XC9301/9302

Series

603

6

GProduct Selection (Notes)

XC9301/02 series is a group of PFM controlled (XC9302 series switches from PWM to PFM control during light loads) step-up and down DC/DC

converters. The series is highly efficient with a wide range of input voltage since its stepping-up and down operation is controlled by PWM

movements. In general, there are several methods available for obtaining a stable output voltage at such times when input voltage is changing

from being higher than the established output voltage to being lower than the established output voltage. Each method has its merits and

demerits but is essential that a method which provides the best results in terms of input & output under actual operating conditions. Below, two

methods are highlighted and their respective performances in terms of efficiency are compared.

This is an efficiency comparison of two ways, step-up DC/DC converter + VR and step-up & down DC/DC converter.

[Step-up DC/DC Converter + VR] (XC6361/62)

N Step-up mode (Input voltage < set output voltage + 0.4V)

After input voltage has been stepped-up to set output voltage + 0.4V by the step-up DC/DC converter, the output voltage will be regulated to

the set value by the VR. (0.4V loss via the VR)

N Step-down mode (Input voltage > set output voltage + 0.4V)

After input voltage has been stepped-up to set output voltage + 0.4V by the step-up DC/DC converter, the output voltage will be regulated to

the set value by the VR. (Input/Output voltage difference loss via the VR)

[Step-up&down DC/DC Converter] (XC9301/02)

N Set ouput voltage obtained as a result of the automatic switching operations of the IC regardless of the difference between input voltage and

set output voltage.

The above graph shows that over a wide input voltage range, the efficiency of the XC9301/02 is more or less constant. On the other hand, the

efficiency of the XC6361/62 is clearly shown to decrease as input voltage increases. In step-down mode in particular, the efficiency of the

XC9301/02 is much better than the XC6361/62. In applications that use either a standard dry 3 cell battery or a 2 cell lithium Ion battery to

obtain an output of 3.3V, for example, the efficiency of the XC9301/02 series is again much better. Because the XC9301/02 series does not

have a series regulator output, we recommend a test with samples for use in applications where ripple voltage is a problem.

GThe performance of the DC/DC converter IC circuit is heavily reliant upon the performance of the surrounding circuitry and components. In

particular, since the VF voltage of the Schottky Diode used will have a direct effect upon efficiency, the smaller the diode, the better the

efficiency obtainable. (Refer to the graph below)

GIt is also recommended that a switching MOSFET with a small ON resistance be used. With the XC9301/02, an ON resistance of 500mΩ or

less is recommended.

Input Voltage vs. Efficiency

40

45

50

55

60

65

70

75

80

85

90

Input Voltage［V］

Step-Up Mode

Set Output Voltage+0.4V

XC6361(STEP-UP DCDC+VR)

XC9301(STEP-UP/DOWN DCDC

2

3

4

5

6

7

8

Step-Down Mode

65

70

75

80

85

0.2

0.4

VF Voltage［V］

GExternal Components Selection (Notes)

06S_15XC9301/02新規 02.9.12 3:28 PM ページ 603