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19-2659; Rev 0; 10/02
KIT ATION EVALU ILABLE AVA
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
General Description Features
o Step-Down Converter Dynamically Adjustable Output Voltage from 0.75V to 3.4V (MAX1958) Dynamically Adjustable Output Voltage from 1V to 3.6V (MAX1959) 800mA Guaranteed Output Current 130mV IC Dropout at 600mA Load Low Quiescent Current 190A (typ) in Skip Mode (MAX1958) 3mA (typ) in PWM Mode 0.1A (typ) in Shutdown Mode 1MHz Fixed-Frequency PWM operation 16% to 100% Duty-Cycle Operation No External Schottky Diode Required Soft-Start o Operational Amplifier 5mA Rail-to-Rail Output Active Discharge in Shutdown 800kHz Gain-Bandwidth Product 120dB Open-Loop Voltage Gain (RL = 100k) o Temperature Sensor Accurate Sensor -11.7mV/C Slope -40C to +125C-Rated Temperature Range o 20-Pin Thin QFN (5mm 5mm), 0.8mm Height (max)
MAX1958/MAX1959
The MAX1958/MAX1959 power amplifier (PA) powermanagement ICs (PMICs) integrate an 800mA, dynamically adjustable step-down converter, a 5mA Rail-toRail(R) operational amplifier (op amp), and a precision temperature sensor to power a heterojunction bipolar transistor (HBT) PA in W-CDMA and N-CDMA cell phones. The high-efficiency, pulse-width modulated (PWM), DCto-DC buck converter is optimized to provide a guaranteed output current of 800mA. The output voltage is dynamically controlled to produce any fixed-output voltage in the range of 0.75V to 3.4V (MAX1958) or 1V to 3.6V (MAX1959), with settling time less than 30s for a full-scale change in voltage and current. The 1MHz PWM switching frequency allows the use of small external components while pulse-skip mode reduces quiescent current to 190A with light loads. The converter utilizes a low on-resistance internal MOSFET switch and synchronous rectifier to maximize efficiency and minimize external component count. The 100% duty-cycle operation allows for an IC dropout voltage of only 130mV (typ) at 600mA load. The micropower op amp is used to provide bias to the HBT PA to maximize efficiency. The amplifier features active discharge in shutdown for full PA bias control. It has 5mA rail-to-rail drive capability, 800kHz gain-bandwidth product, and 120dB open-loop voltage gain. The precision temperature sensor measures temperatures between -40C to +125C, with linear temperature-to-voltage analog output characteristics. The MAX1958/MAX1959 are available in a 20-pin 5mm 5mm thin QFN package (0.8mm max height).
Ordering Information
PART MAX1958ETP MAX1959ETP TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 20 Thin QFN-EP* 20 Thin QFN-EP
*EP = Exposed paddle.
Pin Configuration
SHDN1 VCC
Applications
W-CDMA and N-CDMA Cellular Phones Wireless PDAs and Modems
TOP VIEW
20
19
18
17
AOUT SHDN2 AGND TOUT REF
1 2 3 4 5 10 6 7 8 9
16 15 14
INP
IN+
IN-
PWM INP IN LX PGND
MAX1958/ MAX1959
13 12 11
SHDN3
AGND
COMP
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
THIN QFN 5mm x 5mm
________________________________________________________________ Maxim Integrated Products
OUT
ADJ
Typical Operating Circuit and Functional Diagram appear at end of data sheet.
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
ABSOLUTE MAXIMUM RATINGS
IN, INP, OUT, ADJ, SHDN1, SHDN2, SHDN3, PWM, VCC to PGND ...................................-0.3V to +6V AGND to PGND .....................................................-0.3V to +0.3V COMP, REF to AGND ....................................-0.3 to (VIN + 0.3V) IN+, IN-, AOUT, TOUT to AGND ................-0.3 to (VVCC + 0.3V) LX Current (Note 1).............................................................1.6A Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70C) 20-Pin Thin QFN 5mm x 5mm (derate 20.8mW/C above +70C) .............................1670mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: LX has internal clamp diodes to PGND and INP. Applications that forward bias these diodes should take care not to exceed the IC's package power dissipation limits.
Stresses beyond those listed under "Absolute 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.
ELECTRICAL CHARACTERISTICS (STEP-DOWN CONVERTER)
(VINP = VIN = VVCC = V SHDN1 = 3.6V, VPWM = VPGND = VAGND = V SHDN2 = V SHDN3 = 0, VADJ = 1.25V, COMP = IN- = IN+ = AOUT = TOUT = unconnected, CREF = 0.1F, TA = 0C to +85C, VOUT for MAX1958 = 2.2V, VOUT for MAX1959 = 1.7V, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Supply Voltage Range Undervoltage Lockout Threshold Quiescent Current Rising or falling, hysteresis is 1% MAX1958, PWM = AGND MAX1959, PWM = AGND VPWM = VIN Quiescent Current in Dropout Shutdown Supply Current ERROR AMPLIFIER OUT Voltage Accuracy (MAX1958) VADJ = 1.932V, ILOAD = 0 to 600mA, VPWM = VIN = 3.8V VADJ = 0.426V, ILOAD = 0 to 30mA, VPWM = 0 VADJ = 0.426V, ILOAD = 0 to 30mA, VPWM = VIN = 4.2V OUT Voltage Accuracy (MAX1959) OUT Input Current (MAX1958) OUT Input Current (MAX1959) ADJ Input Current (MAX1958) ADJ Input Current (MAX1959) Positive COMP Output Current (MAX1958) Positive COMP Output Current (MAX1959) VADJ = 2.2V, ILOAD = 0 to 600mA, VPWM = VIN = 4V VADJ = 0.9V, ILOAD = 0 to 30mA, VPWM = 0 VADJ = 0.9V, ILOAD = 0 to 30mA, VPWM = VIN = 4.2V VOUT = 0.75V VOUT = 3.4V VOUT = 1V VOUT = 3.6V VADJ = 0.426V to 1.932V VADJ = 0.9V to 2.2V VADJ = 1V, VOUT = 1.5V, VCOMP = 1.25V VADJ = 1V, VOUT = 1V, VCOMP = 1.25V 3.38 0.739 0.739 3.58 0.985 0.985 2 11 2.5 10 -150 -150 -27 -27 3.40 0.750 0.750 3.60 1.00 1.00 4 17 4.0 16 +1 +1 -14 -14 3.42 0.761 0.761 3.62 1.015 1.015 6 25 6.5 23 +150 +150 -7 -7 A A nA nA A A V V MAX1958 MAX1959 V SHDN1 = 0 CONDITIONS MIN 2.6 2.20 2.35 190 280 3 295 330 0.1 550 600 6 TYP MAX 5.5 2.55 300 450 UNITS V V A mA A A
