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Final Electrical Specifications
LTC1258-2.5 Micropower Low Dropout Reference
May 1998
FEATURES
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DESCRIPTION
The LTC(R)1258-2.5 is a micropower bandgap reference that combines 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 it ideal for battery powered equipment. This reference uses curvature compensation to obtain low temperature coefficient and trimmed thin-film resistors to achieve high output accuracy. The reference can supply up to 10mA and sink up to 2mA, making it ideal for precision regulator applications. The LTC1258-2.5 is stable without an output bypass capacitor, but also is stable with capacitance up to 1F. This feature is important in critical applications where PC board space is a premium and fast settling is demanded. Series references provide power dissipation advantages over shunt references. In addition to supply current, shunt references must also idle the entire load current to operate. The LTC1258-2.5 is available in the 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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200mV Max Dropout at 10mA Output Current 4A Typical Quiescent Current 0.15% Max Initial Accuracy No Output Capacitor Required Output Sources 10mA, Sinks 2mA 40ppm/C Max Drift Over Commercial Temp Range Load Regulation Over Temperature 0.1mV/mA, Source up to 10mA 1.75mV/mA, Sink up to 2mA 2.7V to 12.6V Supply Voltage Range
APPLICATIONS
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Battery Powered Systems Hand-Held Instruments Precision Power Supply A/D and D/A Converters
TYPICAL APPLICATION
Temperature Drift
2.5
2 0.1F GND 4 1 LTC1258-2.5 2.7V TO 12.6V IN OUT 2.5V
REFERENCE VOLTAGE CHANGE (mV)
2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
1258 * TA01
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.
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LTC1258-2.5
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ........................................................ 13V Input Voltages ........................................... -0.3V to 13V Output Voltages ......................................... -0.3V to 13V Output Short Circuit Duration .......................... Indefinite Operating Temperature Range ..................... 0C to 70C Storage Temperature Range (Note 1) ....-65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW OUT 1 IN 2 NC* 3 GND 4 8 7 6 5 NC* NC* NC* NC*
ORDER PART NUMBER LTC1258CS8-2.5 S8 PART MARKING 12582
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 190C/W *CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS.
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VIN IIN VOUT en TC VOUT/VIN VOUT/IOUT PARAMETER Input Voltage Range Input Current
VIN = 2.7V, IOUT = 0mA, TA = 25C unless otherwise noted.
CONDITIONS
q q
MIN 2.7
TYP 4
MAX 12.6 6.5 8.5 2.5037 40 200 0.2 0.3 3.5 5 60 10 100 200
UNITS V A A V Vp-p ppm/C V/V mV/mA mV/mA mV/mA mV/mA mA mA mV mV ppm ppm
Output Voltage (Note 2) Output Voltage Noise (Note 3) Output Voltage Temp Coefficient (Note 4) Line Regulation Load Regulation (Note 5) 0.1Hz f 10Hz TMIN TJ TMAX VIN = 2.7V to 12.6V Sourcing 0mA to 10mA
q q q
2.4963
2.5 20 15 100 0.1 1.75
Sinking 0mA to 2mA
q
ISC VDO VHYST
Short Circuit Output Current Dropout Voltage (Note 6) Output Hysteresis (Note 7)
VOUT Shorted to GND VOUT Shorted to VIN IOUT = 0, VOUT 0.1% IOUT = 10mA, VOUT 0.1% T = -40C to 85C T = 0C to 70C
q q
20 2
40 4
200 50
The q denotes specifications which apply over the operating temperature range. Note 1: If the part is stored outside of the specified operating temperature range, the output may shift due to hysteresis. Note 2: ESD (Electrostatic Discharge) sensitive device. Extensive use of ESD protection devices are used internal to the LTC1258-2.5, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions. Note 3: Peak-to-peak noise is measured with a single highpass filter at 0.1Hz and 2-pole lowpass filter at 10Hz. Note 4: Temperature coefficient is measured by dividing the change in output voltage by the specified operating temperature range.
