6
FN9073.9
October 21, 2015
Pin Descriptions
CPVOUT - This pin represents the output of the charge
pump. The voltage at this pin is the bias voltage for the IC.
Connect a decoupling capacitor from this pin to ground. The
value of the decoupling capacitor should be at least 10x the
value of the charge pump capacitor. This pin may be tied to
the bootstrap circuit as the source for creating the BOOT
voltage.
CT1 and CT2 - These pins are the connections for the
external charge pump capacitor. A minimum of a 0.1µF
ceramic capacitor is recommended for proper operation of
the IC.
OCSET - Connect a resistor (r
OCSET
) from this pin to the
drain of the upper MOSFET (V
IN
). r
OCSET
, an internal 20µA
current source (I
OCSET
), and the upper MOSFET
ON-resistance (r
DS(ON)
) set the converter overcurrent (OC)
trip point according to Equation 1:
An overcurrent trip cycles the soft-start function.
VOUT - This pin provides the external switcher output
voltage to the IC as feedback for the 1.8V fixed output
voltage option. Leave this pin open on the ISL6406 for the
adjustable output voltage option.
VCC - This pin provides bias supply for the ISL6406.
Connect a well-coupled 3.3V supply to this pin.
PHASE - Connect this pin to the upper MOSFET’s source.
This pin is used to monitor the voltage drop across the upper
MOSFET for overcurrent protection.
RT - Connect an external resistor from this pin to ground for
frequency selection. Refer to Figure 3 (RT vs Frequency).
BOOT - This pin provides ground referenced bias voltage to
the upper MOSFET driver. A bootstrap circuit is used to
create a voltage suitable to drive a logic-level N-Channel
MOSFET. A large (~1M) resistor should be connected from
this pin to GND. The purpose of this resistor is to discharge
the BOOT pin during a shutdown condition,
SYNC/EN = LOW so that the gate drivers are quickly
powered off by this bleed resistor.
UGATE - Connect this pin to the upper MOSFET’s gate. This
pin provides the PWM-controlled gate drive for the upper
MOSFET. This pin is also monitored by the adaptive
shoot-through protection circuitry to determine when the
upper MOSFET has turned off.
GND - This pin represents the signal and power ground for
the IC. Tie this pin to the ground island/plane through the
lowest impedance connection available.
LGATE - Connect this pin to the lower MOSFET’s gate. This
pin provides the PWM-controlled gate drive for the lower
MOSFET. This pin is also monitored by the adaptive
shoot-through protection circuitry to determine when the
lower MOSFET has turned off.
COMP and FB - COMP and FB are the available external
pins of the error amplifier. The FB pin is the inverting input of
the internal error amplifier and the COMP pin is the error
amplifier output. These pins are used to compensate the
control feedback loop of the converter.
CPGND - This pin represents the signal and power ground
for the charge pump. Tie this pin to the ground island/plane
through the lowest impedance connection available.
SYNC/EN - This is a dual-function pin. To synchronize with
an external clock, apply a clock with a frequency 1.1x to 2.0x
higher than the part’s natural frequency to this pin. The
device may be disabled by tying this pin to ground. In this
shutdown mode, all functions are disabled and the device
will draw <50µA supply current.
I
PEAK
I
OCSET
R
OCSET
r
DS ON
--------------------------------------------------------=
(EQ. 1)
ISL6406