2
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
ELECTRICAL CHARACTERISTICS (STEP-DOWN CONVERTER) (continued)
(VINP = VIN = VVCC = V SHDN1 = 3.6V, VPWM = VPGND = VAGND = V SHDN2 = V SHDN3 = 0, VADJ = 1.25V, COMP = IN- = IN+ = AOUT = TOUT = unconnected, CREF = 0.1F, TA = 0C to +85C, VOUT for MAX1958 = 2.2V, VOUT for MAX1959 = 1.7V, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Negative COMP Output Current (MAX1958) Negative COMP Output Current (MAX1959) REFERENCE REF Output Voltage REF Load Regulation Undervoltage Lockout Threshold Supply Rejection CONTROLLER P-Channel On-Resistance N-Channel On-Resistance Current-Sense Transresistance P-Channel Current-Limit Threshold P-Channel Pulse-Skipping Current Threshold N-Channel Current-Limit Threshold N-Channel Zero-Crossing Comparator LX Leakage Current LX RMS Current Maximum Duty Cycle Minimum Duty Cycle Oscillator Frequency Thermal-Shutdown Threshold LOGIC INPUTS (PWM, SHDN1) Logic Input High Logic Input Low Logic Input Current 2.6 V < VIN < 5.5 V 2.6 V < VIN < 5.5 V VIN = 5.5V 0.1 1.6 0.6 1 V V A Hysteresis = +15C VPWM = 0 VPWM = VIN = 4.2V 0.85 16 1.00 160 1.15 VPWM = 0 VPWM = VIN VPWM = 0 VIN = 5.5V (Note 1) 100 0 -20.0 1.1 0.12 ILX = 180mA, VIN = 3.6V ILX = 180mA, VIN = 2.6V ILX = 180mA, VIN = 3.6V ILX = 180mA, VIN = 2.6V 0.21 0.25 0.18 0.21 0.5 1.37 0.15 -0.5 20 +0.1 +20.0 1.0 1.6 0.17 0.40 0.5 0.30 0.35 V/A A A A mA A A % % MHz C 10A < IREF < 100A Rising or falling, 1% hysteresis 2.6V < VIN < 5.5V 0.85 1.225 1.250 2.50 1.00 0.07 1.275 6.25 1.10 1.7 V mV V mV/V CONDITIONS VADJ = 1V, VOUT = 2V, VCOMP = 1.25V VADJ = 1V, VOUT = 1.4V, VCOMP = 1.25V MIN 7 7 TYP 14 14 MAX 27 27 UNITS A A
MAX1958/MAX1959
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
ELECTRICAL CHARACTERISTICS (OP AMP)
(VINP = VIN = VVCC = V SHDN2 = 2.7V, V AOUT = VVCC/2, RL = connected from AOUT to VVCC/2, VPGND = VAGND = V SHDN1 = V SHDN3 = VPWM = VADJ = 0, OUT = LX = TOUT = REF = COMP = unconnected, VCM = 0, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Supply Voltage Range VVCC = 2.6V Supply Current Input Offset Voltage Input Bias Current Input Offset Current Input Resistance Input Common-Mode Voltage Range, VCM Common-Mode Rejection Ratio, CMRR Power-Supply Rejection Ratio, PSRR VAGND - 0.1V VCM VVCC + 0.1V 2.6V < VVCC < 5.5V VAGND + 0.05V VAOUT VVCC - 0.05V VAGND + 0.20V VAOUT VVCC - 0.20V VVCC -VVOH VVOL- VAGND Sourcing, VVCC = 5V Sinking, VVCC = 5V 2.6V < VVCC < 5.5V 2.6V < VVCC < 5.5V 0 < V SHDN2 < VVCC 0.7 x VVCC 0.5 1 70 20 0.4 f = 10kHz f = 10kHz AVCL = 1V/V (Note 2) 3 4 52 0.1 470 120 RL = 100k RL = 2k RL = 100k RL = 2k RL = 100k RL = 2k 85 VVCC = 5V V SHDN2 = 0, VVCC = 5.5V VAGND - 0.1V VCM VVCC + 0.1V VAGND - 0.1V VCM VVCC + 0.1V VAGND - 0.1V VCM VVCC + 0.1V VIN- - VIN+ 10mV -0.1 60 70 80 90 120 dB 110 1 35 1 30 11 30 0.3 x VVCC 90 90 mV mV mA V V nA MHz Degrees dB V/s nV/Hz pA/Hz pF s s CONDITIONS MIN 2.6 320 375 0.1 0.4 10 1 4 VVCC + 0.1 TYP MAX 5.5 800 900 2.0 3.0 100 10 mV nA nA M V dB dB A UNITS V
Large-Signal Voltage Gain, AVOL
Output Voltage Swing High, VOH Output Voltage Swing Low, VOL Output Short-Circuit Current SHDN2 Logic Low SHDN2 Logic High SHDN2 Input Current Gain Bandwidth Product, GBW Phase Margin, M Gain Margin, GM Slew Rate, SR Input Voltage Noise Density Input Current Noise Density Capacitive-Load Stability Shutdown Delay Time Enable Delay Time
4
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
ELECTRICAL CHARACTERISTICS (OP AMP) (continued)
(VINP = VIN = VVCC = V SHDN2 = 2.7V, V AOUT = VVCC/2, RL = connected from AOUT to VVCC/2, VPGND = VAGND = V SHDN1 = V SHDN3 = VPWM = VADJ = 0, OUT = LX = TOUT = REF = COMP = unconnected, VCM = 0, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Power-On Time Input Capacitance Total Harmonic Distortion Settling Time to 0.01% Active Discharge Output Impedance f =10kHz, VAOUT = 2VP-P, AVCL =1, VVCC = 5V, RAOUT = 100k to VVCC/2 VAOUT = 4V step, VVCC = 5V, AVCL = 1 V SHDN2 = 0, IAOUT = 1mA CONDITIONS MIN TYP 4 2.5 0.01 10 100 500 MAX UNITS s pF % s
MAX1958/MAX1959
ELECTRICAL CHARACTERISTICS (TEMPERATURE SENSOR)
(VINP = VIN = VVCC = V SHDN3 = 2.7V, VAGND = VPGND = VPWM = V SHDN1 = V SHDN2 = VADJ = 0, IN- = IN+ = AOUT = COMP = LX = OUT = REF = unconnected, CTOUT = 0.01F (min), TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Temperature Sensor Error (Note 3) Output Voltage at +27C Sensor Gain (Note 4) Nonlinearity Load Regulation Line Regulation Quiescent Current SHDN3 Logic High Voltage SHDN3 Logic Low Voltage SHDN3 Current 0 ILOAD 15A 2.6V VVCC 5.5V 2.6V VVCC 5.5V 2.6V < VVCC < 5.5V 2.6V < VVCC < 5.5V VVCC = 5.5V 0.1 1.6 0.6 1.0 10 TA = 0C (Note 2) TA = +25C (Note 2) TA = +85C CONDITIONS MIN -3.5 -2.5 -2.5 1.56 -11.64 0.4 -5 -2.3 18 TYP MAX +3.5 +2.5 +2.5 V mV/C % mV mV/V A V V A C UNITS
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
ELECTRICAL CHARACTERISTICS (STEP-DOWN CONVERTER)
(VINP = VIN = VVCC = V SHDN1 = 3.6V, VPWM = VPGND = VAGND = V SHDN2 = V SHDN3 = 0, VADJ = 1.25V, COMP = IN- = IN+ = AOUT = TOUT = unconnected, CREF = 0.1F, TA = -40C to +85C, VOUT for MAX1958 = 2.2V, VOUT for MAX1959 = 1.7V, unless otherwise noted.) (Note 5)
