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MAX686 Evaluation Kit
General Description
The MAX686 evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board that contains two separate switching-regulator circuits. The first circuit converts a +0.8V to +18V battery voltage to a +18V LCD bias voltage for currents up to 20mA. The second circuit converts a +0.8V to +12V battery voltage to a -17V voltage for currents up to 20mA. The MAX686 requires a +2.7V to +5.5V supply at VIN, but the inductor can be powered from as low as +0.8V. The device features an internal N-channel MOSFET switch, programmable current limit, and internal 6-bit DAC for digital adjustment of the output voltage. The MAX686 EV kit provides low quiescent current and high efficiency for maximum battery life. Operation up to 300kHz allows the use of a tiny surface-mount inductor.
____________________________Features
o Output Voltage: +18V Typical Positive Output (or +12.6V to +24V adjustable with up/down) -17V Typical Negative Output (or -22.7V to -11.4V adjustable with up/down) o Battery Input Voltage: +0.8V to +18V (Positive Output) +0.8V to +12V (Negative Output) o +2.7V to +5.5V VIN Supply Range o Up to 20mA Output Current o 6-Bit DAC-Controlled Output Voltage o Internal 0.5A, 28V N-Channel Switch o 1.3A IC Shutdown Current o Up to 300kHz Switching Frequency o Surface-Mount Components o Fully Assembled and Tested
Evaluates: MAX686
Ordering Information
PART MAX686EVKIT TEMP. RANGE 0C to +70C IC PACKAGE 16 QSOP
Component List
DESIGNATION C1, C8 QTY 2 DESCRIPTION 15F, 35V tantalum capacitors AVX TPSD156M035R0300 or Sprague 593D156X0035E2W 4.7F, 35V tantalum capacitor AVX TPSC475M035R0600 or Sprague 595D475X0035C 1F ceramic capacitor 0.1F ceramic capacitors 2.2F, 25V ceramic capacitor United Chemi-Con/Marcon THCR30E1E225Z 22pF ceramic capacitor 2.2F, 35V tantalum capacitor AVX TAJB225M035R or Sprague 595D225X0035B 100pF ceramic capacitor Schottky diodes Motorola MBR0540T1 DESIGNATION D4 L1, L2 R1, R9 R2, R3, R10, R11 R4, R5, R16, R17, Q1 R6, R7, R8, R12 R13, R14 R15 R18 U1, U2 JU1, JU4 JU2, JU3, JU5, JU6 None None None QTY 0 2 2 4 0 6 1 1 2 2 4 2 1 1 DESCRIPTION Not installed 22H inductors Sumida CD54-220 1M, 1% resistors 110k, 1% resistors Not installed 100k, 5% resistors 2, 5% resistor 100, 5% resistor MAX686EEE 3-pin headers 2-pin headers Shunt MAX686 PC board MAX686 data sheet
C2 C3 C4, C5, C11, C12, C13 C6 C7 C9 C10 D1, D2, D3
1 1 5
1 1 1 1 3
________________________________________________________________ Maxim Integrated Products
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For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
MAX686 Evaluation Kit Evaluates: MAX686
Component Suppliers
SUPPLIER AVX Coilcraft Coiltronics Dale-Vishay Motorola Sprague Sumida United Chemi-Con/ Marcon Vishay/Vitramon PHONE (803) 946-0690 (708) 639-6400 (561) 241-7876 (402) 564-3131 (602) 303-5454 (603) 224-1961 (708) 956-0666 (847) 696-2000 (203) 268-6261 FAX (803) 626-3123 (708) 639-1469 (561) 241-9339 (402) 563-6418 (602) 994-6430 (603) 224-1430 (708) 956-0702 (847) 696-9278 (203) 452-5670
For instructions on selecting the feedback resistors for other output voltages, refer to the Setting the Output Voltage section in the MAX686 data sheet.
Detailed Description
The MAX686 EV kit contains two separate switchingregulator circuits. The first circuit provides an +18V output for currents up to 20mA with 90% typical conversion efficiency. The second circuit provides a -17V output voltage for currents up to 20mA with 82% typical conversion efficiency. Both output voltages can be adjusted with the internal 6-bit DAC. Each output can be controlled by logic signals applied to the UP/DN pads.
Note: Please indicate that you are using the MAX686 when contacting these component suppliers.
Output Voltage Control
The output voltage is set with the combination of a voltage divider and a summing resistor from DACOUT. The 6-bit DAC is controlled with an up/down counter via the UP and DN pins. This EV kit has the UP and DN pins connected to ground via 100k resistors (R7, R8, R13, R14). On power-up, the output voltage is set to midscale. A rising edge on UP increases the output voltage; a rising edge on DN decreases the output voltage. Holding both UP and DN high resets the output voltage to mid-scale. Refer to the section Setting the Output Voltage in the MAX686 data sheet for more information on controlling the MAX686 output voltage.