Note 5: 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 6: Dropout voltage is (VIN - VOUT) when VOUT falls to 0.1% below its nominal value at VIN = VOUT + 0.5V. Note 7: 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 25C, but the IC is cycled to 85C or -40C before successive measurements. Hysteresis is roughly proportional to the square of the temperature change. Hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature.
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LTC1258-2.5
PIN FUNCTIONS
OUT (Pin 1): Reference Output. The output can source up to 10mA and sink up to 2mA. Stable with output bypass capacitor ranges from 0F to 1F. IN (Pin 2): Positive Supply. Bypass with a 0.1F capacitor is recommended if the output loading changes. (VOUT + 0.2V) VIN 12.6V. GND (Pin 4): Negative Supply or Ground Connection. NC (Pins 3, 5, 6, 7, 8): No Connection. Connected internally for post package trim. These pins should be left unconnected.
BLOCK DIAGRAM
APPLICATIONS INFORMATION
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.
1mA IOUT 0mA VOUT 100mV/DIV
10ms/DIV
Figure 1. Reference Output Load Transient Response
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2 IN
+ -
R1 R2 GND 4
OUT
1
2.424V
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The LTC1258-2.5 series low dropout reference does not require a current setting resistor and can operate with any supply voltage from (VOUT + 0.2V) to 12.6V. When the circuitry being regulated does not demand current, the LTC1258-2.5 reduces its dissipation and battery life is extended. If the reference is not delivering load current it dissipates only 12W on a 3V supply, yet the same connection can deliver 10mA of load current when demanded.
1mA IOUT 0mA VOUT 100mV/DIV
0.5ms/DIV
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LTC1258-2.5
APPLICATIONS INFORMATION
Output Bypass Capacitor The LTC1258-2.5 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 a premium. In applications with significant output loading changes, an output bypass capacitor of up to 1F can be used to improve the output transient response. Figure 1 shows the response of the reference to a 1mA to 0A load step with a 1F output capacitor. If more than 1F of output capacitance is required, a resistor in series with the capacitor is recommended to reduce the output ringing. Figure 2 shows the resistor and capacitor values required to achieve critical damping. Internal P-Channel Pass Transistor The LTC1258-2.5 features an internal P-channel MOSFET pass transistor. This provides several advantages over similar designs using a PNP bipolar pass transistor. The LTC1258-2.5 consumes only 4A of quiescent current under light and heavy loads as well as in dropout; whereas, PNP based references waste considerable amounts of current when the pass transistor is saturated. In addition, the LTC1258-2.5 provides a lower dropout voltage (200mV max) than PNP based references.
10k
RESISTOR VALUE ()
TYPICAL APPLICATIONS
Micropower Low Dropout Negative Reference
2 IN 1 8 1 0.1F LTC1258-2.5 OUT GND 4 VOUT = -2.5V
1258 * TA03
0.2V VCC 9V LTC1258-2.5 VCC = 5V 2 0.1F GND 4 IN OUT 1 0.1F 2.5V VIRTUAL GROUND
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- +
1/2 LTC1542 3 4
VSS = -3V
1258 * TA02
RELATED PARTS
PART NUMBER LT1634 LT1460 LTC1440 LTC1540 DESCRIPTION Micropower Precision Shunt Voltage Reference Micropower Series Reference Micropower Comparator with Reference Nanopower Comparator with Reference COMMENTS 0.05% Max, 25ppm/C Max Drift, 1.25V, 2.5V, 4.096V and 5V Outputs 0.075% Max, 10ppm/C Max Drift, 2.5V, 5V and 10V Outputs 3.7A Max ICC, 1% 1.182V Reference, Adjustable Hysteresis 600nA Max ICC, 2% 1.182V Reference, Adjustable Hysteresis
12582i LT/TP 0598 4K * PRINTED IN USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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1k
100
10 1 10 100 OUTPUT CAPACITOR VALUE (F) 1k
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Figure 2. Damping Resistance vs Output Capacitor Value
Supply Splitter
(c) LINEAR TECHNOLOGY CORPORATION 1998

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