PARAMETER Supply Voltage Range Undervoltage Lockout Threshold Quiescent Current Quiescent Current in Dropout Shutdown Supply Current ERROR AMPLIFIER OUT Voltage Accuracy (MAX1958) VADJ = 1.932V, ILOAD = 0 to 600mA, VPWM = VIN = 3.8V VADJ = 0.426V, ILOAD = 0 to 30mA, VPWM = 0 VADJ = 0.426V, ILOAD = 0 to 30mA, VPWM = VIN = 4.2V OUT Voltage Accuracy (MAX1959) OUT Input Current (MAX1958) OUT Input Current (MAX1959) ADJ Input Current (MAX1958) ADJ Input Current (MAX1959) Positive COMP Output Current (MAX1958) Positive COMP Output Current (MAX1959) Negative COMP Output Current (MAX1958) Negative COMP Output Current (MAX1959) REFERENCE REF Output Voltage REF Load Regulation Undervoltage Lockout Threshold Supply Rejection 10A < IREF < 100A Rising or falling, 1% hysteresis 2.6V < VIN < 5.5V 0.85 1.226 1.275 6.25 1.10 1.7 V mV V mV/V VADJ = 2.2V, ILOAD = 0 to 600mA, VPWM = VIN = 4V VADJ = 0.9V, ILOAD = 0 to 30mA, VPWM = 0 VADJ = 0.9V, ILOAD = 0 to 30mA, VPWM = VIN = 4.2V VOUT = 0.75V VOUT = 3.4V VOUT = 1V VOUT = 3.6V VADJ = 0.426V to 1.932V VADJ = 0.9V to 2.2V VADJ = 1V, VOUT = 1.5V, VCOMP = 1.25V VADJ = 1V, VOUT =1V, VCOMP = 1.25V VADJ = 1V, VOUT = 2V, VCOMP = 1.25V VADJ = 1V, VOUT = 1.4V, VCOMP =1.25V 3.36 0.739 0.739 3.570 0.98 0.98 2 11 2.5 10.0 -150 -150 -27.0 -27.0 6.5 6.5 3.44 0.761 0.761 3.625 1.02 1.02 6 25 6.5 23.0 +150 +150 -6.5 -6.5 27.0 27.0 A A nA nA A A A A V V Rising or falling, hysteresis is 1% PWM = AGND (MAX1958) PWM = AGND (MAX1959) MAX1958 MAX1959 V SHDN1 = 0 CONDITIONS MIN 2.6 2.20 TYP MAX 5.5 2.55 300 450 550 600 6 UNITS V V A A A
6
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
ELECTRICAL CHARACTERISTICS (STEP-DOWN CONVERTER) (continued)
(VINP = VIN = VVCC = V SHDN1 = 3.6V, VPWM = VPGND = VAGND = V SHDN2 = V SHDN3 = 0, VADJ = 1.25V, COMP = IN- = IN+ = AOUT = TOUT = unconnected, CREF = 0.1F, TA = -40C to +85C, VOUT for MAX1958 = 2.2V, VOUT for MAX1959 = 1.7V, unless otherwise noted.) (Note 5)
PARAMETER CONTROLLER P-Channel On-Resistance N-Channel On-Resistance P-Channel Current-Limit Threshold P-Channel Pulse-Skipping Current Threshold LX Leakage Current LX RMS Current Maximum Duty Cycle Minimum Duty Cycle Oscillator Frequency LOGIC INPUTS (PWM, SHDN1) Logic Input High Logic Input Low Logic Input Current 2.6V < VIN < 5.5V 2.6V < VIN < 5.5V VIN = 5.5V 1.6 0.6 1 V V A VPWM = 0 0.8 VPWM = 0 VIN = 5.5V (Note 1) 100 0 1.2 ILX = 180mA, VIN = 3.6V ILX = 180mA, VIN = 2.6V ILX = 180mA, VIN = 3.6V ILX = 180mA, VIN = 2.6V 1.1 0.11 -20 0.4 0.5 0.3 0.35 1.6 0.18 +20 1.0 A A A A % % MHz CONDITIONS MIN TYP MAX UNITS
MAX1958/MAX1959
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
ELECTRICAL CHARACTERISTICS (OP AMP)
(VINP = VIN = VVCC = V SHDN2 = 2.7V, VAOUT = VVCC/2, RL = connected from AOUT to VVCC/2, VPGND = VAGND = V SHDN1 = V SHDN3 = VPWM = VADJ = 0, OUT = LX = TOUT = REF = COMP = unconnected, VCM = 0, TA = -40C to +85C, unless otherwise noted.) (Note 5)
PARAMETER Supply Voltage Range VVCC = 2.6V Supply Current Input Offset Voltage Input Bias Current Input Offset Current Input Common-Mode Voltage Range, VCM Common-Mode Rejection Ratio, CMRR Power-Supply Rejection Ratio, PSRR Large-Signal Voltage Gain, AVOL Output Voltage Swing High, VOH Output Voltage Swing Low, VOL SHDN2 Logic Low SHDN2 Logic High SHDN2 Input Current Capacitive-Load Stability Active Discharge Output Impedance VAGND - 0.1V VCM VVCC + 0.1V 2.6V < VVCC < 5.5V VAGND + 0.20V VOUT VVCC - 0.20V, RL = 2k VVCC - VVOH, RL = 2k VVOL - VAGND, RL = 2k 2.6V < VVCC < 5.5V 2.6V < VVCC < 5.5V 0 < V SHDN2 < VVCC AVCL = 1V/V (Note 2) V SHDN2 = 0, IAOUT = 1mA 0.7 x VVCC 120 470 500 VVCC = 5V V SHDN2 = 0, VVCC = 5.5V VAGND - 0.1V VCM VVCC + 0.1V VAGND - 0.1V VCM VVCC + 0.1V VAGND - 0.1V VCM VVCC + 0.1V VAGND - 0.1V 60 70 85 90 90 0.3 x VVCC mV V V nA pF CONDITIONS MIN 2.6 TYP MAX 5.5 800 900 2.0 3.0 100 10 VVCC + 0.1V mV nA nA V dB dB dB UNITS V A
8
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
ELECTRICAL CHARACTERISTICS (TEMPERATURE SENSOR)
(VINP = VIN = VVCC = V SHDN3 = 2.7V, VAGND = VPGND = VPWM = V SHDN1 = V SHDN2 = VADJ = 0, IN- = IN+ = AOUT = COMP = LX = OUT = REF = unconnected, CTOUT = 0.01F (min), TA = -40C to +85C, unless otherwise noted.) (Note 5)
PARAMETER Temperature Sensor Error (Note 3) Load Regulation Line Regulation Quiescent Current SHDN3 Logic High Voltage SHDN3 Logic Low Voltage SHDN3 Current TA = -40C (Note 2) TA = +25C (Note 2) TA = +85C 0 ILOAD 15A 2.6V VVCC 5.5V 2.6V VVCC 5.5V 2.6V < VVCC < 5.5V 2.6V < VVCC < 5.5V VVCC = 5.5V 1.6 0.6 1 CONDITIONS MIN -7 -2.5 -2.5 TYP MAX +4 +2.5 +2.5 -5 -2.3 18 mV mV/V A V V A C UNITS
MAX1958/MAX1959
Note 2: Note 3: Note 4: Note 5:
Guaranteed by design, not production tested. VTOUT = (-4 x 10-6) (T2C) - (1.13 10-2) (TC) + 1.8708V. Linearized gain = VTOUT = -11.64mV/C + 1.8778V. Specifications to -40C are guaranteed by design and not subject to production test.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
MAX1958/59 toc01
EFFICIENCY vs. LOAD CURRENT
SKIP MODE VIN = 3.6V
MAX1958/59 toc02
EFFICIENCY vs. LOAD CURRENT
MAX1958/59 toc03
100 95 90 EFFICIENCY (%) 85 80 75 70 65 VOUT = 3.4V 60 10 100 LOAD CURRENT (mA) PWM VIN = 4.2V SKIP MODE VIN = 3.6V SKIP MODE PWM V = 4.2V VIN = 3.6V IN
100 90 80 EFFICIENCY (%) 70 60 50 40 30 PWM VIN = 4.2V VOUT = 1.5V SKIP MODE VIN = 4.2V PWM VIN = 3.6V
100 90 EFFICIENCY (%) 80 70 60 50 40 SKIP MODE VIN = 3.6V SKIP MODE VIN = 4.2V PWM VIN = 3.6V PWM VIN = 4.2V VOUT = 2.5V 10 100 LOAD CURRENT (mA)
1000
10
100 LOAD CURRENT (mA)
1000
1000
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
DROPOUT VOLTAGE ACROSS P-CHANNEL MOSFET vs. LOAD CURRENT
MAX1958/59 toc04
SUPPLY CURRENT vs. INPUT VOLTAGE SKIP MODE
MAX1958/59 toc05
SUPPLY CURRENT vs. INPUT VOLTAGE FORCED PWM
VOUT = 0.75V PWM = IN MAX1958
MAX1958/59 toc06
300 250 DROPOUT VOLTAGE (mV) 200 150 100 50 0 0
250 230 210 SUPPLY CURRENT (A) 190 170 150 130 110 90 70 50 PWM = AGND VOUT = 1.5V MAX1958
6 5 SUPPLY CURRENT (mA) 4 3 2 1 0
100 200 300 400 500 600 700 800 LOAD CURRENT (mA)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
