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2000 California Micro Devices Corp. All rights reserved.
10/18/2000
1
CMPWR025
CALIFORNIA MICRO DEVICES
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
Dual Input SmartORTM Power Switch
FEATURES
Automatically selects V
CC1
OR V
CC2
input source
Integrated low impedance switches (0.2
TYP)
Operating supply range from 2.8V to 5.5V
Glitch-free output during supply switching
transitions
Low operating supply current of 20A (TYP)
User-selectable hysteresis for supply selection
8-pin SOIC Narrow or 8-pin MSOP packages
PRODUCT DESCRIPTION
California Micro Devices' SmartORTM CMPWR025 is a
dual input power switch that selects between two
different power inputs and delivers it to one output. The
device integrates two very low impedance power
switches and automatically implements an OR function
that selects the higher of the two inputs. A hysteresis is
built in (and is user selectable) to prevent switch chatter.
The CMPWR025 is a much-improved solution to simply
ORing two diodes, due to the greatly reduced losses of
the CMPWR025 when compared to low forward drop
Schottky diodes.
APPLICATIONS
PCI cards for Wake-On-LAN/Wake-On-Ring
Dual power systems
Systems with standby capabilities
Battery backup systems
See Application Note AP211
C0970500
PIN DIAGRAM, TYPICAL APPLICATION CIRCUIT, AND SIMPLIFIED BLOCK DIAGRAM
The CMPWR025 is designed to operate above the 1W
(375mA at 3.3V) sleep mode rating stated in the PCI
Rev 2.2 spec. In fact the CMPWR025 current rating is
dependent upon the power dissipation resulting from the
voltage drop across the internal switch elements. See
the Typical DC Characteristics section in this data sheet
for details.
For IAPC (Instantly Available Personal Computer)
applications see the CAMD Applications Note AP211
"Instantly Available PCI Card Power Management".
Pin Diagram
Typical Application Circuit
Simplified Block Diagram
1
2
3
4
V
CC1
V
CC1
V
CC2
V
CC2
8
7
6
5
HYS
V
OUT
V
OUT
GND
Top View
CMPWR025
8-Pin SOIC Narrow and MSOP Package
V
CC1
V
CC2
HYS
V
CC1
5V
GND
GND
V
OUT
V
OUT
CMPWR025
V
CC2
5V
10F
+
+
+
C
OUT
V
CC1
+
V
CC2
HYS
SW2
0.2
SW1
0.2
V
OUT
GND
GND
GND
GND
2000 California Micro Devices Corp. All rights reserved.
10/18/2000
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
2
CMPWR025
CALIFORNIA MICRO DEVICES
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Note 1: This parameter applies at 25C only.
Note 2: Hysteresis level defines the maximum level of acceptable noise on V
CC
during switching. Excessive parasitic inductance on V
CC
board traces to the CMPWR025 may require an input capacitor to adequately filter the supply noise to below the hysteresis level.
This will ensure that precise switching occurs between V
CC1
and V
CC2
supply inputs.
Note 3: This is the time, after the select/deselect threshold is reached, for the switches to react. Not tested, guaranteed by device design
and characterization.
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5
2000 California Micro Devices Corp. All rights reserved.
10/18/2000
3
CMPWR025
CALIFORNIA MICRO DEVICES
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
INTERFACE SIGNALS
V
CC1
is the primary power source, which is given priority
when present. If pin 8 (HYS) is unconnected, then the
hysteresis level is 75mV (typ.). Whenever the primary
power source drops below the secondary supply V
CC2
by
more than 125mV, it will immediately become dese-
lected. When the primary power source is restored to
within 50mV of the secondary supply, the primary power
source will once again be selected and provide all the
output current.
When V
CC1
is selected, it will supply all the internal
current requirements which are typically 20A. When
V
CC1
is not selected, there will be no current loading on
this input.
V
CC2
is the secondary power source and is selected
when the primary source has fallen below it by more
than 125mV (or 200mV if pin 8 is grounded). The
secondary source will be deselected immediately once
the primary source is restored to within 50mV of V
CC2
.
When V
CC2
is selected, it will supply all the internal
current requirements which are typically 20A. When
V
CC2
is not selected, there will be no current loading on
this input.
GND is the negative reference for all voltages.
V
OUT
provides the power for the load. During normal
operation the impedance from V
OUT
to the selected
supply is typically less than 0.28
, which results in
minimal voltage loss from input to output.
