February 1999
Figure 1. Block diagram.
PBL 3770A
High Performance
Stepper Motor Drive Circuit
PBL3770A
PBL
3770A
16-pin plastic batwing DIP
28-pin plastic PLCC package
20-pin SO
Description
PBL 3770A is a bipolar monolithic circuit intended to control and drive the current in
one winding of a stepper motor. It is a high power version of PBL 3717 and special
care has been taken to optimize the power handling capability without suffering in
reliability.
The circuit consists of a LS-TTL compatible logic input stage, a current sensor, a
monostable multivibrator and a high power H-bridge output stage. The circuit is
pin-compatible with the PBL 3717 industry-standard driver.
Two PBL 3770A and a small number of external components form a complete
control and drive unit for LS-TTL or microprocessor-controlled stepper motor
systems.
Key Features
• Half-step and full-step operation.
• Switched mode bipolar constant
current drive
• Wide range of current control
5 -1800 mA.
• Wide voltage range 10 - 45 V.
• Designed for unstabilized motor
supply voltage.
• Current levels can be selected in
steps or varied continuously.
• Thermal overload protection.
1
GND
V
CC
M
A
M
B
Phase
I
1
I
0
V
R
& &&&
–
+
–
+
–
+
Monostable
t = 0.69 • R • C
Current Sensor
Output Stage
off T T
Schmitt
Trigger Time
Delay
CTE
PBL 3770A
1≥1
≥1
≥1
V
MM
V
MM
≥1
PBL 3770A
PBL 3770A
2
Maximum Ratings
Parameter Pin no. [DIL package] Symbol Min Max Unit
Voltage
Logic supply 6 VCC 07V
Motor supply 3, 14 VMM 045V
Logic inputs 7,8,9 VI-0.3 6 V
Comparator input 10 VC-0.3 VCC V
Reference input 11 VR-0.3 15 V
Current
Motor output current 1, 15 IM-1800 +1800 mA
Logic inputs 7,8,9 II-10 mA
Analog inputs 10,11 IA-10 mA
Temperature
Operating junction temperature TJ-40 +150 °C
Storage temperature Ts-55 +150 °C
Recommended Operating Conditions
Parameter Symbol Min Typ Max Unit
Logic supply voltage VCC 4.75 5 5.25 V
Motor supply voltage VMM 10 40 V
Motor output current IM-1500 +1500 mA
Junction temperature TJ-20 +125 °C
Rise time logic inputs tr2µs
Fall time logic inputs tf2µs
Figure 2. Definition of symbols.
V
CC
I I
M OL
I
CC
I I I
I IH IL
I
A
820 pF 0.5
V
CC
V
V
V
I
IH
IL
V
V
A
R
V
C
I
I
C
A
V
E
V
V
M
MA
V
MM
RR C
820 pF
C
1 k
S
TT
C
R
C
56 k
M
A
M
B
C
V
I MM
GND
Phase
I
1
I
0
V
R
& &&&
–
+
–
+
–
+
Monostable
t = 0.69 • R • C
Current Sensor
Output Stage
off T T
Schmitt
Trigger Time
Delay
CTE
PBL 3770A
1≥1
≥1
≥1
10 2 16
1
15
14
6 [18]
8
7
9
11
4, 5,
12, 13
3
V
MM
V
MM
≥1
Pin no. refers
to DIL-package
PBL 3770A
3
Electrical Characteristics
Electrical characteristics over recommended operating conditions. CT = 820 pF, RT = 56 kohm.
Ref.
Parameter Symbol fig. Conditions Min Typ Max Unit
General
Supply current ICC 2V
MM = 20 to 40 V, I0 = I1 = HIGH. 30 40 mA
VMM = 20 to 40 V, I0 = I1 = LOW, 48 65 mA
fs = 23 kHz
Total power dissipation PDfs = 28 kHz, IM = 1000 mA, VMM = 36 V 1.9 2.3 W
Note 2, 4.
fs = 24 kHz, IM = 1000 mA, VMM = 12 V 1.7 2.1 W
Note 2, 4.
fs = 28 kHz, IM = 1300 mA, VMM = 36 V 2.7 3.2 W
Note 3, 4.
fs = 28 kHz, IM = 1500 mA, VMM = 36 V 3.5 W
Note 3, 4.