HEAVY-LOAD SWITCHING WAVEFORMS (ILOAD = 600mA)
MAX1958/59 toc07
MEDIUM-LOAD SWITCHING WAVEFORMS (ILOAD = 300mA)
MAX1958/59 toc08
LX
5V/div
LX
5V/div
ILX
100mA/div
ILX
100mA/div
VOUT AC-COUPLED
10mV/div
VOUT AC-COUPLED
10mV/div
400ns/div
400ns/div
LIGHT-LOAD SWITCHING WAVEFORMS (PWM = IN, ILOAD = 30mA)
MAX1958/59 toc09
LIGHT-LOAD SWITCHING WAVEFORMS (PWM = AGND, ILOAD = 30mA)
MAX1958/59 toc10
LX
5V/div
LX
5V/div
ILX
100mA/div
ILX
100mA/div
VOUT AC-COUPLED
10mV/div
VOUT AC-COUPLED
10mV/div
400ns/div
400ms/div
10
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
ENTERING AND EXITING SHUTDOWN
MAX1958/59 toc11
MAX1958 ADJ TRANSIENT
MAX1958/59 toc12
VSHDN
5V/div
3.4V VOUT 0.75V
IIN
50mA/div
1.932V VADJ
VOUT
1V/div
0.426V
400s/div
10s/div
LOAD TRANSIENT PWM = AGND
MAX1958/59 toc13
LOAD TRANSIENT PWM = IN
MAX1958/59 toc14
VOUT AC-COUPLED
100mV/div
VOUT AC-COUPLED
100mV/div
400mA IOUT COUT = 10F 100s/div 100s/div IOUT COUT = 10F
400mA
30mA
30mA
LOAD TRANSIENT
MAX1958/59 toc15
OP AMP SUPPLY CURRENT vs. INPUT VOLTAGE
MAX1958/59 toc16
500 450 TA = +125C
VOUT AC-COUPLED
10mV/div ICC (A)
400 350 300 250 200
TA = +85C TA = +25C
VIN
4V 3V
TA = -40C
1ms/div
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
VCC (V)
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
OP AMP INPUT OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE
MAX1958/59 toc17
OP AMP INPUT OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE
VVCC = 5.5V 500 TA = +85C 400 VOS (V) TA = +125C
MAX1958/59 toc18
600 VVCC = 2.5V 500 TA = +85C 400 VOS (V) 300 200 100 0 0 0.5 1.0 1.5 2.0 TA = +25C TA = +125C
600
300 200
TA = +25C
TA = -40C
TA = -40C 100 0 2.5 0 1 2 3 VCM (V) 4 5 6
VCM (V)
OP AMP INPUT BIAS CURRENT vs. COMMON-MODE VOLTAGE
MAX1958/59 toc19
OP AMP OUTPUT SOURCE CURRENT vs. OUTPUT VOLTAGE
VVCC = 5.5V
MAX1958/59 toc20
20 VVCC = 5.5V 15 10 IBIAS (nA) 5 TA = +85C 0 -5 -10 TA = +25C -15 0 1 2 3 VCM (V) 4 5 6 TA = +125C TA = -40C
14 12 10 ISOURCE (mA) 8 6 4 2 0 VVCC = 2.5V
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VAOUT (V)
OP AMP OUTPUT SINK CURRENT vs. OUTPUT VOLTAGE
MAX1958/59 toc21
OP AMP POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
-10 -20 -30 PSRR (dB)
MAX1958/59 toc22
50 45 40 35 ISINK (mA) 30 25 20 15 10 5 0 VVCC = 2.5V VVCC = 5.5V
0
-40 -50 -60 -70 -80 -90 -100
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VAOUT (V)
0.1
1
10
100
1k
10k
FREQUENCY (Hz)
12
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
OP AMP GAIN AND PHASE vs. FREQUENCY
80 2k || 470pF 60 40 GAIN (dB) 20 0 -20 -40 0.1 1 10 100 1k 10k FREQUENCY (Hz) GAIN -150 -210 -270 4s/div OUT PHASE 30 20mV/div -30 -90 PHASE (DEGREES) IN
MAX1958/59 toc23
OP AMP SMALL-SIGNAL TRANSIENT RESPONSE (NONINVERTING)
90
MAX1958/59 toc24
20mV/div
OP AMP SMALL-SIGNAL TRANSIENT RESPONSE (INVERTING)
MAX1958/59 toc25
OP AMP LARGE-SIGNAL TRANSIENT RESPONSE (NONINVERTING)
MAX1958/59 toc26
IN 20mV/div IN
VVCC = 5V 2V/div
20mV/div 2V/div OUT OUT
4s/div
40s/div
OP AMP LARGE-SIGNAL TRANSIENT RESPONSE (INVERTING)
MAX1958/59 toc27
TEMPERATURE SENSOR TOUT VOLTAGE vs. TEMPERATURE
2.25 2V/div 1.75 TOUT (V)
MAX1958/59 toc28
VVCC = 5V IN
1.25
2V/div OUT
0.75
0.25 40s/div -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
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13
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
TEMPERATURE SENSOR ERROR vs. TEMPERATURE
MAX1958/59 toc29
TEMPERATURE SENSOR SUPPLY CURRENT vs. INPUT VOLTAGE
18 16 SUPPLY CURRENT (A) 14 12 10 8 6 4 2
MAX1958/59 toc30
1.5 1.0 0.5 ERROR (C) 0 -0.5 -1.0 -1.5 -40 -25 -10 5 20 35 50 65 80
20
0 95 0 1 2 3 4 5 6 TEMPERATURE (C) INPUT VOLTAGE (V)
Pin Description
PIN 1 2 3 4 5 6 7 NAME AOUT SHDN2 AGND TOUT REF AGND COMP FUNCTION Op-Amp Output. AOUT discharges to AGND during shutdown. Shutdown Control Input for the Op Amp. Drive to AGND to shut down the op amp. Connect to VCC or drive high for normal operation. Analog Ground. Ground for op amp, temperature sensor, and the precision circuits in the DC-to-DC regulator. Connect to pin 6. Analog Voltage Output Representing the Die Temperature. Bypass to AGND with a 0.01F capacitor. Internal 1.25V Reference. Bypass to AGND with a 0.1F capacitor. Analog Ground. Connect to pin 3. Compensation. Typically, connect a 22pF capacitor from COMP to AGND and a 9.1k resistor and 560pF capacitor in series from COMP to AGND to stabilize the regulator (see the Compensation and Stability section). External Reference Input. Connect ADJ to the output of a D/A converter for dynamic adjustment of the regulator's output voltage. OUT regulates at (1.76 x VADJ) for the MAX1958 and (2 x VADJ - 0.8V) for the MAX1959. Shutdown Control Input for the Temperature Sensor. Drive to AGND to shut down the temperature sensor. Connect to VCC or drive high for normal operation. Output Voltage Feedback. Connect OUT directly to the output. OUT is high impedance during shutdown. Power Ground for the DC-to-DC Converter Inductor Connection to the Internal Power MOSFETs Low-Current Supply Voltage Input. Connect to INP at the IC.
8
ADJ
9 10 11 12 13
SHDN3 OUT PGND LX IN
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
Pin Description (continued)
PIN 14 15 16 17 18 19 20 -- NAME INP PWM INP SHDN1 VCC IN+ INExposed Paddle FUNCTION High-Current Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass to PGND with a lowESR 4.7F capacitor. Connect to pin 16. PWM/Skip-Mode Input. Drive low to use PWM mode at medium and heavy loads and pulse-skipping mode at light loads. Drive high to force PWM mode at all loads. Supply Voltage Input. Connect to pin 14. Shutdown Control Input for the Converter. Drive to AGND to shut down the converter. Connect to IN or drive high for normal operation. Supply Input for Op Amp and Temperature-Sensor Circuitry. Connect to INP through an RC filter. Noninverting Input for the Op Amp Inverting Input for the Op Amp Connect to Large AGND Plane. Internally connected to AGND.
