ML2731

PRELIMINARY ML2731 PA Bias Controller GENERAL DESCRIPTION The ML2731 is a power amplifier (PA) bias controller with support circuits for a typical radio transceiver. The IC integrates a PA bias controller, a PA DC switch, a crystal oscillator circuit, a negative voltage generator and two voltage regulators. It can be used with GaAs FETs and silicon bipolar devices. Micro Linear’s ML2731, along with the ML2712 and the ML2713, form a complete transceiver solution for the 2.4 GHz IEEE802.11 communication standard, as well as other wireless ISM communication products. In addition to supporting Micro Linear’s transceiver chip set, the ML2731 can stand alone as: A compact bias voltage controller A compact negative voltage generator A compact crystal oscillator n Sets PA current and power output using a bias control n Integrates a PA DC supply switch n Prevents PA power-on if negative voltage is not present n Integrates all circuits needed for supporting a crystal n Incorporates a fast starting, high switching frequency, n Contains voltage regulators for an oscillator, a negative n Requires less than 1mA of current when powered down n Supply voltage ranges from 3.3V to 5.5V APPLICATIONS voltage generator and a 50mA 3.0V LDO output negative voltage generator requiring only small ceramic capacitors oscillator with 10MHz to 40MHz frequency range loop FEATURES n Cellular and Cordless Radios n WLAN Radios n Radios with GaAs FET Power Amplifiers n Fixed and Mobile radio transceivers SIMPLIFIED BLOCK DIAGRAM ML2731 VPA PA on/off switch and current sense PAEN ICON VBIAS Bias Control NEGEN VNEG C1 C2 Negative voltage generator Voltage Regulator Crystal Oscillator XIN Crystal XOUT Sine & square wave drivers PDN REGO SINO CLKO GaAs FET Power Amplifier ML2712 ML2713 Radio Baseband Controller (e.g. MSM7730B) PRELIMINARY DATASHEET January, 2000 PRELIMINARY TABLE OF CONTENTS ML2731 General Description ................................................................................................................................................... 1 Simplified Block Diagram .......................................................................................................................................... 1 Features ...................................................................................................................................................................... 1 Applications ............................................................................................................................................................... 1 Block Diagram ........................................................................................................................................................... 3 Pin Configuration ....................................................................................................................................................... 4 Pin Descriptions ......................................................................................................................................................... 4 Functional Description ............................................................................................................................................... 6 Introduction .............................................................................................................................................................. 6 External Interfaces ................................................................................................................................................... 6 Mode Control ........................................................................................................................................................... 6 Description Of Operation ........................................................................................................................................... 6 Crystal Oscillator ..................................................................................................................................................... 7 Negative Voltage Generator ..................................................................................................................................... 7 Absolute Maximum Ratings ........................................................................................................................................ 11 Electrical Tables ......................................................................................................................................................... 11 Electrical Characteristics ............................................................................................................................................ 11 Operating Conditions ................................................................................................................................................. 