参数资料
| 型号： | ISL6334AIRZ-T |
| 厂商： | Intersil |
| 文件页数： | 26/31页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR PWM 4PHASE BUCK 40-QFN |
| 标准包装： | 4,000 |
| 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： | 带卷 (TR) |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页当前第26页第27页第28页第29页第30页第31页
ISL6334, ISL6334A
R ISEN = --------------------------- --------------
105 × 10
Thus the total maximum power dissipated in each lower
MOSFET is approximated by the summation of P LOW,1 and
P LOW,2 .
Upper MOSFET Power Calculation
In addition to r DS(ON) losses, a large portion of the upper-
MOSFET losses are due to currents conducted across the
input voltage (V IN ) during switching. Since a substantially
higher portion of the upper-MOSFET losses are dependent on
switching frequency, the power calculation is more complex.
Upper MOSFET losses can be divided into separate
components involving the upper-MOSFET switching times;
the lower-MOSFET body-diode reverse-recovery charge, Q rr ;
and the upper MOSFET r DS(ON) conduction loss.
When the upper MOSFET turns off, the lower MOSFET does
not conduct any portion of the inductor current until the
voltage at the phase node falls below ground. Once the
lower MOSFET begins conducting, the current in the upper
MOSFET falls to zero as the current in the lower MOSFET
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 ..
balance loop as well as setting the overcurrent trip point.
Select values for these resistors by using Equation 30:
R X I OCP (EQ. 30)
N
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
R SENSE depending on the sensing method, and I OCP is the
desired overcurrent trip point. Typically, I OCP can be chosen
to be 1.2x 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.
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 P-P ? t ?
(EQ. 26)
the power stage, since the DC resistance of the current
sense element may be changed according to the operational
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 .
temperature. R X in Equation 30 should be the maximum DC
resistance of the current sense element at the all operational
temperature.
P UP , 2 ≈ V IN ? ------ – ---------- ? ? ---- 2 ? f S
? I M I P-P ? ? t ?
? N 2 ? ? 2 ?
(EQ. 27)
In certain circumstances, it may be necessary to adjust the
value of one or more ISEN resistors. When the components
of one or more channels are inhibited from effectively
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 dissipated as a result is P UP,3 and is approximated in
Equation 28:
dissipating their heat so that the affected channels run hotter
than desired, choose new, smaller values of RISEN for the
affected phases (see the section entitled “Channel-Current
Balance” on page 16). 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, as
shown in Equation 31:
P UP , 3 = V IN Q rr f S
R ISEN , 2 = R ISEN ---------- 2
(EQ. 28)
Finally, the resistive part of the upper MOSFET’s is given in
Δ T
Δ T 1
(EQ. 31)
Equation 29 as P UP,4 .
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, and 28. 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, as shown in Equation 29.
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
? I M ?
I P-P
P UP , 4 ≈ r DS ( ON ) ? ------ ? d + ---------- d
2 2
? N ? 12
Current Sensing Resistor
(EQ. 29)
The load-line regulation resistor is labelled R FB in Figure 6.
Its value depends on the desired loadline requirement of the
application.
The desired loadline can be calculated using Equation 32:
R LL = -------------------------
The resistors connected to the Isen+ pins determine the
gains in the load-line regulation loop and the channel-current
26
V DROOP
I FL
(EQ. 32)
FN6482.2
February 1, 2013
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