参数资料
| 型号： | ISL8502IRZ |
| 厂商： | Intersil |
| 文件页数： | 14/19页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 2.5A 24QFN |
| 标准包装： | 75 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 14 V |
| 输入电压： | 5V，5.5 V ~ 14 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 500kHz ~ 1.2MHz |
| 电流 - 输出： | 2.5A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-VFQFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 24-QFN（4x4） |
ISL8502
Overcurrent Fault Condition and the EN pin will be pulled
LOW. An Overcurrent Fault Condition will result with the
output voltage of the regulator. The value for the feedback
resistor is typically between 1k Ω and 10k Ω .
R 4 = ----------------------------------
regulator attempting to restart in a hiccup mode with the
delay between restarts being 4 soft-start periods. At the end
of the fourth soft-start wait period, the fault counters are
R 1 × 0.6V
V OUT – 0.6V
(EQ. 4)
reset, the EN pin is released, and soft-start is attempted
again. If the overcurrent condition goes away prior to the OC
Fault Counter reaching a count of four, the Overcurrent
Condition Flag will set back to LOW.
If the Overcurrent Condition Flag is HIGH and the
Overcurrent Fault Counter is less than four and an
undervoltage event is detected, the regulator will be shut
down immediately.
UNDERVOLTAGE PROTECTION
If the voltage detected on the FB pin falls 18% below the
internal reference voltage and the overcurrent condition flag is
LOW, then the regulator will be shutdown immediately under an
Undervoltage Fault Condition and the EN pin will be pulled
LOW. An Undervoltage Fault Condition will result with the
regulator attempting to restart in a hiccup mode with the delay
between restarts being 4 soft-start periods. At the end of the
fourth soft-start wait period, the fault counters are reset, the EN
pin is released, and soft-start is attempted again.
THERMAL PROTECTION
If the ISL8502 IC junction temperature reaches a nominal
temperature of +150°C, the regulator will be disabled. The
ISL8502 will not re-enable the regulator until the junction
temperature drops below +130°C.
SHOOT-THROUGH PROTECTION
A shoot-through condition occurs when both the upper and
lower MOSFETs are turned on simultaneously, effectively
shorting the input voltage to ground. To protect from a
shoot-through condition, the ISL8502 incorporates specialized
circuitry, which insures that the complementary MOSFETs are
not ON simultaneously.
Application Guidelines
Operating Frequency
If the output voltage desired is 0.6V, then R 4 is left unpopulated.
Output Capacitor Selection
An output capacitor is required to filter the inductor current and
supply the load transient current. The filtering requirements are
a function of the switching frequency and the ripple current. The
load transient requirements are a function of the slew rate
(di/dt) and the magnitude of the transient load current. These
requirements are generally met with a mix of capacitors and
careful layout.
High frequency capacitors initially supply the transient and slow
the current load rate seen by the bulk capacitors. The bulk filter
capacitor values are generally determined by the ESR
(Effective Series Resistance) and voltage rating requirements
rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the power pins of the load as physically possible. Be
careful not to add inductance in the circuit board wiring that
could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements.
The shape of the output voltage waveform during a load
transient that represents the worst case loading conditions will
ultimately determine the number of output capacitors and their
type. When this load transient is applied to the converter, most
of the energy required by the load is initially delivered from the
output capacitors. This is due to the finite amount of time
required for the inductor current to slew up to the level of the
output current required by the load. This phenomenon results in
a temporary dip in the output voltage. At the very edge of the
transient, the Equivalent Series Inductance (ESL) of each
capacitor induces a spike that adds on top of the existing
voltage drop due to the Equivalent Series Resistance (ESR).
The ISL8502 can operate at switching frequencies from
500kHz to 1.2MHz. A resistor tied from the FS pin to ground
is used to program the switching frequency Equation 3.
V OUT
DV HUMP
R T [ k Ω ] = ------------------------------
48000
f OSC [ kHz ]
(EQ. 3)
DV ESR
DV SAG
DV ESL
Output Voltage Selection
The output voltage of the regulator can be programmed via
an external resistor divider that is used to scale the output
voltage relative to the internal reference voltage and feed it
back to the inverting input of the error amplifier. Refer to
Figure 34.
I OUT
I TRAN
The output voltage programming resistor, R 4 , will depend on
the value chosen for the feedback resistor and the desired
14
FIGURE 33. TYPICAL TRANSIENT RESPONSE
FN6389.2
June 29, 2010
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