LTC1798

LTC1798 Series Micropower Low Dropout References FEATURES s s s s s s s DESCRIPTIO 200mV Max Dropout at 10mA Output Current 4µA Typical Quiescent Current 0.15% Max Initial Accuracy No Output Capacitor Required Output Sources 10mA, Sinks 2mA 40ppm/°C Max Drift Voltage Options: 2.5V, 3V, 4.1V, 5V and Adjustable The LTC®1798/LTC1798-2.5/LTC1798-3/LTC1798-4.1/ LTC1798-5 are micropower bandgap references that combine high accuracy and low drift with very low supply current and small package size. The combination of ultralow quiescent current and low dropout voltage of only 200mV (max) makes them ideal for battery-powered equipment. The output voltage is set by an external resistor divider for the adjustable LTC1798. This series of references uses curvature compensation to obtain low temperature coefficient and trimmed thin-film resistors to achieve high output accuracy. These references can source up to 10mA and sink up to 2mA, making them ideal for precision regulator applications. They are stable without an output bypass capacitor, but are also stable with capacitance up to 1µF. This feature is important in critical applications where PC board space is a premium and fast settling is demanded. The LTC1798 series references provided power dissipation advantages over shunt references. In addition to supply current, shunt references must also idle the entire load current to operate. The LTC1798 series is available in the SO-8 package. , LTC and LT are registered trademarks of Linear Technology Corporation. APPLICATIO S s s s s Battery-Powered Systems Handheld Instruments Precision Power Supplies A/D and D/A Converters TYPICAL APPLICATIO LTC1798-2.5 Temperature Drift 2.5V Battery-Powered Reference LTC1798-2.5 2.7V TO 12.6V 2 0.1µF GND 1798 TA01 4 REFERENCE VOLTAGE CHANGE (mV) 3 2 1 0 –1 –2 –3 –4 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 IN OUT 6 2.5V 4 U 1798 TA02 U U 1 LTC1798 Series ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW *DNC 1 IN 2 **DNC/FB 3 GND 4 8 7 6 5 DNC* DNC* OUT DNC* Supply Voltage ....................................................... 13V Input Voltages .......................................... – 0.3v to 13V Output Voltages ........................................ – 0.3V to 13V Output Short-Circuit Duration .......................... Indefinite Operating Temperature Range (Note 2) ........................................... – 40°C to 100°C Specified Temperature Range ..................... 0°C to 70°C Storage Temperature Range (Note 3) ... – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER LTC1798CS8 LTC1798CS8-2.5 LTC1798CS8-3 LTC1798CS8-4.1 LTC1798CS8-5 S8 PART MARKING 1798 179825 17983 179841 17985 S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 190°C/W * CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS ** DNC FOR LTC1798-2.5/LTC1798-3/ LTC1798-4.1/LTC1798-5, FB FOR LTC1798 Consult factory for parts specified with wider operating temperature range. AVAILABLE OPTIO S OUTPUT VOLTAGE (V) 2.5 3 4.096 5 Adjustable TEMPERATURE RANGE (°C) 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 ACCURACY (%) 0.15 0.15 0.15 0.15 0.4 TEMPERATURE COEFFICIENT (ppm/°C) 40 40 40 40 40 PACKAGE TYPE SO-8 (S8) ORDER NUMBER PART MARKING LTC1798CS8-2.5 LTC1798CS8-3 LTC1798CS8-4.1 LTC1798CS8-5 LTC1798CS8 179825 17983 179841 17985 1798 ELECTRICAL CHARACTERISTICS The q denotes specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT(NOMINAL) + 0.2V, IOUT = 0mA unless otherwise noted. FB = OUT for the LTC1798. SYMBOL VIN IIN VOUT PARAMETER Input Voltage Range Input Current Output Voltage (Note 4) FB = OUT for LTC1798 q CONDITIONS q MIN TYP 4.0 MAX 12.6 6.5 8.5 2.3945 0.4 2.5037 3.0045 4.102 5.0075 0.15 UNITS V µA µA V % V V V V % LTC1798, FB = OUT LTC1798 ADJ LTC1798-2.5 LTC1798-3 LTC1798-4.1 LTC1798-5 LTC1798 All Fixed Options 2.3755 – 0.4 2.4963 2.9955 4.090 4.9925 – 0.15 2.385 2.5 3 4.096 5 2 U W U U WW U W LTC1798 Series The q denotes specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT(NOMINAL) + 0.2V, IOUT = 0mA unless otherwise noted. FB = OUT for the LTC1798. SYMBOL en TC VOUT/VIN VOUT/IOUT PARAMETER Output Voltage Noise (Note 5) Output Voltage Temp Coefficient (Note 6) Line Regulation Load Regulation (Note 7) CONDITIONS 0.1Hz ≤ f ≤ 10Hz TMIN ≤ TJ ≤ TMAX VIN = (VOUT(NOMINAL) + 0.2V) to 12.6V Sourcing 0mA to 10mA Sinking 0mA to 2mA q q q q ELECTRICAL CHARACTERISTICS MIN TYP 8 15 30 0.1 1.75 MAX 40 120 0.3 4.0 6.5 UNITS ppmP-P ppm/°C ppm/V mV/mA mV/mA mV/mA mA mA ISC ∆VDO VHYST IFB Short-Circuit Output Current Dropout Voltage (Note 8) Output Hysteresis (Note 9) FB Pin Input Current VOUT Shorted to GND VOUT Shorted to VIN IOUT = 0, ∆VOUT ≤ 0.1% IOUT = 10mA, ∆VOUT ≤ 0.1% ∆T = – 40°C to 85°C ∆T = 0°C to 70°C LTC1798, OUT = FB q q 20 2 40 4 100 200 200 50 10 mV mV ppm ppm nA Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC1798 is guaranteed functional over the operating temperature range of – 40°C to 100°C. Note 3: If the part is stored outside of the specified operating temperature range, the output may shift due to hysteresis. Note 4: ESD (Electostatic Discharge) sensitive device. Extensive use of ESD protection devices are used internal to the LTC1798, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions. Note 5: Peak-to-peak noise is measured with a single pole highpass filter at 0.1Hz and 2-pole lowpass filter at 10Hz. Note 6: Temperature coefficient is the change in output voltage divided by the nominal output voltage divided by the specified temperature range. Note 7: Load regulation is measured on a pulse basis from no load to the specified load current. Output changes due to die temperature change must be taken into account separately. Note 8: Dropout voltage is (VIN – VOUT) when VOUT falls to 0.1% below its nominal value at VIN = VOUT + 0.5V. Note 9: Hysteresis in output voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25°C, but the IC is cycled hot or cold before successive measurements. Hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature. TYPICAL PERFOR A CE CHARACTERISTICS LTC1798-2.5* Dropout Voltage vs Output Source Current 100 90 DROPOUT VOLTAGE (mV) OUTPUT SHORT-CIRCUIT CURRENT (mA) TA = 25°C 80 70 60 50 40 30 20 10 0 0 1 10 0.1 OUTPUT SOURCE CURRENT (mA) 100 1798 G01 INPUT CURRENT (µA) *Similar performance characteristics can be expected for all voltage options. UW LTC1798-2.5* Input Current vs Temperature 8 VIN = 2.7V 7 6 5 4 3 2 1 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1798 G02 LTC1798 Series Output ShortCircuit Current vs Temperature 70 60 50 40 30 20 10 5 0 –50 –25 0 OUTPUT SHORTED TO VIN 25 50 75 100 125 150 TEMPERATURE (°C) 1798 G03 TA = 25°C VIN = VOUT(NOM) + 0.2V OUTPUT SHORTED TO GND 3 LTC1798 Series TYPICAL PERFOR A CE CHARACTERISTICS LTC1798-2.5* Output Short-Circuit Current vs Input Voltage 25 OUTPUT SHORT-CIRCUIT CURRENT (mA) OUTPUT SHORT-CIRCUIT CURRENT (mA) ∆VOUT FROM NO LOAD (mV) 20 TA = 25°C OUTPUT SHORTED TO VIN 15 10 5 0 2 4 6 8 10 INPUT VOLTAGE (V) 12 14 1258-G04 LTC1798-2.5* Output Voltage vs Input Voltage 2.5010 TA = 25°C 7 POWER SUPPLY REJECTION RATIO (dB) OUTPUT VOLTAGE (V) 2.5005 INPUT CURRENT (µA) 2.5000 2.4995 2 4 6 8 10 INPUT VOLTAGE (V) LTC1798-2.5 0.1Hz to 10Hz Noise 1400 VIN = 2.7V INPUT CURRENT (µA) INPUT CURRENT (µA) 5µV/DIV 1SEC/DIV 1798 G10 4 UW 12 LTC1798-2.5* Output Short-Circuit Current vs Input Voltage 42 5 4 3 2 1 0 –1 –2 –3 –4 12 14 1798 G05 LTC1798 Series Load Regulation TA = 25°C VIN = VOUT(NOM) + 0.2V