XC9303
Series
■NOTES
ON USE
1. PWM/PFM Automatic Switching
If PWM/PFM automatic switching control is selected and the step-down ratio is high (e.g., from 10 V to 1.0 V), the control
mode remains in PFM setting over the whole load range, since the duty ratio under continuous-duty condition is smaller
than the PFM duty ratio of the XC9303 series. The output voltage's ripple voltage becomes substantially high under heavy
load conditions, with the XC9303 series appearing to be producing an abnormal oscillation. If this operation becomes a
concern, set pins PWM1 and PWM2 to High to set the control mode to PWM setting.
2. Ratings
Use the XC9303 series and peripheral components within the limits of their ratings.
3. Notes on How to Select Transistor
Synchronous rectification operation prepares fixed time when switching changes so that the high side P-ch MOSFET and
the low side N-ch MOSFET do not oscillate simultaneously. Also it is designed to prevent the penetration current when the
both MOSFET oscillate at the same time. However, some MOSFET may oscillate simultaneously and worsen efficiency.
Please select MOSFET with high Vth with small input capacity on high side P-ch MOSFET and the low side N-ch MOSFET.
(When using with large current, please note that there is a tendency for ON resistance to become large when the input
capacity of MOSFET is small and Vth is high.)
<The check method of whether selected MOSFET is oscillating simultaneously>
In order to check that MOSFET is not oscillating simultaneously, please observe Lx terminal waveform of coil current at the
time of the continuation mode. If the MOSFET parasitism diode waveform on Lx terminal waveform can be formed in the
period EXT 1 is 'H' and EXT2 is 'L', it can be thought that MOSFETs are not oscillating simultaneously.
4. Instruction on Layout
(1) The performance of the XC9303 DC/DC converter is greatly influenced by not only its own characteristics, but also by
those of the external components it is used with. We recommend that you refer to the specifications of each
component to be used and take sufficient care when selecting components.
(2) Please mount each external component as close to the IC as possible. Wire external components as close to the IC as
possible and use thick, short connecting wires to reduce wiring impedance. In particular, minimize the distance
between the EXT2 pin and the Gate pin of the low side N-ch MOSFET. It may decrease efficiency.
(3) Make sure that the GND wiring is as strong as possible as variations in ground potential caused by ground current at the
time of switching may result in unstable operation of the IC. Specifically, strengthen the ground wiring in the proximity
of the V
SS
pin.
(4) For stable operation, please connect by-pass capacitor between the V
DD
and the GND.
(5) Wiring between the GND pin of C
IN
and the Sauce pin of the low side N-ch MOSFET connect to the GND pin of the IC.
It may result in unstable operation of the IC.
■TYPICAL
APPLICATION CIRCUIT
8/20
TOREX [ TOREX SEMICONDUCTOR ]
