参数资料
| 型号： | ISL6277IRZ-T |
| 厂商： | Intersil |
| 文件页数： | 17/37页 |
| 文件大小： | 0K |
| 描述： | IC PWM REG MULTIPH AMD 48-QFN |
| 标准包装： | 4,000 |
| 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： | 带卷 (TR) |
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ISL6277
Differential Sensing
Rdroop
Figure 14 also shows the differential voltage sensing scheme.
?
Vdroop
SVD
VCC SENSE + V
= V DAC + VSS SENSE
(EQ. 3)
VCC SENSE – VSS SENSE = V DAC – R droop ? ? I droop ? --- ?
(EQ. 4)
COMP
FB
+
E/A
-
INTERNAL TO IC
+
+ -
Idroop
VDAC
DAC
X1
+
-
VCC SENSE
VR LOCAL VO
“CATCH ” RESISTOR
SVC
SVID[7:0]
RTN
VSS SENSE
VSS
“CATCH ” RESISTOR
VCC SENSE and VSS SENSE are the remote voltage sensing signals
from the processor die. A unity gain differential amplifier senses
the VSS SENSE voltage and adds it to the DAC output. The error
amplifier regulates the inverting and non-inverting input voltages
to be equal as shown in Equation 3:
droop
Rewriting Equation 3 and substituting Equation 2 gives Equation 4
the exact equation required for load-line implementation.
5
? 4 ?
FIGURE 14. DIFFERENTIAL SENSING AND LOAD LINE
IMPLEMENTATION
As the load current increases from zero, the output voltage
droops from the VID programmed value by an amount
proportional to the load current, to achieve the load line. The
ISL6277 can sense the inductor current through the intrinsic DC
Resistance (DCR) of the inductors, as shown in Figures 3 and 4,
The VCC SENSE and VSS SENSE signals come from the processor die.
The feedback is open circuit in the absence of the processor. As
Figure 14 shows, it is recommended to add a “catch” resistor to feed
the VR local output voltage back to the compensator, and to add
another “catch” resistor to connect the VR local output ground to the
RTN pin. These resistors, typically 10 ? ~100 ? , provide voltage
feedback if the system is powered up without a processor installed.
C isen
TO IC
or through resistors in series with the inductors as shown in
Figure 5. In both methods, capacitor C n voltage represents the
total inductor current. A droop amplifier converts C n voltage into
an internal current source with the gain set by resistor R i . The
current source is used for load line implementation, current
monitoring and overcurrent protection.
Figure 14 shows the load-line implementation. The ISL6277
drives a current source (I droop ) out of the FB pin, as described by
Equation 1.
Phase Current Balancing
L3
PHASE3
R isen
ISEN3
L2
INTERNAL
PHASE2
R isen
ISEN2
I L3
I L2
R dcr3
R dcr2
R pcb3
R pcb2
V O
I droop = -----------
V Cn
R i
(EQ. 1)
ISEN1
C isen
PHASE1
R isen
L1
I L1
R dcr1
R pcb1
V droop = R droop ? ? I droop ? --- ?
(EQ. 2)
When using inductor DCR current sensing, a single NTC element
is used to compensate the positive temperature coefficient of the
copper winding, thus sustaining the load-line accuracy with
reduced cost.
I droop flows through resistor R droop and creates a voltage drop as
shown in Equation 2.
5
? 4 ?
V droop is the droop voltage required to implement load line.
Changing R droop or scaling I droop can change the load line slope.
Since I droop also sets the overcurrent protection level, it is
recommended to first scale I droop based on OCP requirement,
then select an appropriate R droop value to obtain the desired
load line slope.
C isen
FIGURE 15. CURRENT BALANCING CIRCUIT
The ISL6277 monitors individual phase average current by
monitoring the ISEN1, ISEN2, and ISEN3 voltages. Figure 15
shows the recommended current balancing circuit for DCR
sensing. Each phase node voltage is averaged by a low-pass filter
consisting of R isen and C isen , and is presented to the
corresponding ISEN pin. R isen should be routed to the inductor
phase-node pad in order to eliminate the effect of phase node
parasitic PCB DCR. Equations 5 through 7 give the ISEN pin
voltages:
V ISEN1 = ? R dcr1 + R pcb1 ? ? I L1 (EQ. 5)
V ISEN2 = ? R dcr2 + R pcb2 ? ? I L2
V ISEN3 = ? R dcr3 + R pcb3 ? ? I L3
(EQ. 6)
(EQ. 7)
where R dcr1 , R dcr2 and R dcr3 are inductor DCR; R pcb1 , R pcb2
and R pcb3 are parasitic PCB DCR between the inductor output
side pad and the output voltage rail; and I L1 , I L2 and I L3 are
inductor average currents.
17
FN8270.1
March 8, 2012
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