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19-1454; Rev 0; 4/99
MAX1685 Evaluation Kit
General Description
The MAX1685 evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board that contains a pulse-width-modulated (PWM), step-down DC-DC converter. The EV kit provides a +3.33V output voltage from a +3.5V to +14V input source. It delivers up to 1A output current. The MAX1685 features internal MOSFET switches, low dropout voltage (100% duty-cycle operation), and an accurate +1.25V reference. The MAX1685 EV kit provides low quiescent current, synchronous rectification, and high efficiency (up to 95%) for maximum battery life. Operation at 600kHz allows the use of a tiny surface-mount inductor. The MAX1685 EV kit can also be used to evaluate the MAX1684, which operates at 300kHz and has slightly higher efficiency than the MAX1685. o +3.5V to +14V Input Voltage Range o Fixed or Adjustable Output Voltage +3.33V (Fixed) +1.25V to VIN (Adjustable) o Guaranteed 1A Output Current o 100% Duty Cycle in Dropout o 600kHz Fixed-Frequency PWM Operation o Internal MOSFET Switch and Synchronous Rectifier o 2A IC Shutdown Current o Surface-Mount Components o Fully Assembled and Tested
Features
Evaluates: MAX1684/MAX1685
Component List
DESIGNATION QTY C1 1 DESCRIPTION 22F, 35V tantalum capacitor AVX TPSE226M035R0300 or Sprague 593D226X0035E2T 100F, 10V, low-ESR tantalum capacitor AVX TPSD107M010R0080, Sprague 594D107X0010C2T, or Sanyo 10TPB100M 0.1F ceramic capacitors 0.01F ceramic capacitor 1F, 16V X7R ceramic capacitor Taiyo Yuden EMK316BJ105KL or TDK C3216X7R1C105M Not installed 1A Schottky diode Motorola MBRS130LT3, International Rectifier 10BQ040, Nihon EC10QS03, or Nihon EP10QY03 10H inductor Sumida CDRH6D28-100NC or Sumida CDRH73-100 Not installed 100k 5% resistors MAX1685EEE 3-pin header 2-pin headers Shunt (JU1) MAX1684/MAX1685 PC board MAX1684/MAX1685 data sheet SUPPLIER AVX Dale-Vishay International Rectifier Motorola Nihon Sanyo Sprague Sumida TDK Taiyo Yuden
Ordering Information
PART MAX1685EVKIT TEMP. RANGE 0C to +70C IC PACKAGE 16-QSOP
C2
1
Note: To evaluate the MAX1684, request a MAX1684EEE free sample with the MAX1685 EV kit.
C3, C4, C5, C9 C6 C7 C8
4 1 1 0
Component Suppliers
PHONE 803-946-0690 402-564-3131 310-322-3331 602-303-5454 661-843-7500 619-661-6835 603-224-1961 708-956-0666 847-390-4373 408-573-4150 FAX 803-626-3123 402-563-6418 310-322-3332 602-994-6430 661-843-2798 619-661-1055 603-224-1430 708-956-0702 847-390-4428 408-573-4159
D1
1
L1 R1, R2 R3, R4 U1 JU1 JU2, JU3 None None None
1 0 2 1 1 2 1 1 1
Note: Please indicate that you are using the MAX1685 when contacting these component suppliers.
1
________________________________________________________________ Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
MAX1685 Evaluation Kit Evaluates: MAX1684/MAX1685
Quick Start
The MAX1685 EV kit is fully assembled and tested. Follow these steps to verify board operation. Do not turn on the power supply until all connections are completed. 1) Connect a +3.5V to +14V supply to the VIN pad. Connect ground to the GND pad. 2) Connect a voltmeter and load (if any) to the VOUT pad. 3) Verify that the shunt is across JU1 pins 1 and 2. 4) Turn on the power supply and verify that the output is at +3.33V.
