S-19104N10H-M5T1U Datasheet, PDF (18/40 Pages) Seiko Instruments Inc – VOLTAGE DETECTOR WITH SENSE PIN

FOR AUTOMOTIVE 105°C OPERATION BUILT-IN DELAY CIRCUIT (EXTERNAL DELAY TIME SETTING) VOLTAGE DETECTOR WITH SENSE PIN
S-19104/19106 Series
Rev.1.2_00
2. SENSE pin
2. 1 Error when detection voltage is 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
seen in Figure 24, the detection voltage can be set externally.
For conventional products without the SENSE pin, R_A 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 R_A is large, problems such as oscillation or larger error in the hysteresis width may
occur.
In the S-19104/19106 Series, R_A and R_B 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-19104/19106 Series is large (4 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 24, 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.
Also, the relation between the external setting hysteresis width (V_HX) and the hysteresis width (V_HYS) is calculated
by equation below. Error due to R_SENSE also occurs to the relation in a similar way to the detection voltage.
( ) ^VHX ^{= V}HYS ^×
1+
R_A
R_B
··· (4)
V_DX
R_A
−V_DET
R_B
VDD
SENSE
R_SENSE
VSS
OUT
CD
Figure 24 Detection Voltage External Setting Circuit
Caution
18
If R_A and R_B are large, the SENSE pin input impedance becomes higher and may cause a
malfunction due to noise. In this case, connect a capacitor between the SENSE pin and the VSS
pin.