LTC2920-2IMS8#PBF Linear Technology, LTC2920-2IMS8#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC2920-2IMS8#PBF
• Description: IC SNGL/DUAL PWR SUP CTRLR 8MSOP
• Manufacturer: Linear Technology

Specifications of LTC2920-2IMS8#PBF

• Applications: Single/Dual Power Supply Controller
• Voltage - Supply: 2.3 V ~ 6 V
• Current - Supply: 230µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -

APPLICATIO S I FOR ATIO
I
one of the two LTC2920’s I
the scaling factor:
The new feedback resistors would then be:
And R
WARNING
In some cases, adjusting the feedback resistors on a
switching supply might require recompensating the power
supply. Please refer to the applications information sup-
plied with the power supply for further information.
Selecting the R
with ‘Brick’ Type Power Supply Modules
‘Brick’ power supply modules often have a trim pin which
can be used for voltage margining. Figure 7 shows a
typical connection using the LTC2920 for voltage margin-
ing a power supply module.
The amount of current necessary to adjust the output
voltage of the power supply module is not normally given
directly by the manufacturer. However, by using informa-
tion that is supplied by the manufacturer, a measurement
can be made to determine a simple equation that is useful
for power supply module voltage margining.
Typically, the manufacturer will supply two different equa-
tions for selecting trim resistors: one for trimming the
output voltage up and a different one for trimming the
output voltage down. Trim resistors are nominally placed
Figure 7. Using a Power Module Trim Pin for Voltage Margining
MARGIN
I
R
R
FACTOR
F(NEW)
G(NEW)
SET
current. Select a new I
can then be calculated as descibed above.
= I
= R
= R
POWER MODULE
V
V
MARGIN(OLD)
IN
IN
+
–
F(OLD)
G(OLD)
SET
SENSE
SENSE
TRIM
U
V
V
Resistor Using Voltage Trim Pins
O
O
• I
+
+
–
–
• I
FACTOR
FACTOR
I
MARGIN
/I
U
MARGIN(NEW)
MARGIN
MARGIN
I
M
V
V
PSOUT
O
LTC2920
–
ranges, then calculate
W
current that is within
R
S
2920-1/2 F07
R
SET
U
between the trim pin and the power supply positive voltage
output or the trim pin and the negative power supply
output (ground). The polarity of the voltage trim and trim
resistor configuration are chosen by the manufacturer.
The equations describing the resistor values versus the
desired output voltage changes are typically not linear.
Fortunately, the relationship between trim pin current and
output voltage change is typically linear. The current trim
equation is usually the same (in magnitude) for changing
the output voltage up or down. Once the equation for trim
current is determined, it is much easier to use than trim
resistors. To illustrate this, Figure 8 shows a typical
resistor trim down curve for a power module. Figure 9
shows a typical current trim down curve for the same
power module.
Figure 8. Typical Trim Voltage vs Trim Resistor Curve
Figure 9. Typical Trim Voltage vs Trim Current Curve
100k
100
10k
1M
300
250
200
150
100
LTC2920-1/LTC2920-2
1k
10
1
50
0
0
0
0.1
0.1
TRIM VOLTAGE (V)
TRIM VOLTAGE (V)
0.2
0.2
0.3
0.3
0.4
0.4
2920-1/2 F08
2920-1/2 F09
0.5
0.5
292012fa
9