Turn-off delay td3T
a
= +25°C, dVC/dt ≥ 50 mV/µs. 2.5 µs
Thermal shutdown junction temperature 170 °C
Logic Inputs
Logic HIGH input voltage VIH 2 2.0 V
Logic LOW input voltage VIL 2 0.8 V
Logic HIGH input current IIH 2V
I
= 2.4 V 20 µA
Logic LOW input current IIL 2V
I
= 0.4 V -0.4 mA
Analog Inputs
Comparator threshold voltage VCH 2V
R
= 5.0 V, I0 = I1 = LOW 400 415 430 mV
Comparator threshold voltage VCM 2V
R
= 5.0 V, I0 = HIGH, I1 = LOW 240 250 265 mV
Comparator threshold voltage VCL 2V
R
= 5.0 V, I0 = LOW, I1 = HIGH 70 80 90 mV
Input current IC2 -20 µA
Motor Outputs
Lower transistor saturation voltage IM = 1000 mA 0.5 0.8 V
IM = 1300 mA 0.8 1.3 V
Lower diode forward voltage drop IM = 1000 mA 1.3 1.6 V
IM = 1300 mA 1.5 1.8 V
Upper transistor saturation voltage IM = 1000 mA 1.1 1.3 V
IM = 1300 mA 1.3 1.6 V
Output leakage current I0 = I1 = HIGH, Ta = +25°C 100 µA
Monostable
Cut off time toff 3V
MM = 10 V, ton ≥ 5 µs 273135µs
Thermal Characteristics Ref.
Parameter Symbol Fig. Conditions Min Typ Max Unit
Thermal resistance RthJ-C DIL package. 11 °C/W
RthJ-A 15 DIL package. Note 2. 40 °C/W
RthJ-C PLCC package. 9 °C/W
RthJ-A 15 PLCC package. Note 2. 35 °C/W
RthJ-C SO package. 11 °C/W
RthJ-A 15 SO package. 40 °C/W
Notes
1. All voltages are with respect to ground. Currents are positive into, negative out of specified terminal.
2. All ground pins soldered onto a 20 cm2 PCB copper area with free air convection. Ta = +25°C.
3. DIP package with external heatsink (Staver V7) and minimal copper area. Typical RthJ-A = 27.5°C/W. Ta = +25°C.
4. Not covered by final test program.
PBL 3770A
4
Figure 3. Pin configurations.
Pin Description
SO DIP PLCC Symbol Description
11 10 M
BMotor output B, Motor current flows from MA to MB when Phase is high.
2 2 11 T Clock oscillator. Timing pin connect a 56 kΩ resistor and a 820 pF in
parallel between T and Ground.
3 3,14 12,4 VMM Motor supply voltage, 10 to 40 V. Pin 3(12) and pin 14(4) should be wired together.
4-7, 4,5, 1-3,9, GND Ground and negative supply. Note these pins are used for heatsinking.
14-18 12,13 13-17,28 Make sure that all ground pins are soldered onto a suitable large copper
ground plane for efficient heat sinking.
86 18 V
CC Logic voltage supply normally +5 V.
97 19 I
1Logic input. It controls, together with the I0 input, the current level in the output stage.
The controlable levels are fixed to 100, 60, 20, 0%.
10 8 20 Phase Controls the direction of the motor current of MA and MB outputs.
Motor current flows from MA to MB when the phase input is high.
11 9 21 I0Logic input. It controls, together with the I1 input, the current level in the output stage.
The controlable levels are fixed to 100, 60, 20, 0%.
12 10 23 C Comparator input. This input senses the instaneous voltage across the sensing
resistor, filtered through a RC Network.
13 11 24 VRReference voltage. Controls the threshold voltage of the comparator and hence
the output current. Input resistance: typically 6.8 kΩ ± 20%.
19 15 6 MAMotor output A, Motor current flows from MA to MB when Phase is high.
20 16 8 E Common emitter. Connect the Sence resistor between this pin and ground.
