19-0388; Aev 1; 3/96 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 cutput 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 VIN > 2.7V. These circuits can operate with small capacitors, as low as 0.22uF. An internal linear regulator reduces the MAX840s out- put voltage ripple to 1mVp-p. With a well-filtered control voltage (VCTRL), the MAX843/MAX844 also achieve less than 1mVp-p typical output ripple. Supply current is 750uA, and reduces to less than 1HA in shutdown (MAX840/MAX843). The MAX844s 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 Typical Operating Circuit MAXIM Low-Noise, Regulated, -2V GaAsFET Bias Features # Fixed -2V or Adjustable -0.5V to -9.4V Output at 4mA (MAX840) - 1imVp-p Output Voltage Ripple 2.5V to 10V Input Voltage Range Operate with Small Capacitors (as low as 0.22y1F) Charge-Pump Switching Frequency: 100kHz in Normal Operation 20kHz in Shutdown Mode (MAX844) # 1pA Max Logic-Level Shutdown Over Temp. (MAX840/MAX843) @ Small 8-Pin SO Package Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX840C/D OT to +70T Dice* MAX840ISA -25 CT ta +85C 850 MAX840ESA -40' CT to +85'C 850 MAX843C/D 0T to +70T Dice MAX843 ISA -25'T to +85C 850 MAX843ESA -40'T to +85C 850 MAX844C/D 0T to +70T Dice MAX8441SA -25T to +85C 8350 MAX844ESA -40'CT to +85C 850 * Dice are specified at Ta = +25 only. Vin = 2.5 to 10.0 (3 CALLS) st Pin Configuration O22UF = Ci+ amth | MAXLAA vane us TOP VIEW 7 MAX840 a ct- OUT - LL oT AAAXLAA 3] m GOUT + nar = ot [2 MAX840 [7] avo ~ aT - necouT[s} MAxe43) = [fe] or 7 MAX844 : SHON [4 | rs] raion ONCFF ] SHDN rB GND 30 + () ARE FOR MAXB43/MAXB44 ax! Maxim Integrated Producis 1 For free samples & the latest Ifterature: http://www.maxim-ic.com, or phone 1-800-998-8800 VVSXVW/EVEXVW/OPEXVWMAX840/MAX843/MAX8 44 Low-Noise, Regulated, -2V GaAsFET Bias ABSOLUTE MAXIMUM RATINGS Supply Voltage, Vin to GND... ee -0.3V to 10.5V Operating Temperature Ranges VNEGOUT to GND... eee ceeseee stern -10.5V to 0.3V MAX84 | A ccc cccecteeeeteaeeettaeanes -25C to +85T VIN tO VNEGOUT.....0000cccccccccccccceccsescessetecsvatessensaeeesaees -0.3V to 21V MAX84 EAL ee bite 40 TC to +85 TC Vout to GND (Note 1)... ee eereeeees VNEGOUT te 0.3 Storage Temperature Range............ ce -65C to +150T V SHDN to GND oo eee -0.3V to (VIN + 0.3V) Lead Temperature (soldering, 10sec)... +300 TC Continuous Power Dissipation (Ta = +70) SO (derate 5.88mW/C above +70C) ee 471mW Note 1: The output may be shorted to NEGOUT ar GND if the package power dissipation is not exceeded. Typical short-circuit current fram 4V to GND is 40mA. Stresses beyond those listed under Absolute Maximum Aalings may cause permanent damage to the device. These are siress ratings only, and functional operation of ihe device at ihese or any olher conditions beyond ifose indicated in ie operational sections of ihe specifications is noi implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Figures 