MAX1958/MAX1959
Detailed Description
PWM Step-Down DC-to-DC Converter
The PWM step-down DC-to-DC converter is optimized for low-voltage, battery-powered applications where high efficiency and small size are priorities. It is specifically intended to power the linear HBT PA in N-CDMA/ W-CDMA handsets. An analog control signal (ADJ) dynamically adjusts the converter's output voltage from 0.75V to 3.4V (MAX1958) or 1V to 3.6V (MAX1959) with a settling time of approximately 30s. The MAX1958/ MAX1959 operate at a high 1MHz switching frequency that reduces external component size. The IC contains an internal synchronous rectifier that increases efficiency and eliminates the need for an external Schottky diode. The normal operating mode uses constant-frequency PWM switching at medium and heavy loads and pulse skips at light loads to reduce supply current and extend battery life. An additional forced-PWM mode switches at a constant frequency, regardless of load, to provide a well-controlled noise spectrum for easier filtering in noise-sensitive applications. The MAX1958/MAX1959 are capable of 100% duty-cycle operation to increase efficiency in dropout. Battery life is maximized with a 0.1A (typ) logic-controlled shutdown mode. Normal-Mode Operation Connecting PWM to GND enables PWM/pulse-skipping operation. This proprietary control scheme uses pulseskipping mode at light loads to improve efficiency and reduce quiescent current to 190A for the MAX1958 and 280A for the MAX1959. With PWM/pulse-skipping mode enabled, the MAX1958/MAX1959 initiate pulse-
skipping operation when the peak inductor current drops below 150mA. During pulse-skipping operation, switching occurs only as necessary to service the load, thereby reducing the switching frequency and associated losses in the internal switch, synchronous rectifier, and inductor. During pulse-skipping operation, a switching cycle initiates when the error amplifier senses that the output voltage has dropped below the regulation point. If the output voltage is low, the high-side P-channel MOSFET switch turns on and conducts current through the inductor to the output filter capacitor and load. The PMOS switch turns off when the output voltage rises above the regulation point and the error amplifier is satisfied. The MAX1958/MAX1959 then wait until the error amplifier senses an out-of-regulation output voltage to start the cycle again. At peak inductor currents above 150mA, the MAX1958/MAX1959 operate in PWM mode. During PWM operation, the output voltage is regulated by switching at a constant frequency and then modulating the power transferred to the load using the error comparator. The error amplifier output, the main switch current-sense signal, and the slope compensation ramp are all summed at the PWM comparator (see the Functional Diagram). The comparator modulates the output power by adjusting the peak inductor current during the first half of each cycle based on the output error voltage. The MAX1958/MAX1959 have relatively low AC loop gain coupled with a high-gain integrator to enable the use of a small, low-valued output filter capacitor. The resulting load regulation is 1.5% from 0
15
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
to 600mA. Some jitter is normal during the transition from pulse-skipping mode to PWM mode with loads around 75mA. This has no adverse impact on regulation. Forced-PWM Operation To force PWM operation at all loads, connect PWM to IN. Forced-PWM operation is desirable in sensitive RF and data-acquisition applications to ensure that switching-noise harmonics are predictable and can be easily filtered. This is to ensure that the switching noise does not interfere with sensitive IF and data sampling frequencies. A minimum load is not required during forced-PWM operation because the synchronous rectifier passes reverse inductor current as needed to allow constant-frequency operation with no load. ForcedPWM operation has higher quiescent current than pulse-skipping mode (3mA typically compared to 190A) due to continuous switching. 100% Duty-Cycle Operation The maximum on-time can exceed one internal oscillator cycle, which permits operation at 100% duty cycle. As the input voltage drops, the duty cycle increases until the internal P-channel MOSFET stays on continuously. Dropout voltage at 100% duty cycle is the output current multiplied by the sum of the internal PMOS onresistance (typically 0.25) and the inductor resistance. Near dropout, cycles may be skipped, reducing switching frequency. However, voltage ripple remains small because the current ripple is still low. Dropout Dropout occurs when the desired output regulation voltage is higher than the input voltage minus the voltage drops in the circuit. In this situation, the duty cycle is 100%, so the high-side P-channel MOSFET is held on continuously and supplies current to the output up to the current limit. The output voltage in dropout falls to the input voltage minus the voltage drops. The largest voltage drops occur across the inductor and high-side MOSFET. The dropout voltage increases as the load current increases. During dropout, the high-side, P-channel MOSFET turns on and the controller enters a low-current consumption mode. Every 6s (six cycles), the MAX1958/ MAX1959 check