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参数资料
| 型号： | ISL8009EVAL1Z |
| 厂商： | Intersil |
| 文件页数： | 11/13页 |
| 文件大小： | 0K |
| 描述： | EVALUATION BOARD FOR ISL8009 |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 1.8V |
| 电流 - 输出： | 1.5A |
| 输入电压： | 2.7 ~ 5.5 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 1.6MHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ISL8009 |
ISL8009A
Once the skip mode is entered, the pulse modulation starts being
controlled by the SKIP comparator shown in Figure 25. Each
pulse cycle is still synchronized by the PWM clock. The P-MOSFET
is turned on at the clock and turned off when its current reaches
.
V O
20% of the current limit value (0.2V at the CSA output). As the
average inductor current in each cycle is higher than the average
current of the load, the output voltage rises cycle over cycle.
RSI
MIN
25ns
When the output voltage reaches 1.5% above the nominal
voltage, the P-MOSFET is turned off immediately and the inductor
current is fully discharged to zero and stays at zero. The output
POR
2ms
2ms
voltage reduces gradually due to the load current discharging the
output capacitor. When the output voltage drops to the nominal
voltage, the P-MOSFET will be turned on again at the clock,
repeating the previous operations.
The regulator resumes normal PWM mode operation when the
output voltage drops 1.5% below the nominal voltage.
Mode Control
The ISL8009A has a SKIP pin that controls the operation mode.
When the SKIP pin is driven to low or shorted to ground, the
regulator operates in a forced PWM mode. The forced PWM
mode remains the fixed PWM frequency at light load instead of
entering the skip mode.
Overcurrent Protection
The overcurrent protection is realized by monitoring the CSA
output with the OCP comparator, as shown in Figure 25. The
current sensing circuit has a gain of 0.4V/A, from the N-MOSFET
current to the CSA output. When the CSA output reaches 0.8V,
(which is equivalent to 2A for the switch current) the OCP
comparator is tripped to turn off the P-MOSFET immediately.
Short-Circuit Protection
A short-circuit protection SCP comparator monitors the VFB pin
voltage for output short-circuit protection. When the VFB is lower
than 0.2V, the SCP comparator forces the PWM oscillator
frequency to drop to 1/3 of the normal operation value. This
comparator is effective during start-up or an output short-circuit
event.
RSI/POR Function
When powering up, the open-collector Power-On-Reset output
holds low for about 1ms after VO reaches the preset voltage.
When the active-HI reset signal RSI is issued, POR goes to low
immediately and holds for the same period of time after RSI
comes back to LOW. The output voltage is unaffected (Figure 28).
When the function is not used, connect RSI to ground and leave
the pull-up resistor, R 1 , open at the POR pin.
The POR output also serves as a 1ms delayed Power-Good signal
when the pull-up resistor, R 1, is installed. The RSI pin needs to be
directly or indirectly through another resistor connected to
ground for this to function properly.
11
FIGURE 28. RSI AND POR TIMING DIAGRAM
UVLO
When the input voltage is below the undervoltage lock out (UVLO)
threshold, the regulator is disabled.
Soft-Start-Up
The soft start-up eliminates the in-rush current during the
start-up. The soft-start block outputs a ramp reference to both
the voltage loop and the current loop. The two ramps limit the
inductor current rising speed as well as the output voltage speed
so that the output voltage rises in a controlled fashion. At the
very beginning of the start-up, the output voltage is less than
0.2V; hence the PWM operating frequency is 1/3 of the normal
frequency.
Power MOSFETs
The power MOSFETs are optimized for best efficiency. The
ON-resistance for the P-MOSFET is typically 120m Ω and the
ON-resistance for the N-MOSFET is typically 110m Ω .
Duty Cycle
The ISL8009A features duty cycle operation to maximize the
battery life. When the battery voltage drops to a level that the
ISL8009A can no longer maintain the regulation at the output,
the regulator completely turns on the P-MOSFET. The maximum
drop out voltage under the duty-cycle operation is the product of
the load current and the ON-resistance of the P-MOSFET.
Enable
The Enable (EN) input allows the user to control the turning on or off
of the regulator for purposes such as power-up sequencing. When
the regulator is enabled, there is typically a 600μs delay for waking
up the bandgap reference, then the soft-start-up begins. When the
regulator is disabled, the P-MOSFET and the N-MOSFET are turned
off immediately. The 100 Ω soft discharge resistor from LX to
GDN is activated and pulls the output to 0V.
Thermal Shutdown
The ISL8009A has built-in thermal protection. When the internal
temperature reaches +140°C, the regulator is completely
shutdown. As the temperature drops to +120°C, the ISL8009A
resumes operation by stepping through a soft-start-up.
FN6656.3
February 28, 2013
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