2a and 2c, 2.5V < Vin <= 10V, Vout = -2V, GND = OV, RL = , SHDN = Vin, Ta = Twin to Tmax, unless otherwise noted. Typical values are measured at VIN = 3.6V and Ta = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS Supply Voltage Range VIN 2.5 10 Vv > ne ea to 3mA 21 20 19 MAX840, VFB = OV VND DTV lour= OMA to 4mA 21 2.0 19 Output Voltage VOUT Vin > 2.5V V MAXe4gMAxg44, | louT=OmAto3mA | OS BO 188 VeTRL = 2V > WaaF, ana | 205 20198 Output Voltage Adjust Range VOUT 0.5 to v (VIN - 0.6) FB Voltage VFB MAX840, no load -0.516 0.5 -0.484 Vv FB Leakage Current IFB MAX840, Vee = -0.5V +1 +100 nA CONT Leakage Current ICONT | MAX843/MAX844, VconT = OV +1 +100 nA Supply Current la No load, Vin < 3.6V 750 1300 HA MAX840/MAX843, Vin = 10V, SHDN = 0V 1 Shutdown Supply Current ISHUT MAX844, Vin = 10V, SHDN = ov 940 LA MAX844, Vin < 3.6V, SHDN = OV 175 300 MAX840, VrB = OV 3 8 Vout Load Regulation vin = 3.6V, MAX843/MAX844 mv/mA L = ce or 5009 , 2 8 VeTRL = 2V Vout Ripple C4 = 10nF 1 mVp-p MAX840/MAX843/ Oscillator Frequency Fosc TNs MAX844 80 100 120 kHz MAX844, SHDN = 0V 14 20 26 Input High Voltage VIH SHDN 2.2 Vv Input Low Voltage VIL SHDN 0.35 V Input Current lIN SHDN -1 1 WA Input Capacitance Cin SHDN 10 pF 2 MA AXLAALow-Noise, Regulated, -2V GaAsFET Bias (Circuit of Figure 2a, VIN = 3.6V, Ta = +25C, unless otherwise noted.) OUTPUT VOLTAGE s. OUTPUT CURRENT -2.070 = = N wi -2.060 g \ a! 3 \ 5 NY ao 5 2.050 oO ~~ [hen -P.040 Oo 1 2 38 4 5 6 F 8&8 10 OUTPUT CURRENT {mA} MAXIMUM OUTPUT CURRENT ys. INPUT VOLTAGE 120 MaAKEOOF Vout < -1.95V (CIRCUIT OF FIG 2a) Vout < -1.98V (CIRCUIT OF FIG 2a) o So 80 40 MAXIMUM OUTPUT CURRENT (mA) 3 20 0 2 3.4 5 6 7 8 9 10 INPUT VOLTAGE () NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE 5 2 7 3 z i E 4 8 E / = & / E 5 A 5 3 fo > | c 4 r a | aX =] oO 5 2 A > 3 a z 2 Y" 5 2 LH 2 j a Q 0 2 3 4 85 6 7 8 10 INPUT VOLTAGE () MA AXLAA QUTPUT VOLTAGE vs. INPUT VOLTAGE COVER TEMPERATURE 2.068 : YA 2.080 a L Zr wi 2088 Ta = 485C a - = g _ Lee ~ a a @.060 Ty = 428C 3 _aenl =-d49 e048 Ta=-40C -? 040 2 a 4 5 8 7 8 g 10 INPUT VOLTAGE (V) NEGOUT CURRENT vs. INPUT VOLTAGE 30 25 I} I VNEGOUT = 0.9 x VNEGOUTINO LOAD) MAXBAt- 04 fA 20 High-current operation not recommended for extended periods of time /\ . NEGOUT CURRENT (mA) a t 4nea a to / a | Vour <2mVp-p RIPPLE A | ee | SHUTDOWN CIRCUIT OF FIG 2a) "1 (MAXB44) Vour < 2mp-p RIPPLE 5 (CIRCUIT OF FIG 20) 2 3 SUPPLY CURRENT vs. TEMPERATURE Maxeio0S Vin = 3.6V, -40 -20 0 20 640 60 680 TEM PERATURE (C) 100 4 5 7 8 g 10 INPUT VOLTAGE (V) START-UP TIME vs. INPUT VOLTAGE START-UP TIME (ms) o aa = nh nN nN o ho nm ao a a eo p 2 3 4 5 6 7 8 g INPUT VOLTAGE (V} Typical Operating Characteristics VVSXVW/EVEXVW/OPEXVWMAX840/MAX843/MAX8 44 Low-Noise, Regulated, -2V GaAsFET Bias Typical Operating Characteristics (continued) (Circuit of Figure 2a, VIN = 3.6V, Ta = +25C, unless otherwise noted.) OSCILLATOR