to see if the device is in dropout. The IC remains in this mode until it is no longer in dropout. COMP Clamp The MAX1958/MAX1959 compensation network has a 1V to 2.25V error-regulation range. The clamp optimizes transient response by preventing the voltage on COMP from rising too high or falling too low. Undervoltage Lockout (UVLO) The DC-to-DC converter portion of the MAX1958/ MAX1959 is disabled if battery voltage on IN is below the UVLO threshold of 2.35V (typ). LX remains high impedance until the supply voltage exceeds the UVLO threshold. This guarantees the integrity of the output voltage and prevents excessive current during startup and as the battery supply drops in voltage during use. The op amp and temperature sensor are not connected to the UVLO and therefore continue to operate normally. Synchronous Rectification An N-channel synchronous rectifier operates during the second half of each switching cycle (off-time). When the inductor current falls below the N-channel current-comparator threshold or when the PWM reaches the end of the oscillator period, the synchronous rectifier turns off. This prevents reverse current flow from the output to the input in pulse-skipping mode. During PWM operation, small amounts of reverse current flow through the N-channel MOSFET during light loads. This allows regulation with a constant switching frequency and eliminates minimum load requirements for fixed-frequency operation. The N-channel reverse-current comparator threshold is -500mA. The N-channel zero-crossing threshold in pulse-skipping mode is 20mA (see the Forced-PWM Operation and Normal-Mode Operation sections) Shutdown Mode Driving SHDN1 to ground puts the DC-to-DC converter into shutdown mode. In shutdown mode, the reference, control circuitry, internal-switching MOSFET, and synchronous rectifier turn off and the output (LX) becomes high impedance. Input current falls to 0.1A (typ) during shutdown mode. Drive SHDN1 high for normal operation. Thermal Limit The thermal limit is set at approximately +160C and shuts down only the converter. In this state, both main MOSFETs are turned off. Once the IC cools by 15C, the converter operates normally. A continuous overload condition results in a pulsed output. During thermallimit conditions, the op amp and temperature sensor continue to operate. Current-Sense Comparators The IC uses several internal current-sense comparators. In PWM operation, the current-sense amplifier, combined with the PWM comparator, sets the cycle-by-cycle current limit and provides improved load and line response. This allows tighter specification of the inductor-saturation current limit to reduce inductor cost. A second 150mA current-sense comparator monitors the current through
16
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs
the P-channel switch and controls entry into pulse-skipping mode. A third current-sense comparator monitors current through the internal N-channel MOSFET to prevent excessive reverse currents and determines when to turn off the synchronous rectifier. A fourth comparator used at the P-channel MOSFET detects overcurrent. This protects the system, external components, and internal MOSFETs during overload conditions.
MAX1958/MAX1959
Rail-to-Rail Op Amp
The MAX1958/MAX1959 contain a rail-to-rail op amp that can be used to provide bias for the HBT PA. As the power needs of the PA change, the op amp can be used to dynamically change the bias point for the PA in order to optimize efficiency. Rail-to-Rail Input Stage The op amp in the MAX1958/MAX1959 has rail-to-rail input and output stages that are specifically designed for low-voltage, single-supply operation. The input stage consists of composite NPN and PNP differential stages, which operate together to provide a commonmode range extending beyond both supply rails. The crossover region of these two pairs occurs halfway between VCL and AGND. The input offset voltage is typically 400V. The MAX1958/MAX1959 op amp inputs are protected from large differential input voltages by internal 5.3k series resistors and back-to-back triple-diode stacks across the inputs (Figure 1). For differential input voltages much less than 2.1V (three diode drops), input resistance is typically 4M. For differential voltages greater than 2.1V, input resistance is around 10.6k, and the input bias current can be approximated by the following equation: IBIAS = (VDIFF - 2.1V) 10.6k
Figure 1. Input Protection Circuit
VIN+ 2V/div
VAOUT 2V/div
Figure 2. Op-Amp Output Voltage Swing
Rail-to-Rail Output Stage The MAX1958/MAX1959 op amp can drive down to a 2k load and still typically swing within 35mV of the supply rails. Figure 2 shows the output voltage swing of the MAX1958 configured with AV = 1.57V/V and with VVCC at 4.2V.
Temperature Sensor
The MAX1958/MAX1959 analog temperature sensor's output voltage is a linear function of its die temperature. The slope of the output voltage is approximately -11.64mV/C and there is a 1.878V offset at 0C to allow measurement of positive temperatures. The temperature sensor functions from -40C to +125C .The temperature error is less than 2.5C at temperatures from +25C to +85C. Nonlinearity The benefit of silicon analog temperature sensors over thermistors is the linearity over extended temperatures. The nonlinearity of the MAX1958/MAX1959 is typically 0.4% over the 0C to +85C temperature range.
In the region where the differential input voltage increases to about 2.1V, the input resistance decreases exponentially from 4M to 10.6k as the diodes begin to conduct. It follows that the bias current increases with the same curve.
