S-19243A12A-E8T1U Datasheet, PDF (33/74 Pages) Seiko Instruments Inc – CMOS VOLTAGE REGULATOR WITH SOFT-START FUNCTION

FOR AUTOMOTIVE 125°C OPERATION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR WITH SOFT-START FUNCTION
Rev.3.0_00
S-19243xxxA Series
9. Types in which output voltage is externally set
The S-19243xxxA Series provides the types in which output voltage can be set via the external resistor. The output
voltage can be set by connecting a resistor (R_a) between the VOUT pin and the VADJ pin, and a resistor (R_b)
between the VADJ pin and the VSS pin.
The output voltage is determined by the following formulas.
V_OUT = 1.0 + R_a × l_a ···················· (1)
By substituting I_a = I_VADJ + 1.0 / R_b to above formula (1),
V_OUT = 1.0 + R_a × (I_VADJ + 1.0 / R_b) = 1.0 × (1.0 + R_a / R_b) + R_a × I_VADJ ······· (2)
In above formula (2), R_a × I_VADJ is a factor for the output voltage error.
Whether the output voltage error is minute is judged depending on the following (3) formula.
By substituting I_VADJ = 1.0 / R_VADJ to R_a × I_VADJ
V_OUT = 1.0 × (1.0 + R_a / R_b) + 1.0 × R_a / R_VADJ ················ (3)
If R_VADJ is sufficiently larger than R_a, the error is judged as minute.
VIN
I_VADJ
VOUT
I_a
VADJ
R_VADJ ^Ib
VSS
R_a
1.0 V
R_b
V_OUT
Figure 34
The following expression is in order to determine V_OUT = 6.0 V.
If R_b = 2 kΩ, substitute R_VADJ = 600 kΩ typ. into (3),
R_a = (6.0 / 1.0 − 1) × ((2 k × 600 k) / (2 k + 600 k)) ≅ 9.97 kΩ
Caution The above connection diagrams and constants will not guarantee successful operation. Perform
thorough evaluation using the actual application to set the constants.
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