7
Pin Description
VIN - Supply voltage for the IC. It is recommended to place a
1µF decoupling capacitor as close as possible to the IC.
GND - Small signal ground for the PWM controller stage. All
internal control circuits are referenced to this pin.
PG - The Power good is an open-drain output. A pull-up
resistor should be connected between PG and VIN. It is
asserted active high when the output voltage reaches
94.5% of the nominal value.
FB - The Feedback pin is used to sense the output voltage,
and should be connected to VOUT for normal operation.
VSET - This pin is used to program the output voltages.
Refer to Table 1 below for details.
SYNC - This pin is used for synchronization. The converter
switching frequency can be synchronized to an external
CMOS clock signal in the range of (500kHz to 1MHz).
EN - A logic high enables the converter, logic low forces the
device into shutdown mode reducing the supply current to
less than 10
µA at 25°C. This pin should be pulled up to VCC
via a 10K resistor.
L - This pin is the drain junction of the internal power
MOSFETs and is to be connected to the external inductor.
PGND - Power ground. Connect all power grounds to this pin.
PVCC - This pin provides the Input supply for the internal
MOSFETs. It is recommended to place a 1µF decoupling
capacitor as close as possible to the IC.
CT - Timing capacitor connection to set the 25ms minimum
pulse width for the RESET
signal.
RESET - The outputs of the reset supervisory circuit, which
monitors VIN. The IC asserts these RESET
signals
whenever the supply voltage drops below a preset threshold
and keeps it asserted for at least 25ms after VCC (VIN) has
risen above the reset threshold. These outputs are push-
pull. RESET
is LOW when re-setting the microprocessor.
The PWM will continue to operate until VIN drops below the
UVLO threshold.
Functional Description
The ISL6410, ISL6410A is a synchronous buck regulator
with integrated N- and P-channel power MOSFET and
provides pre-set pin programmable outputs. Synchronous
rectification with internal MOSFETs is used to achieve higher
efficiency and reduced number of external components.
Operating frequency of 750kHz typical allows the use of
small inductor and capacitor values. The device can be
synchronized to an external clock signal in the range of
500kHz to 1MHz. The PG output indicates loss of regulation
on PWM output.
The PWM is based on the peak current mode control
topology with internal slope compensation. At the beginning
of each clock cycle, the high side P-channel MOSFET is
turned on. The current in the inductor ramps up and is
sensed via an internal circuit. On exceeding a preset limit the
high side switch is turned off causing the PWM comparator
to trip. This occurs whenever the output voltage is in
regulation or when the inductor current reaches the current
limit. After a minimum dead time to prevent shoot through
current, the low side N-channel MOSFET turns on and the
current ramps down. As the clock cycle is completed, the low
side switch turns off and the next clock cycle is initiated.
The control loop is internally compensated thus reducing the
amount of external components.
The switch current is internally sensed and the maximum
current limit is 1300mA peak.
Synchronization
The typical operating frequency for the converter is 750kHz.
It is possible to synchronize the converter to an external
clock frequency in the range of 500kHz to 1000kHz when an
external signal is applied to SYNC pin. The device will
automatically detect and synchronize to the rising edge of
the first clock pulse. If the clock signal is stopped, the
converter automatically switches back to the internal clock
and continues its operation without interruption. The switch
over will be initiated if no rising edge triggers are present on
the SYNC pin for a duration of four clock cycles.
Soft-Start
As the EN (Enable) pin goes high, the soft-start function will
generate an internal voltage ramp. This causes the start-up
current to slowly rise preventing output voltage overshoot
and high inrush currents. The soft-start duration is typically
5.5ms with 750kHz switching frequency. When the soft-start
is completed, the error amplifier will be connected directly to
the internal voltage reference.
Enable
Logic low on EN pin forces the PWM section into shutdown.
In the shutdown mode all the major blocks of the PWM
including power switches, drivers, voltage reference, and
oscillator are turned off.
Undervoltage Lockout
An undervoltage lockout circuit prevents the converter from
turning on when the voltage on VIN is less than the values
specified in the Input UVLO Threshold section of the
electrical specification.
TABLE 1.
VSET
ISL6410
Vo
ISL6410A
Vo
High 1.8V 3.3V
Open (NC) 1.5V 1.8V
Low 1.2V 1.2V
ISL6410, ISL6410A
