S-19680AAAH-K8T2U Datasheet, PDF (11/27 Pages) Seiko Instruments Inc – Current consumption during operation

Rev.1.1_00
FOR AUTOMOTIVE 105°C OPERATION CURRENT MONITOR HIGH SIDE SWITCH
S-19680 Series
 Operation
1. Basic operation
Figure 12 shows the block diagram of the S-19680 Series to describe the basic operation.
Connect an external power supply to the VDD pin and a load to the OUT pin. Also, connect the external shunt
resistor (R_SHUNT) between the VDD pin and the VIN pin and the external sense resistor (R_SENSE) between the VDD
pin and the SENSE pin. Due to the IC internal control signal, the Pch output transistor is turned on or off, and the
switch operation is performed between the VIN pin and the OUT pin.
When the Pch output transistor is turned on, the VIN pin and the OUT pin are connected. Since the output current
which flows from the OUT pin to the load (I_OUT) is supplied from VDD via R_SHUNT and the Pch output transistor, the
current which flows in R_SHUNT (I_SHUNT) will be I_SHUNT = I_OUT.
Since a voltage drop (V_SHUNT) occurs by flowing I_SHUNT in R_SHUNT and the Pch output transistor with ON resistance
(R_ON), the voltage supplied to the load (V_OUT) is calculated by using formula (1).
(1) V_OUT = V_DD − I_SHUNT × (R_SHUNT + R_ON)
ISHUNT
R_SHUNT VIN
*1
OUT
V_DD C_IN
C_L R_L
RSENSE SENSE
VDD
Control signal
*1. Parasitic diode
Figure 12
2. Current monitor operation
Figure 13 shows the block diagram of the current monitor operation in the S-19680 Series.
By using R_SHUNT and R_SENSE, the S-19680 Series monitors the current which flows from the VIN pin to the OUT pin.
A resistor with 5.1 Ω can be used for R_SHUNT and 5.1 kΩ for R_SENSE.
The current depending on the load (I_SHUNT) flows in R_SHUNT. The current sense amplifier operates so that the
SENSE pin voltage becomes the same voltage as the VIN pin voltage. V_SHUNT generated in R_SHUNT is calculated
by using formula (2).
(2) V_SHUNT = I_SHUNT × R_SHUNT
Similarly, the same voltage as V_SHUNT is generated in R_SENSE, so the current which flows in R_SENSE (I_SENSE) is
calculated by using formula (3).
(3)
I_SENSE = I_SHUNT ×
R_SHUNT
R_SENSE
The current limit circuit, the load short-circuit detection circuit and the load open detection circuit monitors I_SHUNT
depending on I_SENSE value.
2. 1 Current limit circuit
By the current limit circuit, the S-19680 Series limits the current so that I_SHUNT does not exceed the set value.
The current limit circuit monitors I_SHUNT depending on I_SENSE value. When I_SHUNT reaches the limit current (I_LIM),
the circuit controls the Pch output transistor and limits the current so that I_SHUNT does not exceed I_LIM.
Caution Be aware that I_SHUNT which is larger than I_LIM flows during the period from when I_SHUNT reaches I_LIM to
when the current limit circuit responds.
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