11 Physical Dimensions .................................................................................................................................................. 12 Ordering Information .................................................................................................................................................. 12 WARRANTY Micro Linear makes no representations or warranties with respect to the accuracy, utility, or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. No license, express or implied, by estoppel or otherwise, to any patents or other intellectual property rights is granted by this document. The circuits contained in this document are offered as possible applications only. Particular uses or applications may invalidate some of the specifications and/or product descriptions contained herein. The customer is urged to perform its own engineering review before deciding on a particular application. Micro Linear assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of Micro Linear products including liability or warranties relating to merchantability, fitness for a particular purpose, or infringement of any intellectual property right. Micro Linear products are not designed for use in medical, life saving, or life sustaining applications. © 2000. Micro Linear is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners. Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897; 5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174; 5,767,653; 5,777,514; 5,793,168; 5,798,635; 5,804,950; 5,808,455; 5,811,999; 5,818,207; 5,818,669; 5,825,165; 5,825,223; 5,838,723; 5.844,378; 5,844,941. Japan: 2,598,946; 2,619,299; 2,704,176; 2,821,714. Other patents are pending. 2 PRELIMINARY DATASHEET January, 2000 PRELIMINARY BLOCK DIAGRAM ML2731 SINO 1 CLKO 8 VCC 2 BUFFER AND DRIVERS 10 VNEG XIN 15 XOUT 16 OSCILLATOR AND DIVIDER NEGATIVE VOLTAGE GENERATOR 12 C1 11 C2 PAEN 6 NEGEN 7 PDN 14 REFERENCE GENERATOR AND LOGIC 5 BIAS CONTROL 4 ICON VBIAS REGO 3 REGULATOR SWITCH AND CURRENT SENSE 13 VPA 9 GND January, 2000 PRELIMINARY DATASHEET 3 PRELIMINARY PIN CONFIGURATION ML2731 16-Pin TSSOP (T16) SINO VCC REGO VBIAS ICON PAEN NEGEN CLKO 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 XOUT XIN PDN VPA C1 C2 VNEG GND ML2731 TOP VIEW PIN DESCRIPTIONS Pin # 1 Signal Name SINO I/O O (ANLG) Description Sine wave output. This pin is a low impedance output capable of driving a 2kW load. The signal is sourced with either a crystal interfaced with on-chip components through XOIN (pin 15) and XOUT (pin 16) or with a completely external oscillator through pin 15. Taking PDN (pin 14) high switches off output DC power supply IC regulator output. This is the output from the on IC regulator. It is disabled in the SLEEP mode of operation and enabled in all other modes. The nominal output voltage is 2.9 V and it has a low impedance output which can source up to 50mA PA bias voltage output. This output has limited drive capability of 3mA and is intended to drive the gate or bias of the PA Reference current input. Used by the PA bias control loop to set the PA current level. This input appears as a virtual ground PA Enable. Transitions from high to low on this pin activate the PA current ramp up function, switch the PA voltage supply switch on and enable the PA bias control loop. Transitions from low to high activate the PA current ramp down function and switch the PA voltage supply off Negative Voltage Enable. In conjunction with PDN and PAEN, NEGEN controls the operational mode of the IC and enables the negative voltage generator circuits Clock output. The frequency is set with either a crystal interfaced with on-chip components through XOIN (pin 15) and XOUT (pin 16) or with a completely external oscillator through pin 15. CLKO switches off when device goes into SLEEP mode when PDN is taken high Ground Negative regulator output. This pin is one of the outputs of the negative switching regulator. A capacitor connected serves as a current reservoir. Typically a 100nF capacitor is connected between pin 10 and GND Noise Shunt. Negative voltage generator capacitor connection. This output of the negative switching regulator shunts regulator noise to ground using a 100nF bypass capacitor 2 3 VCC REGO O (ANLG) O (ANLG) 4 5 6 VBIAS ICON PAEN O (ANLG) I (ANLG) I (CMOS) 7 NEGEN I (CMOS) 8 CLKO I (CMOS) 9 10 GND VNEG GND O (ANLG) 11 C2 O (ANLG) 4 PRELIMINARY DATASHEET January, 2000 PRELIMINARY PIN DESCRIPTIONS (continued) Pin # 12 13 14 15 16 ML2731 Description Signal Name C1 VPA PDN XIN XOUT I/O O (ANLG) O (ANLG) I (ANLG) I (ANLG) I (ANLG) Noise Shunt. Negative voltage generator bypass capacitor connection. Typically a 100nF capacitor is connected between pin C1 and C2 PA supply. This is the positive supply for the PA. It is switched by PAEN in conjunction with PDN and NEGEN