S-13A1 Datasheet, PDF (33/74 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR

HIGH RIPPLE-REJECTION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR
Rev.2.1_00
S-13A1 Series
8. Inrush current limit circuit
The S-13A1 Series has a built-in inrush current limit circuit to limit the inrush current and the overshoot of the output
voltage generated at power-on or at the time when the ON / OFF pin is set to ON. The inrush current is limited to
500 mA typ. The inrush current limit circuit starts to operate from the following times.
• Immediately after power-on
• At the time when the ON / OFF pin is set to ON
Figure 33 shows the relation between the inrush current limit time (t_RUSH) and the inrush current limit capacitor (C_SS).
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
Max.
Typ.
Min.
Ta = +25°C
0.5
1
1.5
2
CSS [nF]
Figure 33
(1) C_SS = 0 nF
t_RUSH is determined by the internal capacitor (about 20 pF) and the time constant of the built-in constant current
(about 0.04 μA). t_RUSH value is 0.28 ms min., 0.40 ms typ., 0.52 ms max.
(2) C_SS ≥ 1 nF
t_RUSH can be adjusted by the C_SS which is connected externally between the SSC pin^*1 and the VSS pin. It is
calculated by the following formula depending on the built-in constant (about 1 μA) and the C_SS time constant.
The inrush current limit coefficient is 0.49 min., 0.7 typ., 0.91 max. at Ta = +25°C.
t_RUSH [ms] = the inrush current limit coefficient × C_SS [nF]
(3) 0 nF < C_SS < 1 nF
Since the internal capacitor, the built-in constant current and C_SS have a variation each, t_RUSH is the one of following
(a) and (b) in which the time is longer.
(a) The time determined by the internal capacitor (about 20 pF) and the time constant of the built-in constant
current (about 0.04 μA).
(b) The time determined by C_SS connected externally between the SSC pin^*1 and the VSS pin and the built-in
constant current (about 1 μA).
When 0 nF < C_SS< 1 nF, t_RUSH is the range of the shaded area shown in Figure 33.
*1. Types in which output voltage is internally set of HSOP-8A, HSOP-6, SOT-89-5 only.
33