LB1845(1996) Ver la hoja de datos (PDF) - SANYO -> Panasonic
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LB1845
(Rev.:1996)
(Rev.:1996)
SANYO -> Panasonic
LB1845 Datasheet PDF : 7 Pages
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LB1845
Usage Notes
1.External diode
Since this IC adopts a system based on lower side transistor switching drive, an external diode for the regenerative
current that occurs during switching is required between VBB and VOUT. Use a Schottky barrier diode with a low
feedthrough current.
2.Noise filters
Since spike noise (see Figure 1) occurs when switching to the on state due to the external diode’s feedthrough current,
applications must remove noise from the SENSE pin with a noise filter (Cc, Rc) between the E pin and the SENSE pin.
However, note that if the values of Cc and Rc are too large, the SENSE voltage rise will be slowed, and the current
setting will be shifted towards a higher current level.
3. VREF pin
It is possible to change the output current continuously by continuously changing the VREF pin voltage. However, this
voltage cannot be set to 0 V. The VREF pin input impedance is 26 kΩ (±30%) when VREF is 5 V. Since this pin is used
to set the output current, applications must be designed so that noise does not appear on this pin's input.
4.GND pin
Since this IC switches large currents, care must be taken to avoid ground loops when the IC is mounted in the
application. The section of the PCB that handles large currents should be designed with a low-impedance pattern, and
must be separated from the small signal sections of the circuit. In particular, the ground for the sense resistor Re must
be as close as possible to the IC ground.
5.Operation in hold mode
There are cases where a current somewhat larger than the current setting may flow in hold mode (light load mode).
Since this IC adopts a lower side switching, lower side sense system, the emitter voltage falls and the sense voltage
goes to 0 when the switching state goes to off. The circuit then always turns the output on after the toff period has
elapsed. At this time, due to the light load, the existence of the time td, and the fact that the output goes on even if the
output current is higher than the set current, the output current will be somewhat higher than the set current.
Applications should set the current setting somewhat lower than required if this occurs.
6.Function for preventing the upper and lower outputs being on at the same time
This IC incorporates a built-in circuit that prevents the through currents that occur when the phase is switched. The
table lists the output on and off delay times when PHASE and EANBLE are switched.
On delay time
When PHASE is switched
Off delay time
When ENABLE is on
On delay time
Off delay time
Sink side
10 µs
1.5 µs
9 µs
1.5 µs
Source side
9 µs
3 µs
9 µs
6.5 µs
7.1-2 phase excitation and the double 1-2 phase excitation control sequence
To reduce the vibration that occurs when the motor turns, this IC supports 1-2 phase excitation and double 1-2 phase
excitation by using the output current setting digital input pins I0 and I1 without changing the VREF pin voltage. Tables
1 and 2 list that control sequence, and Figure 2 and Figure 3 present the composite vector diagram for this sequence.2.
Noise filters
Table 1 [1-2 phase excitation] 1/2 step
Phase A
No.
PH1 I11
I01 Current value PH2
0
0
0
0
1
*
1
0
0
1
2/3
0
2
*
1
1
0
0
3
1
0
1
2/3
0
4
1
0
0
1
*
5
1
0
1
2/3
1
6
*
1
1
0
1
7
0
0
1
2/3
1
ENABLE1 = ENABLE2 = 0
Phase B
I12
I02
1
1
0
1
0
0
0
1
1
1
0
1
0
0
0
1
Current value
0
2/3
1
2/3
0
2/3
1
2/3
No. 5505-5/7
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