MAX1678 19-1381 Rev 0 7/98 1-Cell to 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter General Description Features The MAX1678 is a high-efficiency, low-voltage, syn- 0.87V Guaranteed Start-Up chronous-rectified, step-up DC-DC converter intended Up to 90% Efficiency for use in devices powered by 1 to 3-cell alkaline, NiMH, or NiCd batteries or a 1-cell lithium battery. It Built-In Synchronous Rectifier (no external diode) guarantees a 0.87V start-up voltage and features a low Ultra-Small MAX Package, 1.1mm High 37A quiescent supply current. The device includes a 1, N-channel MOSFET power 37A Quiescent Current (85A from 1.5V battery) switch, a synchronous rectifier that acts as the catch 2A Logic-Controlled Shutdown diode, a reference, pulse-frequency-modulation (PFM) control circuitry, and circuitry to reduce inductor ring- Power-Fail Detector ingall in an ultra-small, 1.1mm-high MAX package. Dual Mode Output: Fixed 3.3V The output voltage is preset to 3.3V or can be adjusted Adjustable 2V to 5.5V from +2V to +5.5V using only two resistors. Efficiencies 45mA Output Current at 3.3V for 1-Cell Input up to 90% are achieved for loads up to 50mA. The device also features an independent undervoltage 90mA Output Current at 3.3V for 2-Cell Input comparator (PFI/PFO) and a logic-controlled 2A shut- Inductor-Damping Switch Suppresses EMI down mode. Ordering Information Applications PART TEMP. RANGE PIN-PACKAGE Pagers MAX1678EUA -40C to +85C 8 MAX Remote Controls Note: To order these devices shipped in tape-and-reel, add a -T to the part number. Pointing Devices Personal Medical Monitors Single-Cell Battery-Powered Devices Typical Operating Circuit Pin Configuration INPUT TOP VIEW 0.87V TO V OUT OUTPUT LX OUT 3.3V MAX1678 BATT 1 8 OUT BATT ON PFI 2 7 LX OFF SHDN MAX1678 PFO 3 6 GND LOW-BATTERY PFI PFO LOW-BATTERY SHDN 4 5 FB DETECTOR INPUT GND FB DETECTOR OUTPUT MAX Dual Mode is a trademark of Maxim Integrated Products. Maxim Integrated Products 1 For free samples & the latest literature: 1-Cell to 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter ABSOLUTE MAXIMUM RATINGS BATT, OUT,LX, SHDN to GND ..............................-0.3V to +6.0V Operating Temperature Range ...........................-40C to +85C Junction Temperature......................................................+150C OUT, LX Current.......................................................................1A FB, PFI, PFO to GND ................................-0.3V to (V + 0.3V) Storage Temperature Range .............................-65C to +165C OUT Lead Temperature (soldering, 10sec) .............................+300C Reverse Battery Current (T = +25C) (Note 1) ...............220mA A Continuous Power Dissipation (T = +70C) A MAX (derate 4.1mW/C above +70C) .......................330mW Note 1: The reverse battery current is measured from the Typical Operating Circuits input terminal to GND when the battery is con- nected backward. A reverse current of 220mA will not exceed package dissipation limits but, if left for an extended time (more than 10 minutes), may degrade performance. 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 = 1.3V, I = 0, FB = GND, T = 0C to +85C, unless otherwise noted. Typical values are at T = +25C.) BATT SHDN LOAD A A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Minimum Operating Input V 0.7 V BATT(MIN) Voltage Maximum Operating Input V 5.5 V BATT(MAX) Voltage Start-Up Voltage (Note 2) R = 3k, T = +25C 0.87 V L A Start-Up Voltage Tempco -2 mV/C Output Voltage (Fixed Mode) V V < 0.1V 3.16 3.3 3.44 V OUT FB Output Voltage Range External feedback 2.0 5.5 V (Adjustable Mode) FB Set Voltage V External feedback 1.19 1.23 1.26 V FB N-Channel On-Resistance V = 3.3V 1 1.5 OUT P-Channel On-Resistance V = 3.3V 1.5 2.2 OUT P-Channel Catch Diode Voltage I = 100mA, P-channel switch off 0.8 V DIODE Maximum Peak LX Current I 550 mA LX(MAX) On-Time Constant K 0.9V < V < 3.3V (t = K / V ) 5.60 8 11.2 V-s BATT ON BATT Quiescent Current into OUT I V = 3.5V 37 65 A Q,OUT OUT Quiescent Current into BATT I 4 8 A Q,BATT Shutdown Current into OUT I V = 3.5V 0.1 1 A SHDN,OUT OUT Shutdown Current into BATT I V = 1V 2 3.5 A SHDN,BATT BATT h Efficiency I = 20mA, V = 2.5V (Figure 7) 90 % LOAD BATT FB Input Current V = 1.3V 0.1 10 nA FB PFI Trip Voltage V Falling PFI hysteresis 2% 590 614 632 mV IL,PFI PFI Input Current V = 650mV 0.1 10 nA PFI PFO Low Output Voltage V V = 0, V = 3.3V, I = 1mA 0.04 0.4 V OL PFI OUT SINK PFO Leakage Current V = 650mV, V = 6V 0.01 1 A PFI PFO V 0.2 x V V SHDN Input Low Voltage IL BATT V 0.8 x V V SHDN Input High Voltage IH BATT 0.1 10 nA SHDN Input Current SHDN = GND or BATT 2 MAX1678