XCM517 Datasheet, PDF (17/28 Pages) Torex Semiconductor – 600mA Synchronous Dual Output Step-Down DC/DC Converters

XCM517
Series
˙NOTE ON USE (Continued)
16. Please note the inductance value of the coil. The IC may enter unstable operation if the combination of ambient
temperature, setting voltage, oscillation frequency, and L value are not adequate.
In the operation range close to the maximum duty cycle, The IC may happen to enter unstable output voltage operation even
if using the L values listed below.
<External Components>
●The Range of L Value
f_OSC
V_OUT
L Value
3.0MHz
0.8V＜V_OUT<4.0V 1.0μH～2.2μH
1.2MHz
V_OUT≦2.5V
2.5V＜V_OUT
3.3μH～6.8μH
4.7μH～6.8μH
*When a coil less value of 4.7 μ H is used at
f_OSC=1.2MHz or when a coil less value of 1.5μH is
used at f_OSC=3.0MHz, peak coil current more easily
reach the current limit ILMI. In this case, it may
happen that the IC can not provide 600mA output
current.
17. It may happen to enter unstable operation when the IC operation mode goes into continuous operation mode under the
condition of small input-output voltage difference. Care must be taken with the actual design unit.
<External Components>
˔Instructions of pattern layouts
1. In order to stabilize VIN voltage level, we recommend that a by-pass capacitor (CIN) be connected as close as possible to
the VIN & VSS pins.
2. Please mount each external component as close to the IC as possible.
3. Wire external components as close to the IC as possible and use thick, short connecting traces to reduce the circuit
impedance.
4. Make sure that the PCB GND traces are as thick as possible, as variations in ground potential caused by high ground
currents at the time of switching may result in instability of the IC.
5. This series’ internal driver transistors bring on heat because of the output current and ON resistance of driver transistors.
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