19-0167; Rev 2; 6/95 NUAL KIT MA ATION U EET L H A S V A E T WS DA FOLLO 5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators The MAX830/MAX831/MAX832/MAX833 are monolithic, bipolar, pulse-width-modulation (PWM), switch-mode, stepdown DC-DC regulators. Each is rated at 1A. Very few external components are needed for standard operation because the power switch, oscillator, feedback, and control circuitry are all on-chip. Employing a classic buck topology, these regulators perform high-current step-down functions. These regulators have excellent dynamic and transient response characteristics, while featuring cycle-by-cycle current limiting to protect against overcurrent faults and shortcircuit output faults. They have a wide 8V to 30V input range. Outputs for the MAX831/MAX832/MAX833 are fixed at 5V/3.3V/3V, respectively. The MAX830 output is adjustable. Available in 16-pin SO packages, the MAX830–MAX833 have a preset 100kHz oscillator frequency. In addition, the preset current limit and micropower shutdown can be externally controlled. See the MAX724/MAX726 data sheet for more applications information. _______________________Applications Distributed Power from High-Voltage Buses ___________________________Features ♦ Input Range: Up to 30V ♦ 1A On-Chip Power Switch ♦ Adjustable Output (MAX830) Fixed Outputs: 5V (MAX831) 3.3V (MAX832) 3V (MAX833) ♦ 100kHz Switching Frequency ♦ Excellent Dynamic Characteristics ♦ Few External Components ♦ 8mA Quiescent Current ♦ 16-Pin SO Package ♦ Evaluation Kit Available ______________Ordering Information PART MAX830CWE MAX831CWE MAX832CWE MAX833CWE TEMP. RANGE 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C PIN-PACKAGE 16 Wide SO 16 Wide SO 16 Wide SO 16 Wide SO High-Current, High-Voltage Step-Down Applications Multiple-Output Buck Converter __________Typical Operating Circuit __________________Pin Configuration TOP VIEW INPUT 8V TO 30V 100µH* VSW VIN OUTPUT 5V AT 1A VC 15 V SW V IN 4 MBR350 GND 5 SENSE 470µF 10k 16 V SW V IN 2 V IN 3 100µF MAX831 V IN 1 GND I LIM 6 14 V SW MAX830 MAX831 MAX832 MAX833 GND 7 13 V SW 12 GND 11 V C 10 GND (FB) SENSE 8 9 SHUT 0.047µF Wide SO Tj (MAX) = +125°C, θjA = +55°C/W* STEP-DOWN CONVERTER * CoilCraft DO3316-104 ( ) ARE FOR MAX830 * THIS THERMAL RESISTANCE NUMBER IS WITH THE DEVICE WELL MOUNTED ON 1 oz. COPPER WITH THERMAL PASTE BETWEEN THE IC AND THE UNDERLYING GROUND PLANE. LOWER THERMAL RESISTANCE IS POSSIBLE (SEE APPLICATIONS SECTION). ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX830–MAX833 _______________General Description MAX830–MAX833 5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators ABSOLUTE MAXIMUM RATINGS Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40V Switch Voltage with Respect to Input Voltage. . . . . . . . . . . . . . . . 50V Switch Voltage with Respect to GND (VSW negative) (Note 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20V FB/SENSE Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V, +10V SHUT Voltage (not to exceed VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30V ILIM Voltage (forced). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V Operating Temperature Range. . . . . . . . . . . . . . . . . . . . . 0°C to +70°C Junction Temperature Range . . . . . . . . . . . . . . . . . . . . . 0°C to +125°C Storage Temperature Range . . . . . . . . . . . . . . . . . . . -65°C to +160°C Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300°C Note 1: Do not exceed switch-to-input voltage limitation. 