Operating Mode The MAX1685 operates in one of four modes to optimize performance: a fixed-frequency (PWM) mode switches at a fixed frequency for easy postfiltering; a low-power standby mode; a synchronizable PWM mode that uses an external clock to minimize harmonics; and a normal mode that extends battery life by operating in PWM mode under heavy loads and PFM mode under light loads to reduce power consumption.
Table 1. Jumper JU1 Functions
SHUNT LOCATION 1&2 SHDN PIN Connected to VIN Connected to GND MAX1685 OUTPUT MAX1685 enabled, VOUT = +3.33V Shutdown mode, VOUT = 0
Detailed Description
Jumper Selection
Shutdown Mode The MAX1685 EV kit features a shutdown mode that reduces the MAX1685's quiescent current to 2A, preserving battery life. The 3-pin header, JU1, selects the shutdown mode (Table 1).
2&3
3.5V TO 14V VIN C1 22F 35V 3 IN AIN LX 15 SHDN PGND 1 CVH C3 0.1F LX 13 14 16
L1 10H C2 100F 10V VOUT 1 2 3
VOUT +3.33V
2 VIN SHDN JU2 VL SYNC/PWM VL STBY JU3 9 R3 100k R4 100k C4 0.1F 10 C5 0.1F 8 11 6 JU1 C9 0.1F
D1
1 2 3
U1
MAX1685 SYNC/PWM BOOT 12
JU4 STBY REF 7
C8 OPEN
R1 OPEN
FB
ILIM/SS CC AGND 5 CVL 4 C7 1F 16V VL
R2 SHORT (PC TRACE)
C6 0.01F
Figure 1. MAX1685 EV Kit Schematic
2 _______________________________________________________________________________________
MAX1685 Evaluation Kit
The EV kit operates at 600kHz switching frequency and allows the use of a tiny inductor. The switching frequency can also be synchronized to an external clock ranging from 360kHz to 700kHz. The 2-pin headers JU2 and JU3 select the operating mode (Tables 2 and 3). 4.7pF capacitor at location C8. For output voltages greater than +5.5V, cut the trace between pins 1 and 2 of JU4, and short pins 2 and 3 of JU4. Refer to the Detailed Description section of the MAX1684/ MAX1685 data sheet for further details.
Evaluates: MAX1684/MAX1685
Evaluating Other Output Voltages
The EV kit output is preset to +3.33V. However, the output voltage can also be adjusted between 1.25V and VIN by selecting R1 and R2 values. Select feedback resistor R2 in the 20k to 100k range. R1 is then given by: R1 = R2 [(VOUT / VFB) - 1] where VFB = 1.25V. Be sure to cut the PC trace shorting the pads of R2 before installing the resistor. Install a
Evaluating the MAX1684
This EV kit can also be used to evaluate the MAX1684. Simply replace the MAX1685 with a MAX1684EEE, and change L1 to a 22H, 1.7A inductor. Refer to the Inductor Selection section of the MAX1684/MAX1685 data sheet for more information.
Table 2. Jumper JU2 Functions
SHUNT LOCATION On SYNC/PWM PIN Connected to VL Connected to GND Off (not installed) OPERATING MODE MAX1685 operates in fixed-frequency mode. MAX1685 operates in normal mode. SYNC/PWM pin is driven by an external clock between 360kHz and 700kHz.
Table 3. Jumper JU3 Functions
SHUNT LOCATION On STBY PIN Connected to VL OPERATING MODE Operation depends on the JU2 setting. MAX1685 operates in low-power mode. This overrides the JU2 setting.
Off (not installed)
Connected to GND
Driven from external clock
_______________________________________________________________________________________
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MAX1685 Evaluation Kit Evaluates: MAX1684/MAX1685
1.0"
Figure 2. MAX1685 EV Kit Component Placement Guide-- Component Side
1.0"
Figure 3. MAX1685 EV Kit PC Board Layout--Component Side
1.0"
Figure 4. MAX1685 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) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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