_______________general description the MAX840/max843/max844 low-noise, inverting charge-pump power supplies are ideal for biasing gaasfets in cellular telephone transmitter amplifiers. they operate with inputs down to 2.5v. the MAX840 offers both a -2v preset output and a -0.5v to -9.4v adjustable output. the max843/max844 use an external positive control voltage to set the negative output voltage. input voltage range for all the devices is 2.5v to 10v, and output current is 4ma with v in > 2.7v. these circuits can operate with small capacitors, as low as 0.22?. an internal linear regulator reduces the MAX840? out- put voltage ripple to 1mvp-p. with a well-filtered control voltage (v ctrl ), the max843/max844 also achieve less than 1mvp-p typical output ripple. supply current is 750?, and reduces to less than 1? in shutdown (MAX840/max843). the max844? unregulated output is active in shutdown, with the charge pump switching at 20khz. it provides a low-power lcd supply. ________________________applications cellular phones gaasfet power amplifier modules personal communicators, pdas wireless data loggers continuously adjustable gaasfet bias lcd-bias contrast control regulated negative power supplies ____________________________features ? fixed -2v or adjustable -0.5v to -9.4v output at 4ma (MAX840) ? 2.5v to 10v input voltage range ? operate with small capacitors (as low as 0.22?) ? 1mvp-p output voltage ripple ? charge-pump switching frequency: 100khz in normal operation 20khz in shutdown mode (max844) ? 1? max logic-level shutdown over temp. (MAX840/max843) ? small 8-pin so package MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias ________________________________________________________________ maxim integrated products 1 ( ) are for max843/max844 1 2 3 4 8 7 6 5 in gnd out fb (cont) shdn negout c1- c1+ MAX840
max843
max844 so top view __________________pin configuration MAX840 fb out shdn
negout c1- c1+ in gnd v in = 2.5v to 10.0v
(3 cells) 0.22 m f v out = -2.0v
(v gg of gaasfet) 4.7 m f 0.22 m f 0.22 m f on/off __________typical operating circuit 19-0388; rev 1; 3/96 part MAX840 c/d MAX840isa MAX840esa -40? to +85? -25? to +85? 0? to +70? temp. range pin-package dice* 8 so 8 so evaluation kit manual follows data sheet ______________ordering information * dice are specified at t a = +25? only. max843 c/d 0? to +70? dice* max843isa -25? to +85? 8 so max843esa -40? to +85? 8 so max844 c/d 0? to +70? dice* max844isa -25? to +85? 8 so max844esa -40? to +85? 8 so for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (figures 2a and 2c, 2.5v v in 10v, v out = -2v, gnd = 0v, r l = , shdn = v in , t a = t min to t max , unless otherwise noted. typical values are measured at v in = 3.6v and t a = +25?.) 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. note 1: the output may be shorted to negout or gnd if the package power dissipation is not exceeded. typical short-circuit current from 4v to gnd is 40ma. supply voltage, v in to gnd ..................................-0.3v to 10.5v v negout to gnd ...................................................-10.5v to 0.3v v in to v negout .........................................................-0.3v to 21v v out to gnd (note 1).......................................v negout to 0.3v v s hdn to gnd ............................................-0.3v to (v in + 0.3v) continuous power dissipation (t a = +70?) so (derate 5.88mw/? above +70?) .........................471mw operating temperature ranges max84_i_ _a ...................................................-25? to +85? max84_e_ _a ..................................................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10sec) .............................+300? c4 = 10? v in = 3.6v, r l = or 500 max844, v in 3.6v, shdn = 0v max844, v in = 10v, shdn = 0v MAX840/max843, v in = 10v, shdn = 0v max843/max844, v cont = 0v max843/max844, v ctrl = 2v MAX840, v fb = 0v MAX840, v fb = -0.5v MAX840, no load conditions mvp-p 1 v out ripple mv/ma 28 v out load regulation 38 ? 