参数资料
型号: ISL6326CRZ
厂商: Intersil
文件页数: 12/30页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 40-QFN
标准包装: 50
PWM 型: 电压模式
输出数: 1
频率 - 最大: 275kHz
占空比: 25%
电源电压: 4.75 V ~ 5.25 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: 0°C ~ 70°C
封装/外壳: 40-VFQFN 裸露焊盘
包装: 管件
ISL6326
by the resistor between the FS pin and ground. The PWM
signals command the MOSFET driver to turn on/off the
channel MOSFETs.
For 4-channel operation, the channel firing order is 4-3-2-1:
A simple RC network across the inductor extracts the DCR
voltage, as shown in Figure 3.
The voltage on the capacitor V C , can be shown to be
proportional to the channel current I L , see Equation 5.
? s ? ------------- + 1 ? ? ( DCR ? I )
V C = ---------------------------------------------------------------------
PWM3 pulse happens 1/4 of a cycle after PWM4, PWM2
output follows another 1/4 of a cycle after PWM3, and
PWM1 delays another 1/4 of a cycle after PWM2. For
3-channel operation, the channel firing order is 3-2-1.
? DCR ? L
L
( s ? RC + 1 )
(EQ. 5)
I ( s )
Connecting PWM4 to VCC selects three channel operation
and the pulse times are spaced in 1/3 cycle increments. If
PWM3 is connected to VCC, two channel operation is
selected and the PWM2 pulse happens 1/2 of a cycle after
PWM pulse.
If the RC 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.
V IN
L
Switching Frequency
Switching frequency is determined by the selection of the
frequency-setting resistor, R T , which is connected from FS
pin to GND (see the figures labeled Typical Applications on
page 4 and page 5). Equation 3 is provided to assist in
selecting the correct resistor value.
ISL6605
L
DCR
INDUCTOR
V L
V C (s)
V OUT
C OUT
R T = --------------------------
10
2.5X10
F SW
where F SW is the switching frequency of each phase.
Current Sensing
(EQ. 3)
PWM(n)
ISL6326 INTERNAL CIRCUIT
I n
R
C
R ISEN(n)
(PTC)
ISL6326 senses the current continuously for fast response.
ISL6326 supports inductor DCR sensing, or resistive
CURRENT
sensing techniques. The associated channel current sense
amplifier uses the ISEN inputs to reproduce a signal
proportional to the inductor current, I L . The sense current,
SENSE
+
-
ISEN-(n)
I SEN , is proportional to the inductor current. The sensed
current is used for current balance, load-line regulation, and
ISEN+(n)
C T
I SEN = I -------------------
L R
overcurrent protection.
The internal circuitry, shown in Figures 3 and 4, represents
one channel of an N-channel converter. This circuitry is
repeated for each channel in the converter, but may not be
active depending on the status of the PWM3 and PWM4
pins, as described in the “PWM Operation” on page 11.
INDUCTOR DCR SENSING
An inductor ’s winding is characteristic of a distributed
resistance as measured by the DCR (Direct Current
Resistance) parameter. Consider the inductor DCR as a
separate lumped quantity, as shown in Figure 3. The
channel current I L , flowing through the inductor, will also
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V L .
DCR
ISEN
FIGURE 3. DCR SENSING CONFIGURATION
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
I SEN = I L ? ------------------
R
V L = I L ? ( s ? L + DCR )
12
(EQ. 4)
resistor and the DCR of the inductor.
DCR
ISEN
(EQ. 6)
FN9262.1
May 5, 2008
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