FREQUENCY MAX844 vs. SUPPLY VOLTAGE OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE 150 = 31 s 3 aq 140 3 @ 2 z Lr _ a o = 130 Ta = +25C, +85C = 27 [a5 425C, +85C 2 6 3 120 Ta=-d0S @ 2s 3 A= a Ta=-40C fe 110 f 23 c c o o fz 100 fe 21 5 go 5 1g So SHDN = ao SHDN = HIGH oo, 70 15 2 38 4 8&8 8&8 F B Gg 10 2 3 4 8 8 7 8B g fo SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) MAX840 QUTPUT NOISE AND RIPPLE MAX840 QUTPUT NOISE AND RIPPLE Vout Vout : SO0uV/aiv ImVidiy 10,s/div 10,s/div Vin =3.6V, Vout =-2, IouT = 4mA, AC COUPLED Vin = 3.6V, Vout =-2, lout =4mA, AC COUPLED MAX843/MAX844 QUTPUT NOISE AND RIPPLE MAX843/MAX844 QUTPUT NOISE AND RIPPLE (Cl = C2 = C3 = 1pF, C4 = 10uF) (C1 = C2 = C3 = 0.22uF, C4 =4.7pF) Vout Vout SOOuV/div AimVidiv 10us/div 10,ts/div Vin = 3.6, Vout = -2, lout = 4mA, AC COUPLED Vin =3.6V, VouT= -2V, lout = 4mA, AC COUPLED 4 MA AXLMMLow-Noise, Regulated, -2V GaAsFET Bias Typical Operating Characteristics (continued) (Circuit of Figure 2a, VIN = 3.6V, Ta = +25C, unless otherwise noted.) NOTE: dBy = 20 LOG MA AXLIAM VOUT pV NOISE (dByV} NOISE (dBpV) NOISE (dBaV) 50 40 30 20 40 20 MAX840 NOISE SPECTRUM (Ci =C2=C= 1mF, C4= 10uF) 0.1 1 10 100 1000 FREQUENCY (kHz) MAX840 NOISE SPECTRUM (C1 =C2=C3= 0.22uF, a= 4.7 F) Vin =3.6V, Iout = 4mA 01 1 10 100 1000 FREQUENCY (kHz) MAX843/MAX844 NOISE SPECTRUM (Ci = C2= C3= ipF, C4 = 10)LF) 0.1 1 10 100 1000 FREQUENCY (kHz) VVSXVW/EVEXVW/OPEXVWMAX840/MAX843/MAX8 44 Low -Noise, Regulated, -2V GaAsFET Bias Typical Operating Characteristics (continued) (Circuit of Figure 2a, VIN = 3.6V, Ta = +25C, unless otherwise noted.) MAX843/MAX844 NOISE SPECTRUM 50 40 > a 30 uu wa 9 20 10 0 . VOUT 01 1 10 100 1000 NOTE: dByv = 20 LOG 1pV FREQUENCY (kHz START-UP FROM SHUTDOWN ov E Vout 1idiv H VEHON f 2Vidiv ov 500us/div Vin =3.6, Vout = -2V, lour=4maA LOAC-TRANSIENT RESPCNSE LINE-TRANSIENT RESPONSE Vin =3.6, Vout = -2V Vout 10m Vidiv Vout 20m Vidiv 3.3V VIN .01mA 27M I ama OT Sms/div Smsidiv Vout =-2V, lout=4ma, AC COUPLED MA AXLMMLow-Noise, Regulated, -2V GaAsFET Bias Pin Description PIN waxeaa MAXB43 NAME FUNCTION MAX844 1 1 Ci+ Pasitive Terminal for C1 2 2 C1- Negative Terminal for C1 3 3 NEGOUT Negative Output Voltage (unregulated) 4 4 SHDN Active-Low, TTL Logic-Level Shutdown Input 5 _ FB Dual Made 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). _ 5 CONT Control Voltage Input. To set Vout, connect a resistor divider between OLT and a positive control voltage between OV and 10V (Figure 2c). 