Intersil ISL8202MEVAL1Z, Руководство пользователя

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User Guide 071
UG071.0
May 3, 2016
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3. Connect the positive of a power supply to the VIN connector
and the negative of the power supply to the PGND connector.
Make sure the power supply is not enabled when making
connections and the input power supply voltage is set to a
value between 2.6V and 5.5V.
4. Turn the power supply on.
5. Turn ENABLE switch SW1 to the “ON” position to enable
module operation.
6. The power-good LED should illuminate in green if the module
is operating properly.
7. Measure output voltage, V
OUT
, at test points VOUT and PGND.
Module output should be 1.2V.
Programming the Output Voltage
The ISL8202MEVAL1Z evaluation board has several preset
output voltages, 1.0V, 1.2V, 2.5V and 3.3V, which can be selected
in J1 jumper. Other V
OUT
values other than on-board options can
be set by proper selection of the resistor (R
SET
) connecting from
FB to SGND. In this case, R
SET
for default options (R
9
, R
10
, R
11
,
R
12
) may need to be changed. The output voltage is governed by
Equation 1 .
For most popular V
OUT
values and corresponding R
SET
values,
please refer to Table 1 on page 2 for more information.
Feed-Forward Capacitor Selection
In typical applications where the output capacitors are all ceramic,
a feed-forward capacitor, C
FF
(as annotated as C
12
, C
13
, C
14
, C
15
in
schematic) is needed to be put in parallel with each R
SET
to insure
loop stability in extreme operating conditions. With internal
compensation mode enabled, the C
FF
values for typical operating
conditions are optimized and listed in Table 1 . This is how C
12
,
C
13
, C
14
and C
15
default values are selected. Please note that, for
system parameters that are different from Table 1 or external
instead of internal compensation is used, the optimized value of
C
FF
needs to be adjusted.
Frequency Adjust
The switching frequency of ISL8202M is adjustable ranging from
680kHz to 3.5MHz via a simple resistor R
FS
(as shown in R
7
on
ISL8202MEVAL1Z board) across FS to SGND. The switching
frequency setting is based on
Equation 2 :
When the FS pin is directly tied to VIN, the frequency of operation
is fixed at 1.8MHz. For a recommended switching frequency with
typical operation conditions, refer to
Table 1 . More detailed
information on recommended switching frequency and f
SW
selection range is provided in “Recommended Switching
Frequency” and “Operation Range” .
Recommended Switching Frequency
Selection of switching frequency for each V
IN
and V
OUT
combination needs to take into account a few trade-offs.
Generally, lower switching frequency will lead to higher
efficiency. However, switching frequency should not be
decreased too low due to negative current protection limit.
Moreover, when output voltage is relatively high, low switching
frequency will result in more sub-harmonic oscillation. Therefore,
operating frequency needs to be kept relatively high under high
V
OUT
conditions. However, again, switching frequency cannot be
increased too much. Otherwise, the minimum on-time limit could
be violated. Based on these considerations,
Figure 4 provides the
recommended switching frequency under various typical V
IN
and
across V
OUT
ranges.
Operation Range
By default, the ISL8202MEVAL1Z is configured to operate at
V
OUT
= 1.2V (J1 jumper position is at pins 5 and 6), f
SW
= 1.5MHz
conditions. The V
IN
ranges from 2.6V to 5.5V. The board can also
support a wider operating range to meet the requirement of
specific applications. V
OUT
can be adjusted from 0.6V to 5V. Load
current range is from 0A to 3A. Note that, for continuous
operation at 3A, airflow across the board may be needed. The
f
SW
can also be tuned. However, to ensure sufficient stability
margins, switching frequency can only be adjusted within the
safe operating regions represented with
Figures 5 through 9 .
Operating outside of these areas may lead to system instability.
(EQ. 1)
V
OUT
V
REF
R
SET
100k

+
R
SET
----------------------------------------

=
R
FS
k
  
220 10
3

f
OSC
kHz
 
------------------------------
14 – = (EQ. 2)
FIGURE 4. SWITCHING FREQUENCY RECOMMENDATION
FIGURE 5. OPERATION REGION V
IN
= 5.5V
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.6 1 1.4 1.8 2.2 2.6 3 3.4 3.8 4.2 4.6 5
OUTPUT VOLTAGE (V)
VIN=5V
VIN=4V
VIN=3.3V
VIN=2.6V
S
W
ITCHING FREQUENCY (MHz)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.6 1 1.4 1.8 2.2 2.6 3 3.4 3.8 4.2 4.6 5
OUTPUT VOLTAGE (V)
SWITCHING FREQU
E
NCY (
MHz
)