ISL6420A Datasheet, PDF (11/21 Pages) Intersil Corporation – Advanced Single Synchronous Buck Pulse-Width Modulation PWM Controller

ISL6420A
Typical Performance Curves (Continued)
98
96
94
92
VIN = 12V
90
88
86
84
82
80
01 23 456
LOAD (A)
VIN = 5V
7 8 9 10
FIGURE 7. EFFICIENCY vs LOAD CURRENT (V_OUT = 3.3V)
Pin Descriptions
VIN
This pin powers the controller and must be decoupled
to ground using a ceramic capacitor as close as
possible to the VIN pin.
TABLE 1. INPUT SUPPLY CONFIGURATION
INPUT
PIN CONFIGURATION
5.5V to Connect the input to the VIN pin. The VCC5 pin
28V 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 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 PVCC pin.
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0
25
50
75
100 125
RT (kΩ)
FIGURE 8. OSCILLATOR FREQUENCY vs RT
150
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 8
shows the oscillator frequency vs. the RT resistance.
11
FN9169.4
December 4, 2009