MC33762
http://onsemi.com
6
APPLICATION HINTS
Input Decoupling
As with any regulator, it is necessary to reduce the
dynamic impedance of the supply rail that feeds the
component. A 1.0 mF capacitor either ceramic or tantalum is
recommended and should be connected close to the
MC33762 package. Higher values will correspondingly
improve the overall line transient response.
Output Decoupling
Thanks to a novel concept, the MC33762 is a stable
component and does not require any specific Equivalent
Series Resistance (ESR) neither a minimum output current.
Capacitors exhibiting ESRs ranging from a few mW up to
3.0 W can thus safely be used. The minimum decoupling
value is 1.0 mF and can be augmented to fulfill stringent load
transient requirements. The regulator accepts ceramic chip
capacitors as well as tantalum devices.
Noise Performances
Unlike other LDOs, the MC33762 is a true low−noise
regulator. Without the need of an external bypass capacitor,
it typically reaches the incredible level of 40 mVRMS overall
noise between 100 Hz and 100 kHz. To give maximum
insight on noise specifications, ON Semiconductor includes
spectral density graphics. The classical bypass capacitor
impacts the startup phase of standard LDOs. However,
thanks to its low−noise architecture, the MC33762 operates
without a bypass element and thus offers a typical 40 ms
startup phase.
Protections
The MC33762 hosts several protections, giving natural
ruggedness and reliability to the products implementing the
component. The output current is internally limited to a
maximum value of 180 mA typical while temperature
shutdown occurs if the die heats up beyond 125°C. These
values let you assess the maximum differential voltage the
device can sustain at a given output current before its
protections come into play.
The maximum dissipation the package can handle is given
by:
P
max
+
T
Jmax
* T
A
R
qJA
If T
Jmax
is limited to 125°C, then the MC33762 can
dissipate up to 395 mW @ 25°C. The power dissipated by
the MC33762 can be calculated from the following formula:
Ptot +
ǒ
V
in
I
gnd
(I
out
)
Ǔ
)
ǒ
V
in
* V
out
Ǔ
I
out
or
Vin
max
+
Ptot ) V
out
I
out
I
gnd
) I
out
If a 80 mA output current is needed, the ground current is
extracted from the data−sheet curves: 4.0 mA @ 80 mA. For
a half 2.8 V MC33762 (2.8 V) operating at 25°C, the
maximum input voltage will then be 7.3 V.
Typical Applications
The following picture portrays the typical application of
the MC33762.
Figure 7. A Typical Application Schematic
MC33762
R1
100 k
On/Off
+
C3
1.0 mF
+
C1
1.0 mF
Output 2
Input
1
2
3
4
8
7
6
5
R2
100 k
On/Off
+
C2
1.0 mF
Output 1
Regulator 1 Regulator 2
As for any low noise designs, particular care has to be
taken when tackling Printed Circuit Board (PCB) layout.
Connections shall be kept short and wide. Layout example
as given in the MC33761 application hints can be used as a
starting basis.