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17
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Transfer Function The temperature-to-voltage transfer function has an approximately linear negative slope and can be described by the following equation: VTOUT = -11.64 mV x T + 1.878V C Compensation and Stability The MAX1958/MAX1959 are externally compensated with a resistor and a capacitor (R C and CC, Typical Application Circuit) in series from COMP to AGND. An additional capacitor (C f ) is required from COMP to AGND. The capacitor, CC, integrates the current from the transimpedance amplifier, averaging output capacitor ripple. This sets the device speed for transient response and allows the use of small ceramic output capacitors because the phase-shifted capacitor ripple does not disturb the current-regulation loop. The resistor, RC, sets the proportional gain of the output error voltage by a factor of gm RC. Increasing this resistor also increases the sensitivity of the control loop to output ripple. The series resistor and capacitor set a compensation zero that defines the system's transient response. The load creates a dynamic pole, shifting in frequency with changes in load. As the load decreases, the pole frequency decreases. System stability requires that the compensation zero must be placed to ensure adequate phase margin (at least 30 at unity gain). The following is a design procedure for the compensation network. Select an appropriate converter bandwidth (fC) to stabilize the system while maximizing transient response. This bandwidth should not exceed 1/10 of the switching frequency. Calculate the compensation capacitor, CC, based on this bandwidth: V 1 1 R2 OUT CC = x x gm x R1+ R2 x 2f IOUT(MAX) RCS C Resistors R1 and R2 are internal to the MAX1958/ MAX1959. For the MAX1958, use R1 = 95k and R2 = 125k as nominal values for calculations. For the MAX1959, use R1 = 125k and R2 = 125k as nominal values for calculations. IOUT(MAX) is the maximum output current, RCS = 0.5V/A, and gm = 250S. Select the closest standard value CC that gives an acceptable bandwidth. Calculate the equivalent load impedance, RL, by: RL = VOUT IOUT(MAX)
T is the die temperature in C. Therefore: T= VTOUT - 1.878V -11.64mV / C
To account for the small amount of curvature in the transfer function, use the equation below to obtain a more accurate temperature reading: VTOUT = (-4 x 10-6 x T 2 ) + (-1.13 x 10-2 x T) + 1.8708V
Applications Information
PWM Step-Down DC-to-DC Converter
Setting the Output Voltage The MAX1958/MAX1959 are optimized for highest system efficiency when applying power to a linear HBT PA in N-CDMA/W-CDMA handsets. The supply voltage to the PA is reduced (from 3.4V to as low as 0.75V for MAX1958) when transmitting at less than full power to greatly conserve supply current and extend battery life. The typical load profile for a W-CDMA PA can be seen in Figure 3. The MAX1958/MAX1959 dramatically reduce battery drain in these applications. The MAX1958 output voltage is dynamically adjustable from 0.75V to 3.4V and MAX1959 output voltage is dynamically adjustable from 1V to 3.6V using the ADJ input. The input voltage cannot be lower than the output voltage. VOUT can be adjusted during operation by driving ADJ with an external DAC. The output voltage for the MAX1958 is determined as: VOUT = 1.76 x VADJ The output voltage for the MAX1959 is determined as: VOUT = 2 x VADJ - 0.8V The MAX1958/MAX1959 output voltage responds to a full-scale change in voltage and current in approximately 30s.
Calculate the compensation resistance (RC) to cancel out the dominant pole created by the output load and the output capacitance: 1 1 = 2 x RL x COUT 2 x RC x CC
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Solving for RC gives: R x COUT RC = L CC Calculate the high-frequency compensation pole to cancel the zero created by the output capacitor's equivalent series resistance (ESR): 1 1 = 2 x RESR x COUT 2 x RC x C f Solving for Cf gives: R x COUT Cf = ESR RC Use the calculated value for Cf or 22pF, whichever is larger. Inductor Selection There are several parameters that must be examined when determining an optimum inductor value. Input voltage, output voltage, load current, switching frequency, and LIR. LIR is the ratio of inductor current ripple to DC load current. A higher LIR value allows for a smaller inductor, but results in higher losses and higher output ripple current. A good compromise between size, efficiency, and cost is an LIR of 30%. Once all the parameters are chosen, the inductor value is determined as follows: L= VOUT x ( VIN - VOUT ) VIN x fS x ILOAD(MAX) x LIR LIR IPEAK = ILOAD(MAX) + xI 2 LOAD(MAX) Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the battery or input power source and reduces switching noise in the IC. The impedance of the input capacitor at the switching frequency should be less than that of the input source so that highfrequency switching currents are not required from the source. The input capacitor must meet the ripple current requirement (IRMS) imposed by the switching currents. Nontantalum chemistries (ceramic, aluminum, or organic) are preferred due to their resistance to power-up surge currents. IRMS is calculated as follows: IRMS = ILOAD x VOUT x (VIN - VOUT ) VIN
Output Capacitor Selection The output capacitor is required to keep the output voltage ripple small and to ensure stability of the regulation control loop. The output capacitor must have low impedance at the switching frequency. An additional constraint on the output capacitor is load transients. If it is desired for the output voltage to swing from 0.75V to 3.4V in 30s, the output capacitor should be approximately 4.7F or less. Ceramic capacitors are recommended. The output ripple is approximately:
1 VRIPPLE = LIR x ILOAD(MAX) x ESR + 2 x fS x COUT
where fS is the switching frequency (1MHz). Choose a standard-value inductor close to the calculated value. The exact inductor value is not critical and can be adjusted in order to make trade-offs between size, cost, and efficiency. Lower inductor values minimize size and cost, but they also increase the output ripple and reduce the efficiency due to higher peak currents. On the other hand, higher inductor values increase efficiency, but eventually resistive losses due to extra turns of wire exceed the benefit gained from lower AC current levels. For any area-restricted applications, find a low-core-loss inductor having the lowest possible DC resistance. Ferrite cores are often the best choice. The inductor's saturation current rating must exceed the expected peak inductor current (IPEAK). Consult the inductor manufacturer for saturation current ratings. Determine IPEAK as:
See the Compensation and Stability section for a discussion of the influence of output capacitance and ESR on regulation control-loop stability.
Rail-to-Rail Op Amp
Shutdown Mode The MAX1958/MAX1959 op amp (Figure 4) features a low-power shutdown mode. When SHDN2 is pulled low, the supply current for the amplifier drops to 0.1A, the amplifier is disabled, and the output is actively discharged to AGND with an internal 100 switch. Pulling SHDN2 high enables the amplifier. Due to the output leakage currents of three-state devices and the small internal pullup current for SHDN2, do not leave SHDN2 unconnected. Floating
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19
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
3.4 3.0 PA SUPPLY VOLTAGE (V)
Power-Supply Bypass The power-supply voltage applied to VCC for the op amp and temperature sensor in the MAX1958/ MAX1959 circuit is filtered from INP. Connect V CC to INP through an RC network (R2 and C7 in Figure 4) to ensure a quiet power supply.
