general description the max889 inverting charge pump delivers a regulatednegative output voltage at loads of up to 200ma. the device operates with inputs from 2.7v to 5.5v to produce an adjustable, regulated output from -2.5v to -v in . the max889 is available with an operating frequency of2mhz (t version), 1mhz (s version), or 0.5mhz (r ver- sion). the higher switching frequency devices allow the use of smaller capacitors for space-limited applica- tions. the lower frequency devices have lower quies- cent current. the max889 also features a 0.1? logic-controlled shutdown mode and is available in an 8-pin so pack- age. an evaluation kit, max889sevkit, is available. ________________________applications tft panelshard disk drives camcorders digital cameras measurement instruments battery-powered applications features ? 200ma output current ? up to 2mhz switching frequency ? small capacitors (1f) ? +2.7v to +5.5v input voltage range ? adjustable regulated negative output (-2.5v to -v in ) ? 0.1a logic-controlled shutdown ? low 0.05 output resistance (in regulation) ? soft-start and foldback current limited ? short-circuit and thermal shutdown protected ? 8-pin so package max889 high-frequency, regulated, 200ma, inverting charge pump ________________________________________________________________ maxim integrated products 1 shdn out cap- 12 8 7 agnd fb cap+ gnd in so top view 3 4 6 5 max889 pin configuration max889 in input +2.7v to +5.5v regulated negative output (up to -1 v in , up to 200ma) fb out gnd agnd cap+ on off shdncap- typical operating circuit 19-1774; rev 0; 7/00 for free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.for small orders, phone 1-800-835-8769. ordering information part temp. range pin- package switching frequency max889tesa -40 c to +85 c 8 so 2mhz max889sesa -40 c to +85 c 8 so 1mhz max889resa -40 c to +85 c 8 so 0.5mhz evaluation kit available downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics(v in = v shdn = +5v, capacitors from table 1, t a = 0 c to +85 c , unless otherwise noted. typical values are at t a = +25 c.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in to gnd .................................................................-0.3v to +6v fb, shdn , cap+ to gnd ............................-0.3v to (v in + 0.3v) agnd to gnd .......................................................-0.3v to +0.3v out to gnd .............................................................-6v to +0.3v cap- to gnd ............................................(v out - 0.3v) to +0.3v continuous output current ...............................................250ma output short-circuit duration ........................................indefinite continuous power dissipation (t a = +70 c) 8-pin so (derate 5.88mw/ c above +70 c)...............471mw operating temperature range...........................-40 c to +85 c junction temperature ......................................................+150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering, 10s) ................................+300 c parameter symbol conditions min typ max units supply voltage range v in r load = 100 2.7 5.5 v output voltage range v out r load = 100 -2.5 -v in v i out(max)1 v in = 5v, v out = -3.3v 200 maximum output current i out(max)2 v in = 3.3v, v out = -2.5v 145 ma max889r 6 12 max889s 12 24 quiescent supplycurrent (free-run mode) i q ( free-run ) no load, v fb = v in max889t 24 48 ma max889r 3.3 7 max889s 5.5 12 quiescent supplycurrent (regulated mode) i q ( regulated ) no load, v out regulated to -3.3v max889t 11 22 ma shutdown supply current i shdn v shdn = 0 0.1 50 a open-loop outputresistance (free-run mode) r o v fb = v in 2.0 4.5 output resistance r o(reg1) v out regulated to -3.3v 0.05 shdn, fb input bias current 1 a fb input offset voltage i load = 0 3 35 mv load regulation i out = 0 to 200ma 10 mv in undervoltage lockoutthreshold v in rising (30mv hysteresis) 2.3 2.6 v shdn logic high v ih 0.7 x v in shdn logic low v il v in = +2.7v to +5.5v 0.3 x v in v max889r 0.375 0.5 0.62 max889s 0.75 1 1.25 switching frequency f osc max889t 1.5 2 2.5 mhz thermal shutdown threshold junction temperature rising(15 c hysteresis) 160 c downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump _______________________________________________________________________________________ 3 note 1: specifications to -40 c are guaranteed by design, not production tested. electrical characteristics(v in = v shdn = +5v, capacitors from table 1, t a = -40 c to +85 c , unless otherwise noted.) (note 1) parameter symbol conditions min max units supply voltage range v in r load = 100 2.7 5.5 v output voltage range v out r load = 100 -2.5 -v in v i out(max)1 v in = 5v, v out = -3.3v 200 maximum output current i out(max)2 v in = 3.3v, v out = -2.5v 145 ma max889r 12 