L6238S View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6238S' PDF : 31 Pages View PDF
L6238S
The high current flows from the grounded sub-
strate of the integrated circuit (p-type material),
through one or more epitaxial pockets (n-type ma-
terial) and out the center par pin.
This current can cause adverse operation of the
controllet due to substrate injection and might
possibility damage the internal metalization runs.
The normal current for this input is in the 200µA
range.
Referring to figure 4-13, a simple protection
scheme consisting of a 1K resistor and a low cur-
rent Schottky diode should be added if the appli-
cation causes excessive current (i.e. >1mA) to
flow through the center tap pin.
5.0 PWM MOTOR CURRENT CONTROL
A unique feature of the L6238S in the optional
Pulse Width Modulation (PWM) control of motor
current.
Using Variable-frequency, Constant-OFF time
Current-Mode control, the L6238S can drive
higher power motors without the need for external
drivers, while minimizing internal power dissipa-
tion.
Additional benefits include reduced power supply
consumption (up to 50% savings) and lower watt-
age requirements for the current sensing resistor.
Constant-OFF time Current-Mode control, oper-
ates on the principle of monitoring the motor cur-
rent and comparison it to a reference or control
level.
Figure 5-1
When the motor current reaches this commanded
level, the output drivers turn OFF and remain
OFF for a Constant-OFF time. After this OFF time
the drivers turn back ON to repeat the cycle.
Figure 5.1 is a block diagram of the PWM control
circuitry. When using PWM as opposed to linear
control, two changes are made to the control
loop:
1.The slew rate control is disabled, allowing the
outputs to slew at a minimum rate of 10V/µs.
This is accomplished by closing SW3 and
SW5.
2.The OTA amplifier is taken out of the control
loop via SW6. The lower drivers are now
driven into hard conduction by tying the gates
to the analog supply during the On time of the
PWM cycle.
The current in the motor windings is monitored via
the voltage dropped in the sensing resistor,
Rsense.
This voltage is multiplied by a factor of 4 in the
Current Sense Amplifier (CSA) and sent to nega-
tive input of the PWM Comparator (A2).
The control voltage, Vcontrol, is applied to the posi-
tive input of A2. When the output of the CSA
reaches a level that is equal to the commanded
level, the output of A2 switches low, toggling the
latch comprised of N1 and N2. This causes the
upper drivers to turn off and opens SW1. Q3 turns
OFF allowing the Constant-OFF time capacitors,
VANALOG
Q1
Q2
UPPER A
SLEW RATE
REFERENCE
CURRENT
Q3
PWM/LIN
CONTROL
SW1
3.1V
LOWER A
PWM/SLEW
RSLEW COFF
+
A1
1.2V
-
N1
N2
VPUMP
SW2
1
N3
0
SW3
I1
Islew
VPOWER
OUTPUT
BC
L1
L2
Q4
Cfet
L3
SW4
SW5
A3
+
A2
-
1
0
Cfet
I2
Islew
VANALOG
SW6
1
0
OUTA
Q5
RSENSE
FROM TRANS. LOOP
X4
CSA
VCTRL
CSA
D95IN318
RSLW
22/31
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