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 cir-
cuit 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
1.3µA 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
0°C to +70°C
IC PACKAGE
16 QSOP
Component List
DESIGNATION
C1, C8
QTY
2
DESCRIPTION
15µF, 35V tantalum capacitors
AVX TPSD156M035R0300 or
Sprague 593D156X0035E2W
4.7µF, 35V tantalum capacitor
AVX TPSC475M035R0600 or
Sprague 595D475X0035C
1µF ceramic capacitor
0.1µF ceramic capacitors
2.2µF, 25V ceramic capacitor
United Chemi-Con/Marcon
THCR30E1E225Z
22pF ceramic capacitor
2.2µF, 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
22µH inductors
Sumida CD54-220
1MΩ, 1% resistors
110kΩ, 1% resistors
Not installed
100kΩ, 5% resistors
2Ω, 5% resistor
100Ω, 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
1
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 switching-
regulator circuits. The first circuit provides an +18V out-
put for currents up to 20mA with 90% typical conver-
sion efficiency. The second circuit provides a -17V out-
put 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 volt-
age 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 100kΩ resistors (R7, R8, R13,
R14). On power-up, the output voltage is set to mid-
scale. A rising edge on UP increases the output volt-
age; 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 com-
pleted.
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
V
POK
> 1.125V.
LCDON
can drive an external PNP transistor, Q1,
switching a positive V
OUT
to the LCD. The EV kit pro-
vides 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.
2
_______________________________________________________________________________________
MAX686 Evaluation Kit
Jumper Selection
Shutdown Mode
The MAX686 EV kit features a shutdown mode that
reduces the MAX686’s quiescent current to 1.5µA (typi-
cal), 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,
V
OUT
= 0V
MAX686 enabled,
V
OUT
= -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
V
OUT
= V
BATT
- V
DIODE
MAX686 enabled,
V
OUT
= +18V
_______________________________________________________________________________________
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