MIC2208_10 Datasheet, PDF (15/18 Pages) Micrel Semiconductor – 3mm x 3mm 1MHz 3A PWM Buck Regulator

Micrel, Inc.
R1
CRCW04024992F
Vishay Dale⁽⁴⁾
CRCW04023322F
Vishay Dale⁽⁴⁾
CRCW04026192F
Vishay Dale⁽⁴⁾
R2
CRCW04021003F
Vishay Dale⁽⁴⁾
CRCW04022493F
Vishay Dale⁽⁴⁾
Vishay Dale⁽⁴⁾
R3
CRCW04024991F
Vishay Dale⁽⁴⁾
R4
CRCW04024991F
Vishay Dale⁽⁴⁾
R5
CRCW040210R0F
Vishay Dale⁽⁴⁾
R6
CRCW04021002F
Vishay Dale⁽⁴⁾
U1
MIC2208BML
Micrel, Inc.⁽⁶⁾
Notes:
1. TDK: www.tdk.com
2. Murata: www.murata.com
3. AVX: www.avx.com
4. Vishay: www.vishay.com
5. Wurth Elektronik Midcom, Inc.: www.midcom-inc..com
6. Micrel, Inc.: www.micrel.com
49.9KΩ 1% 0402 Resistor
33.3 kΩ 1% 0402 For 2.5V_OUT
61.9 kΩ 1% 0402 For 1.8 V_OUT
100 kΩ 1% 0402 For 1.5 V_OUT
249 kΩ 1% 0402 For 1.2 V_OUT
Open
For 1.0 V_OUT
499KΩ 1% 0402 Resistor
90.9KΩ 1% 0402 Resistor
10Ω 1% 0402 Resistor
10KΩ 1% 0402 Resistor
1MHz 3A Buck Regulator
MIC2208
1
1
1
1
1
1
Loop Stability and Bode Analysis
Bode analysis is an excellent way to measure small
signal stability and loop response in power supply
designs. Bode analysis monitors gain and phase of a
control loop. This is done by breaking the feedback loop
and injecting a signal into the feedback node and
comparing the injected signal to the output signal of the
control loop. This will require a network analyzer to
sweep the frequency and compare the injected signal to
the output signal. The most common method of injection
is the use of transformer. Figure 7 demonstrates how a
transformer is used to inject a signal into the feedback
network.
The network analyzer will then sweep the source while
monitoring A and R for an A/R measurement. While this
is the most common method for measuring the gain and
phase of a power supply, it does have significant
limitations. First, to measure low frequency gain and
phase, the transformer needs to be high in inductance.
This makes frequencies <100Hz require an extremely
large and expensive transformer. Conversely, it must be
able to inject high frequencies. Transformers with these
wide frequency ranges generally need to be custom
made and are extremely expensive (usually in the tune
of several hundred dollars!). By using an op-amp, cost
and frequency limitations used by an injection
transformer are completely eliminated. Figure 8
demonstrates using an op-amp in a summing amplifier
configuration for signal injection.
Network
Analyzer
“R” Input
Feedback
+8V _MIC922BC5
R1
1k
Network
Analyzer
“A” Input
Output
Figure 7. Transformer Injection
A 50Ω resistor allows impedance matching from the
network analyzer source. This method allows the DC
loop to maintain regulation and allow the network
analyzer to insert an AC signal on top of the DC voltage.
May 2010
15
R3
1k
R4
1k
Network Analyzer
Source
50
Figure 8. Op Amp Injection
M9999-051410-D