S1011 Datasheet, PDF (21/43 Pages) Seiko Instruments Inc – BUILT-IN DELAY CIRCUIT (EXTERNAL DELAY TIME SETTING) VOLTAGE DETECTOR

HIGH-WITHSTAND VOLTAGE BUILT-IN DELAY CIRCUIT (EXTERNAL DELAY TIME SETTING) VOLTAGE DETECTOR
Rev.1.2_00
S-1011 Series
2. SENSE pin
2. 1 Error when detection voltage is set externally
The detection voltage for the S-1011 Series is 10.0 V max., however, in the SENSE detection product with −V_DET =
10.0 V, the detection voltage can be set externally by connecting a node that was resistance-divided by the resistor
(R_A) and the resistor (R_B) to the SENSE pin as shown in Figure 31.
For conventional products without the SENSE pin, external resistor cannot be too large since the resistance-divided
node must be connected to the VDD pin. This is because a feed-through current will flow through the VDD pin
when it goes from detection to release, and if external resistor is large, problems such as oscillation or larger error
in the hysteresis width may occur.
In the S-1011 Series, R_A and R_B in Figure 31 are easily made larger since the resistance-divided node can be
connected to the SENSE pin through which no feed-through current flows. However, be careful of error in the
current flowing through the internal resistance (R_SENSE) that will occur.
Although R_SENSE in the S-1011 Series is large (the S-1011 Series E / G type: 26 MΩ min., the S-1011 Series N / Q
type: 6.8 MΩ min.) to make the error small, R_A and R_B should be selected such that the error is within the allowable
limits.
2. 2 Selection of R_A and R_B
In Figure 31, the relation between the external setting detection voltage (V_DX) and the actual detection voltage
(−V_DET) is ideally calculated by the equation below.
( ) ^VDX ^{= −V}DET ^×
1+
R_A
R_B
··· (1)
However, in reality there is an error in the current flowing through R_SENSE.
When considering this error, the relation between V_DX and −V_DET is calculated as follows.
( ^VDX ^{= −V}DET ^{× 1 +}
= −V_DET × _1 +

( ^{= −V}DET ^{× 1 +}
) ^RA
R_B || R_SENSE
R_A
 ^{RB × RSENSE}
 ^RB ^{+ R}SENSE
) ^RA
R_B
+
R_A
R_SENSE
× −V_DET
··· (2)
By using equations (1) and (2), the error is calculated as −V_DET ×
R_A
R_SENSE
.
The error rate is calculated as follows by dividing the error by the right-hand side of equation (1).
R_A × R_B
R_SENSE × (R_A + R_B)
× 100 [%] =
R_A || R_B
R_SENSE
× 100 [%]
··· (3)
As seen in equation (3), the smaller the resistance values of R_A and R_B compared to R_SENSE, the smaller the error
rate becomes.
Seiko Instruments Inc.
21