6 6 OUT Regulated Negative Output Voltage 7 ? GND Ground 8 8 IN Positive Power-Supply Input Dual Mode is a trademark of Maxim Integrated Products. VVSXVW/EVEXVW/OPEXVW Cte IN lt CHAR te Cte IN MAXIAA To , waxes | LC Tt uaa te . | Cc MAXIA Tc NEGOUT CUT A MAX843 = LL on | MAXG44 NEGOUT l N T + + a 7 ~ + [ N SHDN } FB oOo CONNECT TO SHDN GND TO SET Vout =-2 - + -O.5V FEF | GND GND Figure ta. MAX840 Block Diagram Figure 1b. MAX843/MAX844 Block Diagram MA AXLIAM 7MAX840/MAX843/MAX8 44 Low-Noise, Regulated, -2V GaAsFET Bias 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 (VIN) 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 VOUT. In addition, the linear regu- lators 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). VIN must be 0.6V above the absolute value of VouT to allow proper regulation. The output voltage is calculat- ed from the formula below. Choose R2 to be between 100k and 400kQ9. VOUT = (-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 (VCTRL) (Figure 2c). VOUT = -VCTAL (Re / R1) Shutdown Mode The MAX840/MAX843/MAX844 feature a shutdown mode that reduces the supply current to 1 WA max over temperature (200UA 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 (VIN - |VOUT)). The overall dropout voltage is a function of the charge pumps 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 Ce2s ESR. Therefore, minimizing the ESR of the charge-pump capacitors minimizes the dropout voltage. The output resistance of the entire circuit is approxi- mately: Rout = Ro + 4 x ESRai + ESRc4 + 1/ (is x C1) + Rilinear regulator) where [Ro + Rilinear regulator]. the effective resistance of the internal switches and the resistance across the linear regulator, is approximately 719 at VIN = 2.5V, 48 at VIN = 5V, and 400 at VIN = 10V. C1, C2, and C3 should be 1uF capacitors with less than 0.82 ESR. C4 should be a 10UF capacitor with less than 0.20 ESR. Smaller capacitor values can be used (C1 = C2 = C3 = 0.22uF, C4 = 4.7uF) 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 pumps switching action) cause ground currents in the probes 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 probes tip cover and touch the ground ring on the probe directly to C4s 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 ncise and ripple measurement. MA AXLANLow-Noise, Regulated, -2V GaAsFET Bias Vin ! 8 + 3 1 cit ers 2 eT L 4 OWCFF IN Ci+ MA AXLAA MAX640 Ci- NEGOUT SHDN Liu Vout = -2 g (Vag of GaAsFET) Vin 8 + 03 rd NEGOUT 4] __ CN/OFF ]_ SHDN Ci+ C1- IN MAXIMA MAX40 OUT Vout = (-0.5V)(14+ = grout =( Wy(14+ ) Liu R2 Ri TF {OuF Figure 2a. MAX&840 Standard Application Circuit Figure 2b. MAX840 Adjustable Configuration VIN 3 + 1 cal Ci+ 1LF. Tl MA AXLAA IN G3 Tt 1uF Vout = -0.5 to-9.4 @ 4mA MAX843 (OUT 3 MAX844 et I NEGOUT aT = 4) CN/CFE W] SHDN CONT ND 7 7 Vern (0TO 10) VIN , 1+ cit 02 LET 2 ce o22uF ST 4 ONCFF IN Cit+ JA AXISVI MAX840 C1. CUT NEGOUT SHDN FB C3 LP oz Vout = -2 (Vagof GaAsFED Figure 2c. MAX843/MAX844 Standard Application Circuit MA AXLIAM Figure 2d. MAX840 Application Circuit Using Smaller Capaciiors VVSXVW/EVEXVW/OPEXVWMAX840/MAX843/MAX8 44 Low-Noise, Regulated, -2V GaAsFET Bias Chip Topography in A Ci+ GND GND ct. 0.145! (3.683mm) NEGOUT NEGOUT SHDN FB (CONT) 0.085" > (2.159mm) ( ) ARE FOR MAX843/MAx844 TRANSISTOR COUNT: 148 SUBSTRATE CONNECTED TO IN 10 MA AXLAN