1
2
3
4
5
6
7
8
9
10
18
17
16
15
14
13
12
11
I1
VR
M
B
VCC
T
VMM
GDN
E
Phase 0
C
19
20
GDN
GDN
GDN
GDN
GDN
GDN
GDN
VMM
M
A
PBL
3770A
I
B
T
MM
GND
GND
CC
1
Phase
E
M
GND
GND
V
C
I
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
A
V
MM
R
0
I
V
V
M
PBL
3770A
N/C
A
N/C
E
GND
B
T
N/C
V
C
N/C
I
Phase
I
V
GND
GND
GND
GND
N/C
N/C
MM
GND
GND
GND
GND
GND
CC
5
6
7
8
9
10
11
25
24
23
22
21
20
19
4
3
2
1
28
27
26
12
13
14
15
16
17
18
MM
R
0
1
V
V
M
M
PBL
3770A
PBL 3770A
5
Functional Description
The PBL 3770A is intended to drive a
bipolar constant current through one
winding of a 2-phase stepper motor.
Current control is achieved through
switched-mode regulation, see figure 5
and 6.
Three different current levels and zero
current can be selected by the input
logic.
The circuit contains the following
functional blocks:
• Input logic
• Current sense
• Single-pulse generator
• Output stage
Input logic
Phase input. The phase input
determines the direction of the current in
the motor winding. High input forces the
current from terminal MA to MB and low
input from terminal MB to MA. A Schmitt
trigger provides noise immunity and a
delay circuit eliminates the risk of cross
conduction in the output stage during a
phase shift.
Half- and full-step operation is
possible.
Current level selection. The status of I0
and I1 inputs determines the current level
in the motor winding. Three fixed current
levels can be selected according to the
table below.
Motor current I0I1
High level 100% L L
Medium level 60% H L
Low level 20% L H
Zero current 0% H H
The specific values of the different
current levels are determined by the
reference voltage VR together with the
value of the sensing resistor RS.
The peak motor current can be
calculated as follows:
im = (VR • 0.080) / RS [A], at 100% level
The motor current can also be
continuously varied by modulating the
voltage reference input.
Current sensor
The current sensor contains a reference
voltage divider and three comparators
for measuring each of the selectable
current levels. The motor current is
sensed as a voltage drop across the
current sensing resistor, RS, and
compared with one of the voltage
references from the divider. When the
two voltages are equal, the compara-tor
triggers the single-pulse generator. Only
one comparator at a time is activa-ted by
the input logic.
Single-pulse generator
The pulse generator is a monostable
multivibrator triggered on the positive
edge of the comparator output. The
multivibrator output is high during the
pulse time, toff , which is determined by
the timing components RT and CT.
toff = 0.69 • RT • CT
The single pulse switches off the
power feed to the motor winding,
causing the winding to decrease during
toff .
If a new trigger signal should occur
during toff , it is ignored.
Output stage
The output stage contains four
transistors and two diodes, connected in
an H-bridge. Note that the upper
recirculation diodes are connected to the
circuit externally. The two sinking
transistors are used to switch the power
supplied to the motor winding, thus
driving a constant current through the
winding. See figures 5 and 6.
Overload protection
The circuit is equipped with a thermal
shut-down function, which will limit the
junction temperature. The output current
will be reduced if the maximum permis-
sible junction temperature is exceeded.
It should be noted, however, that it is not
short circuit protected.
Operation
When a voltage VMM is applied across
the motor winding, the current rise
follows the equation:
im = (VMM / R) • (1 - e-(R • t ) / L )
R = Winding resistance
L = Winding inductance
t = time
(see figure 6, arrow 1)
The motor current appears across the
external sensing resistor, RS, as an
analog voltage. This voltage is fed
through a low-pass filter, RCCC, to the
voltage comparator input (pin 10). At the
moment the sensed voltage rises above
the comparator threshold voltage, the
monostable is triggered and its output
turns off the conducting sink transistor.
The polarity across the motor winding
reverses and the current is forced to
circulate through the appropriate upper
protection diode back through the source
transistor (see figure 6, arrow 2).
After the monostable has timed out,
the current has decayed and the analog
Figure 4. Definition of terms.
| V – V |
1/2
1
V
CH
t
on
t
off
f =
s
t
on
t
off
+
Normalized
V
E
MA MB
t
d
t
t
V
CM
V
CL
D = t
on
t
off
+
1t
on
PBL 3770A
6
voltage across the sensing resistor is
below the comparator threshold level.
