LTC2920-2IMS8#PBF Linear Technology, LTC2920-2IMS8#PBF Datasheet - Page 10

• 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: -

LTC2920-1/LTC2920-2
APPLICATIO S I FOR ATIO
Even though the manufacturer does not directly supply the
equation for the trim current, a simple measurement can
be made to calculate an equation for V
of I
To do this, select the trim resistor configuration which
places the trim resistor between the trim pin and ground
(see Figure 10).
With the trim resistor connected to ground, note the
direction of the power module output voltage change. This
is the direction that the power module output voltage will
change when the LTC2920 IN control pin is HIGH, above
V
this configuration can vary among power modules, even
among power modules from the same manufacturer.
Calculate a resistor value from the manufacturer’s equa-
tion, or select it from a chart (if a chart is supplied by the
manufacturer). Pick a value near the middle of the trim
resistor range. Obtain and measure the selected resistor
with an ohmmeter or use a precision 0.1% resistor.
Knowing the correct value of this resistance is critical to
obtaining good results. Make provisions to connect and
disconnect this test resistor between the trim pin and the
power supply module’s negative output pin. (Figure 10.)
Carefully follow all other manufacturer’s application notes
regarding power supply input voltage, minimum and
maximum output voltages, sense pin connections (if any),
minimum and maximum current loads, etc. Failure to do
so may permanently damage the power supply module!
Apply the specified input voltage to the power supply
module. Measure the power supply output voltage V
and the V
resistor.
Subtract the untrimmed (V
power supply output voltages to obtain the trim voltage
(V
and the trim current:
Calculate the linear current trim constant K
10
IH
DELTA
V
I
K
TRIM
. Remember that the direction of the voltage trim for
TRIM
DELTA
TRIM
.
):
= V
= V
T
= V
voltages before and after connecting the trim
TRIM
DELTA
PSNOM
/R
/I
TRIM
TRIM
U
– V
PSTRIM
U
PSNOM
) and trimmed (V
W
TRIM
TRIM
as a function
U
:
PSTRIM
PS
)
For any desired V
R
For 5μA ≤ I
Connect R
pin.
For 167μA < I
Connect R
pin.
If I
used for this application.
The LTC2920 can source or sink current only when the
voltage at the I
In order to be sure that the LTC2920 will operate correctly
in this application, ensure that the V
these limits. To do this, calculate the effective output
resistance of the power supply module’s trim output pin,
R
above, the open circuit voltage is:
To calculate R
trimmed V
The effective TRIM pin source resistance can then be
calculated by:
The voltage at the LTC2920 I
now calculated for both voltage margin directions. Refering
to Figure 10:
Note: be sure to use these equations to verify that V
and V
SET
VT
I
R
R
TRIM
V
V
R
V
V
TRIM
REF
TDELTA
TSINK
TSOURCE
SET
SET
VT
(refer to Figure 10). Using the measurements taken
can now be calculated for the LTC2920.
TSOURCE
= V
falls outside of this range, the LTC2920 cannot be
= V
= 1V/I
= 1V/(I
= V
= V
SET
TDELTA
SET
TTRIM
TRIM
TNOM
= V
MARGIN
= V
REF
between the R
TRIM
are within LTC2920 V
TRIM
between the R
M
TNOM
TRIM
VT
REF
≤ 167μA:
pin is between 0.6 and (V
voltages measured above:
/I
– (R
, subtract the untrimmed V
MARGIN
TRIM
≤ 2mA:
/K
/30)
+ (R
– V
TRIM
VT
TTRIM
• I
VT
:
TRIM
• I
S
MARGIN
pin and the LTC2920 ground
S
TRIM
pin and the LTC2920 V
)
)
M
T
pin for any I
node will stay within
voltages specified in
CC
– 0.6) volts.
TNOM
TRIM
292012fa
TSINK
and
can
CC