參數(shù)資料
型號: LTC4280IUFD
廠商: LINEAR TECHNOLOGY CORP
元件分類: 電源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PQCC24
封裝: 4 X 5 MM, PLASTIC, MO-220, QFN-24
文件頁數(shù): 11/28頁
文件大?。?/td> 286K
代理商: LTC4280IUFD
LTC4280
19
4280f
APPLICATIONS INFORMATION
For a start-up time of 4ms with a 2x safety margin we
choose:
C
t
ms μF
C
ms
TIMER
STARTUP
TIMER
=
2
12 3
8
12 3
./
./μ
μF
068
.
For an overcurrent fault lter time of 5ms we choose:
CF = tFILTER/123ms/μF 47nF
The UV and OV resistor string values can be solved in the
following method. First pick R3 based on ISTRING being
1.235V/R3 at the edge of the OV rising threshold, where
ISTRING > 40μA. Then solve the following equations:
R2 =
V
R3
UV
OV
OV(OFF)
UV(ON)
TH(RISING)
TH
H(FALLING)
UV(ON)
TH(RI
–R3
R1 =
V
UV
(
)
RR
32
+
S
SING)
––
RR
32
In our case we choose R3 to be 3.4kΩ to give a resistor
string current below 100μA. Then solving the equations
results in R2 = 1.16kΩ and R1 = 34.6kΩ.
The FB divider is solved by picking R8 and solving for R7,
choosing 3.57kΩ for R8 we get:
R7 =
V
FB
PWRGD(UP)
TH(RISING)
R
8
resulting in R7 = 30kΩ.
A 0.1μF capacitor, CF, is placed on the UV pin to prevent
supply glitches from turning off the GATE via UV or OV.
The address is set with the help of Table 1, which indicates
binary address 1010011 corresponds to address 19.
Address 19 is set by setting ADR2 high, ADR1 open and
ADR0 high.
Next the value of R5 and R6 are chosen to be the default
values 10Ω and 15k as discussed previously.
UV
OV
FILTER
GND
ON
EN
SDAO
FB
GPIO
INTVCC
TIMER
ADIN
ADR2
ADR1
V
DD
SENSE
+
SENSE
GA
TE
SOURCE
SDAI
SCL
ALER
T
NC
ADR0
R2
R3
CF
Z1
R1
SENSE RESISTOR RS
C3
LTC4280UFD
R8
ILOAD
4280 F05
ILOAD
Figure 5. Recommended Layout
In addition a 0.1μF ceramic bypass capacitor is placed on
the INTVCC pin.
Layout Considerations
To achieve accurate current sensing, a Kelvin connection
is required. The minimum trace width for 1oz copper
foil is 0.02" per amp to make sure the trace stays at a
reasonable temperature. Using 0.03" per amp or wider
is recommended. Note that 1oz copper exhibits a sheet
resistance of about 530μΩ/. Small resistances add up
quickly in high current applications. To improve noise
immunity, put the resistive dividers to the UV, OV and FB
pins close to the device and keep traces to VDD and GND
short. It is also important to put the bypass capacitor for
the INTVCC pin, C3, as close as possible between INTVCC
and GND. A 0.1μF capacitor from the UV pin (and OV pin
through resistor R2) to GND also helps reject supply noise.
Figure 4 shows a layout that addresses these issues. Note
that a surge suppressor, Z1, is placed between supply and
ground using wide traces.
相關(guān)PDF資料
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