参数资料
型号: ISL6564IR-T
厂商: Intersil
文件页数: 13/27页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 40-QFN
标准包装: 4,000
PWM 型: 电压模式
输出数: 1
频率 - 最大: 1.5MHz
占空比: 66.7%
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: -40°C ~ 85°C
封装/外壳: 40-VFQFN 裸露焊盘
包装: 带卷 (TR)
ISL6564
I ( s )
I L
V IN
L
L
DCR
V OUT
PWM
ISL6207
INDUCTOR
V L
C OUT
V C (s)
I SEN
PWM(n)
R
C
ISL6564 INTERNAL CIRCUIT
t HOLD
R ISEN(n)
SAMPLE CURRENT, I n
I n
(PTC)
SWITCHING PERIOD
TIME
FIGURE 3. SAMPLE AND HOLD TIMING
SAMPLE
&
HOLD
+
-
ISEN-(n)
ISEN+(n)
I SEN = I ------------------
L R
I SEN = I L ? ------------------
R
Current Sensing
The ISL6564 supports inductor DCR sensing, MOSFET
r DS(ON) sensing, or resistive sensing techniques. The
internal circuitry, shown in Figures 4, 5, and 6, represents
channel n 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 section.
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 4. 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 4. DCR SENSING CONFIGURATION
The capacitor voltage V C , is then replicated across the
sense resistor R ISEN . The current through the sense resistor
is proportional to the inductor current. Equation 6 shows the
proportion between the channel current and the sensed
current I SEN , is driven by the value of the sense resistor
chosen and the DCR of the inductor.
DCR
(EQ. 6)
ISEN
DCR varies with temperature, so a Positive Temperature
Coefficient (PTC) resistor should be selected for the sense
V L = I L ? ( s ? L + DCR )
(EQ. 4)
resistor R ISEN .
RESISTIVE SENSING
? s ? ------------- + 1 ? ? ( DCR ? I )
V C = ---------------------------------------------------------------------
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 4.
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 matches the inductor L/DCR time
constant, then V C is equal to the voltage drop across the
DCR.
13
If DCR sensing is not utilized, independent current-sense
resistors in series with each output inductor can serve as the
sense element (see Figure 5). This technique is more
accurate, but reduces overall converter efficiency due to the
addition of a lossy element directly in the output path.
FN9156.2
December 27, 2004
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