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STA6940M

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18
10
SANKEN ELECTRIC CO., LTD.
28106.01
Brushed DC Motor Driver IC With PWM Control
STA6940M
The constant-current set point, V
PREF
, and the OCP threshold,
V
OREF
, may be set individually as needed.
• V
PREF
< V
OREF
With this relationship, constant-current control
has priority. In order for OCP to operate, the OCP condition
must be detected before the constant-current control is operat-
ing, that is, during the blanking time. During blanking time, the
voltage V
RS
could reach V
OREF
, initiating OCP.
• V
OREF
< V
PREF
With this relationship, OCP has priority over
constant-current control. At any time while the STA6940M is
powered, if the voltage V
RS
reaches V
OREF
, OCP can operate.
Thermal Shutdown (TSD)
This device has internal thermal protection. The thermal shut-
down function is of the auto-recovery type. The operating princi-
ple is that when the internal control IC (MIC) temperature reaches
T
tsdon
all outputs are disabled. When the temperature drops below
T
tsdoff
the device is reenabled.
When the device outputs are disabled, the function sets the Diag
terminal low. Figure 10 shows the relationship of Diag output and
case temperature, T
C
.
Note: This device utilizes a multi-chip construction, the Control
IC (MIC) and four separate MOSFETs. The temperature sensor is
located on the control IC, however, the primary heat sources are
the MOSFETs. Thus this internal thermal protection cannot react
to sudden changes in MOSFET temperature.
Undervoltage Protection (UVLO)
If any of the voltages of the main supply, V
BB
, logic supply,
V
DD
, or the charge pump, V
CP
(V
CP
-V
BB
), fall below the preset
threshold, the device will be disabled. (The charge pump voltage
is derived from V
BB
using the internal charge pump circuitry and
connected capacitors.) The effects on output to the motor and to
the Diag pin are shown in figure 11.
Note: The V
BB
and V
DD
voltage power-up sequence does not
affect UVLO operation.
T
tsdon
T
tsdoff
V
DD
T
C
(°C)
Diag (V)
Figure 10. Thermal shutdown operation provides a hysteresis in supply
voltage to the MOSFETs, which is monitored and sets the Diag pin output
Figure 11. Operation of the UVLO circuits
V
UVDH
V
DD
0 V
V
UVBH
V
BB
0 V
V
UVCH
Output
Off
Output
On
Output
On
Output
On
Output
Off
Output
Off
V
CP
Diag
0 V
0 V
11
SANKEN ELECTRIC CO., LTD.
28106.01
Brushed DC Motor Driver IC With PWM Control
STA6940M
STA 6940 M
Sense1Sense 2GND
PWM_REF
VDD
IN1
IN2
Diag
CP1 CP2 CP
VBB VBB
OCP_REF
OA
OA
OB
OB
DCM
Micro controller
V
DD
= 3 to 5.5 V
CACB
Rs
C1
R1
R2
R3
C2
C3
Power GndLogic Gnd
R5R4
V
BB
= 10 to 40 V
Application Information
Figure 12. Typical application circuit
Reference Component Values
R1 = 3 k
R2 = 1 k
R3 = 1 k
R4 = 10 k
R5 = 10 k
*R
S
= 0.22
CA = 100 F / 50 V
CB = 10 F / 10 V
C1 = 0.1 F
C2 = 0.1 F
C3 = 0.1 F
*Please choose the proper power rating for R
S
, taking
into consideration the approximate power dissipation, as
follows: P
D
≈ I
O
2
× R
S
× On Duty Cycle.
• Surge voltage less than -1.0 V may occur on OA and OB
outputs, therefore Schottky barrier diodes are recommended
between those pins and GND
• Please take care to reduce noise on the VDD line.
• Noise voltages greater than 0.5 V on the VDD line may cause
malfunction. Please take special care when laying out the return
line and ground pattern.
• Separating IC GND (pin 10), VDD Gnd (signal ground) and
VBB Gnd (power ground) helps reduce noise.
• Logic input terminals (IN1 and IN2) which are not externally
controlled must not be left open; they should be pulled-up or
pulled-down to the VDD or GND terminals, based on the re-
quired mode. Otherwise the device may malfunction.
• Unused logic output terminals (Diag) should be left open.
• The Sense1 and Sense2 terminals must be tied together, and
then connected to R
S
.
• Connecting only one of the Sensex terminals may result in dam-
age to the device.
12
SANKEN ELECTRIC CO., LTD.
28106.01
Brushed DC Motor Driver IC With PWM Control
STA6940M
PWM Constant-Current Control Setting (R1, R2, R3, R
S
)
The PWM fixed current control set point may be changed by
using resistors R1, R2, R3 and R
S
as shown in figure 12.
The formula for calculating Io is as follows:
I
O
V
PREF
/ R
S
,
=
(1)
where
R
3
R
1
+ R
2
+ R
3
V
PREF
V
DD .
=×
(2)
If V
PREF
is set below 0.1 V, external factors such as component
tolerance and wiring impedances may affect the accuracy of the
set current level.
The STA6940M uses a fixed off-time control scheme. During
the off-time, the energy stored in the motor coils dissipates. If
the set current point is too low, the motor current may become
discontinuous and the motor torque will be greatly reduced as a
result. Please take this into consideration when setting the mini-
mal current level. Although setting such a low current level does
not damage the device, the control of the set current level will
become worse. This is illustrated in figure 13.
OCP Point Setting
The formula for setting the OCP point is the similar to that for
constant-current, but using V
OREF
:
I
OCP
V
OREF
/ R
S
,
=
(3)
where
R
2
+R
3
R
1
+ R
2
+ R
3
V
OREF
V
DD .
=×
(4)
Power Supply (VBB, VDD) On/Off Sequence
This device will operate normally regardless of the power-up
sequence of the power supplies.
Internal Logic Circuitry Connection
The following guidelines should be followed when connecting the
internal circuitry:
• Input Logic Terminals (IN1, IN2) These terminals require a
fixed logic level, and when they are unused, they should not be
left open. They should be connected to VDD or GND as neces-
sary.
• Output Terminal (Diag) The Diag terminal has an inter-
nal equivalent circuit as shown in figure 14. Because this is
a CMOS circuit structure, if the terminal is not being used it
should be left open.
Figure 13. Minimum controllable current level Figure 14. Diag terminal equivalent circuit
0
V
RS
Large I
TRIP
Small I
TRIP
Coil current = 0
V
DD
Output, Ox
ESD
STA6940M
protection
circuitry
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18

STA6940M

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Brushed DC Motor Driver 18-Pin ZIP Tube
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