ISL8204MEVAL1Z Intersil, ISL8204MEVAL1Z Datasheet - Page 13

• Manufacturer Part Number: ISL8204MEVAL1Z
• Description: EVAL BOARD 1 FOR ISL8204
• Manufacturer: Intersil

Specifications of ISL8204MEVAL1Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The overcurrent function will trip at a peak inductor
current (I
I
where:
I
R
pins.
r
I
I
Note: ISL8204M, ISL8206M has integrated
4.12kΩ/2.87kΩ resistance (R
equivalent resistance of R
Equation 3:
The scale factor of 2 doubles the trip point of the MOSFET
voltage drop, compared to the setting on the R
resistor. The OC trip point varies in a system mainly due
to the MOSFET r
current and temperature). To avoid overcurrent tripping
in the normal operating load range, find the R
from Equation 3, and use the following values:
where ΔI
input voltage, high output voltage application, such as
20V input to 5V output, the inductor ripple becomes
excessive due to the fix internal inductor value. In such
applications, the output current will be limited from the
rating to approximately 70% of the module’s rated
current.
The relationships between the external R
the typical output current I
ISL8206M are as follows:
R
PEAK
1. The maximum r
2. The minimum I
3. Determine I
SET
DS(ON)
DS
DS
SET
SET
OPEN
50kΩ
20kΩ
10kΩ
R
temperature
Specifications” table on page 3.
= 15A) and 18mΩ @ (V
= 15A).
5kΩ
I
(Ω)
PEAK
is the internal I
SET
is equivalent resistance between ISET and PGND
=
=
R
------------------------------------------------------ -
R
is typically 15mΩ @ (V
2
------------------------------------------- -
L
SET-EX
SET-EX
PEAK
×
>
is the output inductor ripple current. In a high
I
I
r
SET
OUT MAX
DS ON
) determined by Equation 2:
(
(
×
×
+
PEAK
DS(ON)
R
V
OCP (A) @
R
R
P
)
SET
IN
SET-IN
SET-IN
VCC
SET
)
SET
DS(ON)
+
for:
= 12V,
8.1
7.5
6.6
5.5
4.4
(
-------------
= 5V
ΔI
from the “Electrical
variations (i.e. over process,
current source (21.5µA typical).
2
TABLE 3.
L
13
)
SET
OUT(MAX)
at the highest junction
PVCC
SET-IN
can be expressed in
PVCC
= V
). Therefore, the
= V
OCP levels for
GS
GS
= 4.5V,
P
OCP (A) @
V
SET
VCC
IN
ISL8204M, ISL8206M
= 10V,
8.8
8.1
7.4
6.4
5.0
= 12V
values and
SET
= 12V
SET
resistor
(EQ. 4)
(EQ. 2)
(EQ. 3)
The range of allowable voltages detected (2 x I
R
is set too low, the following conditions may occur:
(1) Continuous OCP tripping and retry and (2) It may be
overly sensitive to system noise and inrush current
spikes, so it should be avoided. The maximum usable
setting is around 0.2V across R
MOSFET); values above this might disable the
protection. Any voltage drop across R
than 0.3V (0.6V MOSFET trip point) will disable the OCP.
Note that conditions during power-up or during a retry
may look different than normal operation. During
power-up in a 12V system, the ISL8204M, ISL8206M
starts operation just above 4V; if the supply ramp is
slow, the soft-start ramp might be over well before 12V
is reached. Therefore, with low side gate drive voltages,
the r
up, effectively lowering the OCP trip. In addition, the
ripple current will likely be different at a lower input
voltage. Another factor is the digital nature of the soft-
start ramp. On each discrete voltage step, there is in
effect, a small load transient and a current spike to
charge the output capacitors. The height of the current
spike is not controlled, however, it is affected by the
step size of the output and the value of the output
capacitors, as well as the internal error amp
compensation. Therefore, it is possible to trip the
overcurrent with inrush current, in addition to the
normal load and ripple considerations.
Figure 23 shows the output response during a retry of
an output shorted to PGND. At time T
been turned off due to sensing an overcurrent condition.
There are two internal soft-start delay cycles (T
T
the average power dissipation in retry at an acceptable
level. At time T
cycle, and the output tries to ramp. If the short is still
applied and the current reaches the I
time during the soft-start ramp period, the output will
shut off and return to time T
The retry period is thus two dummy soft-start cycles
plus one variable (which depends on how long it takes
to trip the sensor each time). Figure 23 shows an
example where the output gets about half-way up
before shutting down; therefore, the retry (or hiccup)
time will be around 17ms. The minimum should be
nominally 13.6ms and the maximum 20.4ms. If the
short condition is finally removed, the output should
ramp up normally on the next T
2
SET
) to allow the MOSFETs to cool down in order to keep
) is 0mV to 475mV. If the voltage drop across R
DS(ON)
of the MOSFET will be higher during power-
2
, the output starts a normal soft-start
0
for another delay cycle.
SET
2
cycle.
(0.4V across the
SET
SET
0
, the output has
trip point any
that is greater
December 16, 2010
SET
1
FN6999.2
and
x
SET