitor regulators is inrush current — particularly during power-up and coming out of shutdown mode. Whenever large VIN (or boosted VIN) to VOUT voltage differentials are present, most charge pumps will pull large current spikes from the input supply. Only the effective charge pump output impedance limits the current while the charge pump is enabled. This may disrupt input supply regulation, especially if the input supply is a low power DC/DC converter or linear regulator. The LTC1514-3.3/LTC1514-5 minimize inrush currents both at start-up and under normal high VIN to VOUT operation. Internal soft start circuitry controls the rate at which VOUT may be charged from 0V to its final regulated value. The typical start-up time from VOUT = 0V to 5V is 4ms. This corresponds to an effective VOUT charging current of only 12.5mA for a 10µF output capacitor (27.5mA for 22µF, etc). Note that any output current load present during start-up will add directly to the charging currents mentioned above. The soft start circuitry limits start-up current both at initial power-up and when coming out of shutdown. As the VIN (or boosted VIN) to VOUT voltage differential grows, the effective output impedance of the charge pump is automatically increased by internal voltage sensing circuitry. This feature minimizes the current spikes pulled from VIN whenever the charge pump is enabled and helps to reduce both input and output ripple. Protection Features The LTC1514-X contain thermal shutdown and shortcircuit protection features. The parts will shut down when the junction temperature reaches approximately 150°C and will resume operation once the junction temperature has dropped back to approximately 140°C. The parts will limit output current to 12mA (typ) when a short-circuit condition (VOUT < 100mV) exists. The parts can survive an indefinite short to GND. The LTC1514-X devices use a low thermal resistance SO-8 package (110°C/W vs 150°C/W for standard SO-8). This permits full output current, even at high input supply voltages. Low-Battery Comparator The internal low-battery comparator trips at 1.145 ±3% (LBI ramping negative). Programming the comparator to trip at a higher voltage can easily be done with an external LTC1514-X VBAT R1 1 2 3 R2 4 SHDN VOUT 8 7 LBO VIN LBI C1+ 6 GND C1– 5 VTRIP = 1.145V(1 + R1/R2) (LBI RAMPING NEGATIVE) 1514 F02 Figure 2. Programming the Low-Battery Comparator Trip Voltage 6 LTC1514-3.3/LTC1514-5 U U W U APPLICATIONS INFORMATION resistor divider (see Figure 2). Since the low-battery comparator is kept alive in shutdown, it may be used to protect batteries against deep discharge by shutting down the power supply when the battery voltage gets too low. The open-drain comparator output allows for flexible interfacing between the LBO output and external logic. LBO pull-up resistors in the 50k to 1M range are recommended. U TYPICAL APPLICATIONS N 3.3V Step-Up/Step-Down Supply with Power Good Output 806k 1% 100k LTC1514-3.3 1 SHDN VOUT 2 LBO VIN 3V VTRIP 3 C1+ LBI 499k 4 C1– GND 1% ON OFF POWER GOOD 8 7 6 5 VIN 2V TO 8V + VOUT = 3.3V ± 4% IOUT = 15mA, VIN > 2V IOUT = 50mA, VIN > 3V 10µF + 0.22µF 10µF 1514 TA05 Low Power Battery Backup Supply with Autoswitchover and No Reverse Current BACKED-UP CIRCUITRY MAIN 5V SUPPLY BAT54 499k LTC1514-5 TP0610T 1 1.5M 1% 499k 1% 2 4.6V VTRIP 3 4 499k SHDN VOUT 8 5V BACKUP SUPPLY IOUT = 15mA 7 LBO VIN LBI C1+ 6 GND C1– 5 TRICKLE CHARGE AND LTC1514 IDD + 10µF 3-CELL NiCd BATTERY + 0.1µF 10µF 1514 TA03 Battery/External Power Autoswitch Regulator MBR0520L 6V WALL ADAPTER INPUT 499k 1M 1% LTC1514-5 ON OFF 1 2 3 499k 1% EXTERNAL POWER GOOD 4 SHDN VOUT 22µF 7 LBO VIN LBI C1+ 6 GND C1– 5 5V + 8 0.22µF + CHARGE PATH 10µF 3-CELL NiCd BATTERY 1514 TA06 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. 7 LTC1514-3.3/LTC1514-5 U TYPICAL APPLICATIONS N Low Power Dual Output Supply (Maximum Combined IOUT = 50mA) ON OFF 10Ω Q2 220k 1 Q1 VOUT 3.3V ±4% 47k + 750k 1% 2 VIN LBO 2.2nF LTC1514-5 3 LBI 10µF 402k 1% VOUT SHDN 4 C1+ C1 GND – 8 VOUT 5V ±4% VIN 2.7V TO 10V 7 6 + 0.22µF 5 + 22µF 10µF Q1: TP0610T Q2: MMBT3906LT1 1514 TA04 Step-Up/Step-Down Power Supply with Input Autoswitching CENTRAL SEMI CMPD6263C Si6943DQ Si6943DQ Si6943DQ +6VDC WALL ADAPTER 4 × AAA ALKALINE CELLS MMBZ 5235BLT1 (6.8V) MMBD 914LT1 470k EXT_PWR_GOOD 10k 10k + 7 10µF 25V 1 2.4k 1k 1M VIN LBI LTC1514-5 C1+ 6 2 – 5 2N7002 C1 LBO VOUT 5V 50mA 8 3 + 22µF 10V 0.22µF GND MMBT 3904LT1 100k VOUT SHDN 4 1514 TA07 MMBT 3904LT1 ON OFF U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) 0.189 – 0.197* (4.801 – 5.004) (LTC DWG # 05-08-1610) 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) *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 5 6 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 2 3 4 SO8 0996 RELATED PARTS PART NUMBER LTC1515 Series LTC1516 LTC1517-5 LTC1522 LTC1555/LTC1556 LTC660 8 DESCRIPTION Step-Up/Step-Down Switched Capacitor DC/DC Converters with Reset Micropower, Regulated 5V Charge Pump DC/DC Converter Micropower, Regulated 5V Charge Pump DC/DC Converter Micropower, Regulated 5V Charge Pump DC/DC Converter SIM Power Supply and Level Translators 100mA CMOS Voltage Converter Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com COMMENTS VIN 2V to 10V, 3.3V, 5V and ADJ Versions, IOUT to 50mA IOUT = 20mA (VIN ≥ 2V), IOUT = 50mA (VIN ≥ 3V) LTC1522 Without Shutdown and Packaged in SOT-23 Available in 8-Pin MSOP, 6µA Quiescent Current, IOUT = 20mA Step-Up/Step-Down SIM Power Supply and Level Translators 5V to – 5V Conversion with Low Voltage Loss 151435f LT/TP 0298 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1997