Power down control. Disables all circuits and reduces power consumption to less than 1mA Crystal or oscillator input. This high input impedance is connected to either an oscillator circuit or to a crystal Crystal-tank connection. This low impedance output drives the crystal tank circuit January, 2000 PRELIMINARY DATASHEET 5 PRELIMINARY FUNCTIONAL DESCRIPTION INTRODUCTION EXTERNAL INTERFACES The ML2731 has 3 logic inputs: PAEN, NEGEN and PDN. These control lines are used to select the mode of operation to be either SLEEP, STANDBY, PRETX or TRANSMIT. (See Table 1) DESCRIPTION OF OPERATION Voltage Regulator ML2731 The ML2731 integrates two low noise voltage regulators. The first regulator internally powers the crystal oscillator support circuit, negative voltage generator support circuit and other on chip circuits. The second regulator output (REGO) powers external circuits. (See Figure 1) It has a nominal voltage output of 2.9V and sources up to 50mA of current. The low noise output of this regulator makes it suitable for supplying voltage to sensitive components such as final frequency VCO’s. The regulator output is disabled in the SLEEP mode and is enabled in all other modes. 2.92 PDN 1 0 0 0 NEGEN X 1 0 0 PAEN X X 1 0 Mode SLEEP STANDBY PRETX TRANSMIT 2.90 VOLTAGE (V) Table 1. Circuit Enable Logic 2.88 MODE CONTROL Mode Functions The function of the ML2731 in each mode of operation: SLEEP All the circuits are disabled. Current drain is typically less than 1mA. STANDBY Oscillator circuits, sine and square wave outputs and 3.0V voltage regulator output are all enabled. VPA output is disabled as well as all other circuits. PRETX Oscillator circuits, sine and square wave outputs, 3.0V voltage regulator output, and negative voltage generator are enabled. VBIAS is set to –3.0V. VPA output is disabled and PA bias control loop is inactive. TRANSMIT Crystal oscillator circuits, sine and square wave outputs, 3.0V voltage regulator, negative voltage generator, and VPA output are enabled, and VBIAS is voltage controlled so that the VPA current is proportional to the ICON input voltage. 2.86 2.84 0 10 20 30 40 50 CURRENT (mA) Figure 1. Regulator Ouput Voltage vs. Load Current (REGO) 6 PRELIMINARY DATASHEET January, 2000 PRELIMINARY FUNCTIONAL DESCRIPTION CRYSTAL OSCILLATOR The crystal oscillator circuit is powered by an on chip regulator and generates a square wave signal and a sine wave signal. The sine wave is intended for radio PLL circuits, and the square wave clock for the digital circuits. The frequency range of operation is 10 to 40MHz (determined by the external crystal). The crystal oscillator can also be overdriven by connecting an external oscillator to pin 15 (XIN). The crystal oscillator square wave and sine wave signal outputs are enabled in STANDBY, PRETX and TRANSMIT modes. (See Figures 2 and 3) The oscillator circuit is enabled by the PDN logic control pin and turns on and generates stable output signals within 20mS of being enabled. 3.5 3.0 2.5 ML2731 NEGATIVE VOLTAGE GENERATOR When driven by a 32 MHz crystal, the charge pump of the ML2731 is clocked with a 2.66 MHz signal. Because the clock frequency is so high, the negative voltage generator requires only small ceramic capacitors on C1 and C2 for operation. (Figure 4) Typically they have values of 100nF. The quick response time (Figure 5), due in part to the small circuit capacitance, allows the charge pump to be disabled when not needed thus reducing power consumption. 100nF 100nF 100nF 10 11 12 VNEG C2 C1 Figure 4: Typical C1 and C2 Noise Shunt Configuration NEGEN (pin 7) enables the negative voltage generator during the PRETX and TRANSMIT modes of operation. Output from the negative voltage generator is used internally by the ML2731 to supply the op amp in the PA current control circuit. The resulting voltage is applied to VBIAS for controlling an external PA. The negative voltage generator enables the ML2731 to provide a typical bias voltage in the range of –2.9 V to 0V. 4.0 3.5 0.5 0.0 VNEG BIAS –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 0.8 VOLTAGE (V) 2.0 1.5 1.0 0.5 0.0 –0.5 3.0 VNEG CONTROL (V) 2.5 2.0 1.5 1.0 0.5 0 0 10 20 30 40 50 TIME (ns) Figure 2: Typical 32 MHz Square wave output signal (1kW+10pF load, VCC = 3.3V) 1.9 Cap: 10pF none 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 TIME (ms) 1.8 Figure 5: Typical negative voltage generator on and off timing (using 100nF capacitors on pins C1 and C2) 600 VOLTAGAE (V) 1.7 500 1.6 VNEG (µVRMS) 400 300 1.5 200 100 1.4 0 10 20 30 40 TIME (ns) 50 60 70 80 0 0 2 4 6 8 10 FREQUENCY (MHz) Figure 3: Typical 32 MHz sine wave output signal (1kW+0pF load, and 1kW+10pF load, VCC = 3.3V) Figure 6: Negative voltage output ripple (mV) (using 100nF bypass and reservoir capacitance) January, 2000 BIAS (V) PRELIMINARY DATASHEET 7 PRELIMINARY FUNCTIONAL DESCRIPTION PA SUPPLY DC SWITCH The ML2731 includes a DC