LTC2920-1IS5#PBF Linear Technology, LTC2920-1IS5#PBF Datasheet - Page 8

• Manufacturer Part Number: LTC2920-1IS5#PBF
• Manufacturer: Linear Technology

Specifications of LTC2920-1IS5#PBF

• Number Of Voltage Supervisors: 1
• Operating Supply Voltage (min): 2.3V
• Operating Supply Voltage (max): 6V
• Package Type: TSOT-23
• Operating Temperature Classification: Industrial
• Operating Temp Range: -40C to 85C
• Pin Count: 5
• Mounting: Surface Mount
• Lead Free Status / Rohs Status: Compliant

LTC2920-1/LTC2920-2
APPLICATIO S I FOR ATIO
SELECTING THE R
Selecting R
Containing a Feedback Pin and Two Feedback
Resistors
Calculating the value of the current setting resistor, R
for a power supply with a feedback pin is straight forward.
When the LTC2920 is being added to an existing power
supply design, the power supply feedback resistors R
R
supply output voltage, V
%change, R
First, the margining voltage ΔV
knowing the percentage of the power supply voltage
V
Example: If a 3.3V power supply is to be margined by 5%,
then:
8
R
PSOUT
SET
G
ΔV
ΔV
have already been selected. By knowing R
= 60.6k
Figure 5. 3.3V Supply with 5% Margining (Low Range)
R
PSOUT
PSOUT
SET
change desired.
Figure 4. Simplified Power Supply Model
SET
SET
= %Change • V
= 0.05 • 3.3V = 0.165V
R
R
LTC2920
LTC2920
S
S
with an Existing Power Supply
can be calculated.
I
I
M
M
SET
V
I
MARGIN
U
REF
R
I
= 1.2V
MARGIN
RESISTOR
G
V
PSOUT
= 5.76k
REF
= 16.5μA
R
U
G
PSOUT
+
–
+
–
, and the amount to margin,
PSOUT
–
+
–
+
I
W
FB
I
R
R
FB
can be calculated by
F
F
= 210μA
= 10k
F
, the power
2920-1/2 F04
V
V
U
PSOUT
PSOUT
2920-1/2 F05
F
= 3.3V
SET
and
,
Since ΔV
section, margin current I
Example: If ΔV
If I
low current range. R
In this case, R
and ground.
If I
high current range. R
or simply:
Example: If the value of the feedback resistor R
in the example above then:
In this case, R
and V
If I
necessary to adjust both power supply feedback resistors
R
to calculate the magnitude of the change by dividing the
I
MARGIN
R
F
SET
I
I
MARGIN
R
MARGIN
R
R
ΔV
I
R
MARGIN
and R
MARGIN
MARGIN
MARGIN
SET
SET
SET
Figure 6. 3.3V Supply with 5% Margining (High Range)
SET
= 90k
PSOUT
CC
= 1V/(I
V
= 1V/I
= 30V/I
= 30V/I
.
G
CC
current calculated above by the desired new
PSOUT
. Again, this is usually a simple process. It is easy
is between 150μA and 2mA, use the LTC2920’s
is between 5μA and 167μA, use the LTC2920’s
is less than 5μA, or greater than 2mA, it will be
= ΔV
= 0.165/10k = 16.5μA
= 0.165V/500Ω = 330μA
= 0.05 • 3.3V = 0.165V
R
LTC2920
SET
S
SET
MARGIN
PSOUT
MARGIN
will appear on R
MARGIN
MARGIN
PSOUT
I
would be connected between the R
would be connected between the R
M
V
I
MARGIN
REF
SET
R
= 0.165V and R
SET
= 1.2V
/R
= 1V/16.5μA = 60.6k
/30)
G
= 30V/330μA = 90.1k
= 286Ω
F
= 330μA
is then calculated by:
MARGIN
is then calculated by:
+
–
F
–
+
as noted in the Overview
can be calculated by:
I
R
FB
F
F
= 4.2mA
= 500Ω
= 10k:
V
F
PSOUT
is 500Ω
2920-1/2 F06
292012fa
= 3.3V
S
S
pin
pin