MC34167, MC33167 5.0 A, StepâUp/Down/ Inverting ... - RFPhone
MC34167, MC33167 5.0 A, StepâUp/Down/ Inverting ... - RFPhone
MC34167, MC33167 5.0 A, StepâUp/Down/ Inverting ... - RFPhone
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<strong>MC34167</strong>, <strong>MC33167</strong><br />
Table 1. Design Equations<br />
Calculation Step−<strong>Down</strong> Step−Up/<strong>Down</strong> Voltage−<strong>Inverting</strong><br />
ton<br />
toff<br />
(Notes 1, 2)<br />
Vout VF<br />
Vin Vsat Vout<br />
Vout VF1 VF2<br />
Vin VsatQ1 VsatQ2<br />
|Vout| VF<br />
Vin Vsat<br />
t on<br />
Duty Cycle<br />
(Note 3)<br />
ton<br />
toff<br />
fosc t on<br />
toff 1<br />
ton<br />
toff<br />
fosc t on<br />
toff 1<br />
ton<br />
toff<br />
fosc t on<br />
toff 1<br />
t on f osc t on f osc t on f osc<br />
I L avg I out Iout t on<br />
toff 1<br />
I pk(switch)<br />
L<br />
I Lavg I L<br />
2<br />
V in Vsat Voutton<br />
IL<br />
<br />
V ripple(pp) I L 1<br />
8foscCo 2 (ESR)2<br />
IL avg I L<br />
2<br />
V in VsatQ1 VsatQ2ton<br />
IL<br />
t on<br />
<br />
toff 1 1<br />
foscCo 2 (ESR)2<br />
I out t on<br />
toff 1<br />
IL avg I L<br />
2<br />
V in Vsatton<br />
IL<br />
t on<br />
toff 1 1<br />
f oscCo 2 (ESR)2<br />
V out Vref R 2<br />
R1 1 V ref R 2<br />
R1 1 V ref R 2<br />
R1 1<br />
1. V sat − Switch Output source saturation voltage, refer to Figure 8.<br />
2. V F − Output rectifier forward voltage drop. Typical value for 1N5822 Schottky barrier rectifier is 0.35 V.<br />
3. Duty cycle is calculated at the minimum operating input voltage and must not exceed the guaranteed minimum DC (max) specification of 0.92.<br />
The following converter characteristics must be chosen:<br />
V out − Desired output voltage.<br />
I out − Desired output current.<br />
I L − Desired peak−to−peak inductor ripple current. For maximum output current especially when the duty cycle is greater than 0.5,<br />
it is suggested that I L be chosen minimum current limit threshold of 5.5 A. If the design goal is to use a minimum inductance<br />
value, let I L = 2 (I L avg ). This will proportionally reduce the converter’s output current capability.<br />
V ripple(pp) − Desired peak−to−peak output ripple voltage. For best performance, the ripple voltage should be kept to less than 2% of V out .<br />
Capacitor C O should be a low equivalent series resistance (ESR) electrolytic designed for switching regulator applications.<br />
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