175 300 i shut shutdown supply current 940 1 na ? ?00 i cont cont leakage current na ? ?00 i fb fb leakage current v -0.516 -0.5 -0.484 v fb fb voltage -2.1 -2.0 -1.9 v 2.5 10 v in supply voltage range -0.5 to (v in - 0.6) v out output voltage adjust range v -2.05 -2.0 -1.95 v out output voltage -2.1 -2.0 -1.9 -2.05 -2.0 -1.95 units min typ max symbol parameter 80 100 120 oscillator frequency f osc v in = 3.6v, t a = +25? 14 20 26 khz input high voltage v ih shdn 2.2 v v in 3 2.7v, i out = 0ma to 4ma v in 3 2.5v, i out = 0ma to 3ma v in 3 2.5v, i out = 0ma to 3ma v in 3 2.7v, i out = 0ma to 4ma v MAX840, v fb = 0v max843/max844, v ctrl = 2v input low voltage v il shdn 0.35 v input current i in shdn -1 1 ? input capacitance c in shdn 10 pf MAX840/max843/ max844 max844, shdn = 0v no load, v in 3.6v i q supply current ? 750 1300
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias _______________________________________________________________________________________ 3 -2.040 010 output voltage
vs. output current -2.050 MAX840-01 output current (ma) output voltage (v) 6 -2.070 -2.060 24 8 135 79 -2.040 output voltage vs. input voltage
over temperature -2.050 -2.045 MAX840-02 input voltage (v) output voltage (v) -2.065 -2.060 -2.055 10 6 24 8 3579 t a = +85? t a = +25? t a = -40? 20 0 10 maximum output current
vs. input voltage 60 40 MAX840-03 input voltage (v) maximum output current (ma) 6 120 100 80 24 8 3579 v out < -1.95v
(circuit of fig 2a) v out < -1.95v
(circuit of fig 2d) v out < 2mvp-p ripple
(circuit of fig 2d) v out < 2mvp-p ripple
(circuit of fig 2a) high-current operation not
recommended for extended
periods of time. 0 10 n0-load supply current
vs. input voltage 2 1 MAX840-05 input voltage (v) no-load supply current (ma) 6 5 4 3 24 8 3579 0 10 negout current vs. input voltage 10 5 MAX840-04 input voltage (v) negout current (ma) 6 30 25 20 15 24 8 3579 v negout = 0.9 x v negout(no load) shutdown
(max844) 0 supply current vs. temperature 3 2 1 MAX840-06 temperature (?) supply current (ma) 40 7 6 5 4 -40 0 80 -20 20 60 100 v in = 10v v in = 3.6v 0.4 start-up time vs. input voltage 1.6 1.2 0.8 MAX840-07 input voltage (v) start-up time (ms) 6 2.8 2.4 2.0 24 8 357910 __________________________________________typical operating characteristics (circuit of figure 2a, v in = 3.6v, t a = +25?, unless otherwise noted.)
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias 4 _______________________________________________________________________________________ ____________________________typical operating characteristics (continued) (circuit of figure 2a, v in = 3.6v, t a = +25?, unless otherwise noted.) MAX840 output noise and ripple
(c1 = c2 = c3 = 1 m f, c4 = 10 m f) v in = 3.6v, v out = -2v, i out = 4ma, ac coupled 10 m s/div v out
500 m v/div
MAX840 output noise and ripple
(c1 = c2 = c3 = 0.22 m f, c4 = 4.7 m f) v in = 3.6v, v out = -2v, i out = 4ma, ac coupled 10 m s/div v out
1mv/div
max843/max844 output noise and ripple
(c1 = c2 = c3 = 1 m f, c4 = 10 m f) v in = 3.6v, v out = -2v, i out = 4ma, ac coupled 10 m s/div v out
500 m v/div
max843/max844 output noise and ripple
(c1 = c2 = c3 = 0.22 m f, c4 = 4.7 m f) v in = 3.6v, v out = -2v, i out = 4ma, ac coupled 10 m s/div v out
1mv/div
70 10 oscillator frequency
vs. supply voltage
90 80 MAX840-17 supply voltage (v) oscillator frequency (khz) 6 150 140 120 130 110 100 24 8 3579 t a = +25?, +85? t a = -40? shdn = high 15 10 max844
oscillator frequency vs. supply voltage
19 17 MAX840-18 supply voltage (v) oscillator frequency (khz) 6 31 29 25 27 23 21 24 8 3579 t a = +25?, +85? t a = -40? shdn = low
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias _______________________________________________________________________________________ 5 MAX840 noise spectrum
(c1 = c2 = c3 = 0.22 m f, c4 = 4.7 m f) 50 0 0.1 1 10 100 1000 10 frequency (khz) noise (db m v) 20 30 40 v in = 3.6v,
i out = 4ma max843/max844 noise spectrum
(c1 = c2 = c3 = 1 m f, c4 = 10 m f) 40 -10 0.1 1 10 100 1000 0 frequency (khz) noise (db m v) 10 20 30 v in = 3.6v,
i out = 4ma ____________________________typical operating characteristics (continued) (circuit of figure 2a, v in = 3.6v, t a = +25?, unless otherwise noted.) MAX840 noise spectrum
(c1 = c2 = c3 = 1 m f, c4 = 10 m f) 40 -10 0.1 1 10 100 1000 0 frequency (khz) noise (db m v) 10 20 30 v in = 3.6v,
i out = 4ma v out note: db? = 20 log ______ 1?
