S-816 Datasheet, PDF (15/24 Pages) Seiko Instruments Inc – EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

Rev.5.1_00
EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR
S-816 Series
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 = V_OUT + V_OUT × R_A ÷ ( R_B // ^*1 R_I )
*1. "//" denotes a combined resistance in parallel.
In this case, V_OUT is the output voltage value of the S-816 Series, R_A and R_B is the resistance values of
the external resistances, and R_I 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 R_A and R_B, the output voltage accuracy (V_OUT ±2.0%) of the S-816 Series, and deviations in
the absolute value of the internal resistance (R_I) 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 = V_OUT × 1.02 + V_OUT × 1.02 × R_Amax ÷ ( R_Bmin // R_Imin )
OUTmin = V_OUT × 0.98 + V_OUT × 0.98 × R_Amin ÷ ( R_Bmax // R_Imax )
Where R_Amax, R_Amin, R_Bmax and R_Bmin denote the maximum and minimum of the absolute accuracy of
external resistances R_A and R_B, and R_Imax and R_Imin denote the maximum and minimum deviations of the
absolute value of the internal resistance (R_I) in the IC, respectively.
The deviations in the absolute value of internal resistance (R_I) in the IC vary with the output voltage set
value of the S-816 Series, and are broadly classified as follows:
• Output voltage (V_OUT)
• Output voltage (V_OUT)
• Output voltage (V_OUT)
• Output voltage (V_OUT)
• Output voltage (V_OUT)
2.5 V to 2.7 V ⇒ 3.29 MΩ to 21.78 MΩ
2.8 V to 3.1 V ⇒ 3.29 MΩ to 20.06 MΩ
3.2 V to 3.7 V ⇒ 2.23 MΩ to 18.33 MΩ
3.8 V to 5.1 V ⇒ 2.23 MΩ to 16.61 MΩ
5.2 V to 6.0 V ⇒ 2.25 MΩ to 14.18 MΩ
If a value of R_I 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.
R_I = 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 (V_OUT) 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 (R_A, R_B) and the absolute value of the internal resistance (R_I) of the IC.
In particular, to suppress the influence of deviations in the internal resistance (R_I), the resistance values
of external resistances (R_A, R_B) need to be limited to a much smaller value than that of the internal
resistance (R_I). However, since reactive current flows through the external resistances (R_A, R_B), 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 MΩ) is taken for the external resistances (R_A, R_B), IC is
vulnerable to external noise. Check the influence of this value well with the actual application.
Furthermore, add a capacitor C_C in parallel to the external resistance R_A in order to avoid output
oscillations and other types of instability. (Refer to Figure 13)
Make sure that the capacitance value of C_C is larger than the value given by the following equation:
C_C[F] ≥ 1 ÷ ( 2 × π × R_A[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.
Seiko Instruments Inc.
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