参数资料
| 型号： | ISL6277IRZ |
| 厂商： | Intersil |
| 文件页数： | 28/37页 |
| 文件大小： | 0K |
| 描述： | IC PWM REG MULTIPH AMD 48-QFN |
| 标准包装： | 50 |
| 应用： | 控制器，AMD Fusion? SVI 2.0 CPU GPU |
| 输入电压： | 4.5 V ~ 25 V |
| 输出数： | 2 |
| 输出电压： | 0.006 V ~ 1.55 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 48-VFQFN 裸露焊盘 |
| 供应商设备封装： | 48-QFN（6x6） |
| 包装： | 管件 |
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ISL6277
? L = -------------
Key Component Selection
Inductor DCR Current-Sensing Network
DCR
L
(EQ. 20)
? sns = --------------------------------------------------------
R ntcnet ? ---------------
------------------------------------------ ? C n
R ntcnet + ---------------
PHASE1 PHASE2 PHASE3
R SUM
R SUM
R SUM
I SUM+
1
R sum
N
R sum
N
where N is the number of phases.
(EQ. 21)
L
DCR
L
DCR
L
DCR
R NTCS
R NTC
R O
R P
+
CN VCN
-
RI
I SUM-
Transfer function A cs (s) always has unity gain at DC. The inductor
DCR value increases as the winding temperature increases,
giving higher reading of the inductor DC current. The NTC R ntc
value decrease as its temperature decreases. Proper selection of
R sum , R ntcs , R p and R ntc parameters ensures that V Cn
represents the inductor total DC current over the temperature
R O
R O
I O
FIGURE 22. DCR CURRENT-SENSING NETWORK
Figure 22 shows the inductor DCR current-sensing network for a
3-phase solution. An inductor current flows through the DCR and
creates a voltage drop. Each inductor has two resistors in R sum
and R o connected to the pads to accurately sense the inductor
current by sensing the DCR voltage drop. The R sum and R o
resistors are connected in a summing network as shown, and feed
the total current information to the NTC network (consisting of
R ntcs , R ntc and R p ) and capacitor C n . R ntc is a negative
temperature coefficient (NTC) thermistor, used to temperature
compensate the inductor DCR change.
The inductor output side pads are electrically shorted in the
schematic but have some parasitic impedance in actual board
layout, which is why one cannot simply short them together for the
current-sensing summing network. It is recommended to use
1 ? ~10 ? ? R o to create quality signals. Since R o value is much smaller
than the rest of the current sensing circuit, the following analysis
range of interest.
There are many sets of parameters that can properly
temperature-compensate the DCR change. Since the NTC
network and the R sum resistors form a voltage divider, V cn is
always a fraction of the inductor DCR voltage. It is recommended
to have a higher ratio of V cn to the inductor DCR voltage so the
droop circuit has a higher signal level to work with.
A typical set of parameters that provide good temperature
compensation are: R sum = 3.65k ? , R p = 11k ? , R ntcs = 2.61k ?
and R ntc = 10k ? (ERT-J1VR103J). The NTC network parameters
may need to be fine tuned on actual boards. One can apply full
load DC current and record the output voltage reading
immediately; then record the output voltage reading again when
the board has reached the thermal steady state. A good NTC
network can limit the output voltage drift to within 2mV. It is
recommended to follow the Intersil evaluation board layout and
current sensing network parameters to minimize engineering
time.
V Cn (s) also needs to represent real-time I o (s) for the controller to
achieve good transient response. Transfer function A cs (s) has a
pole w sns and a zero w L . One needs to match w L and w sns so
A cs (s) is unity gain at all frequencies. By forcing w L equal to w sns
and solving for the solution, Equation 22 gives Cn value.
C n = ---------------------------------------------------------------
R ntcnet ? ---------------
------------------------------------------ ? DCR
R ntcnet + ---------------
ignores it.
The summed inductor current information is presented to the
capacitor C n . Equations 17 thru 21 describe the frequency
domain relationship between inductor total current I o (s) and C n
voltage V Cn (s):
L
R sum
N
R sum
N
(EQ. 22)
V Cn ? s ? = ? ------------------------------------------ ? ------------- ? ? I o ? s ? ? A cs ? s ?
? R ntcnet + --------------- ?
R ntcnet = ----------------------------------------------------
1 + -------
A cs ? s ? = -----------------------
1 + -------------
? ?
? R ntcnet DCR ?
? R sum N ?
N
? R ntcs + R ntc ? ? R p
R ntcs + R ntc + R p
s
? L
s
? sns
28
(EQ. 17)
(EQ. 18)
(EQ. 19)
For example, given N = 3, R sum = 3.65k ? , R p = 11k ? ,
R ntcs = 2.61k ? , R ntc = 10k ? , DCR = 0.88m ? and L = 0.36μH,
Equation 22 gives C n = 0.406μF.
Assuming the compensator design is correct, Figure 23 shows the
expected load transient response waveforms if C n is correctly
selected. When the load current I core has a square change, the
output voltage V core also has a square response.
If C n value is too large or too small, V Cn (s) does not accurately
represent real-time I o (s) and worsens the transient response.
Figure 24 shows the load transient response when C n is too
small. V core sags excessively upon load insertion and may create
a system failure. Figure 25 shows the transient response when
FN8270.1
March 8, 2012
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