LTC3829EFE#PBF Linear Technology, LTC3829EFE#PBF Datasheet - Page 19

• Manufacturer Part Number: LTC3829EFE#PBF
• Description: IC BUCK SYNC ADJ 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3829EFE#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

applicaTions inForMaTion
The NTC resistor has a negative temperature coefficient,
meaning its value decreases as temperature rises. The
V
creases and in turn, the V
compensate the DCR temperature coefficient. The NTC
resistor, however, is nonlinear and the user can linear-
ize its value by building a resistor network with regular
resistors. Consult the NTC manufacture data sheets for
detailed information.
Another use for the ITEMP pins, in addition to NTC com-
pensated DCR sensing, is adjusting V
between the nominal values of 30mV, 50mV and 75mV for
a more precise current limit. This is done by applying a
voltage less than 0.5V to the ITEMP pin. V
be varied per the previous equation and the same duty cycle
limitations will apply. The current limit can be adjusted using
this method either with a sense resistor or DCR sensing.
NTC Compensated DCR Sensing
For DCR sensing applications where a more accurate
current limit is required, a network consisting of an NTC
thermistor placed from the ITEMP pin to ground will
provide correction of the current limit over temperature.
Figure 2b shows this network. Resistors R
linearize the impedance the ITEMP pin sees. To implement
NTC compensated DCR sensing, design the DCR sense
filter network per the same procedure mentioned in the
previous selection, except calculate the divider components
using the room temperature value of the DCR. For a single
output rail operating from one phase:
1. Set the ITEMP pin resistance to 50k at 25°C. With
2. Calculate the ITEMP pin resistance and the maximum
R
V
ITEMP
ITEMP
ITEMP
10µA flowing out of the ITEMP pin, the voltage on the
ITEMP pin will be 0.5V at room temperature. Current
limit correction will occur for inductor temperatures
greater than 25°C.
inductor temperature which is typically 100°C. Use the
equations:
100
100
voltage, therefore, decreases as temperature in-
C
C
= .
V
ITEMP
0 5
10
V
µA
100
– .
1 3
C
I
MAX
SENSEMAX(ADJ)
• •
DCR MAX R
(
SENSE(MAX)
will increase to
) •
SENSE(MAX)
S
and R
2
/
to values
(
V
R
SENS
1
P
+
will
will
R
E E MAX
2
(
)
•
(
100
)
Calculate the values for R
graph the following R
the y-axis and R
Next, find the value of R
which will be the point where the curves intersect. Once
R
The resistance of the NTC thermistor can be obtained
from the vendor’s data sheet either in the form of graphs,
tabulated data or formulas. The approximate value for the
NTC thermistor for a given temperature can be calculated
from the following equation:
where:
Figure 5 shows a typical resistance curve for a 100k therm-
istor and the ITEMP pin network over temperature.
Starting values for the NTC compensation network are
listed below:
But, the final values should be calculated using the above
equations and checked at 25°C and 100°C.
P
R
R
R = resistance at temperature T, which is in degrees C
R
B = B-constant of the thermistor.
• NTC R
• R
• R
R R
is known, solve for R
°
S
S
O
C
=
S
P
= R
= R
= resistance at temperature T
–
= 20k
= 50k
25
O
ITEMP25C
ITEMP100C
• exp
O
°
C
= 100k
)
• . /



0 4 100
P
B
on the x-axis.
•
– R

 
– R
T
S
NTC25C
+
NTC100C
versus R
S
1
273
P
P
.
and R
that satisfies both equations
|| R
–
|| R
T
S
O
P
P
. A simple method is to
+
equations with R
P
1
O
273
, typically 25°C
LTC3829
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