February 1999
Description
The PBL 3771/1 is a switch-mode, constant-current driver IC (chopper) with two
channels, one for each winding of a two-phase stepper motor. The circuit is especially
developed for use in microstepping applications in conjunction with the matching dual
DAC (Digital-to-Analog Converter) PBM 3960. A complete driver system consists of
these two ICs, a few passive components and a microprocessor for generation of the
proper control and data codes required for microstepping.
The PBL 3771/1 contains a clock oscillator, which is common for both driver
channels; a set of comparators and flip-flops implementing the switching control; and
two H-bridges with internal recirculation diodes. Voltage supply requirements are +5 V
for logic and +10 to +45 V for the motor. Maximum output current is 650 mA per
channel.
A special logic function is used to select slow or fast current decay in the output
stage for improved high-speed microstepping.
The close match between the two driver channels guarantees consistent output
current ratios and motor positioning accuracy.
PBL 3771/1
Precision Stepper Motor Driver
Figure 1. Block diagram.
28-pin PLCC package
22-pin plastic DIP package
24-pin SO package
Key Features
• Dual chopper driver in a single
package.
• 650 mA output current per channel.
• Close matching between channels for
high microstepping accuracy.
• Selectable slow/fast current decay for
improved high-speed microstepping.
• Improved low-level linearity.
• Specially matched to Dual DAC
PBM 3960.
• Selection of packages, 22-pin
“batwing” DIP, 24 pin "batwing" SOIC
or 28-lead PLCC with lead-frame for
heat-sinking through PC board
copper.
RC
PBL 3771/1
V
MM1
V
MM2
M
A1
M
B1
M
B2
M
A2
GNDC
2
V
R2
CD
2
Phase
2
V
CC
C
1
V
R1
CD
1
Phase
1
E
1
E
2
V
CC
S
RQ
+
–
+
–
Logic
S
RQ
+
–
+
–
Logic
+
–
1
PBL 3771/1
PBL 3771/1
PBL
3771/1
PBL 3771/1
2
Maximum Ratings
Parameter Pin no. (DIL) Symbol Min Max Unit
Voltage
Logic supply 11 VCC 07V
Motor supply 3, 20 VMM 045V
Logic inputs 7, 8, 15, 16 VI-0.3 6 V
Comparator inputs 10, 13 VC-0.3 VCC V
Reference inputs 9, 14 VR-0.3 7.5 V
Current
Motor output current 1, 4, 19, 22 IM-700 +700 mA
Logic inputs 7, 8, 15, 16 II-10 mA
Analog inputs 10, 13 IA-10 mA
Oscillator charging current 12 IRC 5mA
Temperature
Operating junction temperature TJ-40 +150 °C
Storage temperature** TS-55 +150 °C
** Circuit only. The packaging can handle max 60°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-650 650 mA
Junction temperature **** TJ-20 +125 °C
Rise time logic inputs tr2µs
Fall time logic inputs tf2µs
Oscillator timing resistor RT2 15 20 kohms
*** In microstepping mode, “sine/cosine” drive where I1 = 650 • cos(θ) and I2 = 650 • sin(θ) mA, otherwise 500 mA/channel both
channels fully on.
****See operating temperature chapter.
Figure 2. Definitions of symbols. Figure 3. Definition of terms.
50 %
V
CH
t
on
t
off
V
E
| V – V |
MA MB
t
d
t
t
f =
ston toff
+
D = t
t
on off
+
1t
on
I I
M OL
ICC
I I I
I IH IL
IA
3 300 pF
VCC
I
I
C
A
VEV
V
VMM
C
820 pF
1 kW
RS
RT
T
CC
RC
15 kW I MM
IRC RC
PBL 3771/1
20
12
11
VMM1
VMM2
MA1
MB1
MB2
MA2
GNDC2
VR2
CD2
Phase2
VCC
C1
VR1
CD1
Phase1E1
E2
VCC
22
19
16 13
S
RQ
15 14 5, 6, 17, 18
+
–
+
–
Logic
21
S
RQ
+
–
+
–
Logic
+
–
3
1
4
2
10
98
7
V
V
V
I
IH
IL V
V
A
R
V
V
CH
C
M
MA
Pin numbers refer to
DIL-package
PBL 3771/1
3
Electrical Characteristics
Electrical characteristics over recommended operating conditions, unless otherwise noted. -20°C - TJ - +125°C.