Quick Start
The MAX686 EV kit is fully assembled and tested. Follow these steps to verify board operation. VIN and VBATT are separated on each circuit to demonstrate operation of VBATT down to +0.8V. VIN and VBATT can be connected together and to a single supply from +2.7V to +5.5V via jumpers JU3 and JU6. Do not turn on the power supply until all connections are completed. Positive Output 1) Connect a +2.7V to +5.5V supply to the VIN pad, and connect a +0.8V to +18V supply to the VBATT pad. Connect the grounds to the GND pads. 2) Connect a voltmeter and load, if any, to the VOUT pad. 3) Place the shunt on JU1 across pins 2 and 3. 4) Turn on the power supplies and verify that the output voltage is typically +18V. Negative Output 1) Connect a +2.7V to +5.5V supply to the VIN pad, and connect a +0.8V to +12V supply to the VBATT pad. Connect the grounds to the GND pads. 2) Connect a voltmeter and load, if any, to the -VOUT pad. 3) Place the shunt on JU4 across pins 2 and 3. 4) Turn on the power supplies and verify that the output voltage is typically -17V.
Controlling the LCD Using POK and LCDON
LCDON can be used to turn on a positive LCD bias voltage when VBATT is above the desired threshold. A resistor-divider (R16-R17) from VBATT to POK controls the open-drain output LCDON, which pulls low when VPOK > 1.125V. LCDON can drive an external PNP transistor, Q1, switching a positive VOUT to the LCD. The EV kit provides additional pads for Q1, R4, and R5. Choose a PNP with low saturation voltage at the required load current. R4 limits the base current in Q1. R5 is used to turn off Q1 when LCDON is floating. R4 and R5 can be the same value. Refer to the section Controlling the LCD Using POK and LCDON in the MAX686 data sheet for instructions on selecting resistors R4, R5, R16, and R17.
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MAX686 Evaluation Kit
Jumper Selection
Shutdown Mode The MAX686 EV kit features a shutdown mode that reduces the MAX686's quiescent current to 1.5A (typical), preserving battery life. The 2-pin header JU1 selects the shutdown mode for the positive output, while JU4 selects the shutdown mode for the negative output. Tables 1 and 2 list the selectable jumper options. Current Limit The 2-pin header JU2 selects the current limit for the positive output circuit, while JU3 selects the current limit for the negative output. Table 3 lists the selectable jumper options. The MAX686 EV kit comes configured for a 500mA current limit.
Evaluates: MAX686
Table 2. Jumper JU4 Functions (Negative Output)
SHUNT LOCATION 1&2 2&3 SHDN PIN Connected to GND Connected to VIN MAX686 OUTPUT Shutdown mode, VOUT = 0V MAX686 enabled, VOUT = -17V
Table 3. Jumpers JU2 and JU3 Functions
SHUNT LOCATION On Off ISET PIN Connected to GND Connected to VIN CURRENT LIMIT (mA) 250 500
Table 1. Jumper JU1 Functions (Positive Output)
SHUNT LOCATION 1&2 2&3 SHDN PIN Connected to GND Connected to VIN MAX686 OUTPUT Shutdown mode VOUT = VBATT - VDIODE MAX686 enabled, VOUT = +18V
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Evaluates: MAX686
MAX686 Evaluation Kit
Figure 1a. MAX686 EV Kit Positive Output Schematic
C1 15F, 35V C3 1F VBATT L1 22H 12 VCC LX VOUT 16 5 VDD C13 0.1F PGND 7 SHDN 14 R4* 56k R5* 56k 2 1 R6 100k VIN 6 ISET FB R2 9 REF 8 110k 1% C4 0.1F DACOUT 2 UP POK N.C. GND 3 DN POL 4 13 15 11 VBATT R7 100k R16 OPEN R17 SHORT R3 110k 1% 10 JU2 3 JU1 1 2 3 Q1* 1 CMPT2907 C2 4.7F 35V D1 MBR0540 C5 0.1F JU3 R18 100 VOUTSW
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U1 MAX686
R1 1M, 1% VOUT LCDON C7 22pF DACOUT POK R8 100k * NOT SUPPLIED WITH EV KIT
VIN 2.7V TO 5.5V
SHDN
REF 1.25V
UP
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DN
GND
C8 15F, 35V C11 0.1F VBATT D4 OPEN -VOUT D2 MBR0540 PGND 7 SHDN 14 N.C. C10 100pF R9 1M 1% REF R10 110k, 1% 1 D3 MBR0540 C9 2.2F 35V JU6 C6 2.2F L2 22H R15 2
VIN 2.7V TO 5.5V VCC LX 5 VDD
12 16
Figure 1b. MAX686 EV Kit Negative Output Schematic
2 1 R12 100k VIN 6 ISET FB 9 REF 8 11 C12 0.1F DACOUT 2 UP N.C. GND 3 DN R14 100k POL 13 4 VIN 15 POK R13 100k R11 110k 1% DACOUT 10 JU5 3 JU4
SHDN
U2 MAX686
LCDON
REF 1.25V
UP
DN
Evaluates: MAX686
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GND
MAX686 Evaluation Kit
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MAX686 Evaluation Kit Evaluates: MAX686
1.0"
Figure 2. MAX686 EV Kit Component Placement Guide
1.0"
Figure 3. MAX686 EV Kit PC Board Layout--Component Side
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MAX686 Evaluation Kit Evaluates: MAX686
1.0"
Figure 4. MAX686 EV Kit PC Board Layout--Solder Side
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MAX686 Evaluation Kit Evaluates: MAX686
NOTES
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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