LB1939T_09 SANYO [Sanyo Semicon Device], LB1939T_09 Datasheet - Page 6

• Manufacturer Part Number: LB1939T_09
• Description: 2 Channel H Bridge Constant Voltage/Constant Current Driver IC
• Manufacturer: SANYO [Sanyo Semicon Device]

Application Circuit Example 3
Notes on Constant Current Control Settings
The LB1939T constant current control circuit has the
structure shown in the figure at the right. The voltage input
to the VC pin is resistor divided internally (by 70 kΩ and
20 kΩ resistors) to 1/4.5 and input to the plus (+) input of
the constant current control amplifier as reference.
The minus (–) input of this constant current control
amplifier is connected, through the wire bond resistor Rb
(= 0.1 Ω), to the RFG pin. The constant current control
circuit operates by comparing the voltage generated by the
external current detection resistor connected to the RFG
pin and the reference voltage mentioned above.
Note that the voltage at VA will be that given by the
following formula since the bias current Ib (= 1.5 µA)
flows from the constant current control amplifier plus (+)
input during constant current control operation.
Therefore, the logical expression for setting the constant
current Iout is as follows.
VA = VC/4.5 + Ib 20 kΩ
Iout = VA/(RFB + Rb)
= VC/4.5 + 0.03
= (VC/4.5 + 0.03) / (RFB + Rb) ......(1)
Channel 1 operates in constant voltage control mode: OUT outputs V
Channel 2 operates in constant current control mode: The RFG voltage is controlled so that Vref/4.5 = 0.2 V.
* : FC1 is left open.
CPU
3 k
6 k
S-GND
ENA1
ENA2
SVDD
IN1
IN2
VC1
VDD
Vref
LB1939T
LB1939T
VC2 RFG1 RFG2
VS2
70 k
20 k
VC
VS1
OUT2
OUT3
OUT4
OUT1
DD
FC2
Ib = 1.5 A
3K/(3K + 6K)
VA
Constant current
control amplifier
1.95
RFG
R L
OUT1
OUT2
Pad
RFB
VS
Rb = 0.1
Iout
No. 6194-6/7
A13864