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 (VIN = 25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN Input Supply Voltage Range Switch-On Voltage (Note 2) Switch-Off Leakage Supply Current (Note 3) Minimum Supply Voltage (Note 5) 1.4 VIN = 25V, VSW = 0V VIN = 30V, VSW = 0V 150 TA = +25°C 250 VIN ≤ 30V, VSENSE = 5.5V (MAX831/MAX832/ MAX833) or VFB = 2.5V (MAX830) V µA 8 11 mA VSHUT = 0.1V (Note 4) 140 500 µA Normal mode 7.3 8.0 Startup mode 3.5 4.8 1.7 2.2 RLIM = 10kΩ (Note 7) 1.2 1.2 TA = +25°C TA = +25°C Switching Frequency Switching-Frequency Line Regulation 8V ≤ VIN ≤ 30V Error-Amplifier Voltage Gain 1V ≤ VC ≤ 4V Error-Amplifier Transconductance VFB = 2.0V (MAX830) or VSENSE = 2.0V (MAX831/832/833) VFB = 2.5V (MAX830) or VSENSE = 5.5V (MAX831/832/833) V A 0.8 85 90 90 100 85 VFB or VSENSE = 0V (Note 6) 2 V ISW = 1A Maximum Duty Cycle Error-Amplifier Sink Current UNITS 30 1.1 RLIM = 7kΩ (Note 7) Error-Amplifier Source Current MAX ISW = 0.2A ILIM open Switch-Current Limit (Note 6) TYP 8 TA = +25°C 20 TA = +25°C 2000 0.03 % 110 120 kHz 0.10 %/V V/V TA = +25°C 3000 5000 9000 µmho TA = +25°C 100 140 225 µA TA = +25°C 0.6 1.0 1.7 mA _______________________________________________________________________________________ 5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators (VIN = 25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS SENSE Voltage VC = 2V SENSE Divider Resistance TA = +25°C SENSE Voltage Tolerance (Note 8) VOUT (nominal) = 5V (MAX831), 3.3V (MAX832), or 3V (MAX833) FB Bias Current VFB = VREF (MAX830) Reference Voltage VC = 2V (MAX830) (Note 9) TYP MAX 4.85 5.00 5.15 MAX832 MAX833 3.20 2.90 3.30 3.00 3.40 3.10 MAX831 3.0 5.0 8.0 MAX832 2.5 4.2 7.0 MAX833 2.2 3.8 6.5 ±0.5 ±2.0 ±0.5 ±3.0 TA = +25°C 2.155 TA = +25°C Reference Voltage Tolerance (Notes 8, 9) VREF (nominal = 2.21V) (MAX830) Output Voltage Line Regulation 8V ≤ VIN ≤ 30V VC Voltage 0% duty cycle VC Voltage Temperature Coefficient SHUT Current MIN MAX831 V kΩ % 0.5 2.0 µA 2.21 2.265 V ±0.5 ±1.5 ±1.0 ±2.5 0.005 0.020 % TA = +25°C %/V 1.5 V 0% duty cycle -4 mV/°C VSHUT = 5V 10 20 VSHUT = 0.1V (shutdown) SHUT Threshold UNIT (shutdown) 50 0.10 0.20 0.50 µA V Note 2: For switch currents between 0.2A and 1A, maximum switch-on voltage can be calculated via linear interpolation. Note 3: By setting the SENSE pin to 5.5V (or the FB pin to 2.5V), the VC pin is forced to its low clamp level and the switch duty cycle is forced to zero, approximating the zero load condition. Note 4: Device shut down. Switch leakage current not included. Note 5: For proper regulation, total voltage from VIN to GND must be ≥ 8V after start-up. During start-up mode, device is switching but not regulating. Note 6: To avoid extremely short switch-on times, the switch frequency is internally scaled down when VFB or VSENSE is less than 1.3V. Switch current limit is tested with VSENSE or VFB adjusted to give a 1µs minimum switch-on time. I 1A Note 7: RLIM = LIM × 7.6kΩ + 1kΩ . Typical value only. Minimum to maximum deviation in current limit will be ±30%, comparable to that with ILIM pin open. Note 8: All conditions of input voltage, output voltage, temperature, and load current. Note 9: FB is at the reference voltage when the MAX830 output voltage is in regulation. _______________________________________________________________________________________ 3 MAX830–MAX833 ELECTRICAL CHARACTERISTICS (continued) MAX830–MAX833 5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators ______________________________________________________________Pin Description PIN NAME FUNCTION SENSE (MAX831/ 2/3) For the MAX831/MAX832/MAX833, SENSE input is the internal error amplifier’s input, and should be directly connected to VOUT. SENSE also aids current limiting by reducing oscillator frequency when VOUT is low. FB (MAX830) For the MAX830, the FB input is the internal error amplifier's input, and should be connected to the midpoint of a potential divider between VOUT and GND (Figure 1). The output voltage, during regulation, will be that value that forces 2.21V (VREF) at the FB pin. 11 VC Error-amplifier output. A series RC network connected to this pin compensates the device. Output swing is limited to about 5.8V in the positive direction and -0.7V in the negative direction. VC can also synchronize the device to an external TTL clock in the 115kHz to 170kHz range. 5, 7, 10, 12 GND Ground requires a short, low-noise connection to ensure good load regulation. The internal reference is referred to GND, so errors at this pin are multiplied by the error amplifier. Use thick copper for low thermal resistance. 