MAX1687 /MAX1688 19-1426 Rev 0 2/99 Step-Up DC-DC Converters with Precise, Adaptive Current Limit for GSM General Description Features Low 450mA Peak Battery Current The MAX1687/MAX1688 step-up DC-DC converters deliv- Provides 2A, 5V GSM Burst er up to 2W from a single Li-Ion or three NiMH cells. The devices are ideal for burst-load applications such as GSM 90% Efficiency cell phones and wireless LANs, where the RF power Internal Power MOSFETs and Current-Sense amplifiers require short, high current bursts. The Resistor MAX1687/MAX1688 reduce battery surge current by slow- Output Disconnects from Input During Shutdown ly charging a reservoir capacitor, which supplies the nec- 3A Shutdown Current essary peak energy for the load current burst. As a result, Precise Voltage-Controlled Current Limit the peak battery current is limited, thus maximizing battery (MAX1687) life and minimizing battery voltage sag and transient dips. Adaptive Constant-Recharge-Time Capability An internal synchronous rectifier provides over 90% con- (MAX1688) version efficiency and eliminates the need for an external Schottky diode. A logic shutdown mode reduces the shut- 1.25V to 6V Adjustable Output down current to only 3A. The devices can be disabled 2.7V to 6V Input Range during current bursts (RF transmit mode) to eliminate (1 Li-Ion cell or 3 NiMH cells) switching noise. Switching Frequency Can Exceed 1MHz The switching frequency of the MAX1687/MAX1688, con- Standby Mode Disables DC-DC During trolled by the selected inductor, can exceed 1MHz. Two Transmission Burst external resistors set the output voltage from 1.25V to 6V. Low Inrush Current at Start-Up The MAX1687 controls peak battery current, while the MAX1688 features a more advanced, adaptive constant- recharge-time algorithm that maximizes battery life. The Ordering Information MAX1687/MAX1688 are available in thin 16-pin TSSOP (1.1mm max height) or standard 8-pin SO packages. PART* TEMP. RANGE PIN-PACKAGE MAX1687EUE -40C to +85C 16 TSSOP MAX1687ESA -40C to +85C 8 SO Applications MAX1688EUE -40C to +85C 16 TSSOP MAX1688ESA -40C to +85C 8 SO GSM Phones *Ug. Wireless Handsets PC Cards (PCMCIA) Typical Operating Circuit Pin Configurations V OUT 2.7V TO 6V LX1 LX2 UP TO 6V TOP VIEW IN OUT 1 Li-lon IN 1 16 OUT OR IN 2 15 OUT 3 NiMH OR MAX1687 LX1 3 14 LX2 3 ALKALINE MAX1688 FB LX1 4 MAX1687 13 LX2 ON MAX1688 ON LIM CHG 5 12 PGND OFF 0 TO 1V FB 6 11 PGND (LIM) CONTROL INPUT REF 7 10 AGND CHG REF N.C. 8 9 ON GND ARE FOR MAX1688 TSSOP ( ) ARE FOR MAX1687 Pin Configurations continued at end of data sheet. ARE FOR MAX1688 Pg Maxim Integrated Products 1 For free samples & the latest literature: Step-Up DC-DC Converters with Precise, Adaptive Current Limit for GSM ABSOLUTE MAXIMUM RATINGS IN, ON, LX1, CHG, LIM, FB, OUT, REF to GND.......-0.3V to +7V Operating Temperature Range ...........................-40C to +85C LX2 to GND ..............................................................-0.3V to +8V Storage Temperature Range .............................-65C to +150C IN, LX1 Average Current..........................................................1A Lead Temperature (soldering, 10sec) ............................+300 C Continuous Power Dissipation (T = +70C) A TSSOP (derate 5.7mW/C above +70C) ....................457mW SO (derate 5.88mW/C above +70C).........................471mW 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 (V = V = +3V, V = 1V (MAX1687), V = 1V (MAX1688), V = 1.5V, V = 6V, T = 0C to +85C, unless otherwise noted. IN ON LIM CHG FB OUT A Typical values are at T = +25C.) A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Voltage Range 2.7 6 V Input Undervoltage Lockout IN rising, 1% hysteresis 2.4 2.5 2.6 V Output Voltage Range V 6 V REF V = 1.5V 24 mA FB Input Supply Current Shutdown, V = 4.2V, LX2 connected to LX1, IN 310 A V = 0, ON = GND OUT Shutdown Delay t 0.7 1.2 1.8 ms DELAY Reference Voltage V I = 0 to 10A 1.225 1.25 1.275 V REF REF FB Set Voltage V rising, 2% hysteresis 1.212 1.250 1.288 V FB FB Transconductance g V = 1.125V, V = 3V (MAX1688) 0.18 0.2 0.22 mmho mFB FB OUT I Source Current V = 0, V = 3V (MAX1688) 60 110 A CHG FB OUT V = V = 1V 0.744 0.8 0.856 LIM CHG Peak Current I A PEAK V = V = 0.65V 0.46 0.5 0.54 LIM CHG Ripple Current I V = V = 1V 170 200 230 mA RIPPLE LIM CHG Sense Resistor R 0.1 0.18 SENSE ON Input Low Voltage V V = 2.7V 0.6 V IL IN V = 6V 1.8 IN ON Input High Voltage V V IH V = 4.2V 1.5 IN I V = 1.5V 0.05 0.2 FB FB I V = 0 or 3V 0.02 0.1 ON ON Input Current A T = +25C 0.02 0.1 A I V = 1V LIM LIM T = 0C to +85C 2 A N-Channel On-Resistance V = 2.7V 0.4 0.8 IN P-Channel On-Resistance V = 2.7V 0.3 0.7 IN Precharge On-Resistance V = 4V, V = 0, V = 0 30 70 IN FB OUT LX2 Leakage Current V = V = 6V, V = V = 0 0.05 10 A IN LX2 OUT ON 2 MAX1687/MAX1688