To properly measure voltage ripple on either the input or
output of any regulator with a switching regulator near
by, a proper ring in tip measurement is required.
Standard oscilliscope probes come with a grounding clip,
or a long wire with an alligator clip. Unfortunately, for
high frequency measurements, this ground clip can pick
up high frequency noise and erroneously inject it into the
measured output ripple.
The MIC2619 evaluation boards accommodate a home
made ring in tip measurement by probing across input
and output capacitors. This requires the removing of the
oscilloscope probe sheath and ground clip from a
standard oscilloscope probe and wrapping a non-
shielded bus wire around the oscilloscope probe (as
shown on the left). If there does not happen to be any
non-shielded bus wire immediately available, the leads
from axial resistors will work. By maintaining the
shortest possible ground lengths on the oscilloscope
probe, true ripple measurements can be obtained.
March 2010
4
M9999-030210-A
Micrel, Inc.
Feedback resistors
The MIC2619 utilizes a feedback pin to compare the
output to an internal reference. The output voltage is
adjusted by selecting the appropriate feedback resistor
network values. The desired output voltage can be
calculated as follows:
MIC2619 Evaluation Board
Over-Voltage Protection (OVP)
The OVP pin provides over-voltage protection on the
output of the MIC2619. When the OVP circuit is tripped,
the output voltage remains at the set OVP voltage.
Because the OVP circuit operates at a lower frequency
than the feedback circuit, output ripple will be higher
while in an OVP state. OVP requires a resistor divider
network to the output and GND to set the OVP voltage. If
the output voltage overshoots the set OVP voltage, the
MIC2619 OVP circuit will shut off the switch; saving itself
and other sensitive circuitry downstream. The accuracy
of the OVP pin is ±5% and therefore, should be set
above the output voltage to ensure noise or other
variations will not cause a false triggering of the OVP
circuit. Caution should be exercised to not exceed the
35V rating of the output voltage.
To set the OVP voltage, replace the R1 and R2 resistor
values on the evaluation board with the calculated
values using the following equation:
V
OVP
=
1.265
× ⎜
⎜
⎞
⎛
R
V
OUT
=
1.265
× ⎜
1
+
1
⎟
⎟
⎜
R
⎠
⎝
2
⎞
⎛
R
1
+
1
⎟
⎟
⎠
⎝
R
2
R3 (kΩ)
29.4
53.6
69.8
84.5
107
133
147
187
226
267
R6 (kΩ)
10
10
10
10
10
10
10
10
10
10
V
OUT
or
V
OVP
(V)
5.0
8.0
10
12
15
18
20
25
30
35
Table 1. VOUT or OVP Example Resistor Va
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be acurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
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