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19-1876; Rev 0; 12/00
MAX1742/MAX1842 Evaluation Kits
General Description
The MAX1742 and MAX1842 evaluation kits (EV kits) provide a +1.8V adjustable output voltage from a +3V to +5.5V input source. The MAX1742 delivers up to 1A of output current, and the MAX1842 delivers up to 2.5A of output current. The MAX1742/MAX1842 are step-down switching regulators with internal synchronous-rectifiers that operate up to 1MHz, which minimizes external components. The devices feature resistor-programmable, fixed off-time current-mode operation for superior load- and line-transient response, and achieve efficiencies up to 95%. The MAX1742/MAX1842 EV kits can also be used to evaluate other output voltages by adding feedback resistors R1 and R2 or by using the jumper-selectable +1.1V, +1.5V, +1.8V, or +2.5V settings.
____________________________Features
o 1A Output Current for MAX1742 2.5A Output Current for MAX1842 o Up to 1MHz Switching Frequency o Up to 95% Efficiency o Synchronous Rectification for Improved Efficiency o No External Schottky Diode Required o Output Voltage +1.1V, +1.5V, +1.8V, or +2.5V Selectable +1.1V to VIN Adjustable o +3V to +5.5V Input Voltage Range o <1A (typ) IC Shutdown Current o Surface-Mount Construction o Fully Assembled and Tested
Evaluate: MAX1742/MAX1842
Ordering Information
PART MAX1742EVKIT MAX1842EVKIT TEMP. RANGE 0C to +70C 0C to +70C IC PACKAGE 16 QSOP 16 QSOP
Component List
DESIGNATION QTY DESCRIPTION 10F, 6.3V, X5R ceramic capacitor Taiyo Yuden JMK316BJ106ML, Murata GRM42-6X5R106K6.3, or Panasonic ECJ3YB0J106K MAX1742 47F, 6.3V low-ESR capacitor Sanyo 6TPA47M (POSCAP) MAX1842 100F, 6.3V low-ESR capacitor Sanyo 6TPC100M (POSCAP) 2.2F, 10V, X5R ceramic capacitor Taiyo Yuden LMK212BJ225MG 0.01F, 50V, X7R ceramic capacitor 470pF, 50V, X7R ceramic capacitor 1F, 10V, X7R ceramic capacitor Taiyo Yuden LMK212B105KG or Murata GRM40X7R105K010 Not installed R1 R2 R3 R4 R5 U1 NONE 0 0 1 1 1 1 3 DESIGNATION C8 JU1, JU3 JU2 QTY 1 2 1 DESCRIPTION 33F, 10V low-ESR capacitor Sanyo 10TPA33M (POSCAP) 2-pin headers 4-pin header MAX1742 5.3H, 1.9A inductor Sumida CDRH5D28-5R3NC MAX1842 2.2H, 3.8A inductor Sumida 4762-TO54, Coiltronics UP1B-2R2, or Murata LQS66C2R2M04 Not installed Not installed 10 5% resistor 1M 5% resistor 75k 1% resistor MAX1742EEE or MAX1842EEE Shunts
C1
1
C2
1
L1
1
C3 C4 C5
1 1 1
C6 C7
1 0
________________________________________________________________ Maxim Integrated Products
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MAX1742/MAX1842 Evaluation Kits Evaluate: MAX1742/MAX1842
Component Suppliers
SUPPLIER AVX Coiltronics Murata Panasonic Sanyo Sprague Sumida Taiyo Yuden PHONE 803-946-0690 561-241-7876 814-237-1431 201-392-7522 619-661-6835 603-224-1961 847-956-0666 408-573-4150 FAX 803-626-3123 561-241-9339 814-238-0490 201-392-4441 619-661-1055 603-224-1430 847-956-0702 408-573-4159
Jumper Selection
The 2-pin header JU1 selects the MAX1742/MAX1842 shutdown mode. Table 1 lists the jumper options.
