MIC26603 MICREL [Micrel Semiconductor], MIC26603 Datasheet - Page 22

• Manufacturer Part Number: MIC26603
• Description: 28V, 6A Hyper Light Load Synchronous DC/DC Buck Regulator
• Manufacturer: MICREL [Micrel Semiconductor]

Micrel, Inc.
Step 2. Select R
voltage ripple using Equation 24:
Then the value of R
Step 3. Select C
as short for a wide range of the frequencies.
Setting Output Voltage
The MIC26603 requires two resistors to set the output
voltage as shown in Figure 7.
The output voltage is determined by the equation:
where, V
A typical value of R1 can be between 3kΩ and 10kΩ. If
R1 is too large, it may allow noise to be introduced into
the voltage feedback loop. If R1 is too small, it will
decrease the efficiency of the power supply, especially
at light loads. Once R1 is selected, R2 can be calculated
using:
July 2011
FB
Figure 7. Voltage-Divider Configuration
K
R
R2
V
= 0.8V.
OUT
div
inj
=
=
=
V
=
(R1//R2)
OUT
V
ΔV
inj
V
inj
FB
FB
as 100nF, which could be considered
V
FB(pp)
inj
according to the expected feedback
IN
×
−
×
is obtained as:
R1
V
(1
FB
+
×
×
R2
R1
(
D
K
f
×
SW
1
)
div
(1
×
-
−
D)
τ
1)
Eq. 21
Eq. 22
Eq. 23
Eq. 24
22
In addition to the external ripple injection added at the
FB pin, internal ripple injection is added at the inverting
input of the comparator inside the MIC26603, as shown
in Figure 8. The inverting input voltage V
1.2V. As V
clamped. The clamped V
because it is reflected as a DC error on the FB terminal.
Therefore, the maximum output voltage of the MIC26603
should be limited to 5.5V to avoid this problem.
Thermal Measurements
Measuring the IC’s case temperature is recommended to
insure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heatsink, resulting in a
lower case measurement.
Two methods of temperature measurement are using a
smaller thermal couple wire or an infrared thermometer.
If a thermal couple wire is used, it must be constructed
of 36 gauge wire or higher then (smaller wire size) to
minimize the wire heat-sinking effect. In addition, the
thermal couple tip must be covered in either thermal
grease or thermal glue to make sure that the thermal
couple junction is making good contact with the case of
the IC. Omega brand thermal couple (5SC-TT-K-36-36)
is adequate for most applications.
Wherever
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, a IR
thermometer from Optris has a 1mm spot size, which
makes it a good choice for measuring the hottest point
on the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
OUT
Figure 8. Internal Ripple Injection
possible,
is increased, the swing of V
an
INJ
reduces the line regulation
infrared
thermometer
M9999-071311-A
INJ
is clamped to
MIC26603
INJ
will be
is