max889s 24 quiescent supplycurrent (free-run mode) i q ( free-run ) no load, v fb = v in max889t 48 ma max889r 7 max889s 12 quiescent supplycurrent (regulated mode) i q ( regulated ) no load, v out regulated to -3.3v max889t 22 ma shutdown supply current i shdn v shdn = 0 50 a open-loop outputresistance (free-run mode) r o v fb = v in 4.5 shdn fb input bias current 1 a fb input offset voltage i load = 0 35 mv in undervoltage lockoutthreshold v in rising (30mv hysteresis) 2.3 2.6 v shdn logic high v ih 0.7 x v in shdn logic low v il v in = +2.7v to +5.5v 0.3 x v in v max889r 0.375 0.62 max889s 0.75 1.25 switching frequency f osc max889t 1.5 2.5 mhz typical operating characteristics (circuit of figure 1, v in = v shdn = +5v, capacitors from table 1, t a = +25?, unless otherwise noted.) output voltage vs. load current max889 toc01 output load current (ma) output voltage (v) -3.33 -3.32 -3.31 -3.30 -3.29 -3.28 -3.27 -3.26 -3.25 0 200 400 600 800 max889t max889s max889r 0 10 20 30 40 max889r output ripple vs. load current vs. c out max889 toc02 load current (ma) output ripple (mv) 0 150 200 50 100 250 300 350 c out = 22 f c out = 47 f c out = 10 f 0 10 20 30 40 max889s output ripple vs. load current vs. c out max889 toc03 load current (ma) output ripple (mv) 0 150 200 50 100 250 300 350 c out = 4.7 f c out = 22 f c out = 10 f downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump 4 _______________________________________________________________________________________ 0 10 3020 40 50 0 100 50 150 200 250 300 350 max889t output ripple vs. load current vs. c out max889 toc04 load current (ma) output ripple (mv) c out = 2.2 f c out = 4.7 f c out = 10 f 0 3020 10 40 50 60 70 80 90 100 02 0 0 100 300 400 500 efficiency vs. load current (v in = 5v, v out = -3.3v) max889 toc05 load current (ma) efficiency (%) max889t max889r max889s 0 3020 10 5040 9080 70 60 100 0 50 100 150 200 250 300 350 efficiency vs. load current (v in = 3.3v, v out = -2.5v) max889 toc06 load current (ma) efficency (%) max889r max889t max889s typical operating characteristics (continued) (circuit of figure 1, v in = v shdn = +5v, capacitors from table 1, t a = +25?, unless otherwise noted.) max889s load-transient response max889 toc10 40 s/div ab 20 to 200ma load stepcircuit of figure 4 a: i out , 100ma/div b: v out , 20mv/div, ac-coupled max889s line-transient response max889 toc11 40 s/div ab i out = 200ma circuit of figure 4a: v in , 2v/div b: v out , 10mv/div, ac-coupled max889s startup and shutdown max889 toc12 2ms/div ab i out = 200ma a: v out , 1v/div b: i in , 100ma/div c: v shdn , 10v/div c 0 0 1.50 2.001.75 2.502.25 2.75 3.00 2.5 3.5 4.0 3.0 4.5 5.0 5.5 free-run output resistance vs. input voltage max889 toc07 input voltage (v) r out ( ) 1.0 1.5 2.0 2.5 3.0 free-run output resistance vs. temperature max889 toc08 temperature ( c) r out ( ) -40 20 40 -20 0 60 80 0 42 86 10 12 2.5 3.5 4.0 3.0 4.5 5.0 5.5 quiescent supply current vs. input voltage (regulated mode) max889 toc09 input voltage (v) quiescent current (ma) max889t max889s max889r v out = -2.5v downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump _______________________________________________________________________________________ 5 pin description pin name function 1 in power-supply positive voltage input 2 cap+ positive terminal of flying capacitor 3 gnd power ground 4 cap- negative terminal of flying capacitor 5 out inverting charge-pump output 6 shdn shutdown control input. drive shdn low to shut down the max889. connect shdn to in for normal operation. 7f b feedback input. connect fb to a resistor-divider from in (or other positive reference voltagesource) to out for regulated output voltages. connect to in for free-run mode. 8 agnd analog ground detailed description the max889 high-current regulated charge-pump dc-dc inverter provides up to 200ma. it features the high- est available output current while using small capacitors (table 1). the three versions available differ in their switching frequencies (f osc ) max889r/ max889s/max889t with f osc = 500khz/1mhz/2mhz, respectively. higher frequencies allow the use of small-er components (table 1). even smaller capacitor values than those listed in table 1 are suitable when the devices are loaded at less than their rated output cur- rent. designed specifically for compact applications, a complete regulating circuit requires only three small capacitors and two resistors, figure 1. in addition, the max889 includes soft-start, shutdown control, short-cir- cuit, and thermal protection. the oscillator, control circuitry, and four power mosfet switches are included on-chip. the charge pump runs continuously at the operating frequency. during one-half of the oscillator period, switches s1 and s2 close (figure 2), charging the transfer capacitor (c fly ) to the