isl9106 Intersil Corporation, isl9106 Datasheet - Page 11

• Manufacturer Part Number: isl9106
• Description: 1.2a 1.6mhz Low Quiescent Current High Efficiency Synchronous Buck Regulator
• Manufacturer: Intersil Corporation

Mode Selection
The MODE pin is provided on ISL9106 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.
RSI Signal
The RSI signal is an input signal, which can reset the PG
signal. As shown in Figure 24, 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.
Overcurrent Protection
The overcurrent protection is provided on ISL9106 when
over load condition happens. It is realized by monitoring the
CSA output with the OCP comparator, as shown in Figure 24.
When the current at P-Channel MOSFET is sensed to reach
the current limit, the OCP comparator is trigged to turn off
the P-Channel MOSFET immediately.
Short-Circuit Protection
ISL9106 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.
Undervoltage Lockout (UVLO)
When the input voltage is below the Undervoltage Lock Out
(UVLO) threshold, ISL9106 is disabled.
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.
Power MOSFETs
The power MOSFETs are optimized to achieve better
efficiency. The ON-resistance for the P-Channel MOSFET is
typically160mΩ and the typical ON-resistance for the
N-Channel MOSFET is 150mΩ.
Low Dropout Operation
The ISL9106 features low dropout operation to maximize the
battery life. When the input voltage drops to a level that
ISL9106 can no longer operate under switching regulation to
IN
, the regulator operates in either SKIP
11
ISL9106
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
the sum of output voltage plus the voltage drop cross the
inductor and the P-Channel MOSFET switch.
Thermal Shut Down
The ISL9106 provides built-in thermal protection function.
The thermal shutdown threshold temperature is typical
+150°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 ISL9106 resumes operation
starting from the soft-start-up.
Applications Information
Inductor and Output Capacitor Selection
To achieve better steady state and transient response,
ISL9106 typically uses a 2.2µH inductor. The peak-to-peak
inductor current ripple can be expressed as follows:
In Equation 1, usually the typical values can be used but to
have a more conservative estimation, the inductance should
consider the value with worst case tolerance; and for
switching frequency f
Specifications” table on page 2 can be used.
To select the inductor, its saturation current rating should be
at least higher than the sum of the maximum output current
and half of the delta calculated from Equation 1. Another
more conservative approach is to select the inductor with the
current rating higher than the P-Channel MOSFET peak
current limit.
Another consideration is the inductor DC resistance since it
directly affects the efficiency of the converter. Ideally, the
inductor with the lower DC resistance should be considered
to achieve higher efficiency.
Inductor specifications could be different from different
manufacuturers so please check with each manufacturer if
additional information is needed.
For the output capacitor, a ceramic capacitor can be used
because of the low ESR values, which helps to minimize the
output voltage ripple. A typical value of 10µF/6.3V ceramic
capacitor should be enough for most of the applications and
the capacitor should be X5R or X7R.
ΔI
=
V
-------------------------------------- -
O
•
L f
⎛
⎜
⎝
1
•
–
S
---------
V
V
IN
O
⎞
⎟
⎠
S
, the minimum f
IN
under this condition is
S
from the “Eletrical
June 29, 2007
(EQ. 1)
FN6509.0