MC34164-3 Datasheet, PDF (17/23 Pages) Freescale Semiconductor, Inc – 3.0 A 1.0 MHz Fully Integrated DDR Switch-Mode Power Supply

TYPICAL APPLICATIONS
PROTECTION AND DIAGNOSTIC FEATURES
COMPONENT SELECTION
SWITCHING FREQUENCY SELECTION
The switching frequency defaults to a value of 1.0 MHz
when the FREQ pin is grounded, and 200 KHz when the
FREQ pin is connected to VDDI. Intermediate switching
frequencies can be obtained by connecting an external
resistor divider to the FREQ pin. The table below shows the
resulting switching frequency versus FREQ pin voltage.
Table 5. Switching Frequency Adjustment
FREQUENCY
200
253
307
360
413
466
520
573
627
680
733
787
840
893
947
1000
VOLTAGE APPLIED TO PIN FREQ
2.341 – 2.500
2.185 - 2.340
2.029 - 2.184
1.873 - 2.028
1.717 – 1.872
1.561 – 1.716
1.405 - 1.560
1.249 - 1.404
1.093 - 1.248
0.936 - 1.092
0.781 - 0.936
0.625 - 0.780
0.469 - 0.624
0.313 - 0.468
0.157 - 0.312
0.000 - 0.156
Inductor calculation is straight forward, being
where,
Maximum OFF time percentage
Switching period.
Drain – to – source resistance of FET
Winding resistance of Inductor
Output current ripple.
OUTPUT FILTER CAPACITOR
For the output capacitor, the following considerations are
more important than the actual capacitance value, the
physical size, the ESR and the voltage rating:
Transient Response percentage, TR_%
Maximum Transient Voltage, TR_v_dip = Vo*TR_%
Maximum current step,
Inductor Current rise time,
Figure 7. Resistor Divider for Frequency Adjustment
SELECTION OF THE INDUCTOR
where,
D_max = Maximum ON time percentage.
I_O = Rated output current.
Vin_min = Minimum input voltage at PV_IN
As a result, it is possible to calculate
Analog Integrated Circuit Device Data
Freescale Semiconductor
34712
17