ISL97516 Intersil Corporation, ISL97516 Datasheet - Page 7

• Manufacturer Part Number: ISL97516
• Description: PWM Step-Up Regulator
• Manufacturer: Intersil Corporation

Schottky Diode
In selecting the Schottky diode, the reverse break down
voltage, forward current and forward voltage drop must be
considered for optimum converter performance. The diode
must be rated to handle 2.0A, the current limit of the
ISL97516. The breakdown voltage must exceed the
maximum output voltage. Low forward voltage drop, low
leakage current, and fast reverse recovery will help the
converter to achieve the maximum efficiency.
Input Capacitor
The value of the input capacitor depends the input and
output voltages, the maximum output current, the inductor
value and the noise allowed to put back on the input line. For
most applications, a minimum 10µF is required. For
applications that run close to the maximum output current
limit, input capacitor in the range of 22µF to 47µF is
recommended.
The ISL97516 is powered from the VIN. A High frequency
0.1µF bypass cap is recommended to be close to the VIN
pin to reduce supply line noise and ensure stable operation.
Loop Compensation
The ISL97516 incorporates a transconductance amplifier in
its feedback path to allow the user some adjustment on the
transient response and better regulation. The ISL97516
uses current mode control architecture which has a fast
current sense loop and a slow voltage feedback loop. The
fast current feedback loop does not require any
compensation. The slow voltage loop must be compensated
for stable operation. The compensation network is a series
RC network from COMP pin to ground. The resistor sets the
high frequency integrator gain for fast transient response
and the capacitor sets the integrator zero to ensure loop
stability. For most applications, the compensation resistor in
the range of 2k to 7.5k and the compensation capacitor in
the range of 3nF to 10nF.
Soft-Start
The soft-start is provided by an internal 6µA current source
charges the external C
limited by the voltage on the capacitor. This in turn controls
the rising rate of the output voltage. The regulator goes
through the start-up sequence as well after the EN pin is
pulled to HI.
Frequency Selection
The ISL97516 switching frequency can be user selected to
operate at either constant 620kHz or 1.25MHz. Connecting
F
620kHz. When connecting F
frequency is set to 1.25MHz.
Shutdown Control
When the EN pin is pulled down, the ISL97516 is shutdown
reducing the supply current to <1µA.
SEL
pin to ground sets the PWM switching frequency to
SS
, the peak MOSFET current is
SEL
7
high or V
DD
, the switching
ISL97516
Maximum Output Current
The MOSFET current limit is nominally 2.0A and guaranteed
1.7A. This restricts the maximum output current, I
based on the following formula:
I
where:
ΔI
V
F
I
D = MOSFET turn-on ratio:
Table 1 gives typical maximum I
switching frequency and 10µH inductor.
Cascaded MOSFET Application
An 25V N-channel MOSFET is integrated in the boost
regulator. For the applications where the output voltage is
greater than 25V, an external cascaded MOSFET is needed
as shown in Figure 12. The voltage rating of the external
MOSFET should be greater than A
D
L
L-AVG
S
DIODE
L
I
I
ΔI
=
=
L
L-AVG
= switching frequency, 600kHz or 1.2MHz
=
L
= MOSFET current limit
I
1
L-AVG
= inductor ripple current
V
------------------------------------------------------------------------------
–
V
=
IN
--------------------------------------------
V
IN
L
= Schottky diode forward voltage, typically, 0.6V
2.5
2.5
2.5
3.3
3.3
3.3
= average inductor current
OUT
5
5
I
-------------
1 D
×
×
OUT
(V)
–
[
(
+
(
V
V
(
O
V
+
1 2 ⁄
O
IN
V
+
+
DIODE
V
V
×
DIODE
DIODE
ΔI
L
)
)
) V
TABLE 1.
V
×
–
OUT
F
12
12
12
S
5
9
5
9
9
IN
(V)
]
OUT
VDD
values for 1.2MHz
.
I
OMAX
December 22, 2006
1150
870
500
380
655
500
990
750
OMAX
(EQ. 7)
(EQ. 8)
(EQ. 9)
(mA)
FN9261.1
,