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19-2611; Rev 0; 10/02
MAX1875 Evaluation Kit
General Description
The MAX1875 evaluation kit (EV kit) demonstrates a lowcost application circuit. This dual-PWM synchronous DCto-DC converter operates from unregulated AC adapters and generates precision, low-voltage rails for broadband gateways, digital TVs, cable modems, and settop boxes. The MAX1875 EV kit provides dual 1.8V and 3.3V output voltages from an 8V to 18V input voltage range. It delivers up to 3.5A output current for the 1.8V output and the 3.3V output, with greater than 90% efficiency. Both converters operate 180 degrees out-of-phase to reduce input ripple current. The EV kit operates at 100kHz switching frequency. This EV kit is a fully assembled and tested circuit board. It also allows evaluation of other output voltages in the 0.75V to 15V range. The MAX1875 EV kit can also be used to evaluate the MAX1876 and MAX1858.
PART MAX1875EVKIT
Features
o 8V to 18V Input Voltage Range o 1.8V and 3.3V Adjustable Output Voltages o 3.5A Output Current (1.8V Output) o 3.5A Output Current (3.3V Output) o Lossless Foldback Current Limit o 100kHz Switching Frequency o RST Output with 140ms Delay (MAX1876/MAX1858 only) o 180 Degree Out-of-Phase Operation o 24-Pin QSOP Package o Low-Cost Components o Fully Assembled and Tested
Evaluates: MAX1875/MAX1876/MAX1858
Ordering Information
TEMP RANGE 0C to +70C IC PACKAGE 24 QSOP
Component List
DESIGNATION QTY C1, C4 C5, C6, C12 C7 C8 C9, C10, C11, C13, C14 C17 C18 C19 C20 2 3 1 1 5 1 1 1 1 DESCRIPTION 390F, 25V aluminum electrolytic capacitors Sanyo 25MV390AX 0.1F ceramic capacitors (0805) 0.39F ceramic capacitor (0805) 0.33F ceramic capacitor (0805) 470F, 10V aluminum electrolytic capacitors Sanyo 10MV470AX 2200pF ceramic capacitor (0805) 1500pF ceramic capacitor (0805) 0.22F, 16V X5R ceramic capacitor (0805) Taiyo Yuden EMK212BJ224KG 4.7F, 10V X5R ceramic capacitor (1206) Taiyo Yuden LMK316BJ475ML 0.22F, 50V X7R ceramic capacitor (0805) Taiyo Yuden UMK212BJ224MG or TDK C2012X7R1H224M 0.01F ceramic capacitors (0805) Not installed (open) 100mA, 30V dual Schottky diode 23-pin SOT Central Semiconductor CMPSH-3A 15H 5A power inductor DESIGNATION QTY L2 N1A, N1B, N2A, N2B D2-D5 R1 R2, R4 R3 R5 R6 R7 R8 R9 R10 R11 R12, R13 R14 R15 JU1, JU2 U1 None None 1 2 0 1 2 1 1 1 1 1 1 1 1 2 1 1 2 1 2 1 DESCRIPTION 27H 5A power inductor Dual N-channel MOSFETs 8-pin SO Fairchild FDS6990A Not installed (open) 8.06k 1% resistor (0805) 10k 1% resistors (0805) 23.2k 1% resistor (0805) 60.4k 1% resistor (0805) 2.7k 5% resistor (0805) 2k 5% resistor (0805) 49.9k 1% resistor (0805) 69.8k 1% resistor (0805) 100k 5% resistor (0805) 20 5% resistor (0805) 3.9 5% resistors (0805) 154k 1% resistor (0805) 84.5k 1% resistor (0805) 3-pin headers MAX1875EEG 24-pin QSOP Shunts MAX1875 PC board
C21 C22, C23 C2, C3, C15 D1 L1
1 2 0 1 1
________________________________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
MAX1875 Evaluation Kit Evaluates: MAX1875/MAX1876/MAX1858
Component Suppliers
SUPPLIER Central Semiconductor Fairchild Nihon Sanyo Taiyo Yuden TDK Tyco Electronics (Transpower) PHONE 516-435-1110 408-721-2181 847-843-7500 619-661-6835 408-573-4150 847-390-4373 888-978-2638 FAX 516-435-1824 408-721-1635 847-843-2798 619-661-1055 408-573-4159 847-390-4428 605-886-8995 WEBSITE www.centralsemi.com www.fairchildsemi.com www.niec.co.jp www.sanyovideo.com www.t-yuden.com www.component.tdk.com www.trans-power.com
Note: Please indicate that you are using the MAX1875 when contacting these component suppliers.
