S1F76640 Series
Negative Voltage ConversionS1F76640 can boost input voltage to negative power on the negative potential side by using the circuit shown in Figure 8.6. (In case of 3 times step-up, remove the capacitor C3 and the diode D4 and short-circuit the both ends of D4. In case of 2 times step-up, remove the capacitor C2 and the diode D3 and short-circuit the both ends of D3.) But the output voltage drops by the forward voltage VF of the diode. When GND is 0V, VDD is 5V and VF is 0.6V as shown in Figure 8.6 for example, VO is calculated as follows: VO = –15V–×4 0.6V = –12.6V(In case of 3 times step-up, VO is calculated to –10V–×30.6V = –8.2V, and in case of 2 times step-up, VO is calculated to –5V–×20.6V = –3.8V.)
| 1 | RV | VRI 16 | | | | VO' |
| | | | | | |
| 2 | VREG | VO 15 | | | | |
| 3 | TC1 | CAP3+ 14 | | | | |
| 4 | TC2 | CAP2+ 13 | + | – | | |
| 5 | POFF | CAP2– 12 | D3 | – |
| | |
| | C2 | |
| 6 | VSS | CAP1+ 11 | | | + C0 |
| + | – | D2 | |
| | | | | |
| 7 | OSC1 | CAP1– 10 | | C1 | | |
| | | | | D1 | |
| 8 | OSC2 | VDD 9 | | | |
| | | | |
Figure 8.6 Negative Voltage Conversion (Example of 3 times step-up circuit)
Negative Voltage Conversion + Positive Voltage ConversionWhen the 3 times step-up operation shown in Figure 8.1 and the positive voltage conversion in Figure 8.6 are combined, the circuit shown in Figure 8.7 can be formed and 20V and –12.6V can be obtained from the input 5V. However, the output impedance is higher than in case of connection of either one only (the negative voltage conversion or the positive voltage conversion).
1 | RV | VRI | 16 | | | VO' |
| | | | | |
2 | VREG | VO 15 | | | VO' |
3 | TC1 | CAP3+ 14 | | |
| | |
4 | TC2 | CAP2+ 13 | + | + | – |
| | | | – |
5 | POFF | CAP2– | 12 | | + |
| + |
6 | VSS | CAP1+ 11 | | – |
+ – | – |
7 | OSC1 | CAP1– 10 | – | + |
| |
| | |
8 | OSC2 | VDD | 9 | | | |
Figure 8.7 Negative Voltage Conversion + Positive Voltage Conversion
S1F70000 Series Technical Manual