S1142A Datasheet, PDF (16/32 Pages) Seiko Instruments Inc – HIGH-WITHSTAND VOLTAGE LOW CURRENT CONSUMPTION

HIGH-WITHSTAND VOLTAGE LOW CURRENT CONSUMPTION LOW DROPOUT CMOS VOLTAGE REGULATOR
S-1142A/B Series
Rev.4.2_00
6. Overshoot of output voltage
Overshoot of output voltage occurs depending on the condition such as the rising speed of input voltage (V_IN).
Overshoot voltage is the difference between the maximum value of output voltage generated by the fluctuation of
V_IN and the actual output voltage (V_OUT(E)) value.
6. 1 At normal operation
As shown in Figure 13, V_gs is the voltage difference between V_IN and gate voltage of output driver.
The error amplifier controls V_gs in order to keep the output voltage constant depending on the fluctuation of V_IN
and the output load.
V_IN
V_ref
−
+
V_gs
Output driver
Output voltage
Output
capacitance ^{Output load}
Figure 13 Circuit Diagram
6. 2 Occurrence of overshoot
If V_IN voltage rises at a fast speed, V_gs may become large when gate voltage of output driver can not follow the
speed of V_IN. When V_gs becomes large, the current supplied from output driver is increased transiently. Thereby,
output voltage rises, and then overshoot occurs.
Note that overshoot voltage is greatly affected by the following use conditions or temperature, etc.
• When V_IN rises in the range of 2.0 V to V_OUT(E).
• When the rising speed of V_IN is fast.
• When the output capacitance is small.
• When the output load is small.
Input voltage (V_IN)
Rising speed of V_IN =
ΔV
t
ΔV
V_IN = 2.0 V to V_OUT(E)
Output voltage (V_OUT(E))
V_OUT(E)
V_IN = 2.0 V to V_OUT(E)
Overshoot voltage
Rising time (t)
Figure 14 V_IN and Overshoot Voltage
Caution Under the following conditions, overshoot voltage tends to become larger especially.
• When V_IN rises from around 98% of V_OUT(E).
• When the rising speed of V_IN is 10 mV/μs or more.
Remark When overshoot of the S-1142A/B Series has some influences, consider to use the S-1142C/D Series.
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Seiko Instruments Inc.