9-1198; Rev 1; 8/00 KIT ATION EVALU E L B AVAILA 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator The MAX1705/MAX1706 are high-efficiency, low-noise, step-up DC-DC converters with an auxiliary linearregulator output. These devices are intended for use in battery-powered wireless applications. They use a synchronous rectifier pulse-width-modulation (PWM) boost topology to generate 2.5V to 5.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator ABSOLUTE MAXIMUM RATINGS ONA, ONB, FBLDO, OUT, POUT to GND...................-0.3V to 6V PGND to GND.....................................................................±0.3V POUT to OUT ......................................................................±0.3V LX to PGND ............................................-0.3V to (VPOUT + 0.3V) CLK/SEL, REF, FB, TRACK, LDO, LBN, LBP, LBO to GND.................
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator (VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF), LX = open, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC-DC SWITCHES POUT Leakage Current VLX = 0V, V ONB = VOUT = 5.0V 0.1 20 µA LX Leakage Current VLX = V ONB = VOUT = 5.0V 0.1 20 µA CLK/SEL = GND 0.23 0.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator ELECTRICAL CHARACTERISTICS (continued) (VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF), LX = open, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator (VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF), LX = open, TA = -40°C to +85°C, unless otherwise noted, Note 4.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS LINEAR REGULATOR FBLDO Regulation Voltage FBLDO = LDO, ILOAD = 1mA FBLDO Input Current VFBLDO = 1.
Typical Operating Characteristics (Circuit of Figure 2, TA = +25°C, unless otherwise noted.) MAX1705 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V) 60 50 L = 10µH VOUT = 3.3V A: VIN = 0.9V B: VIN = 2.7V 1: PFM MODE 2: PWM MODE 40 30 20 10 50 L = 10µH VOUT = 5V A: VIN = 0.9V C: VIN = 2.4V E: VIN = 3.6V 1: PFM MODE 2: PWM MODE 40 20 10 1 10 100 800 PWM MODE 700 VOUT = 5V 600 VOUT = 3.3V 500 400 PFM MODE 300 VOUT = 3.3V 200 VOUT = 5V 100 0 0 0.1 0.1 1000 1 10 100 1000 0 0.5 1.0 1.5 2.
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator (Circuit of Figure 2, TA = +25°C, unless otherwise noted.) LINEAR-REGULATOR REGION OF STABLE C6 ESR vs. LOAD CURRENT LINEAR-REGULATOR POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 50 MAX1705/6 TOC11 100 MAX1705/6 TOC10 60 C6 = 22µF UNCOMPENSATED 10 C6 ESR (Ω) 30 20 STABLE REGION VOUT = 4V TO 5V VLDO = 3.3V ILDO = 200mA C5 = 0.33µF 10 0.
____________________________Typical Operating Characteristics (continued) (Circuit of Figure 2, TA = +25°C, unless otherwise noted.) MAX1705/6 TOC17 MAX1705/6 TOC16 MAX1705/6 TOC15 A MAX1705 POWER-ON DELAY (PWM MODE) MAX1705 LOAD-TRANSIENT RESPONSE MAX1705 LINE-TRANSIENT RESPONSE A B A 3V 2.5V 3.3V C B B 0mA D VIN = 1.2V, LOAD = 1kΩ, ONB TIED TO OUT A = ONA, 2V/div B = VLDO, 2V/div C = VOUT, 2V/div D = INDUCTOR CURRENT, 500mA/div VIN = 1.2V, VOUT = 3.3V A = VOUT, 50mV/div, 3.
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator PIN NAME FUNCTION 1 LBP Low-Battery Comparator Noninverting Input. Common-mode range is 0.5V to 1.5V. 2 LBN Low-Battery Comparator Inverting Input. Common-mode range is 0.5V to 1.5V. 3 REF 1.250V Reference Output. Bypass REF with a 0.33µF capacitor to GND. REF can source up to 50µA. 4 TRACK 5 GND Ground 6 OUT Step-Up Converter Feedback Input, Used During Track Mode.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator Detailed Description The MAX1705/MAX1706 are designed to supply both power and low-noise circuitry in portable RF and dataacquisition instruments. They combine a linear regulator, step-up switching regulator, n-channel power MOSFET, p-channel synchronous rectifier, precision reference, and low-battery comparator in a single 16pin QSOP package (Figure 1).
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706 INPUT 0.9V TO 3.6V L1 10µH (22µH) C7 22µF D1 R5 LX BOOST OUTPUT 3.6V POUT (TO PGND) R6 LBP OUT LBN TRACK REF C8 0.33µF C9 0.33µF C3 R1 0.1µF 191kΩ PGND (TO PGND) MAX1705 MAX1706 R2 100kΩ FB ONA (TO OUT) LDO OUTPUT 3.3V ONB LDO CLK/SEL FBLDO C5* 0.33µF LBO GND NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATH. C4 220µF (100µF) C1* R7 100kΩ R3 165kΩ C6 22µF C2* R4 100kΩ *OPTIONAL.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator POUT Q POUT Q P IFB* LOGIC HIGH D R IREF* R P LX Q N S LX IFB* ICS S N Q IREF* CURRENTLIMIT LEVEL R PGND OSC CURRENTLIMIT LEVEL PGND *SEE FIGURE 1 Figure 3. Simplified PWM Controller Block Diagram current limit for the MAX1705, and 950mA (max) for the MAX1706. During PWM operation, the circuit operates with a continuous inductor current.
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator Low-Voltage Startup Oscillator The MAX1705/MAX1706 use a CMOS, low-voltage startup oscillator for a 1.1V guaranteed minimum startup input voltage at +25°C. On startup, the low-voltage oscillator switches the n-channel MOSFET until the output voltage reaches 2.15V. Above this level, the normal stepup converter feedback and control circuitry take over. Once the device is in regulation, it can operate down to a 0.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator LBP is less than 50nA, R6 can be a large value (such as 270kΩ or less) without sacrificing accuracy. Connect the resistor voltage-divider as close to the IC as possible, within 0.2in. (5mm) of the LBP pin. The inputs have a 0.5V to 1.5V common-mode input range, and a 16mV input-referred hysteresis. The low-battery comparator can also be used to monitor the output voltage, as shown in Figure 5.
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator ⎛ V ⎞ R3 = R4 ⎜ LDO - 1⎟ ⎝ VFBLDO ⎠ where VFBLDO, the linear-regulator feedback trip point, is 1.250V. Since the input bias current into FBLDO is less than 50nA, R4 can be a large value (such as 270kΩ or less). Connect the resistor voltage-divider as close to the IC as possible, within 0.2in. (5mm) of the FBLDO pin.
MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator reduces peak currents drawn from the input source and reduces input switching noise. The input voltage source impedance determines the size required for the input capacitor. When operating directly from one or two NiCd cells placed close to the MAX1705/MAX1706, use a 22µF, low-ESR input filter capacitor.
1 to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator LX CONTROL INPUTS MAX1705 MAX1706 POUT GND ONB ON/OFF MAX1705 MAX1706 MAX1705/MAX1706 µC 270kΩ OUT VDD I/O LDO ONA PA I/O µC 0.1µF RF I/O 270kΩ Figure 11. Momentary Pushbutton On/Off Switch Figure 10. Typical Phone Application Table 5. Typical Available Output Current NO.
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.) QSOP.EPS MAX1705/MAX1706 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH 21-0055 F 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product.
