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19-0034; Rev 0; 5/92
MAX731 Evaluation Kit
_______________General Description
The MAX731 evaluation kit (EV kit) facilitates assembly and evaluation of Maxim's MAX731 +5V step-up currentmode DC-DC converter. The EV kit includes all needed components (unassembled) and a printed circuit board. When completed, the EV kit is a working DC-DC step-up converter with +5V output voltage at 200mA. Typical full-load efficiencies are 82% to 87%. The MAX731 uses current-mode pulse-width modulation (PWM) to provide precise output regulation and low subharmonic noise. Typical no-load supply current is 2mA. The MAX731 features cycle-by-cycle current limiting, overcurrent limiting, external shutdown, and programmable soft-start protection. The EV kit components are suitable for through-hole mounting to make construction and evaluation easy. Refer to the MAX731 data sheet for detailed electrical and operating specifications.
____________________________Features
o Load Currents Guaranteed to 200mA with No External MOSFET o Step-Up from a 2.0V Input o 170kHz High-Frequency Current-Mode PWM o 82% to 87% Typical Efficiencies at Full Load o Overcurrent and Soft-Start Protection o Shutdown Capability
MAX731 EV Kit
______________Ordering Information
PART MAX731EVKIT-DIP TEMP. RANGE 0C to +70C BOARD TYPE Through Hole
______________________________EV Kit
____________________Component List
DESIGNATION IC1 None C1, C7 C2, C8 C3 C4, C5, C6 D1 R1 J2 QTY 1 1 2 2 1 3 1 1 1 DESCRIPTION MAX731CPA Printed circuit board 0.1F ceramic capacitors 150F, 25V electrolytic capacitors MAXC001 4.7F capacitor 0.15F ceramic capacitors Schottky diode 1N5817 1/4W, 5% 10k resistor Jumper SOURCE Maxim Maxim
Maxim
Motorola
L1
1
22H inductor
Sumida RCH-110-220M Coilcraft PCH-27-223 Wilco ITS220 FAX (708) 956-0702 FAX 03-3607-5428 FAX (708) 639-1469 FAX 8862-268-2092 FAX (317) 293-9462
_______________Terminal Description
TERMINAL NAME VIN SHDN FUNCTION Positive Input. Connect to positive teminal of voltage power supply. SHUTDOWN - active low. Ground to power down; ties to VIN for normal operation. Output power FET is held off when SHDN is low. Circuit Ground. Connect to negative terminal of input voltage supply. This is also the output voltage negative terminal. Positive Output. Connect to load. 1
Sumida USA Sumida Japan Coilcraft USA Coilcraft Taiwan Wilco
(708) 956-0666 03-3607-5111 (708) 639-6400 8862-268-2146 (317) 293-9300
GND VOUT
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
MAX731 Evaluation Kit MAX731 EV Kit
________________Operating Principle
This switch-mode regulator uses a current-mode pulsewidth modulation (PWM) controller as a simple boost regulator to convert an unregulated 2.0V DC voltage to a higher output. The current-mode PWM architecture provides cycle-by-cycle current limiting and excellent load-transient response. For detailed description, see the MAX731/MAX752 data sheet. inductors. When installing the inductors, make sure one end is connected on the trace leading to VIN. The other inductor terminal connects to the same trace as diode D1. Only one of the jumpers must be installed; install J2 for the MAX731. Examine the board for parts incorrectly inserted before applying power. Verify that the electrolytic capacitors' positive terminal aligns with the plus (+) sign on the printed circuit board. The cathode ban on D1 must be as indicated on the board legend.
_____________Assembly Instructions
CAUTION: Observe the following safety measures. 1. Do not apply power until all components are installed. 2. Do not solder or work on circuit while power is applied. 3 Never apply more than the maximum supply voltage to VIN. The EV kit is shipped unassembled. You will need the following tools for assembly: 1. Long-nose pliers 2. Wire cutters 3. 30W soldering iron and rosin-core solder 4. Hook-up wire (#18-22AWG) for the input and output connections CAUTION: Using a high-wattage soldering iron or acid-core solder may damage the board and components. Install the components as shown in Figure 1 and solder them in place. Observe polarity on the capacitors, diode, and IC. Keep all leads short. Inspect the completed board for cleanliness, shorts, and solder splashes. A socket may be added for IC1, but it may degrade performance with high load currents. In general, sockets are not recommended. The printed circuit board accommodates a variety of
_____________________________Testing
When testing, use an adjustable bench power supply as a source (VIN). Start with no load, then add a resistive load before connecting to the actual circuit. This procedure minimizes the chances of damaging the device and ensures that accurate data is collected in an orderly manner. The bench power supply should have a 3A to 6A capability, and its current limiting should be set to prevent interaction with the EV kit's peak currents. The input voltage range is 2.0V to 5.0V. The maximum load current is 200mA.
Shutdown
The DC-DC converter operates only if SHDN is connected to VIN. Even with SHDN grounded, however, there is a DC path from VIN to VOUT, and VOUT will be one diode drop lower than VIN. This is due to the basic topography of step-up converters, and would be the case even with IC1 removed from the circuit. Some current (VIN/10k) also flows from VIN to SHDN, due to R1.
Internal Reference
The +1.23V bandgap reference supplies up to 100A at VREF. A 4.7F reference bypass capacitor is recommended for the MAX731.
2
_______________________________________________________________________________________
MAX 731 Evaluation Kit MAX731 EV Kit
VIN
C2 150F J1 R1 10k L1 C1 0.1F IC1 1 2 3 V+ 8 VOUT 7 J2 D1 1N5817
INSTALL J2 FOR THE MAX731.
C8 C7 0.1F 150F
SHDN
SHDN VREF
VOUT
MAX731
SS CC LX GND
6 5
C3
C4 4 4.7F 0.15F
Figure 1c. DIP PC Layout, Component Side (1X scale)
C5 0.15F
C6 0.15F
Figure 1a. EV Kit Schematic
Figure 1d. DIP PC Layout, Solder Side (1X scale)
Figure 1b. DIP PC Layout, Through-Hole Placement (1X scale)
_______________________________________________________________________________________
3
MAX731 Evaluation Kit MAX731 EV Kit
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
4 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1992 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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