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias 6 _______________________________________________________________________________________
start-up from shutdown v in = 3.6v, v out = -2v, i out = 4ma 500 m s/div v out
1v/div 0v 0v v shdn
2v/div
line-transient response v out = -2v, i out = 4ma, ac coupled 5ms/div v out
10mv/div v in 2.7v 3.3v
load-transient response v in = 3.6v, v out = -2v 5ms/div v out
20mv/div 0.01ma i out 4ma ____________________________typical operating characteristics (continued) (circuit of figure 2a, v in = 3.6v, t a = +25?, unless otherwise noted.) max843/max844 noise spectrum
(c1 = c2 = c3 = 0.22 m f, c4 = 4.7 m f) 50 0 0.1 1 10 100 1000 10 frequency (khz) noise (db m v) 20 30 40 v in = 3.6v,
i out = 4ma v out note: db? = 20 log ______ 1?
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias _______________________________________________________________________________________ 7 ______________________________________________________________pin description dual mode is a trademark of maxim integrated products. max843 max844 1 2 3 4 8 7 6 5 MAX840 name function 1 c1+ positive terminal for c1 pin 2 c1- negative terminal for c1 3 negout negative output voltage (unregulated) 5 fb dual mode feedback input. when fb is grounded, the output is preset to -2v. to select other output voltages, connect fb to an external resistor divider (figure 2b). 4 shdn active-low, ttl logic-level shutdown input 8 in positive power-supply input 7 gnd ground 6 out regulated negative output voltage cont control voltage input. to set v out , connect a resistor divider between out and a positive control voltage between 0v and 10v (figure 2c). MAX840 -0.5v
ref charge
pump in n c1+ c1- negout shdn out connect to
gnd to set
v out = -2v fb gnd max843
max844 charge
pump in n c1+ c1- negout shdn
out control
voltage cont gnd r2 r1 figure 1a. MAX840 block diagram figure 1b. max843/max844 block diagram
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias 8 _______________________________________________________________________________________ _______________detailed description the MAX840/max843/max844 are low-noise, inverting, regulated charge-pump power supplies designed for biasing gaasfet devices, such as power-amplifier modules in cellular handsets. the applied input voltage (v in ) is first inverted to a neg- ative voltage at negout by a capacitive charge pump. this voltage is then regulated by an internal low-noise linear regulator, and appears at out (figure 1). the minimum (most negative) output voltage achievable is the inverted positive voltage, plus the 0.6v required by the post-regulator. for the MAX840, the linear regulator reduces ripple noise induced by the charge-pump inverter to 1mvp-p at v out . in addition, the linear regu- lator? excellent ac rejection attenuates noise from the incoming supply. __________applications information setting the output voltage for the MAX840, select either a fixed or adjustable output voltage. connect fb directly to gnd for a fixed -2v output (figure 2a). select an alternate output volt- age by connecting fb to the midpoint of a resistor voltage divider from out to gnd (figure 2b). v in must be 0.6v above the absolute value of v out to allow proper regulation. the output voltage is calculat- ed from the formula below. choose r2 to be between 100k and 400k . v out = (-0.5v)(1 + r2 / r1) for the max843/max844, set the output voltage by connecting a resistor voltage divider between out and a positive control voltage (v ctrl ) (figure 2c). v out = -v ctrl (r2 / r1) shutdown mode the MAX840/max843/max844 feature a shutdown mode that reduces the supply current to 1 a max over temperature (300? max for the max844). when the MAX840/max843 are in shutdown, the outputs (out, negout) and the charge-pump oscillator are dis- abled. when the max844 is in shutdown, only the lin- ear