input voltage (cap- = gnd, cap+ = in). during theother half cycle, switches s3 and s4 close (figure 3), transferring the charge on c fly to the output capacitor (cap+ = gnd, cap- = out). voltage regulation voltage regulation is achieved by controlling the flying-capacitor charging rate. the max889 controls the charge on c fly by modulating the gate drive to s1 (figure 2) to supply the charge necessary to maintainoutput regulation. when the output voltage droops, c fly charges higher due to increased gate drive. since the device switches continuously, the regulationscheme minimizes output ripple, and the output noise spectrum contains well-defined frequency components. feedback voltage is sensed with a resistor-divider between an externally supplied positive reference or the supply voltage and the negative inverted output. the feedback loop servos fb to gnd. the effective output impedance in regulation is 0.05 . the output remains in regulation until dropout is reached. dropoutdepends on the output voltage setting and load current (see output voltage vs. load current in typical operating characteristics ). free-run mode (unregulated voltage inverter) the max889 may be used in an unregulated voltageinverter mode that does not require external feedback resistors, minimizing board space. connecting fb to in places the max889 in free-run mode. in this mode, the charge pump operates to invert directly the input sup- ply voltage (v out = -(v in - i out x r o )). output resis- tance is typically 2 and can be approximated by the following equation: r o ? [1 / (f osc x c fly ) ] + 2r sw + 4esr cfly + esr cout the first term is the effective resistance of an idealswitched-capacitor circuit (figures 2 and 3), and r sw is the sum of the charge pump s internal switch resis- tances (typically 0.8 at v in = 5v). the last two terms take into consideration the equivalent series resistance downloaded from: http:///
max889 (esr) of the flying and output capacitors. the typicaloutput impedance is more accurately determined from the typical operating characteristics . current limit and soft-start the max889 features a foldback current-limit/soft-startscheme that allows it to limit inrush currents during startup, overload, and output short-circuit conditions. additionally, it permits a safe, timed recovery from fault conditions. this protects the max889 and prevents low-current or higher output impedance input supplies (such as alkaline cells) from being overloaded at start- up or short-circuit conditions. the max889 features two current-limit/soft-start levels with corresponding response to rising and falling out- put voltage thresholds of -0.6v and -1.5v. when the falling output voltage crosses -1.5v, such as during an overload condition, the input current is immediately lim- ited to 400ma by weakening the charge-pump switch- es. when the falling output voltage crosses -0.6v, such as during a short-circuit condition, the max889 further weakens the charge-pump switches, immediately limit- ing input current to 200ma. during startup or short-circuit recovery, the max889 limits input current to 200ma with charge-pump switch- es at their weakest level. rising output voltage crossing -0.6v initiates a 2ms timer, after which the max889 increases switch strength to the next level. the rising output voltage crossing -1.5v initiates a 2ms timer, after which the max889 provides full-strength operation. shutdown when shdn (a cmos-compatible input) is driven low, the max889 enters 0.1? shutdown mode. charge- pump switching halts. connect shdn to in or drive high for normal operation. thermal shutdown the max889 features thermal shutdown with hysteresisfor added protection against fault conditions. when the die temperature exceeds 160 c, the internal oscillator stops, suspending device operation. the max889resumes operation when the die temperature falls 15 c. this prevents the device from rapidly oscillating aroundthe temperature trip point. applications information resistor selection (setting the output voltage) the accuracy of v out depends on the accuracy of the voltage biasing r1 in figure 1. use a separate refer-ence voltage if greater accuracy than provided by v in is desired (figure 4). keep the feedback node as smallas possible, with resistors mounted close to the fb pin. high-frequency, regulated, 200ma, inverting charge pump 6 _______________________________________________________________________________________ figure 1. typical application circuit. max889t in input 5.0v output-3.3v c in 4.7 f c out 4.7 f c fly 1 f fb r1100k r166.5k out gnd cap+ on off 4 2 3 shdncap- 1 7 5 6 8 figure 3. transferring charge on c fly to c out s2 out c out c fly s1 in s4 s3 f osc cap+ cap- figure 2. charging c fly s2 out c out c fly s1 cap+ cap- in s4 s3 f osc downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump _______________________________________________________________________________________ 7 adjust the output voltage to a negative voltage from -2.5v to -v in with external resistors r1 and r2 as shown in figures 1 and 4. fb servos to gnd. chooser1 to be 100k or less. calculate r2 for the desired output voltage: v out = -v ref (r2 / r1) r2 = r1 (v out / -v ref ) where v ref can be either v in or a positive reference source.typically, choose a voltage-divider current of at least 30? to minimize the effect of fb input current and capacitance: r1 v ref / 30? r2 < -v out / 30? capacitor selection the appropriate capacitors used with the max889depend on the switching frequency. table 1 provides suggested values for c in , c fly , and c out . surface-mount ceramic capacitors are preferred forc in , c out , and c fly due to their small size, low cost, and low esr. to ensure proper operation over theentire temperature range, choose ceramic capacitors with x7r (or equivalent) low-temperature-coefficient (tempco) dielectrics. see table 2 for a list of suggested capacitor suppliers. the output capacitor stores the charge transferred from the flying capacitor and services the load between oscillator cycles. a good general rule is to make the output capacitance at least five-times greater than the flying capacitor. output voltage ripple is largely dependent on c out . choosing a low-esr capacitor of sufficient value is impor-tant in minimizing the peak-to-peak output voltage ripple, which is approximated by the following equation: where c out is the output capacitor value, esr cout is the output capacitor s esr, and f osc is the max889 switching frequency. ceramic capacitors have the lowestesr and are recommended for c out . where larger capacitance at low cost is desired, a low-esr tantalumcapacitor may be used for c out . see table 2 for a list of suggested capacitor suppliers.to ensure stability over the entire operating temperature range, choose a low-esr output capacitor using the fol- lowing equation: where c out is the output capacitor value, and f min is the minimum oscillator frequency in the electrical characteristics table. to ensure stability for regulated output mode, suitableoutput capacitor esr should be determined by the follow- ing equation: power dissipation the power dissipated in the max889 depends on theinput voltage, output voltage, and output current. device power dissipation is accurately described by: p diss = i out (v in - (-v out )) + (i q ? v in ) where i q is the device quiescent current. p diss must be less than the package dissipation rating (see absolute maximum ratings ). pay particular attention to power dis- sipation limits when generating small negative voltagesfrom large positive input voltages. layout considerations the max889 s high oscillator frequencies demand good layout techniques that ensure stability and helpmaintain the output voltage under heavy loads. take the following steps to ensure optimum layout: 1) mount all components as close together as possible. 2) place the feedback resistors r1 and r2 close to the fb pin, and minimize the pc trace length at the fb circuit node. 3) keep traces short to minimize parasitic inductance and capacitance. 4) use a ground plane with c in and c out placed in a star ground configuration (see the max889sevkit layout). r 19.2 x 10 i r2 r1 esr -3 out ?? ?? ?? ?? + ?? ? ?? ? 1 c 15.5 f r1 r1 + r2 i out min out ?? ? ?? ? ?? ? ?? ? v = i 2 x f c 2 x i esr ripple out osc out out cout + downloaded from: http:///
max889 high-frequency, regulated, 200ma, inverting charge pump maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2000 maxim integrated products printed usa is a registered trademark of maxim integrated products. soicn.eps table 1. capacitor selection table part frequency c fly c out c in regulated c in free-run max889r 0.5mhz 4.7 f2 2 f2 2 f 4.7 f max889s 1mhz 2.2 f1 0 f1 0 f 2.2 f max889t 2mhz 1 f 4.7 f 4.7 f1 f production method manufacturer series phone fax avx tps series 803-946-0690 803-626-3123 kemet 494 series 864-963-6300 864-963-6521 matsuo 267 series 714-969-2491 714-960-6492 surface-mounttantalum sprague 593d, 595d series 603-224-1961 603-224-1430 s ur face- m ount p ol ym er sanyo poscap-apa 619-661-6835 619-661-1055 avx x7r 803-946-0690 803-626-3123 kemet x7r 864-963-6300 864-963-6521 matsuo x7r 714-969-2491 714-960-6492 s ur face- m ount c er am i c murata grm x7r 814-237-1431 814-238-0490 table 2. low-esr capacitor manufacturers chip information transistor count: 1840process: bicmos package information figure 4. separate vref for voltage divider max889t in input 5.0v output-3.3v c in 4.7 f c out 4.7 f v ref 5v c fly 1 f fb r1100k r266.5k out gnd agnd cap+ on off 4 2 3 shdncap- 1 7 5 6 8 v out = -v ref r2 r1 downloaded from: http:///
|
