S816 datasheet(15/24 Pages) SII

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EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

Rev.6.1_00

S-816 Series

Seiko Instruments Inc.

The S-816 Series has an internal impedance resulting from R1 and R2 between the VOUT and the VSS

pin, as shown in Figure 13. Therefore, the influence of the internal resistances (R1, R2) of the IC has to

be taken into consideration in defining the output voltage (OUT).

The output voltage (OUT) is expressed by the following equation:

OUT

= VOUT + VOUT × RA ÷ ( RB //

*1 R

I )

*1. "//" denotes a combined resistance in parallel.

In this case, VOUT is the output voltage value of the S-816 Series, RA and RB is the resistance values of

the external resistances, and RI is the resistance value (R1

+R2) of the internal resistances in the IC.

The accuracy of the output voltage (OUT) is determined by the absolute accuracy of external connecting

resistances RA and RB, the output voltage accuracy (VOUT

±2.0%) of the S-816 Series, and deviations in

the absolute value of the internal resistance (RI) in the IC.

The maximum value (OUTmax) and the minimum value (OUTmin) of the output voltage (OUT), including

deviations, are expressed by the following equations:

OUTmax

= VOUT × 1.02 + VOUT × 1.02 × RAmax ÷ ( RBmin // RImin )

OUTmin

= VOUT × 0.98 + VOUT × 0.98 × RAmin ÷ ( RBmax // RImax )

Where RAmax, RAmin, RBmax and RBmin denote the maximum and minimum of the absolute accuracy of

external resistances RA and RB, and RImax and RImin denote the maximum and minimum deviations of the

absolute value of the internal resistance (RI) in the IC, respectively.

The deviations in the absolute value of internal resistance (RI) in the IC vary with the output voltage set

value of the S-816 Series, and are broadly classified as follows:

• Output voltage (VOUT) 2.5 V to 2.7 V  3.29 MΩ to 21.78 MΩ

• Output voltage (VOUT) 2.8 V to 3.1 V  3.29 MΩ to 20.06 MΩ

• Output voltage (VOUT) 3.2 V to 3.7 V  2.23 MΩ to 18.33 MΩ

• Output voltage (VOUT) 3.8 V to 5.1 V  2.23 MΩ to 16.61 MΩ

• Output voltage (VOUT) 5.2 V to 6.0 V  2.25 MΩ to 14.18 MΩ

If a value of RI given by the equation shown below is taken in calculating the output voltage (OUT), a

median voltage deviation of the output voltage (OUT) will be obtained.

= 2 ÷ ( 1 ÷ (Maximum value of internal resistance of IC) + 1 ÷ (Minimum value of internal resistance of IC) )

The closer the output voltage (OUT) and the output voltage set value (VOUT) of the IC are brought to each

other, the more the accuracy of the output voltage (OUT) remains immune to deviations in the absolute

accuracy of external resistances (RA, RB) and the absolute value of the internal resistance (RI) of the IC.

In particular, to suppress the influence of deviations in the internal resistance (RI), the resistance values

of external resistances (RA, RB) need to be limited to a much smaller value than that of the internal

resistance (RI). However, since reactive current flows through the external resistances (RA, RB), there is a

tradeoff between the accuracy of the output voltage (OUT) and the reactive current. This should be taken

into consideration, according to the requirements of the intended application.

Note that when larger value (more than 1 M

Ω) is taken for the external resistances (RA, RB), IC is

vulnerable to external noise. Check the influence of this value well with the actual application.

Furthermore, add a capacitor CC in parallel to the external resistance RA in order to avoid output

oscillations and other types of instability. (Refer to Figure 13)

Make sure that the capacitance value of CC is larger than the value given by the following equation:

CC[F]

≥ 1 ÷ ( 2 × π × RA[Ω] × 6000 )

Caution

The above connection diagram and constant will not guarantee successful operation.

Perform through evaluation using the actual application to set the constant.

S816 Datasheet(PDF) 15 Page - Seiko Instruments Inc

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