ISL6420 Datasheet, PDF (10/19 Pages) Intersil Corporation – Advanced Single Synchronous Buck Pulse-Width Modulation (PWM) Controller

ISL6420
Pin Descriptions
VIN - This pin powers the controller and must be closely
decoupled to ground using a ceramic capacitor as close to
the VIN pin as possible.
TABLE 1. INPUT SUPPLY CONFIGURATION
INPUT
PIN CONFIGURATION
5.6V to 16V
Connect the input to the VIN pin. The VCC5
pin will provide a 5V output from the internal
LDO. Connect PVCC to VCC5.
5V +±10%
Connect the input to the VCC5 pin. Connect
the PVCC and VIN pins to VCC5.
SGND - This pin provides the signal and power ground for
the IC. Tie this pin to the ground plane through the lowest
impedance connection.
LGATE - This pin provides the PWM-controlled gate drive for
the lower MOSFET.
PHASE - This pin is the junction point of the output filter
inductor, the upper MOSFET source and the lower MOSFET
drain. This pin is used to monitor the voltage drop across the
upper MOSFET for overcurrent protection. This pin also
provides a return path for the upper gate drive.
UGATE - This pin provides the PWM-controlled gate drive
for the upper MOSFET.
BOOT - This pin powers the upper MOSFET driver. Connect
this pin to the junction of the bootstrap capacitor and the
cathode of the bootstrap diode. The anode of the bootstrap
diode is connected to the VCC5 pin.
FB - This pin is connected to the feedback resistor divider
and provides the voltage feedback signal for the controller.
This pin sets the output voltage of the converter.
COMP - This pin is the error amplifier output pin. It is used as
the compensation point for the PWM error amplifier.
PGOOD - This pin provides a power good status. It is an
open collector output used to indicate the status of the
output voltage.
RT - This is the oscillator frequency selection pin.
Connecting this pin directly to VCC5 will select the oscillator
free running frequency of 300kHz. By placing a resistor from
this pin to GND, the oscillator frequency can be programmed
from 100kHz to 1.4MHz. Figure 7 shows the oscillator
frequency vs the RT resistance.
CDEL - The PGOOD signal can be delayed by a time
proportional to a CDEL current of 2µA and the value of the
capacitor connected between this pin and ground. A 0.1µF
will typically provide 125ms delay. When in the Voltage
Margining mode the CDEL current is 100µA typical and
provides the delay for the output voltage slew rate, 2.5ms
typical for the 0.1µF capacitor.
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0
25
50
75
100
125
150
RT (kΩ)
FIGURE 7. OSCILLATOR FREQUENCY vs RT
PGND - This pin provides the power ground for the IC. Tie
this pin to the ground plane through the lowest impedance
connection.
PVCC - This pin is the power connection for the gate drivers.
Connect this pin to the VCC5 pin.
VCC5 – This pin is the output of the internal 5V LDO.
Connect a minimum of 4.7µF ceramic decoupling capacitor
as close to the IC as possible at this pin. Refer to Table 1.
ENSS - This pin provides enable/disable function and soft-
start for the PWM output. The output drivers are turned off
when this pin is held below 1V.
OCSET - Connect a resistor (ROCSET) from this pin to the
drain of the upper MOSFET. ROCSET, an internal 100µA
current source (IOCS), and the upper MOSFET on
resistance r_DS(ON) set the converter overcurrent (OC) trip
point according to the following equation:
I_OC
=
I_{--O-----C----S----S----E----T-----}•_----R_{----O-----C----S----E----T-}
R_DS(ON)
(EQ. 1)
An overcurrent trip cycles the soft-start function.
GPIO1/REFIN - This is a dual function pin. If VMSET/MODE
is not connected to VCC5 then this pin serves as GPIO1.
Refer to Table 2 for GPIO1 commands interpretation.
If VMSET/MODE is connected to VCC5 then this pin will
serve as REFIN. As REFIN, this pin is the non-inverting input
to the error amplifier. Connect the desired reference voltage
to this pin in the range of 0.6V to 1.25V.
Connect this pin to VCC5 to use internal reference.
REFOUT - If VMSET/MODE pin is connected to VCC5, then
this pin serves as REFOUT. It provides buffered reference
output for REFIN. Connect 2.2µF capacitor to this pin when
used as REFOUT. If not used to source current, connect a
1µF bypass capacitor to this pin.
10
FN9151.4
July 18, 2005