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215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
CALIFORNIA MICRO DEVICES
AP-211
Vcc
output
Figure 5.
Equivalent circuit with line parasitic
Figure 5.
Equivalent circuit with line parasitic
C
+
Power supply
R
s
R
t
L
t
V
cc_in
CM PWR-150
R
L
Hysteresis
Hysteresis is illustrated in Figure 4 and is defined as the
difference between the enabling threshold (when the regulator
turns on) and the disabling threshold (when the regulator
turns off). The hysteresis level sets up the maximum level of
acceptable noise or disturbance on V
or V
AUX
. This is
particularly critical during power transitions.
As shown in Figure 5, the voltage seen by the device is given
by:
V
cc_in
= V
cc
(R
s
X I) - (R
t
X I) (L
t
X dI/dt)
Assuming an ideal situation where there is no parasitic
inductance, the hysteresis level should follow the equation
below.
V
hysteresis
> (R
s
X I) + (R
t
X I)
Where R
is the power supply output impedance and R
is the
interconnect series resistance (between supply and regulator).
Figure 4.
Input voltage transient and hysteresis
where, V
cc
is the power supply voltage,
R
s
is the power supply output impedance,
R
is the interconnect series resistance (between supply
and regulator), and
L
is the trace (line) inductance (between supply and
regulator).
In order to avoid disturbance and given the hysteresis of the
devices, the recommended maximum total resistance is shown
in Table 3.
Table 3.
Recommended maximum series resistances
during turn off to prevent chatter
The worst case condition occurs during turn on, when there
is in-rush current. During turn on, the current is rising from
0A to a high in-rush current. The in-rush current level and
duration is increased when the initial output capacitor voltage
is 0V, and when the capacitor value is larger. We can assume
an in-rush current equal to twice the maximum DC load current
of the device. Table 4 below gives a recommendation for the
maximum series resistances during turn on.
Table 4.
Recommended maximum series resistances
during turn on to prevent chatter
Although a filter capacitor at the input can reduce the effective
source impedance for short transients, long in-rush current
durations may still cause chatter.
CMPWR100 POWER MANAGEMENT
APPLICATION
Device Operation
The CMPWR100 is a power management device able to
generate a continuous 3.3V at 200mA from two voltage
sources: a 5V main supply (V
) or a 3.3V auxiliary supply
(V
). The device integrates a low dropout voltage regulator,
an integrated low impedance switch, and control circuitry to
switch from the V
to V
supply. When the 5V is present,
the device automatically enables the regulator that produces
3.3V output at V
. When only the 3.3V is present, the
device provides a direct connection from the V
pin to the
V
pin with a very low impedance of 0.2
typically. This
will minimize power consumption when in sleep mode.
The worst case is when a maximum current of 200mA is
flowing which results in a power dissipation (loss) across the
switch of only 8mW.
s
]
0
0
5
2
1
r
e
V
5
e
y
m
[
1
H
x
]
a
A
0
0
2
0
5
0
5
m
m
[
I
e
c
n
a
t
e
R
e
c
e
P
M
P
M
P
M
D
C
C
C
[
W
]
7
5
r
0
0
5
0
5
2
1
1
0
R
R
R
W
W
W
5
0
0
0
0
0
5
2
1
s
]
0
0
5
2
1
r
e
V
5
e
y
m
[
1
H
x
a
m
]
I
h
s
m
4
0
1
0
1
u
[
r
n
I
e
c
n
a
t
e
R
e
0
5
2
c
e
R
W
R
W
R
W
D
P
P
P
A
0
0
0
[
W
]
3
2
5
0
0
0
5
1
1
0
M
M
M
C
C
C
0
5
5
7
0
0
0
0
0
5
1
r
VCC transient
V
time [usec]
V
Enable threshold
Disable threshold
Hysteresis