During the cold-start interval when both inputs are
initially applied, the internal circuitry provides a soft
turn-on for the switches, which limits peak in-rush
current.
HYS is the user-selectable hysteresis input. The hyster-
esis level is set to 150mV when grounding pin 8. The
default hysteresis level is set to 75mV by leaving pin 8
unconnected. Using 150mV hysteresis is recommended,
especially in environments with noisy power supplies,
high power supply resistances or high load currents.
If the hysteresis level is set to 150mV, the primary
supply V
CC1
must now fall 200mV below the secondary
supply V
CC2
before it becomes deselected.
Important note: There is an internal connection
between pins 1 and 2. These pins must be connected
externally.
There is an internal connection between pins 3 and 4.
These pins must be connected externally.
There is an internal connection between pins 6 and 7.
These pins must be connected externally.
S
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O
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h
2000 California Micro Devices Corp. All rights reserved.
10/18/2000
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
4
CMPWR025
CALIFORNIA MICRO DEVICES
SELECTION THRESHOLD DIAGRAMS
Supply Selection Threshold Diagram (Hysteresis Pin Floating)
Supply Selection Threshold Diagram (Hysteresis Pin Grounded)
ON
ON
S
W2
S
W1
V
CC1
V
CC2
V
CC1SEL
(50mV)
V
HYS1
(75mV)
V
CC1DES1
(75mV)
ON
OFF
OFF
OFF
ON
ON
S
W2
S
W1
V
CC1
V
CC2
V
CC1SEL
(50mV)
V
HYS2
(150mV)
V
CC1DES1
(200mV)
ON
OFF
ON
OFF
OFF
OFF
2000 California Micro Devices Corp. All rights reserved.
10/18/2000
5
CMPWR025
CALIFORNIA MICRO DEVICES
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
TYPICAL DC CHARACTERISTICS
Switch Resistance vs. V
CC
with Temperature in Figure
1 shows the switch resistance measured at 500mA load,
over a wide V
CC
voltage range. The resistance is shown
at ambient temperatures of 0C, 25C, and 70C. When
the temperature rises from 25C to 70C, the switch
resistance increases by about 20%.
0.40
0.35
0.30
0.25
0.20
0.15
0.10
2.5
3.5
4.0
4.5
V
CC
(V)
Switc
h Resistance (
)
5.0
5.5
6.0
3.0
70C
25C
0C
Figure 1.
Switch Resistance vs. V
CC
with Temperature
Supply Current vs. V
CC
with Temperature in Figure 2
shows how the small internal supply current varies with
V
CC
voltage and temperature. This current will be drawn
from the selected V
CC
input, and will be dissipated
through ground pin 5. This current is independent of
load current.
40
35
30
25
20
15
10
2.5
3.5
4.0
4.5
V
CC
(V)
I
CC
(A)
5.0
5.5
6.0
3.0
70C
25C
0C
Figure 2. Supply Current vs. V
CC
with Temperature (No Load)
150
175
200
125
100
75
50
25
0
2.5
4.5
Temperature (C)
Hysterresis V
olta
g
e
(mA)
5.5
6.5
7.5
3.0
V
CC1SEL
V
HYS1
V
HYS2
Figure 3. Hysteresis Voltage vs.Temperature
POWER DISSIPATION
AND OUTPUT CURRENT CONSIDERATION
The CMPWR025 is supplied in standard SOIC or MSOP
packages, which have a maximum power dissipation
rating of 0.3W. It is important that the heat generated
within the part does not exceed this rating. The heat
generated by the load current is given by:
P
DISS
= V
SW
X I
LOAD
or P
DISS
= R
SW
X (I
LOAD
)
2
At a typical load of 375mA the P
DISS
is just 0.4 x (0.375)
2
= 56mW.
A primary consideration is Maximum Junction Tempera-
ture, T
J(max)
, which can be calculated using the following
formula:
T
J(max)
= T
A
+
JA
X P
DISS
Where: T
A
= The Ambient Temperature
JA
= Thermal Resistance = 100 C/W
P
DISS
=
Power Dissipation
In the above example operating at an ambient of 70C,
T
j(max)
would be:
T
J(max)
= 70C + (0.056W)(100C/W) = 75.6C
Maximum power dissipation, including the power from
the other circuitry within the device, suggests a current
rating of approximately:
P
DISS
P
INT
R
SW
= I
LOAD
0.3W 100W
0.4
= 865mA
Note that this is beyond the maximum current rating of
the device, which is to 750mA maximum.
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