The sinking transistor then turns on
and the motor current starts to increase
again, The cycle is repeated until the
current is turned off via the logic inputs.
When both I1 and I0 are high, all four
transistors in the output H-bridge are
turned off, which means that inductive
current recirculates through two opposite
free-wheeling diodes (see figure 6, arrow
3). this method of turning off the current
results in a faster current decay than if
only one transistor was turned off and
will therefore improve speed
performance in half-stepping mode.
Heatsinking
The junction temperature of the chip
highly effects the lifetime of the circuit. In
high-current applications, the
heatsinking must be carefully conside-
red.
The Rthj-a of the PBL 3770A can be
reduced by soldering the ground pins to
a suitable copper ground plane on the
printed circuit board (see figure 14) or by
applying an external heatsink type V7 or
V8, see figure 14.
The diagram in figure 13 shows the
maximum permissible power dissipation
versus the ambient temperature in °C,
for heatsinks of the type V7, V8, or a 20
cm2 copper area respectively. Any
external heatsink or printed circuit board
copper must be connected to electrical
ground.
For motor currents higher than approx
600 mA, some form of heatsinking is
recommended to assure optimal
reliability.
The diagrams in figures 12 and 13 can
be used to determine the required
heatsinking of the circuit. In some
systems, forced-air cooling may be
available to reduce the temperature rise
of the circuit.
Applications Information
Motor selection
Some stepper motors are not designed
for continuous operation at maximum
current. As the circuit drives a constant
current through the motor, its tempera-
ture can increase, both at low- and high-
speed operation.
Some stepper motors have such high
core losses that they are not suited for
switched-mode operation.
Figure 5. Motor current (I
M
),
Vertical : 200 mA/div,
Horizontal: 1 ms/div,
expanded part 100
µ
s/div.
Figure 6. Output stage with current paths
for fast and slow current decay.
Figure 7. Principal operating sequence.
0
200 mA/div 1 ms/div
100µs/div
Fast Current Decay
Slow Current Decay
Motor Current
Time
1 2 3
3
21
External recirculation
diodes
R
S
I
0A
I
1A
Ph
A
Ph
B
I
0B
I
1B
I
MA
I
MB
100%
–100%
60%
–60%
20%
–20%
100%
–100%
60%
–60%
Half step mode at 100 % Full step mode at 60 %
Stand by mode
at 20 %
Full step position
Half step position
PBL 3770A
7
Figure 8. Typical stepper motor driver application with PBL 3770A.
Figure 9. Typical source saturation vs.
output current.
In order to minimize electromagnetic
interference, it is recommended to route
MA and MB leads in parallel on the
printed circuit board directly to the
terminal connector. The motor wires
should be twisted in pairs, each phase
separately, when installing the motor
system.
Unused inputs
Unused inputs should be connected to
proper voltage levels in order to obtain
the highest possible noise immunity.
Ramping
A stepper motor is a synchronous motor
and does not change its speed due to
load variations. This means that the
torque of the motor must be large
enough to match the combined inertia of
the motor and load for all operation
modes. At speed changes, the requires
torque increases by the square, and the
required power by the cube of the speed
change. Ramping, i.e., controlled
acceleration or deceleration must then
be considered to avoid motor pull-out.
VCC , VMM
The supply voltages, VCC and VMM, can
be turned on or off in any order. Normal
dv/dt values are assumed.
Before a driver circuit board is
removed from its system, all supply
voltages must be turned off to avoid
destructive transients being generated
by the motor.
Switching frequency
The motor inductance, together with the
pulse time, toff, determines the switching
frequency of the current regulator. The
choice of motor may then require other
values on the RT, CT components than
those recommended in figure 6, to
obtain a switching frequency above the
audible range. Switching frequencies
above 40 kHz are not recommended
because the current regulation can be
affected.
Analog control
As the current levels can be continu-
ously controlled by modulating the VR
input, limited microstepping can be
achieved.
VSat (V)
1.8
1.6
1.4
1.2
1.0
.8
.6
.4
.2
00 .40 .80 1.2
IM (A)
Tj = 125°C
j
T = 25°C
1.6
V
Sat
(V)
1.8
1.6
1.4
1.2
1.0
.8
.6
.4
.2
00 .40 .80 1.2
I
M
(A)
T
j
= 125°C
j
T = 25°C
1.6
Figure 10. Typical sink saturation vs.
output current.
