参数资料
型号: ISL6327CRZ-T
厂商: Intersil
文件页数: 24/29页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM 48-QFN
标准包装: 4,000
PWM 型: 控制器
输出数: 6
频率 - 最大: 1MHz
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: 48-VFQFN 裸露焊盘
包装: 带卷 (TR)
ISL6327
ramps up to assume the full inductor current. In Equation 26,
the required time for this commutation is t 1 and the
approximated associated power loss is P UP,1 .
When the integrated temperature compensation function is
disabled by pulling the TCOMP pin to GND, the sensed
current will be dependent on the operational temperature of
P UP , 1 ≈ V IN ? ------ + --------- ? ? ---- 1 ? f S
? N 2 ? ? 2 ?
I M I PP ? t ?
(EQ. 26)
the power stage, since the DC resistance of the current
sense element may be changed according to the operational
temperature. R X in Equation 30 should be the maximum DC
At turn-on, the upper MOSFET begins to conduct and this
transition occurs over a time t 2 . In Equation 27, the
approximate power loss is P UP,2 .
resistance of the current sense element at all the operational
temperature.
In certain circumstances, it may be necessary to adjust the
P UP , 2 ≈ V IN ? ------ – --------- ? ? ---- 2 ? f S
? I M I PP ? ? t ?
? N 2 ? ? 2 ?
(EQ. 27)
value of one or more ISEN resistors. When the components
of one or more channels are inhibited from effectively
dissipating their heat so that the affected channels run hotter
A third component involves the lower MOSFET’s reverse
recovery charge, Q rr . Since the inductor current has fully
commutated to the upper MOSFET before the lower
MOSFET’s body diode can draw all of Q rr , it is conducted
through the upper MOSFET across VIN. The power
than desired, choose new, smaller values of RISEN for the
affected phases (see the section titled “Channel-Current
Balance” on page 12). Choose R ISEN,2 in proportion to the
desired decrease in temperature rise in order to cause
proportionally less current to flow in the hotter phase.
R ISEN , 2 = R ISEN ---------- 2
dissipated as a result is P UP,3 and is approximately
P UP , 3 = V IN Q rr f S
(EQ. 28)
Δ T
Δ T 1
(EQ. 31)
I PP2
? I M ?
P UP , 4 ≈ r DS ( ON ) ? ------ ? d + ---------- d
Finally, the resistive part of the upper MOSFET’s is given in
Equation 29 as P UP,4 .
2
(EQ. 29)
? N ? 12
The total power dissipated by the upper MOSFET at full load
can now be approximated as the summation of the results
from Equations 26, 27, 28 and 29. Since the power
equations depend on MOSFET parameters, choosing the
correct MOSFETs can be an iterative process involving
repetitive solutions to the loss equations for different
MOSFETs and different switching frequencies.
In Equation 31, make sure that Δ T 2 is the desired temperature
rise above the ambient temperature, and Δ T 1 is the measured
temperature rise above the ambient temperature. While a
single adjustment according to Equation 31 is usually
sufficient, it may occasionally be necessary to adjust R ISEN
two or more times to achieve optimal thermal balance
between all channels.
Load-Line Regulation Resistor
The load-line regulation resistor is labelled R FB in Figure 5.
Its value depends on the desired loadline requirement of the
application.
The desired loadline can be calculated using Equation 32:
R LL = -------------------------
Current Sensing Resistor
The resistors connected to the Isen+ pins determine the
V DROOP
I FL
(EQ. 32)
R ISEN = ----------------------- --------------
85 × 10 6
gains in the load-line regulation loop and the channel-current
balance loop as well as setting the overcurrent trip point.
Select values for these resistors by the Equation 30.
R X I OCP (EQ. 30)
N
where I FL is the full load current of the specific application,
and VR DROOP is the desired voltage droop under the full
load condition.
Based on the desired loadline R LL , the loadline regulation
resistor can be calculated using Equation 33:
NR R
R FB = ----------------------------------
where R ISEN is the sense resistor connected to the ISEN+
pin, N is the active channel number, R X is the resistance of
the current sense element, either the DCR of the inductor or
ISEN LL
R X
(EQ. 33)
R SENSE depending on the sensing method, and I OCP is the
desired overcurrent trip point. Typically, I OCP can be chosen
to be 1.3 times the maximum load current of the specific
application.
With integrated temperature compensation, the sensed
current signal is independent on the operational temperature
of the power stage, i.e. the temperature effect on the current
sense element R X is cancelled by the integrated
temperature compensation function. R X in Equation 30
should be the resistance of the current sense element at the
room temperature.
24
where N is the active channel number, R ISEN is the sense
resistor connected to the ISEN+ pin, and R X is the
resistance of the current sense element, either the DCR of
the inductor or R SENSE depending on the sensing method.
If one or more of the current sense resistors are adjusted for
thermal balance, as in Equation 31, the load-line regulation
resistor should be selected based on the average value of
the current sensing resistors, as given in Equation 34:
FN9276.4
May 5, 2008
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