13, 14, 15, 16 VSW Internal power switch output (rated for 1A load current) 1, 2, 3, 4 VIN VIN supplies power to the internal circuitry and also connects to the collector of the internal power switch. VIN must be bypassed with a low-ESR capacitor, typically 100µF. 6 ILIM Switch-current limit can be reduced by connecting an external resistor (RLIM) from ILIM to GND (See Note 7 in Electrical Characteristics). Leave ILIM floating for maximum current limit. 9 SHUT 8 Shutdown is achieved by pulling SHUT low. Leave SHUT floating for normal operation. __________Applications Information Although the MAX830–MAX833 are high-efficiency step-down voltage converters, certain precautions are required to avoid excessive chip temperature (the absolute maximum rating for this parameter, T j , is +125°C). The 16-pin SO package has thermal resistance of +55°C/W when mounted properly; this limits continuous chip power dissipation to the 1W range. When installing these chips: 1) Use wide and, if possible, thick copper traces to connect the leads (especially the GND pins) to reduce thermal resistance. 2) Bond the package firmly to the board or use a clipstyle heatsink. A very small drop of thermal paste between the chip package and the copper ground plane is also helpful. 3) Confirm that the range of device operation is such that the chip temperature does not exceed the allowed maximum of T j = +125°C. This can be determined from Tables 1 and 2. Tables 1 and 2 show numbers for maximum allowed load current based on not exceeding the Tj = +125°C limit. If the input voltage range, ambient temperature, and/or output voltage setting allow for an unsafe level of load current, limit the load current to a safe value by connecting the appropriate resistor from the ILIM pin to GND. With no external resistor, the preset switch cur4 rent limit (typically 1.7A) will limit the load current to about 1.3A. Table 1 shows safe operating load currents for the MAX830 for various values of input and output voltage and at three different ambient temperatures of TA = +25°C, +45°C, and +70°C, respectively. Table 2 shows the same information, but for the fixed output voltage MAX831, MAX832, and MAX833. When consulting these tables, note that power surges of less than 30sec need not be considered from a thermal standpoint. It is important for proper regulation, however, that a power surge not require a peak switch current exceeding the 1.2A (min) switch current limit. Also, the inductor’s current rating should exceed IPEAK. For highest efficiency, the inductor series resistance should be 0.4Ω or less. IPEAK and ILOAD are related by the following formula: [VOUT x (VIN - VOUT)] IPEAK = ILOAD + —————————— VIN x L x 200,000 Example: MAX830 with VIN = 30V, VOUT = 15V, ILOAD = 0.5A continuous, L = 100µH and TA = +70°C: IPEAK = 0.86A (which is below 1.2A (min) preset switch current limit); and from Table 1: maximum ILOAD allowed = 0.8A continuous (i.e., operation is safe). _______________________________________________________________________________________ 5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators MAX830–MAX833 Table 1. MAX830 Maximum Load Current (continuous with qjA = +55°C/W) vs. Output Voltage and Ambient Temperature CONTINUOUS LOAD CURRENT OUTPUT VOLTAGE TA = +25°C TA = +45°C TA = +70°C Up to 10V 1A 1A 1A 10V to 15V 1A 1A 0.8A 15V to 20V 1A 0.8A 0.7A 20V to 25V 0.8A 0.7A 0.6A Table 2. MAX831/MAX832/MAX833 Maximum Load Current (continuous with qjA = +55°C/W) vs. Ambient Temperature CONTINUOUS LOAD CURRENT OUTPUT VOLTAGE TA = +25°C TA = +45°C TA = +70°C 1A 1A 1A Fixed: 5V, 3.3V or 3V INPUT UP TO 30V 100µH VSW VIN 100µF VOUT MBR350 R1 MAX830 VC 470µF FB R2 10k GND 0.047µF [ VOUT = 1 + R1 R2 ] x 2.21V STEP-DOWN CONVERTER Figure 1. MAX830 Typical Operating Circuit _________________________________________________________________________________________________ _______________________________________________________________________________________ 5