V
F
(V)
1.8
1.6
1.4
1.2
1.0
.8
.6
.4
.2
00 .40 .80 1.2
I
M
(A)
T
j
= 25°C
j
T = 125°C
1.6
Figure 11. Typical lower diode voltage
drop vs. recirculating current.
Interference
As the circuit operates with switched-
mode current regulation, interference-
generation problems can arise in some
applications. A good measure is then to
decouple the circuit with a 0.1 µF
ceramic capacitor, located near the
package across the power line VMM and
ground.
Also make sure that the VRef input is
sufficiently decoupled. An electrolytic
capacitor should be used in the +5 V rail,
close to the circuit.
The ground leads between RS, CC and
circuit GND should be kept as short as
possible. This applies also to the leads
connecting RS and RC to pin 16 and pin
10 respectively.
Phas
e
I1
I0
TCE
M
A
M
B
V
M
M
V
C
C
V
R
GN
D
Phase
BI1
B
I0
B
PBL 3770A
1
16 3,
14
8
7
9
21
01
6
4, 5
12, 13
1
1
5
Phase
AI1
A
I0
A
1
1
5
Diodes are
UF 4001 or
BYV27
t
r
r
100
ns
Phas
e
I
1
I
0
TCE
V
M
M
V
C
C
V
R
GN
D
M
A
M
B
PBL 3770A
1
16 3,
14
8
7
9
21
01
6
4, 5
12, 13
STEPPER
MOTOR
820
pF
820
pF
1
k
56
k
0.5
820
pF
820
pF
1
k
56
k
0.5
V (+5
V)
C
C
V (+5
V)
C
C
V
M
M
V
M
M
PBL 3770A
8
Sensor resistor
The RS resistor should be of a non-
inductive type power resistor. A 0.5 ohm
resistor, tolerance ≤ 1%, is a good
choice for 800 mA max motor current at
VR = 5V.
The peak motor current, im , can be
calculated by using the formula:
im = (VR • 0.080) / RS [A], at 100% level
External recirculation diodes
Recirculation diodes must be connected
across each motor terminal and the
supply voltage, VMM. The anodes shall be
connected to the motor terminals and
the cathodes to the VMM voltage. Ultra-
fast recovery diodes should be used for
maximum performance and reliability.
Ordering Information
Package Part No.
DIP Tube PBL 3770ANS
PLCC Tube PBL 3770AQNS
PLCC Tape & Reel PBL 3770AQNT
SO Tube PBL 3770ASOS
SO Tape & Reel PBL 3770ASOT
Information given in this data sheet is believed to be
accurate and reliable. However no responsibility is
assumed for the consequences of its use nor for any
infringement of patents or other rights of third parties
which may result from its use. No license is granted
by implication or otherwise under any patent or
patent rights of Ericsson Components AB. These
products are sold only according to Ericsson
Components' general conditions of sale, unless
otherwise confirmed in writing.
Specifications subject to change
without notice.
1522-PBL 3770/6Uen. Rev E
© Ericsson Components AB 1999
Figure 15. Copper foil used as a heatsink.
Figure 14. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK.
Figure 12. Typical power dissipation vs.
motor current.
P
D
(W)
2.0
1.5
1.0
.5
00 .50 1.0 1.5
I
M
(A)
2.5
V
MM
= 36 V
V
MM
= 12 V
3.0
Figure 13. Allowable power dissipation
vs. ambient temperature.
50 150
T
Amb
(°C)
0
2.0
4.0
3.0
1.0
P
D
(W)
100
With Staver V7 (27.5°C/W)
With Staver V8 (37.5°C/W)
PCB heatsink (40°C/W)
Ericsson Components AB
SE-164 81 Kista-Stockholm, Sweden
Telephone: +46 8 757 50 00
38.0 mm
18,5 mm
11,6 mm
38.0 mm
33,5 mm
38,5 mm
Thermal resistance [°C/W]
PCB copper foil area [cm ]
2
90
80
70
60
50
40
30 5101520 30 3525
PLCC package
DIP package
16-pin
DIP
20-pin
SO
28-pin
PLCC
