MIC4575 Evaluation Board

MIC4575 Evaluation Board
Micrel
MIC4575 Evaluation Board
200kHz Buck Switching Regulator
Precautions
The MIC4575 has no protection from reversed polarity being
applied to its input. Any momentary reversal of the dc power
supply connections can cause permanent damage to the
circuit. Use extreme care with these connections.
The safest way to power up the MIC4575 evaluation board is
to set the power supply to zero volts and then gradually
increase the supply voltage. Monitor the input supply current
while increasing the input voltage. If the circuit draws excessive current, immediately shut off the main supply and check
for proper power supply connections. This simple procedure
can avoid most catastrophic failures.
Output Voltage Configuration
The MIC4575 is available in 3.3V fixed, 5.0V fixed, and
adjustable output-voltage versions. The evaluation board
uses the adjustable output version to provide industry standard output voltages of 2.5V, 3.3V, 5V, or 6V, by jumper
selection.
General Description
Designed for distributed power systems, the MIC4575 is a
monolithic, step-down switching regulator capable of 1.0A
output current and can operate from input voltages ranging
from 4V to 24V. It has a logic-compatible enable that provides
200µA of quiescent current in shutdown mode.
The Micrel MIC4575 is an enhanced version of the popular
LM2575, a 52kHz step-down (buck) switching regulator. The
MIC4575 features a 200kHz switching frequency that reduces the inductor size by a factor of four, freeing up precious
board space.
The MIC4575 evaluation board is designed for applications
up to 1A. MIC4574 and MIC4576 evaluation boards, for 0.5A
and 3A applications respectively, are also available.
Requirements
The MIC4575 evaluation board requires a power supply
capable of at least 1.3A at up to 24V. The load may be up to
1A maximum.
2.5V Output
Efficiency
Operation
80
EFFICIENCY (%)
Figure 1 shows the schematic of the evaluation board circuit.
When the internal high-side switch turns on, one side of the
inductor is fed from the input voltage. During this period,
current flows from the input, through the internal output
switch, output inductor, and load. When the output switch
turns off, the SW pin voltage drops until the clamp diode is
forward biased. During this portion of the cycle, current flows
through the diode, inductor, and load. Figures 2a through 2c
show the efficiency for 5V, 2.5V, and 3.3V outputs versus
input voltage and output current.
60
8V
12V
18V
24V
40
20
10
100
1000
OUTPUT CURRENT (mA)
Figure 2a. 5V Output Efficiency
L1
1
8V to 24V
C1
22µF
35V
SHUTDOWN
5
ENABLE
SW
VIN
MIC4575BU
FB
SHDN
GND
5.0V/1A
2
68µH
4
D1
MBRS130
3
R1
3.01k
1%
R2
3.01k
1%
JP1A
2.5V
C3
3300pF
R3
1.82k
1%
JP1B
3.3V
R4
1k
1%
JP1C
5V
C2*
220µF
10V
R5
806Ω
1%
JP1D
6V
* 330µF required for 2.5V operation
Figure 1. Buck Converter (8V–24V to 5V/1A)
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
December 1997
1
MIC4575 Evaluation Board
MIC4575 Evaluation Board
Micrel
Input Voltage
The minimum input voltage rating varies with output voltage.
Table 2 lists the lowest input voltage the MIC4575 can
operate from.
Table 1 shows standard 1% resistor values for jumper
selectable output voltages.
Jumper
Position
Output
Voltage
R1
R2–R5
(nearest 1%)
JP1A
2.5V
3.01k
3.01k
JP1B
3.3V
3.01k
1.82k
JP1C
5V
3.01k
1.00k
JP1D
6V
3.01k
806Ω
Output
Voltage
2.5V
3.3V
5V
6V
12V
Table 1. Programming Resistor Values
Programming resistors R2, R3, R4, and R5 are used to set the
output voltage according to the equation:
Table 2. Minimum Input Voltages
Enable/Shutdown Mode
To activate the MIC4575, set the enable switch to the ON
position. To put the MIC4575 into its micropower (200µA)
shutdown state, set the enable switch to the OFF position.
2.5V Output Option
Although the evaluation board will operate normally at 2.5V
output, the phase margin falls below 20°. A 330µF output
capacitor (C2†) is recommended to increase the phase
margin above 20°.
R1

VOUT = 1.25V 1 +


R2 
The adjustable regulator can be replaced with MIC4575-3.3
or MIC4575-5.0 fixed output voltage devices for evaluation.
To configure the board for fixed devices, connect the feedback pin (pin 4) directly to the output voltage by removing the
voltage adjustment jumper and placing a zero-ohm jumper
across R1.
3.3V Output
Efficiency
5V Output
Efficiency
100
EFFICIENCY (%)
EFFICIENCY (%)
90
70
50
30
10
VIN
(Minimum)
5V
6V
8V
9V
15V
8V
12V
18V
24V
80
60
40
10
100
1000
OUTPUT CURRENT (mA)
Figure 2b. 2.5V Output Efficiency
8V
12V
18V
24V
100
1000
OUTPUT CURRENT (mA)
Figure 2c. 3.3V Output Efficiency
Item
Part Number
Source
C1
C2
†C2
C3
TPSE226M035R0300
TPSE227M010R0100
TPSE337M006R0100
3300pF ceramic X7R
AVX
(803) 448-9411
D1
MBRS130LT3
Motorola
(800) 521-6274
L1
D03316P-683
Coilcraft
(708) 639-2361
U1
MIC4575BU
Micrel
(408) 944-0800
Table 3. Bill of Materials
MIC4575 Evaluation Board
2
December 1997
MIC4575 Evaluation Board
Micrel
Component Side
Silk Screen (Component Side)
December 1997
3
MIC4575 Evaluation Board
MIC4575 Evaluation Board
Micrel
Solder Side
Silk Screen (Solder Side)
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 1997 Micrel Incorporated
MIC4575 Evaluation Board
4
December 1997