L6285 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
L6285 Datasheet PDF : 16 Pages
| |||
Charge Pump
The charge pump circuitry generates the overvol-
tage needed to drive the gate of the high side out-
put DMOS power transistors.It is realized by us-
ing two external capacitors (C1 and C2) and two
integrated diodes that operate as a full wave recti-
Figure 7: Charge Pump Circuit
L6285
fier (see Fig. 7). The oscillator peak to peak out-
put voltage is stored by C2 and summed to the
Power Supply Voltage Vp..
The voltage present at the pin BOOT1, is then the
overvoltage needed to supply the gate of the high
side DMOS drivers.
THERMAL PROTECTION
The thermal protection shuts down the chip be-
fore it can reach a dangerous temperature.
Additional informations to the microprocessor are
available at the A0TH, A1TH pins.
A0TH
0
1
1
0
A1TH
0
0
1
1
THERMAL PROTECTION
OK
PREALARM
ALARM
NOT POSSIBLE
CIRCUIT STATUS
OPERATING
OPERATING
THERMAL SHUTDOWN
APPLICATION INFORMATION
A typical application circuit is shown in Fig.8. By
this application it is possible to drive two unipolar
stepper motors (M1,M2) and one DC motor (M3).
As it can be seen, only two external Zener diodes
(D1,D2) are needed to clamp the voltage tran-
sients generated by the stray inductance of the
motor windings. This is recommended when the
peak current is not more than three to four hun-
dred mAmps. For a power supply voltage of
VP=24V ±10%, D1=D2 must be 30V ±5%-1W
(1N4751A or equivalent). Both the VP and the VS
pins need bypass capacitors (C1,C2,C3); to sup-
ply the high-side DMOS (Source Transistors) at
pin.15 ,only two external capacitors (C4,C5) com-
plete the charge pump circuitry. The oscillator fre-
quency, that is twice the chopping frequency for
M1 and M2, is mainly defined by the network
R6C6:
fosc = [0.69 (Rch + Rdsc) Cosc ]-1 , where
Rch = R6 ; Rdsc = 600 ohm typ.
At the same time, the lockout duration (or protec-
tion window) needed for a correct chopping be-
havior, is given by :
Tlockout = 0.69 Rdsc Cosc
The shown values (fig.8) give a nominal fre-
quency a little bit more than 41KHz and a protec-
tion window of 1.4 µs roughly. The Schottky diode
D3 and the pull-up resistor R5 driven via an open-
collector transistor can generate the Reset func-
tion. The chopping current is sensed across R1
A/B; R2 A/B that must be of a not inductive type.
The DC motor PWM Open Loop Voltage Control
operates at a frequency defined by C7, charged
with a typical constant current source (I = 240
µA), up to V1 = 0.67 VS. Since the discharge
time is very short, it can be written :
fosc = I / Cosc V1, where Cosc = C7.
Tha values indicated in figure give a typical fre-
quency of about 22 KHz.
11/16
Share Link: 