LB1940T-TLM-H Datasheet, PDF (6/8 Pages) ON Semiconductor – 2-ch H-Bridge Constant Current Driver

Application Circuit Diagram
LB1940T
CPU
VDD
VS2
VS1
ENA1
ENA2
OUT1
OUT2
IN1
LB1940T ^OUT3
IN2
OUT4
S-GND
FC1
SVDD
FC2
Vref VC1 VC2 RFG1 RFG2
Ra
RfB
RfB
Rb
At constant-current control: The OUT current is controlled so that the RFG pin voltage is equal to the VC input pin
voltage.
For example, IOUT = 200mA (= 0.2V/1) when VC = 0.2V and RFB = 1.
*: There is no priority relationship between respective input voltages (ENA, IN) and respective supply voltages
(VDD, VS). For example, operation with VIN = 5V, VDD = 3V, VS = 2V is possible.
Note: The input voltage range to the reference voltage input pin VC for constant-current setting is from 0.19V to
1.0V.
Constant current setting
The composition of the constant-control circuit of this IC is as shown
in the figure below.
The voltage entered in the VC pin is entered as a reference to the “+”
side input of the constant-current control amplifier.
The “-” side of this constant-current control amplifier is connected to
the RFG pin via the wire bonded resistor Rb (= 0.1).
The constant-current control circuit consists of comparison of the
voltage generated at the external current detection resistor with the
above reference voltage.
In addition, since the bias current Ib (= 1.5μA) flows out of the
positive (+) input of the constant current control amplifier during the
constant current control, if the voltage is input to the VC pin by
dividing the VREF voltage by 4.5 according to the dividing resistance
(70k and 20k) as shown in the figure, the formula for calculating
the VC voltage is as follows :
VC = VREF/4.5+Ib20k = VREF/4.5+0.03
Therefore, the theoretical equation to set the constant current IOUT is as follows:
IOUT = VC/(RFB+Rb) = (VREF/4.5+0.03)/(RFB+Rb)
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