參數(shù)資料
型號: LTC3867IUF#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 0.1 A SWITCHING CONTROLLER, 1200 kHz SWITCHING FREQ-MAX, PQCC24
封裝: 4 X 4 MM, LEAD FREE, PLASTIC, MO-220WGGD, QFN-24
文件頁數(shù): 11/36頁
文件大?。?/td> 380K
代理商: LTC3867IUF#PBF
LTC3867
19
3867f
After determining the components for the temperature
compensation network, check the results by plotting IMAX
versusinductortemperatureusingthefollowingequations:
IMAX =
VSENSEMAX(ADJ) – VSENSE / 2
DCR(MAX) at 25
°C 1+ TL(MAX) –25°C
(
)0.4/100
(
)
where:
VSENSEMAX(ADJ) = VSENSE(MAX)
1.8V –
VITEMP
2.8
1.3
– A
VITEMP = 30A RS +RP ||RNTC
(
)
Use typical values for VSENSE(MAX). Subtracting constant
A will provide a minimum value for VSENSE(MAX). These
values are summarized in Table 1.
Table 1
ILIM
GND
FLOAT
INTVCC
VSENSE(MAX) TYP
30mV
50mV
75mV
A
5mV
7mV
The resulting current limit should be greater than or equal
toIMAXforinductortemperaturesbetween25°Cand100°C.
These are typical values for the NTC compensation network:
NTC RO = 100k, B-constant = 3000 to 4000
RS ≈ 20k
RP ≈ 50k
GeneratingtheIMAXversusinductortemperaturecurveplot
first using the above values as a starting point and then
adjusting the RS and RP values as necessary is another
approach. Figure 7 shows a typical curve of IMAX versus
inductor temperature.
The same thermistor network can be used to correct for
temperatures less than 25°C. But make sure VITEMP is
greater than 0.6V for duty cycles of 25% or more, oth-
erwise temperature correction may not occur at elevated
ambients. For the most accurate temperature detection,
place the thermistors next to the inductor as shown in
Figure 8. Take care to keep the ITEMP pin away from the
switch nodes.
APPLICATIONS INFORMATION
Figure 6. Resistance Versus Temperature for the ITEMP Pin
Network and the 100k NTC
Figure 7. Worst-Case IMAX Versus Inductor Temperature Curve
with and without NTC Temperature Compensation
Figure 8. Thermistor Location. Place Thermistor Next to
Inductor for Accurate Sensing of the Inductor Temperature,
But Keep the ITEMP Pin Away from the Switch Nodes and Gate
Drive Traces
INDUCTOR TEMPERATURE (°C)
10
RESIST
ANCE
(k)
100
1000
10000
–40
20
40
60
100
80
120
1
–20
0
3867 F06
THERMISTOR RESISTANCE
RO = 100k
TO = 25°C
B = 4334 FOR 25°C/100°C
RITMP
RS = 20k
RP = 43.2k
100k NTC
INDUCTOR TEMPERATURE (°C)
–40
I MAX
(A)
15
20
25
20
60
120
3867 F07
10
5
0
–20
0
40
80 100
CORRECTED
IMAX
NOMINAL
IMAX
UNCORRECTED
IMAX
RS = 20k
RP = 43.2k
NTC THERMISTOR:
RO = 100k
TO = 25°C
B = 4334
VOUT
RNTC
L1
SW1
3867 F08
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