LTC2920-2CMS8#TR Linear Technology, LTC2920-2CMS8#TR Datasheet - Page 13

• Manufacturer Part Number: LTC2920-2CMS8#TR
• Description: IC SNGL/DUAL PWR SUP CTRLR 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC2920-2CMS8#TR

• Applications: Single/Dual Power Supply Controller
• Voltage - Supply: 2.3 V ~ 6 V
• Current - Supply: 230µA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Input: -

APPLICATIO S I FOR ATIO
PREVENTING I
Connecting V
Connecting the LTC2920-2 V
and should be used when conditions permit. It requires no
external components and provides the best protection
from power supply overvoltage (Figure 16).
Connecting V
If the margined power supplies derive their V
different sources, or if a common V
to the LTC2920-2, power the LTC2920-2 using a diode
OR’d connection (Figure 17). Note that in this example,
Power Supply 2 has only a 1.8V output. Power Supply 1
will supply the LTC2920-2 under normal operation condi-
tions. If Power Supply 1 fails, or if it is sequenced up after
Figure 17. Dual Diode Connected V
CC
CC
Figure 16. Connecting V
M
to a Common V
to Diode OR’d Supplies
FAULT CURRENT IN THE LTC2920-2
POWER SUPPLY 1
POWER SUPPLY 2
V
IN
FB
FB
I
I
M2
M1
LTC2920-2
U
GND
OUT
OUT
V
CC
U
V
FB
V
FB
I
I
M2
LTC2920-2
M1
IN
IN
GND
BAT54C
CC
OUT
OUT
V
CC
to V
IN
IN
CC
W
2920-1/2 F16
cannot supply power
IN
to V
is the best choice
2920-1/2 F17
IN
V
3.3V
V
1.8V
OUT1
OUT2
CC
U
IN
from
Power Supply 2, Power Supply 2 supplies enough voltage
to keep the LTC2920 from sinking fault current into the I
and I
under these conditions but it will not cause overvoltage to
occur.
Connecting V
Supplies Being Margined
If it is not practical to power the LTC2920-2 from the V
and/or V
connect the V
diode (Figure 18). This solution works with power supply
feedback voltages less that 1.5V and I
>30μA. Be sure to account for the diode drop across all
temperatures to ensure the LTC2920-2 V
specifications are met.
V
If the LTC2920 is both powered by and margins a power
supply that is marginally stable, oscillations can occur. In
these cases, it may be necessary to provide an additional
filtering resistor between the LTC2920 and the power
supply being margined (see Figure 19). The oscillation is
most likely to occur when the LTC2920 is sourcing current
from the I
with the C
the filter resistor R
much voltage drop across the resistor the application can
tolerate and how much current the LTC2920 will sink
under worst-case conditions. In the LTC2920 low current
range, a safe value for the LTC2920 I
maximum LTC2920 quiescent current plus 4 times the
I
the LTC2920 I
cent current plus 1.2 times the I
Example: If the I
In this example, the power supply voltage is 3.3V. Drop-
ping 0.5V across R
of 2.8V. This is well above the LTC2920’s minimum V
MARGIN
CC
I
CCMAX
Power Supply Filtering
M2
current. In the high current range, a safe value for
pins. The LTC2920-2 will not operate normally
OUT
BYP
MARGING
= I
= 1mA + (4 • 100μA ) = 1.4mA
LTC2920-1/LTC2920-2
s of the power supplies being margined,
Q
capacitor form a lowpass filter. The value of
CC
CC
CC
+ (4 • I
MARGIN
to Power Sources Other than the
current is the maximum LTC2920 quies-
pin of the LTC2920-2 using a Schottky
BYP
pin. The R
BYP
MARGIN
can be calculated by deciding how
will provide a V
current is 100μA, then:
)
BYP
MARGIN
resistor in combination
CC
CC
current.
MARGIN
CC
at the LTC2920
current is the
and V
currents
13
MARGIN
292012fa
IN
M1
CC
s