switch for connecting the supply voltage to an external PA. PAEN activates the DC switch during TRANSMIT mode. To ensure the external PA devices power up correctly, the chip has control circuits preventing the PA supply DC switch from being enabled if the VBIAS voltage is more positive than –3.0V. Typically, the PA supply DC switch produces a voltage drop of 100mV while conducting a 500mA current. Parameters determining the maximum current capability of the DC switch are the maximum voltage drop that can be tolerated by the external PA and the thermal limitations of the ML2731. PA CURRENT CONTROL LOOP ML2731 The current control loop allows the PA current to be set by the reference current on the ICON pin. This enables the ML2731 to control PA output power and to compensate for PA current variations due temperature changes. In addition, it removes the need for calibration of PA current in manufacturing because the PA current control loop adjusts the PA bias be proportional to a reference voltage. The PA current can typically is between 30 to 500mA. The current control loop is enabled by the PAEN pin. PA CURRENT CONTROL LOOP AND PA RAMP COMPONENT VALUES The ICON input pin is at virtual ground. The reference current on the ICON pin is determined by the value of REXT, connected to the ICON input, the voltage reference (VREF), and the voltage source impedance. For the fixed voltage source in the above circuit, the PA current is determined by the formula: VPA current = [Vcc(R1/(R2+REXT))*2000] / REXT + Offset The offset current (minimum PA current) is typically 30mA A typical REXT resistor value is 12kW. Typical reference voltages are in the range 0 to 3.0V to enable the PA current to be controlled over the range of 30mA to 500mA. For slow PA ramp on/off times (e.g. >10msec) the PA bias control loop has a sufficiently fast settling time to enable the ramp to be controlled by ramping the ICON voltage input. For fast, e.g. 0µsec >200µs PDN VNEG PAEN 3V VControl Voltage 0V 0V VBIAS Voltage -3V Current VPAout current >0µsec >0µsec ML2731 VREF VPA Current 1 0.9 0.8 0.7 0.6 VREF (V) 160 140 120 VPA current (mA) 100 80 60 40 20 0 0 5 10 Time (µsec) 15 20 0.5 0.4 0.3 0.2 0.1 0 Figure 12: VPA output vs VREF (TRANSMIT mode, REXT = 12kW, capacitance on VBIAS = 3.3nF) Charge VNEG caps discharge VNEG caps Timeconstant set by external caps on VPA Timeconstant set by external caps on VBIAS Figure 11: PA Bias Control Loop Operation 1 0 -1 Drain Current(dB) Where ICON is a fixed value (i.e. the VPA current is not ramped up and down by changing the value of ICON) then the time taken for the VPA current to ramp up following PAEN being enabled is determined by the capacitor values on VBIAS and VPA. The time taken for the current to ramp down following PAEN being disabled is determined by the capacitance value on VPA only. Example timings are: 1msec ramp-up for 2nF VBIAS capacitance 4msec ramp-up for 22nF VBIAS capacitance An example of a 3 step current ramp up and ramp down, with 3.3nF capacitance on VBIAS, is shown in Figure 12. -2 -3 -4 -5 -6 -7 10 3.3nF 100 Frequency(KHz) 2.2nF 1.5nF 100 Figure 13: Bandwidth of PA Current control loop for 3.3nF, 2.2nF and 1.5nF VBIAS capacitance 10 PRELIMINARY DATASHEET January, 2000 PRELIMINARY ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS Absolute maximum ratings are those values beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. VCC ......................................................................... 6.0V All Other Inputs .................... GND – 0.3V to VCC + 0.3V Junction Temperature .............................................. 150°C Storage Temperature Range ..................... – 65°C to 150°C Lead Temperature (Soldering, 10 sec) ..................... 260°C ML2731 OPERATING CONDITIONS Commercial Temperature Range .................... 0°C to 70°C Extended Temperature Range .................... –20°C to 70°C VCC Range .................................................. 3.3V to 5.5V Thermal Resistance (qJA) ................................... 100°C/W ELECTRICAL TABLES Unless otherwise specified, VCC = 3.3, TA = Operating Temperature Range. (Note 1) SYMBOL POWER CONSUMPTION PARAMETER CONDITIONS MIN TYP MAX UNITS All circuits, supply current, all circuits disabled Supply current, oscillator enabled, regulator enabled Supply current, oscillator and negative voltage generator enabled. Supply current, all circuits enabled NEGATIVE VOLTAGE GENERATION Negative Bias Voltage Maximum current, VBIAS Turn on time, to –3V on VBIAS VCONTROL VOLTAGE INPUT Input control voltage range VOLTAGE REGULATOR OUTPUT Output voltage Output current OSCILLATOR AND OUTPUTS Frequency Range Turn on time SINO voltage range, Peak-to-Peak CLKO, low CLKO, high Capacitive Load on CLKO Capacitive Load on SINO PA SUPPLY VOLTAGE Voltage Current DC Connected 10pF load on CLKO and SINO 0mA from VREG 10pF load on CLKO and SINO