rev. 0 a information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700www.analog.com fax: 781/326-8703 ? analog devices, inc., 2002 ADR280 1.20 v ultralow power high psrr voltage reference features 1.20 v precision output excellent line regulation, 2 ppm/v typical high power supply ripple rejection, C80 db at 220 hz ultralow power, supply current 16 a max temperature coefficient, 40 ppm/ o c max low noise, 12.5 nv/ hz typical wide operating range, 2.4 v to 6 v compact 3-lead sot-23 package applications gsm, gprs, 3g mobile stations portable battery-operated electronics low voltage converter references wireless devices pin configuration 3-lead sot-23 (rt suffix) v out v+ 1 2 3 ADR280 v general description the ADR280 is a 1.2 v band gap core reference with excellent line regulation and power supply rejection designed specifically for applications experiencing heavy dynamic supply variations, such as data converter references in gsm, gprs, and 3g mobile station applications. devices, such as the ad6535 which has an analog baseband ic with on-board baseband and audio codecs, voltage regulators, and battery charger, rely on the ADR280? ability to reject input battery voltage variations dur- ing rf power amplifier activity. in addition to mobile stations, the ADR280 is suitable for a variety of general-purpose applications. most band gap refer- ences include internal gain for specific outputs, which simplifies the user? design but compromises on the cost, form factor, and flexibility. the ADR280, on the other hand, optimizes the band gap core voltage and allows users to tailor the voltage, current, or transient response by simply adding their preferred op amps. the ADR280 operates on a wide supply voltage range from 2.4 v to 6 v. it is available in a compact 3-lead sot-23 package and is specified over the extended industrial tem- perature range of ?0 c to +85 c. temperature ? c 15 ?5 ?0 100 ?0 line regulation ?ppm/v 020406080 ?0 ? 0 5 10 3v to 5v figure 1. line regulation vs. temperature
rev. 0 ?2? ADR280especifications electrical characteristics parameter symbol conditions min typ 1 max unit output voltage 2 v out 1.195 1.200 1.205 v temperature coefficient tcvo 0 c < t a < 50 c5 20 ppm/ o c line regulation v out / v in 2.55 v < v in < 5.5 v, no load 2 12 ppm/v supply current i in 2.4 v < v in < 5.5 v, no load 10 16 a ground current i gnd ve grounded, i load = 10 a1220 a input voltage range v in 2.4 5.5 v operating temperature range t a e40 +85 c nominal load capacitance c out 1 f output noise voltage v n f = 10 hz to 10 khz 12.5 vrms output noise density e n f = 400 khz 12.5 nv/ hz h ja is specified for the worst-case conditions, i.e., ja is specified for device sol- dered in circuit board for surface-mount packages. ordering guide temperature package package top output number of model range description option mark voltage parts per reel ADR280art-reel7 e40 c to +85 c sot-23 rt3 rba 1.200 3,000 ADR280art-reel e40 c to +85 c sot-23 rt3 rba 1.200 10,000 caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the ADR280 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. pin descriptions pin no. mnemonic description 1v +h igh supply voltage input 2v out output voltage 3v el ow supply voltage input pin configuration v out v+ 1 2 3 ADR280 ve
rev. 0 t ypical performance characteristicseADR280 ?3? temperature e c 1.20225 e40 100 e20 v out e v 020406080 no load 1.202 1.20175 1.2015 1.20125 1.201 1.20075 1.2005 1.20025 1.2 tpc 1. v out vs. temperature temperature e c e40 100 e20 i in e a 020406080 v in = 5v 15 14 13 12 11 10 9 v in = 3v tpc 2. supply current vs. temperature temperature e c 15 e15 e40 100 e20 line regulation e ppm/v 020406080 e10 e5 0 5 10 3v to 5v tpc 3. line regulation tpc 4. noise voltage peak-to-peak 10 hz to 10 khz tpc 5. output noise density plot (v in = 3.6 v, c out = 1 f, c in = 1 f) tpc 6. voltage noise density 0 hz to 100 khz
rev. 0 ?4? ADR280 tpc 7. settling time theory of operation the ADR280 provides the basic core 1.2 v band gap reference. it contains two npn transistors, q9 and q17, with their emitter areas scaled in a fixed ratio. the difference in their vbes produces a ptat (proportional to absolute temperature) voltage that can- cels the ctat (complementary to absolute temperature) q9 vbe voltage. as a result, a core band gap voltage, that is almost a con- stant 1.2 v over temperature, is generated (see figure 2). precision laser trimming of the internal resistors and other proprietary circuit techniques are used to enhance the initial accuracy, temperature curvature, and temperature drift performance. r1 r3 r5 r7 r9 q17 q9 q18 r8 q3 r6 q5 q6 r4 q1 pnp3 r2 r12 q2 q10 r13 c1 q7 r10 r11 ve v+ v out i1 figure 2. simplified architecture applications the ADR280 should be decoupled with a 0.1 f ceramic cap at the output for optimum stability. it is also a good practice to include 0.1 f ceramic caps at the ic supply pin. these capaci- tors should be mounted close to their respective pins (see figure 3). v+ v out 0.1 f 0.1 f ve ADR280 figure 3. basic configuration the low supply voltage input pin ve can be elevated above ground; a 1.2 v differential voltage can therefore be established above ve (see figure 4). v+ v out 0.1 f 0.1 f ve ADR280 +5v +1.2v +2.5v figure 4. floating references
