参数资料
| 型号： | ISL6267HRZ |
| 厂商： | Intersil |
| 文件页数： | 24/33页 |
| 文件大小： | 0K |
| 描述： | IC PWM CTRLR MULTIPHASE 48TQFN |
| 标准包装： | 50 |
| 系列： | Robust Ripple Regulator™ (R³) |
| 应用： | 控制器，AMD Fusion? CPU GPU |
| 输入电压： | 4.5 V ~ 25 V |
| 输出数： | 2 |
| 输出电压： | 0.013 V ~ 1.55 V |
| 工作温度： | -10°C ~ 100°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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ISL6267
V Cn ( s ) = ? ----------------------------------------- × ------------ ? × I o ( s ) × A cs ( s )
N ?
R sum
?
MOSFET r DS(ON) voltage drop, which is proportional to the
inductor current. A phase comparator inside the controller
monitors the phase voltage during on-time of the low-side
MOSFET and compares it with a threshold to determine the zero
crossing point of the inductor current. If the inductor current has
not reached zero when the low-side MOSFET turns off, it will flow
through the low-side MOSFET body diode, causing the phase
node to have a larger voltage drop until it decays to zero. If the
domain relationship between inductor total current I o (s) and C n
voltage V Cn (s):
? ?
? R ntcnet DCR ?
(EQ. 18)
N
? R ntcnet + -------------- ?
R ntcnet = ---------------------------------------------------
1 + ------
A cs ( s ) = ----------------------
1 + ------------
ω L = ------------
I SUM+
ω sns = ------------------------------------------------------
R ntcnet × --------------
----------------------------------------- × C n
inductor current has crossed zero and reversed the direction
when the low-side MOSFET turns off, it will flow through the
high-side MOSFET body diode, causing the phase node to have a
spike until it decays to zero. The controller continues monitoring
the phase voltage after turning off the low-side MOSFET. To
minimize the body diode-related loss, the controller also adjusts
the phase comparator threshold voltage accordingly in iterative
steps such that the low-side MOSFET body diode conducts for
approximately 40ns.
Key Component Selection
Inductor DCR Current-Sensing Network
PHASE1 PHASE2 PHASE3
R SUM
R SUM
R SUM
( R ntcs + R ntc ) × R p
R ntcs + R ntc + R p
s
ω L
s
ω sns
DCR
L
1
R sum
N
N
R sum
R ntcnet + --------------
where N is the number of phases.
(EQ. 19)
(EQ. 20)
(EQ. 21)
(EQ. 22)
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
range of interest.
R O
R O
I O
FIGURE 20. DCR CURRENT-SENSING NETWORK
Figure 20 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 Ω ~10 Ω R o to create quality signals. Since R o value is much
smaller than the rest of the current sensing circuit, the following
analysis ignores it.
The summed inductor current information is presented to the
capacitor C n . Equations 18 thru 22 describe the frequency
24
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 Ω , R p = 11k Ω , R ntcs = 2.61k Ω
and R ntc = 10k Ω (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 23 gives Cn value.
January 8, 2013
FN7801.1
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