Ref.
Parameter Symbol fig. Conditions Min Typ Max Unit
General
Supply current ICC 38 50 mA
Total power dissipation PDVMM = 40 V, IM1= 450 mA, IM2= 0 mA. 1.4 1.6 W
Notes 2, 3.
VMM = 40 V, IM1 = IM2 = 318 mA. 1.6 1.8 W
Notes 2, 3.
Turn-off delay td3T
a = +25°C, dVC/dt ≥ 50 mV/µs. 1.0 1.5 µs
Note 3.
Logic Inputs
Logic HIGH input voltage VIH 2.0 V
Logic LOW input voltage VIL 0.8 V
Logic HIGH input current IIH VI = 2.4 V 20 µA
Logic LOW input current IIL VI = 0.4 V -0.4 mA
Reference Inputs
Input resistance RRTa = +25°C 5 kohms
Input current IRTa = +25°C, VR = 2.5 V. 0.5 1.0 mA
Turn-off voltage VTO 20 29 38 mV
Comparator Inputs
Threshold voltage VCH RC = 1 kohms, VR = 2.5 V 430 450 470 mV
| VCH1 - VCH2 | mismatch VCH,diff RC = 1 kohms 1 mV
Input current IC-10 1 µA
Motor Outputs
Lower transistor saturation voltage IM = 500 mA 1.00 1.20 V
Lower transistor leakage current VMM = 41 V, VE = VR = 0 V, VC = VCC 300 µA
Lower diode forward voltage drop IM = 500 mA 1.10 1.25 V
Upper transistor saturation voltage IM = 500 mA 1.20 1.35 V
Upper transistor leakage current VMM = 41 V, VE = VR = 0 V, VC = VCC 300 µA
Upper diode forward voltage drop IM = 500 mA 1.00 1.25 V
Chopper Oscillator
Chopping frequency fs3C
T
= 3300 pF, RT = 15 kohms 25.0 26.5 28.0 kHz
Thermal Characteristics
Ref.
Parameter Symbol fig. Conditions Min Typ Max Unit
Thermal resistance RthJ-BW 13 DIL package. 11 °C/W
RthJ-A 13 DIL package. Note 2. 40 °C/W
RthJ-BW 13 PLCC package. 9 °C/W
RthJ-A 13 PLCC package. Note 2. 35 °C/W
RthJ-BW 13 SO package. 13 °C/W
RthJ-A 13 SO package. Note 2. 42 °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.
3. Not covered by final test program.
4. Switching duty cycle D = 30%, fS = 26.5 kHz.
PBL 3771/1
4
C
MM2
E
B2
B1
GND
MM1
C
RC
V
M
GND
GND
GND
GND
Phase
CD
A1
GND
GND
GND
GND
GND
1
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
V
R2
V
R1
CD
1
CC
2
2
A2
V
M
M
V
M
Phase
2
1
2
E
1
PBL 3771/1QN
1
2
3
4
5
6
7
8
9
10
11
22
21
20
19
18
17
16
15
14
13
12
B1
E
MM1
A1
GND
GND
1
1
R1
C
CC
M
V
M
GND
GND
Phase
CD
V
RC
M
V
M
Phase
CD
V
V
R2
2
2
A2
MM2
B2
1
E
2
1
C
2
PBL
3771/1N
Figure 4. Pin configuration.
Pin Description
Refer to figure 4.
SO DIP PLCC Symbol Description
21 8 M
B1 Motor output B, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH.
