MAX856 Evaluation Kit
____________________________Features
♦ Low 0.8V to 6V Input Supply Voltage
♦ New µMAX Package
♦ 85% Efficiency at 100mA
♦ 25µA Quiescent Current
♦ 1µA Shutdown Mode
♦ 125mA and 500mA Switch Current Limits
Permit Use of Low-Cost Inductors
♦ Up to 500kHz Switching Frequency
♦ ±1.5% Reference Tolerance Over Temperature
♦ Low-Battery Detector (LBI/LBO)
♦ Surface-Mount Construction
♦ Fully Assembled and Tested
____________________Component List
______________Ordering Information
DESIGNATION
QTY
C1
1
0.1µF ceramic capacitor
PART
MAX856EVKIT-MM
C2, C3
2
68µF, 10V, low-ESR tantalum
capacitors;
Sprague 595D686X0010D7
DESCRIPTION
R1, R2,
R3, R4, R5
0
Open
L1
1
47µH power inductor; Coilcraft
D01608-473 or Sumida CD43-470
D1
1
20V, 500mA Schottky diode;
Motorola MBRS0530
U1
1
MAX856CUA (8-pin µMAX)
None
2
3-pin headers
None
2
Shunts
None
1
2.00" x 2.00" PC board
None
1
MAX856 data sheet
To contact Sprague, phone (603) 224-1961 or fax
(603) 224-1430. To contact Murata Erie, phone (404) 436-1300.
Refer to MAX856–MAX859 data sheet for other component suppliers’ phone numbers.
TEMP. RANGE
0°C to +70°C
BOARD TYPE
Surface Mount
_________________________Quick Start
The MAX856 EV kit is a fully assembled and tested surface-mount board. Follow the steps below to verify
board operation. Do not turn on the power supply
until all connections are completed.
1) Connect a 1.8V to 4.5V supply to the pad marked
VIN. The ground connects to the GND pad.
2) Connect a voltmeter and load (if any) to the VOUT
pad.
3) Place the shunt on J1 across pins 1 and 2.
4) Place the shunt on J2 across pins 1 and 2 for a 5V
output voltage. If a 3.3V output is desired, the
shunt goes across pins 2 and 3, and the input voltage must be less than 3.6V.
5) Turn on the power and verify that the output voltage
is 5V.
6) Refer to the section Evaluating the MAX857,
MAX858, MAX859 to modify the board for different
output voltages.
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
Evaluates: MAX856/MAX857/MAX858/MAX859
_______________General Description
The MAX856 evaluation kit (EV kit) is a fully assembled
and tested surface-mount printed circuit board. It can
also evaluate the MAX858 or the adjustable-output
MAX857/MAX859.
The MAX856–MAX859 are CMOS, step-up, DC-DC
switching regulators for small, low input voltage or battery-powered systems. The MAX856/MAX858 accept a
positive input voltage between 0.8V and 6V and convert
it to a higher, pin-selectable output voltage of 3.3V or
5V. The MAX857/MAX859 adjustable versions accept
0.8V to 6V input voltages and generate a higher,
adjustable output voltage in the 2.7V to 6V range.
Typical full-load efficiencies for the MAX856–MAX859
are greater than 85%.
A movable jumper on the EV kit selects either a 3.3V or
5.0V output voltage. Additional pads on the board’s solder
side accommodate resistors for the LBI/LBO low-battery
detector or MAX857/MAX859 output adjustment.
Evaluates: MAX856/MAX857/MAX858/MAX859
MAX856 Evaluation Kit
_______________Detailed Description
Input Source
The input source for the MAX856 evaluation board
must be greater than 1.8V for start-up (0.8V for operation once started), and less than the output voltage
plus 0.3V. A typical input voltage range would be the
2.0V to 3.3V range of a 2-cell NiCd battery. An input
voltage greater than the selected output voltage (but
less than 7V) will not damage the circuit. However, the
MAX856 output will equal the input voltage minus the
0.3V drop of the Schottky diode, D1.
The input current depends on the power delivered to
the load. The following equations show how to calculate the expected input current requirement.
