L6238S View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6238S' PDF : 31 Pages View PDF
Figure 4-3
L6238S
4.3 Charge Pump
The charge pump circuitry is used as a means of
doubling the analog supply voltage in order to al-
low the upper N-channel DMOS transistors to be
driven like P-channel devices. The energy stored
in the reservoir capacitor is also used to drive the
lower drivers in a brake mode if the analog supply
is lost. Figure 4-3 is a simplified schematioc of the
charge pump circuitry.
Figure 4-4
A capacitor, Cpump, is used to retrieve energy
from the analog supply and then ”pumps” it into
the storage capacitor, Cresvr.
An internal 300KHz oscillator first turns ON Q2 to
quickly charge Cpump to approximately the rail
voltage. The oscillator then turns ON Q1 while
turning OFF Q2. Since the bottom plate of Cpump,
is now effectively at the rail voltage via D2.
A zener-referenced series-pass regulator supplies
VCTRL
VPUMP
UPPER A
SW2
+
A2
-
SW3
1
LOWER A
0
A3
X4
I2
Islew
VANALOG
1
0
I1
Islew
Cfet
VPOWER
OUTPUT
BC
Q1
Cfet
L1
L2
L3
OUTA
Q2
RSENSE
CSA
RS
Q3
Q4
Q5
PWM SLEW/RC
SLEW RATE
REFERENCE CURRENT
3.1V
RSLW
D95IN315
17/31
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