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19-0167; Rev 2; 6/95
5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators
_______________General Description
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.
UAL IT MAN TION K T VALUA A SHEE E T WS DA FOLLO
___________________________Features
o Input Range: Up to 30V o 1A On-Chip Power Switch o Adjustable Output (MAX830) Fixed Outputs: 5V (MAX831) 3.3V (MAX832) 3V (MAX833) o 100kHz Switching Frequency o Excellent Dynamic Characteristics o Few External Components o 8mA Quiescent Current o 16-Pin SO Package o Evaluation Kit Available
MAX830-MAX833
______________Ordering Information
PART MAX830CWE MAX831CWE MAX832CWE MAX833CWE TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 16 Wide SO 16 Wide SO 16 Wide SO 16 Wide SO
_______________________Applications
Distributed Power from High-Voltage Buses High-Current, High-Voltage Step-Down Applications Multiple-Output Buck Converter
__________Typical Operating Circuit
__________________Pin Configuration
TOP VIEW
INPUT 8V TO 30V VIN 100F VSW
100H*
OUTPUT 5V AT 1A
V IN 1 V IN 2 V IN 3
16 V SW 15 V SW 14 V SW
MAX831
VC 10k 0.047F SENSE
MBR350
V IN 4 GND 5
470F GND
I LIM 6 GND 7 (FB) SENSE 8
MAX830 MAX831 MAX832 MAX833
13 V SW 12 GND 11 V C 10 GND 9 SHUT
Wide SO
Tj (MAX) = +125C, jA = +55C/W* ( ) 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).
STEP-DOWN CONVERTER
* CoilCraft DO3316-104
________________________________________________________________ Maxim Integrated Products
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5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators MAX830-MAX833
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 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.
ILIM Voltage (forced). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5V Operating Temperature Range. . . . . . . . . . . . . . . . . . . . . 0C to +70C Junction Temperature Range . . . . . . . . . . . . . . . . . . . . . 0C to +125C Storage Temperature Range . . . . . . . . . . . . . . . . . . . -65C to +160C Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300C
ELECTRICAL CHARACTERISTICS
(VIN = 25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Supply Voltage Range Switch-On Voltage (Note 2) Switch-Off Leakage ISW = 0.2A ISW = 1A VIN = 25V, VSW = 0V VIN = 30V, VSW = 0V TA = +25C 8 140 7.3 3.5 1.2 TA = +25C 85 TA = +25C Switching Frequency VFB or VSENSE = 0V (Note 6) Switching-Frequency Line Regulation Error-Amplifier Voltage Gain Error-Amplifier Transconductance Error-Amplifier Source Current VFB = 2.0V (MAX830) or VSENSE = 2.0V (MAX831/832/833) VFB = 2.5V (MAX830) or VSENSE = 5.5V (MAX831/832/833) 8V VIN 30V 1V VC 4V TA = +25C TA = +25C TA = +25C 3000 100 TA = +25C 90 85 20 0.03 2000 5000 140 9000 225 0.10 %/V V/V mho A 1.7 1.2 0.8 90 100 110 120 kHz % CONDITIONS MIN 8 TYP MAX 30 1.1 1.4 150 250 11 500 8.0 4.8 2.2 A UNITS V V A mA A V
Supply Current (Note 3)
VIN 30V, VSENSE = 5.5V (MAX831/MAX832/ MAX833) or VFB = 2.5V (MAX830) VSHUT = 0.1V (Note 4)
Minimum Supply Voltage (Note 5)
Normal mode Startup mode ILIM open RLIM = 10k (Note 7) RLIM = 7k (Note 7)
Switch-Current Limit (Note 6) Maximum Duty Cycle
Error-Amplifier Sink Current
TA = +25C
0.6
1.0
1.7
mA
2
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5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SENSE Voltage VC = 2V CONDITIONS MAX831 MAX832 MAX833 MAX831 SENSE Divider Resistance TA = +25C MAX832 MAX833 SENSE Voltage Tolerance (Note 8) FB Bias Current Reference Voltage Reference Voltage Tolerance (Notes 8, 9) Output Voltage Line Regulation VC Voltage VC Voltage Temperature Coefficient SHUT Current SHUT Threshold VOUT (nominal) = 5V (MAX831), 3.3V (MAX832), or 3V (MAX833) VFB = VREF (MAX830) VC = 2V (MAX830) (Note 9) TA = +25C VREF (nominal = 2.21V) (MAX830) 1.0 8V VIN 30V 0% duty cycle 0% duty cycle VSHUT = 5V VSHUT = 0.1V (shutdown) (shutdown) 0.10 0.20 TA = +25C 0.005 1.5 -4 10 20 50 0.50 2.5 0.020 %/V V mV/C A V 2.155 TA = +25C MIN 4.85 3.20 2.90 3.0 2.5 2.2 TYP 5.00 3.30 3.00 5.0 4.2 3.8 0.5 0.5 0.5 2.21 0.5 MAX 5.15 3.40 3.10 8.0 7.0 6.5 2.0 3.0 2.0 2.265 1.5 % % A V k V UNIT
MAX830-MAX833
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 1s minimum switch-on time. Note 7: RLIM = LIM x 7.6k + 1k .
1A I
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.
_______________________________________________________________________________________
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5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators MAX830-MAX833
______________________________________________________________Pin Description
PIN NAME SENSE (MAX831/ 2/3) FB (MAX830) 11 5, 7, 10, 12 13, 14, 15, 16 1, 2, 3, 4 6 9 VC GND VSW VIN ILIM SHUT FUNCTION 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. 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. 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. 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. Internal power switch output (rated for 1A load current) 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 100F. 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. Shutdown is achieved by pulling SHUT low. Leave SHUT floating for normal operation.
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__________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 +125C). The 16-pin SO package has thermal resistance of +55C/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 = +125C. 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 = +125C 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 = +25C, +45C, and +70C, 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 0.4 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 = 100H and TA = +70C: 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).
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5V/3.3V/3V/Adjustable-Output, 1A, Step-Down, PWM, Switch-Mode DC-DC Regulators
Table 1. MAX830 Maximum Load Current (continuous with qjA = +55C/W) vs. Output Voltage and Ambient Temperature
OUTPUT VOLTAGE Up to 10V 10V to 15V 15V to 20V 20V to 25V CONTINUOUS LOAD CURRENT TA = +25C 1A 1A 1A 0.8A TA = +45C 1A 1A 0.8A 0.7A TA = +70C 1A 0.8A 0.7A 0.6A
MAX830-MAX833
Table 2. MAX831/MAX832/MAX833 Maximum Load Current (continuous with qjA = +55C/W) vs. Ambient Temperature
OUTPUT VOLTAGE Fixed: 5V, 3.3V or 3V CONTINUOUS LOAD CURRENT TA = +25C 1A TA = +45C 1A TA = +70C 1A
INPUT UP TO 30V VIN 100F VSW
100H
VOUT
MBR350
MAX830
VC 10k GND 0.047F FB
R1 470F R2
VOUT = 1 + R1 R2
[
]
x 2.21V
STEP-DOWN CONVERTER
Figure 1. MAX830 Typical Operating Circuit
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