isl8560 Intersil Corporation, isl8560 Datasheet - Page 11

• Manufacturer Part Number: isl8560
• Description: Dc/dc Power Switching Regulator
• Manufacturer: Intersil Corporation

Typical Performance Curves
Applications Information
Product Description
The ISL8560 is a non-synchronous, integrated FET 2A step-
down regulator which operates from an unregulated input of
9V to 60V. The output voltage is user-adjustable with a pair
of external resistors. Frequency of operation is adjustable
from 100kHz to 600kHz set by RTCT. An external signal with
higher frequency can be injected to SYNCH to synchronize
the controller.
The buck controller drives an internal N-Channel MOSFET
and requires an external diode to deliver load current up to
2A. A Schottky diode is recommended for improved
efficiency and performance over a standard diode. The
converter output is regulated down to 1.21V from an input
source.
The PWM control loop uses a single output voltage loop with
input voltage feed forward which simplifies feedback loop
compensation and rejects input voltage variation. External
feedback loop compensation allows flexibility in output filter
component selection.
The buck regulator is equipped with a lossless current limit
scheme. The current limit in the buck regulator is achieved by
monitoring the drain-to-source current of the internal switching
power MOSFET. The current limit threshold is internally set at
4.5A peak. Additional feature includes programable soft-start to
support proper start up of wide output capacitance range.
Start-Up and Shut-Down
When the EN pin is connected to a logic high, the ISL8560 is
in the shut-down mode. All the control circuitry and both
MOSFETs are off, and V
total input current is less than 110µA.
When the EN pin is tied to GND, and V
approximately 9V, the regulator begins to switch. The output
OUT
11
falls to zero. In this mode, the
IN
(Continued)
reaches
FIGURE 28. OUTPUT SHORT CIRCUIT
ISL8560
voltage is gradually increased to ensure proper soft-start
operation.
When the EN reaches logic LOW, the regulator repeats the
start-up procedure, including the soft-start function. Connect
a capacitor from SS pin to ground. This capacitor, along with
an internal 10μA current source sets the soft-start interval of
the converter, t
Operating Frequency
The ISL8560 can operate at switching frequencies from
100kHz to 600kHz. A resistor tied from the RTCT pin to VIN
and a capacitor from RTCT to GND are used to program the
switching frequency through the following equation.
Caution: When the ISL8560 is in disabled state, the voltage
across RTCT pin will reach V
voltage rating of the RTCT capacitor is rated as high as the
input voltage.
Output Voltage Selection
The output voltage of the regulator can be programmed via
an external resistor divider that is used to scale the output
voltage relative to the internal reference voltage and feed it
back to the inverting input of the error amplifier. Refer to
Figure 30.
The output voltage programming resistor, R
the value chosen for the feedback resistor and the desired
output voltage of the regulator. The value for the feedback
resistor is typically between 1kΩ and 10kΩ.
If the output voltage desired is 1.21V, then R
unpopulated.
C
C
R
SS
1
3
[
nF
=
[
μF
------------------------------------- -
V
]
R
OUT
]
=
≈
2
PGOOD = 5V/DIV
---------------- -
R kΩ
×
8.3 t
6.25
V
[
–
1.21V
OUT
LX = 10V/DIV
1.21V
⋅
IL = 2A/DIV
SS
]
SS
⎛
⎝
= 2V/DIV
----------------------------- - 0.3
f
.
OSC
s [ ]
1000
[
kHz
]
–
IN
voltage. Make sure that the
⎞
⎠
3
, will depend on
3
is left
September 18, 2007
(EQ. 1)
FN9244.6
(EQ. 3)
(EQ. 2)