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| 型号： | ISL6567IRZ-TS2698 |
| 厂商： | Intersil |
| 文件页数： | 11/25页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 24-QFN |
| 标准包装： | 6,000 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1.5MHz |
| 占空比： | 66% |
| 电源电压： | 4.9 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-VFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
ISL6567
sensing is a no-added-cost method to sense current for load
line regulation, channel current balance, module current
sharing, and overcurrent protection.
(typically). Figure 5 details a normal soft-start startup.
Equation 6 helps determine the approximate time period
during which the controlled output voltage is ramped from 0V
I SS
The ISEN pins are used as current inputs for each channel.
Internally, a virtual ground is created at the ISEN pins. The
R ISEN resistors are used to size the current flow through the
ISEN pins, proportional to the lower MOSFETs’ r DS(ON) voltage,
during their conduction periods. The current thus developed
through the ISEN pins is internally averaged, then the current
error signals resulting from comparing the average to the
individual current signals are used for channel current
balancing.
to the desired DC-set level.
C SS ? V REF
t SS = ---------------------------
(EQ. 6)
V OUT (0.5V/DIV)
Select the value for the R ISEN resistors based on the room
temperature r DS(ON) of the lower MOSFETs and the full-load
total converter output current, I FL . As this current sense path is
also used for OC detection, ensure that at maximum power
train temperature rise and maximum output current loading
GND>
V intREF (0.5V/DIV)
V SS (1V/DIV)
the OC protection is not inadvertently tripped. OC protection
current level through the ISEN pins is listed in the “Electrical
GND>
EN (5V/DIV)
R ISEN = ------------------------ ? -------
50 × 10
r DS ( ON ) I FL
– 6 2
(EQ. 5)
FIGURE 5. NORMAL SOFT-START WAVEFORMS FOR ISL6567-
CHANNEL-CURRENT BALANCE
Another benefit of multi-phase operation is the thermal
advantage gained by distributing the dissipated heat over
multiple devices and greater area. By doing this, the designer
avoids the complexity of driving multiple parallel MOSFETs and
the expense of using expensive heat sinks and exotic magnetic
materials.
All things being equal, in order to fully realize the thermal
advantage, it is important that each channel in a multi-phase
converter be controlled to deliver about the same current at
any load level. Intersil’s ISL6567 ensure current balance by
comparing each channel’s current to the average current
delivered by both channels and making appropriate
adjustments to each channel’s pulse width based on the
resultant error. The error signal modifies the pulse width to
correct any unbalance and force the error toward zero.
Conversely, should a channel-to-channel imbalance be desired,
such imbalance can be created by adjusting the individual
channel’s R ISEN resistor. Asymmetrical layouts, where one
phase of the converter is naturally carrying more current than
the other, or where one of the two phases is subject to a more
stringent thermal environment limiting its current-carrying
capability, are instances where this adjustment is particularly
useful, helping to cancel out the design-intrinsic thermal or
current imbalances.
SOFT-START
The soft-start function allows the converter to bring up the
output voltage in a controlled fashion, resulting in a linear
ramp-up. As soon as the controller is fully enabled for
operation, the SS pin starts to output a small current which
charges the external capacitor, C SS , connected to this pin. An
internal reference clamp controlled by the potential at the SS
pin releases the reference to the input of the error amplifier
with a 1:1 correspondence for SS potential exceeding 0.7V
11
BASED MULTI-PHASE CONVERTER
Whenever the ISL6567’s power-on reset falling threshold is
tripped, or it is disabled via the EN pin, the SS capacitor is
quickly discharged via an internal pull-down device
(represented as the 1mA, typical, current source).
As the SS pin’s positive excursion is internally clamped to
about 3.5V, insure that any external pull-up device does not
force more than 3mA into this pin.
Should OC protection be tripped while the ISL6567 is
operating in internal-reference mode and the SS pin not be
allowed to fully discharge the SS capacitor, the ISL6567
cannot continue the normal SS cycling.
OVERCURRENT PROTECTION
The individual channel currents, as sensed via the PHASE pins
and scaled via the ISEN resistors, as well as their combined
average are continuously monitored and compared with an
internal overcurrent (OC) reference. If the combined channel
current average exceeds the reference current, the overcurrent
comparator triggers an overcurrent event. Similarly, an OC
event is also triggered if either channel’s current exceeds the
OC reference for 7 consecutive switching cycles.
FN9243.4
August 9, 2011
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