参数资料
型号: ISL6334IRZ
厂商: Intersil
文件页数: 15/31页
文件大小: 0K
描述: IC CTRLR PWM 4PHASE BUCK 40-QFN
标准包装: 50
应用: 控制器,Intel VR11.1
输入电压: 3 V ~ 12 V
输出数: 1
输出电压: 0.5 V ~ 1.6 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 40-VFQFN 裸露焊盘
供应商设备封装: 40-QFN(6x6)
包装: 管件
ISL6334, ISL6334A
I ( s )
V IN
L
a limitation. The worst-case peak-to-peak inductor ripple
current should be kept less than 70% of the OCP trip point
L
DCR
V OUT
(internal mirrored current = ~70μA). Care should be taken to
avoid operation with negative current feedback exceeding
ISL6596
INDUCTOR
V L
V C (s)
R
C
C OUT
this threshold, as this may lead to momentary loss of current
balance between phases and disruption of normal circuit
operation. Note that the negative current can especially
affect coupled inductor designs, where the effective
inductance is the leakage between the two channels, much
PWM(n)
ISL6334, ISL6334A INTERNAL CIRCUIT
I n
R ISEN(n)
lower than the specified mutual inductance (LM). To limit the
impact, a higher R ISEN value (1.5x to 2x) can be used to
reduce the effective negative current seen by the controller
in coupled inductor designs. Refer to Intersil's application
note, AN1268 for a detailed coupled inductor discussion and
ripple current calculation.
CURRENT
SENSE
+
-
ISEN-(n)
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense resistor
R SENSE in series with each output inductor can serve as the
ISEN+(n)
C T
current sense element (see Figure 5). This technique is more
accurate, but reduces overall converter efficiency due to the
I SEN = I ------------------
L R
? s ? ------------- + 1 ? ? ( DCR ? I )
V C ( s ) = ---------------------------------------------------------------------
I SEN = I L ? -----------------------
R
DCR
ISEN
FIGURE 4. DCR SENSING CONFIGURATION
The voltage on the capacitor V C , can be shown to be
proportional to the channel current I L . See Equation 5.
L
? DCR ? L (EQ. 5)
( s ? RC + 1 )
If the R-C network components are selected such that the
RC time constant (= R*C) matches the inductor time
constant (= L/DCR), the voltage across the capacitor V C is
equal to the voltage drop across the DCR, i.e., proportional
to the channel current.
With the internal low-offset current amplifier, the capacitor
voltage V C is replicated across the sense resistor R ISEN .
Therefore, the current out of ISEN+ pin, I SEN , is proportional
to the inductor current.
Because of the internal filter at ISEN- pin, one capacitor, C T ,
is needed to match the time delay between the ISEN- and
ISEN+ signals. Select the proper C T to keep the time
constant of R ISEN and C T (R ISEN x C T ) close to 27ns.
Equation 6 shows that the ratio of the channel current to the
sensed current, I SEN , is driven by the value of the sense
resistor and the DCR of the inductor.
additional power loss on the current sense element R SENSE .
The same capacitor C T is needed to match the time delay
between ISEN- and ISEN+ signals. Select the proper C T to
keep the time constant of R ISEN and C T (R ISEN x C T ) close to
27ns.
Equation 7 shows the ratio of the channel current to the
sensed current I SEN .
R SENSE
(EQ. 7)
ISEN
The inductor DCR value will increase as the temperature
increases. Therefore, the sensed current will increase as the
temperature of the current sense element increases. In order
to compensate the temperature effect on the sensed current
signal, a Positive Temperature Coefficient (PTC) resistor can
be selected for the sense resistor R ISEN , or the integrated
temperature compensation function of ISL6334, ISL6334A
should be utilized. The integrated temperature compensation
function is described in “External Temperature Compensation”
I SEN = I L ? ------------------
R
DCR
ISEN
(EQ. 6)
The current sense circuitry operates in a very similar manner
for negative current feedback, where inductor current is
flowing from the output of the regulator to the PHASE node,
opposite of flow pictured in Figures 4 and 5. However, the
range of proper operation with negative current sensing has
15
FN6482.2
February 1, 2013
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