Output Voltage Selection
The MAX1742 and MAX1842 EV kits are shipped with the output voltage set to +1.8V. To change the output voltage to +1.1V, +1.5V, or +2.5V, move the shunt on JU2 to the location listed in Table 2. For other voltages, remove the shunt on JU3, place a shunt on JU2 (1-3), and add resistors R1 and R2. Never operate the board with the shunt removed from jumper JU3, unless resistors R1 and R2 are installed. Use the following equation for calculating the resistors: R2 = R1 (VOUT / 1.1 - 1) Typical values for R1 are 10k to 56k. Note: The switching frequency of the MAX1742 and MAX1842 EV kits is 900kHz when the input voltage is +5V and the output voltage is +1.8V. This frequency will change when the input or output voltages change. When operated from a 3.3V input voltage, the switching frequency will be 650kHz. Do not operate the MAX1742 or MAX1842 above 1MHz. To set the switching frequency, change the TOFF resistor (R5) and the inductor. Refer to the MAX1742/MAX1842 IC data sheet to determine the values.
Note: Please indicate that you are using the MAX1742 or MAX1842 when contacting these suppliers.
Quick Start
The MAX1742 and MAX1842 EV kits are fully assembled and tested surface-mount boards. Follow the steps below to verify board operation. Do not turn on the power supply until all connections are completed. 1. Verify that a shunt is on JU1 (shutdown disable) to enable operation and on JU2 (1-4) to set the output voltage for 1.8V. 2. Connect a voltmeter and load (if any) to VOUT and GND. 3. Connect a +3V to +5.5V supply to the pads marked VIN and GND. 4. Turn on the power and verify that the output voltage is +1.8V. 5. Refer to the Output Voltage Selection section to modify the board for a different output voltage.
Input Capacitors
The MAX1742 and MAX1842 EV kits have a 33F tantalum polymer capacitor and a 10F ceramic capacitor on the input, but only the 10F is actually needed. The 33F capacitor may be needed to stabilize the input if a lab power supply is connected to the EV kit through long wires or if it has a poor transient response. In a typical application, where the MAX1742/MAX1842 input is directly connected to the output of a regulated supply, the additional capacitance will not be needed.
Detailed Description
The MAX1742 and MAX1842 EV kits provide a +1.8V output voltage from a +3V to +5.5V input voltage. The MAX1742 EV kit delivers up to 1A of output current, and the MAX1842 EV kit delivers up to 2.5A of output current. Continuous operation at 2.5A with high ambient temperatures may be limited due to thermal consideration. (See the MAX1742/MAX1842 data sheet, Extended Current Limit section).
Table 1. Jumper JU1 Function
SHUNT LOCATION Open Closed (Default) SHDN PIN Connected to GND through 1M (R4) Connected to VIN MAX1742/MAX1842 OUTPUT Shutdown mode, VOUT = 0 MAX1742/MAX1842 enabled, VOUT = +1.8V.
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MAX1742/MAX1842 Evaluation Kits Evaluate: MAX1742/MAX1842
Table 2. Output Voltage Configurations
OUTPUT VOLTAGE (V) 1.1 1.5 *1.8 2.5 Adjustable (Set by resistor divider R1/R2) JU3 Closed Closed Closed Closed Open JU2 1-3 Open 1-4 1-2 1-3
*Default
VIN +3V TO +5.5V L1 GND C8 33F 10V R3 10 C1 10F 6.3V 2 IN 4 IN C2
MAX1742 5.3H 47F, 6.3V
MAX1842 2.2H 100F, 6.3V
L1 LX LX 16 14 C2
12 C3 2.2F R4 1M JU1 1
VOUT +1.8V
VCC
U1 MAX1742 MAX1842
SHDN
5 6 7
SS COMP TOFF FBSEL 11
3 LX 15 PGND 13 PGND 8 FB 10 REF 9 GND
GND
PGND C6 1F
GND R2 OPEN
C4 0.01F
C5 470pF
R5 75k 1%
C7 OPEN
JU3
R1 OPEN 2 JU2 3 1 4
Figure 1. MAX1742/MAX1842 EV Kits Schematic
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MAX1742/MAX1842 Evaluation Kits Evaluate: MAX1742/MAX1842
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Figure 2. MAX1742/MAX1842 EV Kits Component Placement Guide--Component Side
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Figure 3. MAX1742/MAX1842 EV Kits PC Board Layout-- Component Side
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Figure 4. MAX1742/MAX1842 EV Kits PC Board Layout-- Solder Side
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) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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