S-1702 Datasheet, PDF (29/45 Pages) Seiko Instruments Inc – Built-in overcurrent protection circuit

SUPER-LOW CURRENT CONSUMPTION 150 mA VOLTAGE REGULATOR WITH BUILT-IN HIGH-ACCURACY VOLTAGE DETECTOR AND RESET INPUT FUNCTION
Rev.2.2_01
S-1702 Series
3. 2 Delay circuit
3. 2. 1 Internal delay types (S-1702Axx, Bxx, Cxx, Dxx, Exx, Fxx, Gxx, Hxx, Jxx, Kxx)
In the internal delay types, when VSENSE is turned on, the delay circuit makes a certain delay, after the point
when VSENSE has reached the release voltage (+VDET), and sets the VDOUT pin to output an output signal
(refer to point B in Figure 29). The delay circuit does not make delay when VSENSE is the detection voltage
(−VDET) or less (refer to point A in Figure 29).
The delay time (tD) is fixed in the internal circuit of internal delay types.
3. 2. 2 External delay types (S-1702Lxx, Mxx, Nxx, Pxx)
In the external delay types, the delay time of the detection signal can be set by connecting a capacitor (CD)
between the CD and VSS pins.
The delay time (tD) is determined according to the built-in constant current, approx. 100 nA (typ.), and the time
constant of the external capacitor (CD), and can be calculated by the following equation.
tD [ms] = Delay constant × CD [nF]
The delay constant (Ta = +25°C) is as follows.
Delay constant: 5.3 (min.), 6.3 (typ.), 7.3 (max.)
Figure 33 shows the equivalent circuit of the CD pin (external delay type).
V_IN
V_IN
CD
C_D
V_SS
V_SS
V_SS
Figure 33 Equivalent Circuit of CD Pin (External Delay Type)
Caution 1.
2.
Design the board so that a current will not flow into or flow out from the CD (RESX) pin,
because this pin’s impedance is high. (Otherwise that may provide incorrect delay time.)
There is no limit for the capacitance of the external capacitor (CD) as long as the leakage
current of the capacitor can be ignored against the built-in constant current value.
Leakage current causes deviation in delay time. When the leakage current is the built-in
constant current or more, the IC does not release.
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