Temperature Sensor
1.0 0.4 0.0 0 30 300 PA SUPPLY CURRENT (mA) 600
The temperature sensor provides information about the MAX1958/MAX1959 die temperature. The voltage at TOUT (VTOUT) is related to die temperature as follows: VTOUT = (-4 x 10-6 x T 2 ) + (-1.13 x 10-2 x T) + 1.8708V For stable operation, bypass TOUT to AGND with at least a 0.01F capacitor. Temperature Sensor Error Due to Die Self-Heating When the 800mA converter and the op amp are both operated at heavy load while the temperature sensor is enabled, the indicated temperature at TOUT deviates several degrees from the actual ambient temperature due to die self-heating effects. At light loads, when die self-heating is low, TOUT tends to be a good approximation of the ambient temperature. At heavier loads, the die self-heating is appreciable; TOUT gives a good approximation of the die temperature, which can be several degrees higher than the ambient temperature. Sensing Circuit Board and Ambient Temperature Temperature sensors like those found in the MAX1958/MAX1959 that sense their own die tempera-
Figure 3. Typical W-CDMA Power Amplifier Load Profile
SHDN2 may result in indeterminate logic levels, and could adversely affect op-amp operation. Driving Capacitive Loads The MAX1958/MAX1959 op amp is unity-gain stable for capacitive loads up to 470pF. Applications that require a greater capacitive drive capability should use an isolation resistor (R ISO ) between the output and the capacitive load (Figure 5). Note that this alternative results in a loss of gain accuracy because RISO forms a voltage-divider with RLOAD.
Table 1. Recommended Inductors
MANUFACTURER 800mA Application Sumida Toko 700mA Application Sumida Toko 400mA Application Murata Sumida 300mA Application Murata LQH1C4R7M04 4.7 650 0.34 1.6 x 3.2 x 2 LQH3C4R7M34 CDRH2D11-4R7 4.7 4.7 200 170 450 500 2.5 x 3.2 x 2 3.2 x 3.2 x 1.2 CMD4D11-4R7 976AS-4R7 = P5 4.7 4.7 166 320 750 740 3.5 x 5.3 x 1.2 3.6 x 3.6 x 1.2 CDRH3D16-4R7 972AS-4R7M = P5 4.7 4.7 80 220 900 960 3.8 x 3.8 x 1.8 4.6 x 4.6 x 1.2 PART NO. INDUCTANCE (H) DC RESISTANCE (m) RATED DC MAX CURRENT (mA) DIMENSIONS LxWxH (mm)
Note: Efficiency may vary depending upon the inductor's characteristics. Consult the inductor manufacturer for saturation current ratings. 20 ______________________________________________________________________________________
W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
VIN 2.6V TO 5.5V
R2 20 SHDN2 VCC C7 0.1F OFFSET IN+
R6 VAOUT = VIN+ x 1+ R7
INP
MAX1958/ MAX1959
AOUT VREF R6 6.8k INR7 12k
HBT
PA
Figure 4. Op-Amp Configuration
tures must be mounted on, or close to, the object whose temperature they are intended to measure. There is a good thermal path between the exposed paddle of the package and the IC die; therefore, the MAX1958/MAX1959 can accurately measure the temperature of the circuit board to which they are soldered. If the sensor is intended to measure the temperature of a heat-generating component on the circuit board, it should be mounted as close as possible to that component and should share supply and ground traces (if they are not noisy) with that component where possible. This maximizes the heat transfer from the component to the sensor. The thermal path between the plastic package and the die is not as good as the path through the exposed paddle, so the MAX1958/MAX1959, like all temperature sensors in plastic packages, are less sensitive to the temperature of the surrounding air than they are to the temperature of its exposed paddle. They can be successfully used to sense ambient temperature if the circuit board is designed to track the ambient temperature. As with any IC, the wiring and circuits must be kept insulated and dry to avoid leakage and corrosion, especially if the part is operated at cold temperatures where condensation can occur.
MAX1958/ MAX1959
AOUT R6 IN-
RISO 100
CLOAD
RLOAD
R7
Figure 5. Configuration for Driving Larger Capacitive Loads
The junction-to-ambient thermal resistance (JA) is the parameter used to calculate the rise of a device junction temperature (TJ) due to its power dissipation. The JA for the 20-pin QFN package is +50C/W. For the MAX1958/MAX1959, use the following equation to calculate the rise in die temperature:
TJ = TA + JA x PD(CONVERTER) + PD(OPAMP) + PD( TEMPSENSOR)
(
)
The power dissipated by the DC-to-DC converter dominates in this equation. It is then reasonable to assume
21
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
that the rise in die temperature due to the converter is a good approximation of the total rise in die temperature. Therefore:
TJ TA + JA x PD(CONVERTER) = TA + JA x (VIN x IIN - VOUT x IOUT )
(
)
This equation assumes that the losses in the inductor are relatively small. For inductors with high DC resistance, inductor loss must be accounted for in the calculation. The temperature rise due to power dissipation by the converter can be quite significant.
PC Board Layout and Routing
High switching frequencies and large peak currents make PC board layout a very important part of design. Good design minimizes EMI, noise on the feedback paths, and voltage gradients in the ground plane, all of which can cause instability or regulation errors.
Connect the inductor, input filter capacitor, and output filter capacitor as close together as possible and keep their traces short, direct, and wide. Connect their ground pins at a single common node in a star ground configuration. Keep noisy traces, such as those from the LX pin, away from the output feedback network. Position the bypass capacitors as close as possible to their respective pins to minimize noise coupling. For optimum performance, place input and output capacitors as close to the device as possible. Connect AGND and PGND to the highest quality system ground. The MAX1958 evaluation kit illustrates an example PC board layout and routing scheme. Optimize performance of the op amp by decreasing the amount of stray capacitance at the op amp's inputs and output. Decrease stray capacitance by placing external components as close to the device as possible to minimize trace lengths and widths.
Typical Operating Circuit
L1 4.7H SUMIDA CDRH3D16-4R7 LX C2 4.7F PWM PGND
VIN 2.6V TO 5.5V C1 4.7F
INP IN
SHDN1 R2 20
OUT AOUT R6 6.8k VREF VCC
VCC C7 0.1F SHDN2 SHDN3 DAC ADJ
MAX1958/ MAX1959
INR7 12k
HBT PA
TOUT COMP
RC 9.1k Cf 22pF CC 560pF
VTOUT C6 0.01F
OFFSET IN+ EXPOSED PADDLE
REF AGND
C5 0.1F
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Functional Diagram
IN REF COMP ADJ ERROR AMPLIFIER SLOPE COMPENSATION CURRENT SENSE SHDN1 PWM PWM COMPARATOR PWM CONTROL 1MHz OSCILLATOR
INP
REFERENCE COMP CLAMP
MAX1958/ MAX1959
LX
PGND OUT
VCC IN+ AOUT OP AMP INSHDN2 ACTIVE DISCHARGE TEMPERATURE SENSOR AGND TOUT
AGND
SHDN3
Chip Information
TRANSISTOR COUNT: 3704 PROCESS: BiCMOS
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W-CDMA/N-CDMA Cellular Phone HBT PA Management ICs MAX1958/MAX1959
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
D2
C L
0.15 C A
D
b D2/2
0.10 M C A B
PIN # 1 I.D.
D/2
0.15 C B
k
PIN # 1 I.D. 0.35x45
E/2 E2/2 E (NE-1) X e
C L
E2
k L
DETAIL A
e (ND-1) X e
C L
C L
L
L
e 0.10 C A 0.08 C
e
C
A1 A3
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
1 2
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
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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.
24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
QFN THIN.EPS

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