rev. 0 ADR280 ?5? the ADR280 provides the core 1.2 v band gap voltage and is only able to drive a maximum load of 100 a. users can simply buffer the output for high current or sink/source current applica- tions, such as adc or lcd driver references (see figure 5). v+ v out 0.1 f 0.1 f ve ADR280 v out u1 u2 u2 = ad8541, sc70 ad8601, sot-23e5 figure 5. buffered output users can also tailor any specific need for voltage and dynamics with an external op amp and discrete components (see figure 5). depending on the specific op amp and pcb layout, it may be necessary to add a compensation capacitor, c2, to prevent gain peaking and oscillation. the exact value of c2 needed requires some trial and error but usually falls in the range of a few pf. v+ v out 0.1 f ve ADR280 u1 5v 5v 1.2v u2 1.8v r1 r2 60k 0.1% 120k 0.1% c2 2.2pf v+ ve ad8541 v o c1 figure 6. 1.8 v reference low cost, low power current source because of its low power characteristics, the ADR280 can be converted to a current source with just a setting resistor. in addition to the ADR280 current capability, the supply voltage and the load limit the maximum current. the circuit in figure 7 produces 100 a with 2 v compliance at 5 v supply. the load current is the sum of i set and i gnd . i gnd will increase slightly with load; an r set of 13.6 k yields 100 a of load current. v+ v out 0.1 f ve ADR280 u1 5v 1.2v 13.6k c1 r set rl 1k i l 100 a i gnd i l = i set + i gnd i set + e figure 7. low cost current source precision low power current source by adding a buffer to redirect the i gnd in figure 8, a current can be precisely set by r set with the equation i l = 1.2 v/r set . v+ v out 0.1 f ve ADR280 u1 5v c2 r set rl 1k i l 100 a i l = 1.2v/r set v+ ve 5v u2 12k ad8541 figure 8. precision low power current source boosted current source adding one more buffer to the previous circuit boosts the current to the level that is limited only by the buffer u2 current handling capability (see figure 9). v+ v out 0.1 f ve ADR280 u1 5v c1 r set 230 rl 500 i l 5ma i l = 1.2v/r set v+ ve 5v u3 v+ ve 5v u2 u2 = u3 = ad8542, ad822 1.2v + e figure 9. precision current source
rev. 0 ?6? ADR280 negative reference a negative reference can be precisely configured, as shown in figure 10, without using any expensive tight tolerance resistors. the voltage difference between v out and ve is 1.2 v. since v out is at virtual ground, u2 will close the loop by forcing the ve pin to be the negative reference output. v+ v out 0.1 f ve ADR280 u1 5v v+ ve e2.7v ad8541 e1.2v ev ref u2 c1 figure 10. negative reference boosted reference with scalable output a precision user defined output with boosted current capability can be implemented with the circuit shown in figure 11. in this circuit, u2 forces v o to be equal to v ref (1 + r2/r1) by regulating the turn-on of m1; the load current is therefore fur- nished by the 5 v supply. for higher output voltage, u2 must be changed and the supply voltage of m1 and u2 must also be elevated and separated from the u1 input voltage. in this configu- ration, a 100 ma load is achievable at a 5 v supply. the higher the supply volt age, the lower the current handling it because of the heat generated on the mosfet. for heavy capacitive loads, additional buffering is needed at the output to enhance the tran- sient response. v+ v out ve ADR280 u1 5v v+ ve u2 r1 r2 rl 25 v o 10.8k 0.1% 10k 0.1% c2 1pf 1.2v ad8541 0.1 f c1 m1 2.5v/100ma m1 = fdb301n, 2n7000, 2n7002, or equivalent figure 11. 2.5 v boosted reference gsm and 3g mobile station applications the ADR280 voltage reference is ideal for use with analog baseband ics in gsm and 3g mobile station applications. figure 12 illustrates the use of the ADR280 with the ad6535 gsm analog baseband. the ad6535 provides all of the data converters and power management functions needed to imple- ment a gsm mobile station, including baseband and audio codecs, voltage regulators, and a battery charger. besides low current consumption and a small footprint, the ADR280 is opti- mized for excellent power supply rejection ratio (psrr) necessary for optimum ad6535 device performance when the main bat- tery voltage fluctuates during rf power amplifier activity. digital baseband ad6535 analog baseband baseband codec audio codec power management radio ADR280 voltage reference figure 12. gsm mobile station application
rev. 0 ADR280 ?7? outline dimensions 3-lead plastic surface-mount package [sot-23] (rt-3) dimensions shown in millimeters 3.04 2.90 2.80 pin 1 1.40 1.30 1.20 2.64 2.10 1.90 bsc 1 2 3 seating plane 1.12 0.89 0.10 0.01 0.50 0.30 0.54 ref 0.20 0.08 0.60 0.50 0.40 0.95 bsc compliant to jedec standards to-236ab tape and reel dimensions (rt-3) dimensions shown in millimeters 4.10 4.00 3.90 1.55 1.50 1.50 8.30 8.00 7.70 3.20 3.10 2.90 2.05 2.00 1.95 1.85 1.75 1.65 3.55 3.50 3.45 2.80 2.70 2.60 1.10 1.00 0.90 0.35 0.30 0.25 13.20 13.00 12.80 9.90 8.40 8.40 20.20 min 1.50 min 7" reel 100.00 or 13" reel 330.00 7" reel 50.00 min or 13" reel 100.00 min 14.40 max 0.75 min direction of unreeling 1.00 min
c 03065 ?0?11/02(0) printed in u.s.a. ?8?
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