Quick Start
Before beginning, the following equipment is required: * 8V to 18V power supply * Electronic loads capable of sinking 3.5A each * Digital multimeters (DMMs) * 100MHz dual-trace oscilloscope Follow these steps to verify board operation. Do not turn on the power supply until all connections are completed: 1) Ensure that the circuit is connected correctly to the supply and electronic loads before applying any power. Set electronic loads in resistive mode. 2) Verify that the shunts are across JU1 pins 1 and 2 as well as JU2 pins 2 and 3. 3) Turn on power supply. 4) Verify that the output voltages are 1.8V and 3.3V.
Jumper Settings
Table 1. Jumper JU1 Functions (EN Mode Selection)
JU1 1 and 2 2 and 3 Not Installed EN PIN Connected to VL Connected to GND Connected to EN pad MAX1875 OUTPUT MAX1875 enabled, VOUT1 = 1.8V, VOUT2 = 3.3V Shutdown mode, VOUT1 = 0V, VOUT2 = 0V MAX1875 must be enabled by an external signal
Table 2. Jumper JU2 Functions (SYNC Mode Selection)
JU2 1 and 2 SYNC PIN Connected to VL EFFECT Used to sync up an additional MAX1875. CKO is 2x DH1 and phase shifted by 90 degrees. Used to sync up an additional single buck. CKO is the same frequency and phase as DH1. External clock is applied to SYNC input (200kHz typ)
Evaluating Other Output Voltages
The EV kit outputs are programmed for 1.8V and 3.3V. However, the output voltages can also be adjusted between 1V and 15V by selecting R1/R2 and R3/R4 values. Select the feedback resistors R2 and R4. R1 and R3 are then given by: R1 (or R3) = R2 (or R4) x [(VOUT / VFB) - 1] where VFB = 1V. Refer to the MAX1875 data sheet for selection of output capacitors, inductors, and compensation networks.
2 and 3 Not Installed
Connected to GND Connected to SYNC pad
Evaluating the MAX1876 and MAX1858
Replace U1 with the MAX1876/MAX1858.
2
_______________________________________________________________________________________
BST1 BST2 1 L D1 VL 3 VIN 7 C3 OPEN C4 390F 25V 8 C21 0.22F 50V C12 0.1F 5 V+ 14 DH1 DH2 BST2 LX2 5 6 D3 OPEN 3 C23 0.01F N2-B 17 DL1 DL2 GND PGND U1 11 R7 2k 12 COMP1 COMP2 1 R6 2.7k VL C7 0.39F D4 OPEN 13 RST VOUT1 JU1 24 EN REF 6 C19 0.22F ILIM1 10 VOUT2 8 CKO R14 154k 1% 4 OSC ILIM2 3 R8 49.9k 1% R5 60.4k 1% R15 84.5k 1% R9 69.8k 1% (MAX1876 ONLY) 1 2 VL 3 9 SYNC 1 2 JU2 3 VL C17 2200pF C18 1500pF FB1 MAX1875 FB2 R2 10k 1% D5 OPEN 2 4 7 18 20 R13 22 3.9 C6 0.1F 21 L2 27H BST2 1 VOUT2 3.3V BST1 LXI 16 R12 3.9 15 23 N2-A 2 19 VL N1-B C20 4.7F 10V VL 5V R11 20 R 2
VIN 8V TO 18V 5 4 BST1 C5 0.1F 8 N1-A 2 1 7
Figure 1. MAX1875 EV Kit Schematic
C1 C2 390F OPEN 6 25V 3 L1 15H D2 OPEN C22 0.01F R3 23.2k 1% C15 C13 C14 470F 470F OPEN 10V 10V GND R1 8.06k 1% R4 10k 1% C8 0.33F R10 100k
GND
VOUT1 1.8V
GND
C10 C11 C9 470F 470F 470F 10V 10V 10V
RST
EN
SYNC
Evaluates: MAX1875/MAX1876/MAX1858
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CKO
MAX1875 Evaluation Kit
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MAX1875 Evaluation Kit Evaluates: MAX1875/MAX1876/MAX1858
Figure 2. MAX1875 EV Kit Component Placement Guide-- Top Silkscreen
Figure 3. MAX1875 EV Kit PC Board Layout--Component Side
Figure 4. MAX1875 EV Kit 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) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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