Input Power = Output Power / Efficiency
and
Input Current = Input Power / Input Voltage
To calculate the input current for a typical operating circuit, assume a 3.3V input voltage, a 5V output voltage,
and a 50mA load. The expected efficiency can be
taken from the graphs on the MAX856–MAX859 data
sheet. Under the above conditions, the MAX856 delivers 85% efficiency.
Input Power = (5.0V x 50mA) / 85%
Input Power = 294mW
and
Input Current = 294mW / 3.3V
Input Current = 89mA
Once started, the MAX856 actually operates from the
regulated output voltage. This means that the input
voltage can fall below the 1.8V minimum start-up voltage. Typically, the regulated output will be maintained
even if the input voltage drops to 0.8V.
2
Jumper Selection
Two 3-pin headers select the shutdown mode and output voltage. Table 1 lists the selectable jumper options.
Table 1. Jumper Selection
J1 Shunt J2 Shunt SHDN Pin
Location Location Connection
3V/5V Pin
Connection
MAX856
Output
1&2
1&2
VOUT
GND
5.0V
1&2
2&3
VOUT
VOUT
3.3V
2&3
1&2
GND
GND
VIN - 0.3V
2&3
2&3
GND
VOUT
VIN - 0.3V
Using the Low-Battery Indicator
The MAX856 has an additional comparator useful for
monitoring the input source’s voltage level. Resistor
locations R3 and R4 on the bottom of the printed circuit
board are connected as a voltage divider between the
LBI pad and the MAX856 LBI pin. Note that a printed
circuit board trace across R4 shorts the LBI pin to
ground when this function is not used. Cut the trace
before installing R4. Refer to the Low-Battery Detection
section of the MAX856–MAX859 data sheet for instructions on selecting values for resistors R3 and R4.
Another location on the board facilitates the addition of
a pull-up resistor on the LBO output. LBO is an opendrain output that can sink 2mA. Install resistor R5 if an
external circuit is to be driven from LBO.
_______________________________________________________________________________________
MAX856 Evaluation Kit
Evaluating the MAX857, MAX858, MAX859
The MAX856 EV kit can also evaluate the MAX857,
MAX858, or MAX859. The MAX858 can be substituted
directly for the MAX856.
The MAX857 or MAX859 can be used to generate output voltages in the 2.7V to 5.5V range using external
resistors. Besides replacing the IC, the only other modification required is to remove the shunt on J2 and add
the output voltage-divider resistors R1 and R2 (located
on the board’s solder side). The Output Voltage
Selection section of the MAX856–MAX859 data sheet
gives instructions for calculating R1 and R2 values.
VIN
1.8V to 4.5V
1
SHDN
3
C2
68µF
R1
OPEN
R5
OPEN
2
J1
1
SHDN
3
2 3/5
2
1
J2
3
R2
OPEN
C1
0.1µF
4
VREF
LBO
U1
L1
47µH
LX 8
7
MAX856 GND
OUT
LBI
D1
MBRS0530
C3
68µF
10V
VOUT
+5V
6
5
R3
OPEN
LBI
R4
0Ω
(SHORT)
LBO
Figure 1. MAX856 EV Kit Schematic
_______________________________________________________________________________________
3
Evaluates: MAX856/MAX857/MAX858/MAX859
Notes About Inductor Selection
The difference between the MAX756/MAX757 and
MAX856–MAX859 is the inductor peak current limit. The
MAX856–MAX859 have lower limits, allowing the use of
physically smaller (and less expensive) inductors.
However, efficiency suffers if the inductor’s DC series
resistance (DCR) increases significantly. To reduce the
ripple current for low output current configurations,
increase the inductor value. Inductor values between
22µH and 47µH typically have low DCR (good efficiency) and acceptable peak currents.
The MAX856 data sheet shows operating efficiency
graphs with a wide range of inductors. Inductors with
low DCR and high current capabilities deliver efficiencies greater than 80%. Physically smaller inductors of
the same value can have efficiencies below 80%
because of their higher DCR.
Evaluates: MAX856/MAX857/MAX858/MAX859
MAX856 Evaluation Kit
Figure 2. MAX856 EV Kit Component Placement Guide—
Component Side
Figure 3. MAX856 EV Kit Component Placement Guide—
Solder Side
Figure 4. MAX856 EV Kit PC Board Layout—Component Side
Figure 5. MAX856 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
© 1995 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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