SINKING SOURCING TA = 25°C OUTPUT SHORTED TO GND 41 2 4 6 8 10 INPUT VOLTAGE (V) –5 0 1 10 0.1 OUTPUT CURRENT (mA) 100 1798 G06 LTC1798-2.5* Input Current vs Input Voltage 60 LTC1798-2.5 PSRR vs Frequency VIN = 2.7V 50 40 30 20 10 0 TA = 25°C 6 5 14 1798 G07 4 2 4 6 8 10 INPUT VOLTAGE (V) 12 14 1798 G08 10 1k 100 FREQUENCY (Hz) 10k 1798 G09 LTC1798-5 Input Current vs Input Voltage in Dropout 250 TA = – 55°C TA = 25°C 1000 TA = 125°C 800 600 400 200 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 0 200 LTC1798-2.5 Input Current vs Input Voltage in Dropout 1200 TA = 125°C 150 TA = 25°C 100 TA = – 55°C 50 0 0.5 1 1.5 2 2.5 3 3.5 INPUT VOLTAGE (V) 4 4.5 5 1798 G11 1798 G12 LTC1798 Series PI FU CTIO S DNC (Pins 1, 5, 7, 8): Do Not Connect. Connected internally for post package trim. These pins must be left unconnected. IN (Pin 2): Positive Supply. Bypassing with a 0.1µF capacitor is recommended if the output loading changes. (VOUT + 0.2V) ≤ VIN ≤ 12.6V. DNC (Pin 3): (LTC1798-2.5/LTC1798-3/LTC1798-4.1/ LTC1798-5) Do Not Connect. Connected internally for post package trim. This pin must be left unconnected. FB (Pin 3): (LTC1798) Resistor Divider Feedback Pin. Connect a resistor divider from OUT to GND and the center tap to FB. This pin sets the output potential.  R1 + R2 VOUT = 2.385V   ; R1 is connected from OUT  R2  to FB and R2 from FB to GND. Selecting R2 ≥ 10k will make IOUT < 250µA. GND (Pin 4): Negative Supply or Ground Connection. OUT (Pin 6): Reference Output. The output can source up to 10mA and sink up to 2mA. It is stable with output bypass capacitor ranging from 0µF to 1µF. BLOCK DIAGRA W U U U 2 IN + OUT 6 2.385V – R1 FB 3 (LTC1798) R2 GND 4 1798 BD NOTE: R1 AND R2 ARE NOT CONNECTED FOR LTC1798 5 LTC1798 Series APPLICATIO S I FOR ATIO Longer Battery Life Series references have an advantage over shunt style references. To operate, shunt references require a resistor between the power supply and the output. This resistor must be chosen to supply the maximum current that is demanded by the circuit being regulated. When the circuit being controlled is not operating at this maximum current, the shunt reference must always sink this current, resulting in high power dissipation and short battery life. The LTC1798 series low dropout references do not require a current setting resistor and can operate with any supply voltage from (VOUT(NOMINAL) + 0.2V) to 12.6V. When the circuitry being regulated does not demand current, the LTC1798 series reduces its dissipation and battery life is extended. If the reference is not delivering load current it dissipates only 10.8µW when operating on a 2.7V supply for LTC1798-2.5, yet the same connection can deliver 10mA of load current when demanded. Output Bypass Capacitor The LTC1798 series is designed to be stable with or without capacitive loads. With no capacitive load, the reference is ideal for fast settling applications, or where PC board space is at a premium. In applications with significant output loading changes, an output bypass capacitor of up to 1µF can be used to improve the output transient response. Figure 1 shows the response of the reference to a 1mA to 0 µA load step with a 1µF output capacitor. If more than 1µF of output RESISTOR VALUE (Ω) 1mA IOUT 0mA VOUT 100mV/DIV IOUT 10ms/DIV 1798 F01a Figure 1. Reference Output Load Transient Response, 1µF Output Capacitor 6 U capacitance is required, a resistor in series with the capacitor is recommended to reduce the output ringing. Figure 2 illustrates the use of a damping resistor for capacitive loads greater than 1µF. Figure 3 shows the resistor and capacitor values required to achieve critical damping. LTC1798-5 5.2V TO 12.6V 0.1µF 2 IN GND 4 OUT 6 5V COUT >1µF DAMPING RESISTOR