AN8017SA Datasheet, PDF (20/25 Pages) Panasonic Semiconductor – 1.8-volt 2-channel step-up DC-DC converter control IC

AN8017SA
Voltage Regulators
s Application Notes (continued)
[8] Setting of Off-terminal connection resistor
The start circuit starts its operation when Q1 is turned on. In an organization in which Q1 turns off/on when Q2
turns on/off in figure 9, the input voltage V_IN at which the start circuit operates is obtained by the equation:
V_IN = V_BEQ1 × (R_OFF + R1 + R2) / R2
Therefore, R_OFF can be set by:
R_OFF = R2 · V_IN / V_BEQ1 − R1 − R2
R_OFF
Off 15
Start circuit
Also, in case of limiting the Off terminal current by R_OFF ,
R1
set it by the above equation. However, take the values as:
Q2 30 kΩ
V_BEQ1 = 0.7 V (T = 25°C)
V_BEQ1 fluctuation with temperature: −2 mV/°C
Q1
R2
60 kΩ
Temperature coefficient of R1 and R2: +6 000 PPM/°C
Figure 9. Off terminal peripheral circuit
[9] Sequential operation
It is possible to turn on/off the output of DC-DC converter individually by turning on/off Q1 and Q2 as shown in
figure 10. However, pay particular attention to the current flowing into the V_REF terminal when Q2 is turned off since
sink capability of V_REF terminal is approximately 100 µA.
0.1 µF
1.19 V
Q2
Unlatch2
0.9 V
0.9 V
Unlatch1
0.2 V
Q1
Figure 10
V₂
Control block
V₁
20