参数资料
| 型号： | ISL85001IRZ-T |
| 厂商： | Intersil |
| 文件页数： | 12/17页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 1A 12DFN |
| 标准包装： | 6,000 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 19 V |
| 输入电压： | 4.5 V ~ 25 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 1A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-VFDFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 12-DFN（4x3） |
ISL85001
voltage, V OUT , of the regulator; see Equation 2. The value for the
feedback resistor is typically between 1k Ω and 10k Ω .
There is 100ns blanking time for noise immunity. It is
recommended to operate the duty cycle higher than the
R 4 = ----------------------------------
R 1 × 0.6V
V OUT – 0.6V
If the output voltage desired is 0.6V, then R P is left
unpopulated.
(EQ. 2)
blanking time to insure proper overcurrent protection.
Undervoltage Protection
If the voltage detected on the buck regulator FB pin falls 25%
below the internal reference voltage, the undervoltage fault
R1
V OUT
condition flag is set. The regulator is shutdown. The controller
enters a recovery mode similar to the overcurrent hiccup
mode. No action is taken for 4 soft-start cycles and the internal
undervoltage counter and fault condition flag are reset. A
EA
R4
normal soft-start cycle is attempted and normal operation
continues if the fault condition has cleared. If the undervoltage
0.6V
REFERENCE
FIGURE 20. EXTERNAL RESISTOR DIVIDER
The buck output can be programmed as high as 19V. Proper
heatsinking must be provided to insure that the junction
temperature does not exceed +125°C.
When the output is set greater than 2.7V, it is recommended to
pre-load at least 10mA and make sure that the input rise time is
much faster than the VOUT1 rise time. This allows the BOOT
capacitor adequate time to charge for proper operation.
Protection Features
The ISL85001 limits current in the power devices to limit on-chip
power dissipation. Overcurrent limits on the regulator protect the
internal power device from excessive thermal damage.
Undervoltage protection circuitry on the buck regulator provides a
second layer of protection for the internal power device under high
current condition.
Buck Regulator Overcurrent Protection
During the PWM on-time, the current through the internal
switching MOSFET is sampled and scaled through an internal
pilot device. The sampled current is compared to a nominal
1.7A overcurrent limit. If the sampled current exceeds the
overcurrent limit reference level, an internal overcurrent fault
counter is set to 1 and an internal flag is set. The internal
power MOSFET is immediately turned off and will not be
turned on again until the next switching cycle.
The protection circuitry continues to monitor the current and
turns off the internal MOSFET as described. If the overcurrent
condition persists for eight sequential clock cycles, the
overcurrent fault counter overflows, indicating an overcurrent
fault condition exists. The regulator is shut down and
power-good goes low. If the overcurrent condition clears prior
to the counter reaching four consecutive cycles, the internal
flag and counter are reset.
The protection circuitry attempts to recover from the
overcurrent condition after waiting 4 soft-start cycles. The
internal overcurrent flag and counter are reset. A normal soft-
start cycle is attempted and normal operation continues if the
fault condition has cleared. If the overcurrent fault counter
overflows during soft-start, the converter shuts down and this
hiccup mode operation repeats.
12
counter overflows during soft-start, the converter is shut down
and this hiccup mode operation repeats.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in
the ISL85001. There is a sensor on the chip to monitor the
junction temperature of the internal LDO and PWM switching
power N-Channel MOSFET. When the junction temperature (T J )
of the sensor exceeds +150°C, the thermal sensor sends a
signal to the fault monitor.
The fault monitor commands the buck regulator to shut down.
The buck regulator soft-starts turn on again after the IC’s junction
temperature cools by +20°C. The buck regulator experiences
hiccup mode operation during continuous thermal overload
conditions. For continuous operation, do not exceed the +125°C
junction temperature rating.
Application Guidelines
Operating Frequency
The ISL85001 operates at a fixed switching frequency of
500kHz.
Buck Regulator 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.
Embedded processor systems are capable of producing
transient load rates above 1A/ns. 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.
FN6769.2
May 29, 2012
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