ISL8009AIRZ-TK Intersil, ISL8009AIRZ-TK Datasheet - Page 11

• Manufacturer Part Number: ISL8009AIRZ-TK
• Description: IC REG SYNC BUCK 1.5A 8-DFN
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of ISL8009AIRZ-TK

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 5.5 V
• Current - Output: 1.5A
• Frequency - Switching: 1.6MHz
• Voltage - Input: 2.7 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

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 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. 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 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
The POR output also serves as a 1ms delayed Power-
Good signal when the pull-up resistor, R
The RSI pin needs to be directly or indirectly through
another resistor connected to ground for this to function
properly.
1
, open at the POR pin.
11
1,
is installed.
ISL8009A
.
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 120mΩ
and the ON-resistance for the N-MOSFET is typically
110mΩ.
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 100Ω 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.
POR
RSI
V
O
FIGURE 28. RSI AND POR TIMING DIAGRAM
2ms
25ns
MIN
2ms
November 19, 2009
FN6656.2