CMS06 datasheet(17/63 Pages) NISSHINBO

17 / 63 page

R1245x

No. EA-269-240903

TECHNICAL NOTES

• External components must be connected as close as possible to the ICs and make wiring as short as

possible. Especially, the capacitor connected in between VIN pin and GND pin must be wiring the shortest.

If their impedance is high, internal voltage of the IC may shift by the switching current, and the operating

may be unstable. Make the power supply and GND lines sufficient. In the wiring of the power supply, GND,

LX, VOUT and the inductor, large current by switching may flow. To avoid the bad influence, the wiring

between the resistance, “RUP” for setting the output voltage and loading, and the wiring between the inductor

and loading must be separated.

• The ceramic capacitors have low ESR (Equivalent Series Resistance) and recommended for the ICs. The

recommendation of CIN capacitor between VIN and GND is 10 F or more for A/B/C/D version, 4.7 F or

more for E/F version, and 2.2 F or more for G/H version. Verify the bias dependence and the temperature

characteristics of the ceramic capacitors. Recommendation conditions are written based on the case which

the recommendation parts are used with the R1245x.

• The R1245x is designed with the recommendation inductance value and ceramic capacitor value and phase

compensation has been made. If the inductance value is large, due to the lack of current sensing amount

of the current mode, unstable operation may result. On the contrary, if the inductance value is small, the

current sensing amount may increase too much, low frequency oscillation may occur when the on duty ratio

is beyond 50%. Not only that, if the inductance value is small, according to the increase of the load current,

the peak current of the switching may increase, as a result, the current may reach the current limit value

and the current limit may work.

• As for the diode, use the Schottky diode with small capacitance between terminals. The reference

characteristic of the capacitance between terminals is around 100 pF or less at 10 V. If the capacitance

between terminals is large, excess switching current may flow and the operation of the IC may be unstable.

If the capacitance between terminals of the Schottky diode is beyond 100 pF at 10 V or unknown, verify the

load regulation, line regulation, and the load transient response. If a diode with a small current rating and a

large Vf is used, the LX terminal voltage may exceed the negative MAXIMUM rating when the VOUT is

shorted, depending on the configuration of the peripheral circuit, and the IC may be damaged. This depends

on the short-circuit conditions, other peripheral components, and the board layout, but please be especially

careful when using a diode with a Vf value of more than 0.7V at 4-5A.

• If the VOUT Terminal is shorted under high input voltage conditions, the limit current value may become

significantly larger. (Refer to “MINIMUM ON TIME” page) In the case, we recommended the foldback

protection version or a version with frequency of 500kHz or less. Also, please take external measures for

current protection such as using a fuse, as necessary.

• Output voltage can be set by adjustment of the values of R1 and R2. The equation of setting the output

voltage is VOUT = VFB  (R1 + R2) / R2. If the values of R1 and R2 are large, the impedance of FB pin

increases, and pickup the noise may result. The recommendation value range of R2 is approximately

between 1.0 kΩ to 16 kΩ. If the operation may be unstable, reduce the impedance of FB pin.

• For the CE pin, as an ESD protection element, a diode to VIN pin is formed internal of the IC. If CE pin

voltage may become higher than VIN pin voltage, to prevent flowing large current from CE pin to VIN pin,

connect 10 k or more resistor between CE and VIN pin.

• Connect the backside heat radiation tub of the DFN(PL)2020-9/HSOP-8E to the GND. As for multi-layered

boards, to make better power dissipation, putting some thermal via on the thermal pad in the land pattern

and radiation of the heat to another layer is effective.

CMS06 Datasheet(PDF) 17 Page - Nisshinbo Micro Devices Inc.

CMS06 Datasheet(HTML) 17 Page - Nisshinbo Micro Devices Inc.

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