regulator is disabled and the negout output remains enabled. however, the charge-pump oscilla- tion frequency is reduced to 20khz, reducing the available power at negout. the output voltage at negout can be used to bias an lcd while in shut- down. capacitors use capacitors with low effective series resistance (esr) to maintain a low dropout voltage (v in - | v out | ). the overall dropout voltage is a function of the charge pump? output resistance and the voltage drop across the linear regulator (n-channel pass transistor). at the 100khz switching frequency, the charge-pump output resistance is a function of c1 and c2? esr. therefore, minimizing the esr of the charge-pump capacitors minimizes the dropout voltage. the output resistance of the entire circuit is approxi- mately: r out = r o + 4 x esr c1 + esr c4 + 1 / (f s x c1) + r (linear regulator) where [r o + r (linear regulator) ], the effective resistance of the internal switches and the resistance across the linear regulator, is approximately 71 at v in = 2.5v, 48 at v in = 5v, and 40 at v in = 10v. c1, c2, and c3 should be 1? capacitors with less than 0.8 esr. c4 should be a 10? capacitor with less than 0.2 esr. smaller capacitor values can be used (c1 = c2 = c3 = 0.22?, c4 = 4.7?) with a small increase in output noise and ripple (figure 2d). all capacitors should be either surface-mount chip tanta- lum or ceramic types. external capacitor values can be adjusted to optimize size and cost. layout and grounding good layout is important, primarily for good noise perfor- mance. take the following steps to ensure good layout: 1) mount all components as close together as possible. 2) keep traces short to minimize parasitic inductance and capacitance. this includes connections to fb. 3) use a ground plane. noise and ripple measurement accurately measuring the output noise and ripple is a challenge. slight momentary differences in ground potential between the MAX840/max843/max844 circuit and the oscilloscope (which results from the charge pump? switching action) cause ground currents in the probe? wires, inducing sharp voltage spikes. for best results, measure directly across the output capacitor (c4). do not use the ground lead of the oscilloscope probe; instead, remove the probe? tip cover and touch the ground ring on the probe directly to c4? ground terminal. you can also use a tektronix chassis-mount test jack (part no. 131-0258) to connect your scope probe directly. this direct connection gives the most accurate noise and ripple measurement.
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias _______________________________________________________________________________________ 9 MAX840 fb out shdn negout c1- c1+ in gnd v in c3
1 m f v out = -2v
(v gg of gaasfet) c4
10 m f c1
1 m f c2
1 m f 1 on/off 2 3 45 6 8 7 MAX840 fb out shdn negout c1- c1+ in gnd v in c3
1 m f v out = (-0.5v) 1+ r2
r1 c4
10 m f c1
1 m f c2
1 m f r2
100k r1
100k ( ) 1 2 3 4 5 6 8 7 on/off max843
max844 cont out shdn negout c1- c1+ in gnd v in c3
1 m f v out = -0.5v to -9.4v @ 4ma c4
10 m f c1
1 m f c2
1 m f r2
100k r1
100k v ctrl (0v to 10v) 1 2 3 45 6 8 7 on/off MAX840
fb out shdn negout c1- c1+ in gnd v in c3
0.22 m f v out = -2v
(v gg of gaasfet) c4
4.7 m f c1
0.22 m f c2
0.22 m f 1 2 3 45 6 8 7 on/off figure 2a. MAX840 standard application circuit figure 2b. MAX840 adjustable configuration figure 2d. MAX840 application circuit using smaller capacitors figure 2c. max843/max844 standard application circuit
MAX840/max843/max844 low-noise, regulated, -2v gaasfet bias 10 ______________________________________________________________________________________ ( ) are for max843/max844 transistor count: 148 substrate connected to in ___________________chip topography in negout negout shdn 0.145"
(3.683mm) 0.085"
(2.159mm) fb (cont) gnd gnd out c1- c1+
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