ISL9187 Intersil Corporation, ISL9187 Datasheet - Page 10

• Manufacturer Part Number: ISL9187
• Description: (ISL9107 / ISL9108) 1.5A 1.6MHz Low Quiescent Current High Efficiency Synchronous Buck Regulator
• Manufacturer: Intersil Corporation

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Mode Selection
The MODE pin is provided on ISL9107 and ISL9108 to
select the operation mode. When it is driven to logic low or
ground, the regulator operates in forced PWM mode. Under
forced PWM mode, the device remains at the fixed PWM
operation (typical at 1.6MHz), regardless of if the load
current is high or low.
When the MODE pin is driven to logic high or connected to
input voltage V
mode or fixed PWM mode depending on the different load
conditions.
Overcurrent Protection
The overcurrent protection is provided when an overload
condition happens. It is realized by monitoring the CSA output
with the OCP comparator, as shown in Figure 17. When the
current at P-Channel MOSFET is sensed to reach the current
limit, the OCP comparator is triggered to turn off the
P-Channel MOSFET immediately.
Short-Circuit Protection
As shown in Figure 17, the device has a Short-Circuit
Protection (SCP) comparator, which monitors the FB pin
voltage for output short-circuit protection. When the FB
voltage is lower than 0.2V, the SCP comparator forces the
PWM oscillator frequency to drop to 1/3 of its normal
operation frequency.
Soft Start-Up
The soft start-up eliminates the inrush current during the
circuit 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.
CLOCK
V
OUT
I
L
0
IN
, the regulator operates in either SKIP
10
8 CYCLES
FIGURE 19. SKIP MODE OPERATION WAVEFORMS
20% PEAK CURRENT LIMIT
ISL9107, ISL9108
1.015*V
OUT_NOMINAL
V
OUT_NOMINAL
Power MOSFETs
The power MOSFETs are optimized to achieve better
efficiency. The ON-resistance for the P-Channel MOSFET is
typically 0.16Ω and the typical ON-resistance for the
N-Channel MOSFET is 0.15Ω.
Low Dropout Operation
The ISL9107 and ISL9108 feature low dropout operation to
maximize the battery life. When the input voltage drops to a
level that the device can no longer operate under switching
regulation to maintain the output voltage, the P-Channel
MOSFET is completely turned on (100% duty cycle). The
dropout voltage under such condition is the product of the
load current and the ON-resistance of the P-Channel
MOSFET. Minimum required input voltage V
condition is the sum of the output voltage plus the voltage
drop cross the inductor and the P-Channel MOSFET switch.
Thermal Shut Down
The ISL9107 and ISL9108 provide a built-in thermal
protection function. The thermal shutdown threshold
temperature is typical +160°C with typical +25°C hysteresis.
When the internal temperature is sensed to reach +150°C,
the regulator is completely shut down and as the
temperature is sensed to drop to +125°C (typical), the device
resumes operation starting from the soft start-up.
RSI Signal
The RSI signal is an input signal, which can reset the PG
signal. As shown in Figure 17, the power-good signal is
gated by the RSI signal. When the RSI is high, the PG signal
remains low, regardless of the output voltage condition. This
function is provided on ISL9107 only.
Power-Good
The ISL9107 offers a power-good (PG) signal. When the
output voltage is not within the power-good window, the PG
pin outputs an open-drain low signal. When the output
voltage is within the power-good window, an internal
power-good signal is issued to turn off the open-drain
MOSFET so that the PG pin can be externally pulled to high.
IN
December 21, 2007
under this
FN6612.0