ISL9110IRTNZ-T Datasheet, PDF (13/20 Pages) Intersil Corporation – 1.2A High Efficiency Buck-Boost Regulators

ISL9110, ISL9112
well above the audio frequency range (f_SW becomes typically
60kHz). This mode of operation, however, reduces the efficiency
at light load.
Thermal Shutdown
A built-in thermal protection feature protects the ISL9110,
ISL9112 if the die temperature reaches +155°C (typical). At this
die temperature, the regulator is completely shut down. The die
temperature continues to be monitored in this thermal-shutdown
mode. When the die temperature falls to +125°C (typical), the
device will resume normal operation.
When exiting thermal shutdown, the ISL9110, ISL9112 will
execute its soft-start sequence.
External Synchronization
An external sync feature is provided. Applying a clock signal with
a frequency between 2.75MHz and 3.25MHz at the MODE/SYNC
input forces the ISL9110, ISL9112 to synchronize to this external
clock. The MODE/SYNC input supports standard logic levels.
Buck-Boost Conversion Topology
The ISL9110, ISL9112 operates in either buck or boost mode.
When operating in conditions where VIN is close to VOUT, the
ISL9110 alternates between buck and boost mode as necessary
to provide a regulated output voltage.
L1
PVIN 5
LX1
4
SWITCH A
LX2
2
SWITCH D
1 VOUT
SWITCH B
SWITCH C
FIGURE 27. BUCK BOOST TOPOLOGY
Figure 27 shows a simplified diagram of the internal switches
and external inductor.
PWM Operation
In buck PWM mode, Switch D is continuously closed, and Switch
C is continuously open. Switches A and B operate as a
synchronous buck converter when in this mode.
In boost PWM mode, Switch A remains closed and Switch B
remains open. Switches C and D operate as a synchronous boost
converter when in this mode.
PFM Operation
During PFM operation in buck mode, Switch D is continuously
closed, and Switch C is continuously open. Switches A and B
operate in discontinuous mode during PFM operation.
During PFM operation in boost mode, the ISL9110, ISL9112
closes Switch A and Switch C to ramp up the current in the
inductor. When inductor current reaches a certain threshold, the
device turns off Switches A and C, then turns on Switches B and
D. With Switches B and D closed, output voltage increases as the
inductor current ramps down.
In most operating conditions, there will be multiple PFM pulses
to charge up the output capacitor. These pulses continue until
V_OUT has achieved the upper threshold of the PFM hysteretic
controller. Switching then stops, and remains stopped until V_OUT
decays to the lower threshold of the hysteretic PFM controller.
Operation With VIN Close to VOUT
When the output voltage is close to the input voltage, the
ISL9110, ISL9112 will rapidly and smoothly switch from boost to
buck mode as needed to maintain the regulated output voltage.
This behavior provides excellent efficiency and very low output
voltage ripple.
Output Voltage Programming
The ISL9110 is available in fixed and adjustable output voltage
versions. To use the fixed output version, the VOUT pin must be
connected directly to FB.
In the adjustable output voltage version (ISL9110IRTAZ), an
external resistor divider is required to program the output
voltage. The FB pin has very low input leakage current, so it is
possible to use large value resistors (e.g. R1 = 1MΩ and
R2 = 324kΩ) in the resistor divider connected to the FB input.
The ISL9112 is available in a fixed output version only. The
factory programmed output voltage can be changed via the I²C
interface. Details about the ISL9112 programmable VOUT
voltage can be found in the section “Register Description
(ISL9112)” on page 13.
Digital Slew Rate Control (ISL9112 only)
When changing voltages using the I²C interface, the ISL9110 can
be programmed to control the rate of voltage increase or
decrease as it transitions from one voltage setting to the next.
The default configuration disables this digital slew rate feature.
To enable the slew rate feature, an I²C command is sent to the
ISL9112, changing the value of the SLEWRATE bit field to a value
other than 0b000. Details about the digital slew rate settings can
be found in Table 3.
Register Description (ISL9112)
The ISL9112 has a two I²C accessible control registers that are
used to set output voltage, operating mode, and digital slew rate.
These registers can be read and written to at any time that the
ISL9112 is enabled. Attempts to communicate with the ISL9112
via its I²C interface when the ISL9112 is disabled (EN = Low) are
not supported.
13
FN7649.2
July 13, 2012