32 10 E
1Common emitter, channel 1. This pin connects to a sensing resistor to ground.
43 11 V
MM1 Motor supply voltage, channel 1, 10 to 40 V. VMM1 and VMM2 should be connected together.
54 12 M
A1 Motor output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH.
6,7, 5,6, 1-3,9, GND Ground and negative supply. Note: these pins are used thermally for heat-sinking.
18,19 17,18 13-17,28 Make sure that all ground pins are soldered onto a suitably large copper ground
plane for efficient heat sinking.
8 7 18 Phase1Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1
to MB1 when Phase1 is HIGH.
98 19 CD
1Current decay control, channel 1. A logic HIGH on this input results in
slow
current decay,
a LOW results in
fast
current decay, see “Functional Description.”
10 9 20 VR1 Reference voltage, channel 1. Controls the threshold voltage for the comparator and hence
the output current. Input resistance is typically 2.5 kohms, ±20%.
11 10 21 C1Comparator input channel 1. This input senses the instantaneous voltage across the
sensing resistor, filtered by an RC network. The threshold voltage for the comparator is
(0.450 / 2.5) • VR1, i.e. 450 mV at VR1 = 2.5 V.
12 11 22 VCC Logic voltage supply, nominally +5 V.
13 12 23 RC Clock oscillator RC pin. Connect a 15 kohm resistor to VCC and a 3300 pF capacitor to
ground to obtain the nominal switching frequency of 26.5 kHz.
14 13 24 C2Comparator input channel 2. This input senses the instantaneous voltage across the
sensing resistor, filtered by an RC network. The threshold voltage for the comparator is
(0.450 / 2.5) • VR1, i.e. 450 mV at VR1 = 2.5 V.
15 14 25 VR2 Reference voltage, channel 2. Controls the threshold voltage for the comparator and hence
the output current. Input resistance is typically 2.5 kohms, ±20%.
16 15 26 CD2Current decay control, channel 2. A logic HIGH on this input results in
slow
current decay,
a LOW results in
fast
current decay, see “Functional Description.”
17 16 27 Phase2Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2
to MB2 when Phase2 is HIGH.
20 19 4 MA2 Motor output A, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
21 20 5 VMM2 Motor supply voltage, channel 2, 10 to 40 V. VMM1 and VMM2 should be connected together.
22 21 6 E2Common emitter, channel 2. This pin connects to a sensing resistor to ground.
23 22 7 MB2 Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
1
2
3
4
5
6
8
9
10
11
22
21
20
19
18
17
16
15
14
1312
GND
MA
1
CD
1
MA
2
GND
NC
Phase
1
PBL
3771/1 SO
MB
1
E
1
VMM
1
NC
MB
2
E
2
VMM
2
VR
1
VR
2
C
2
C
1
CD
2
V
cc
RC
23
24
GND
GND
Phase
2
7
PBL 3771/1
5
FAST Current Decay
SLOW Current Decay
Motor Current
Time
132
Figure 5. Output stage with current paths
during turn -on, turn-off and phase shift. Figure 6. Typical stepper motor application with PBL 3771/1.
Functional Description
Each channel of the PBL 3771/1
consists of the following sections: an
H-bridge output stage, capable of driving
up to 650 mA continuous motor current
(or 500 mA, both channels driven), a
logic section that controls the output
transistors, an S-R flip-flop, and two
comparators. The oscillator is common
to both channels.
Constant current control is achieved
by switching the current to the windings.
This is done by sensing the (peak)
voltage across a current-sensing
resistor, RS, effectively connected in
series with the motor winding, and
feeding that voltage back to a
comparator. When the motor current
reaches a threshold level, determined by
the voltage at the reference input, VR,
the comparator resets the flip-flop, which
turns off the output transistors. The
current decreases until the clock
oscillator triggers the flip-flop, which
turns on the output transistors again,
and the cycle is repeated.
The current-decay rate during the
turn-off portion of the switching cycle,
can be selected fast or slow by the CD
input.
In slow current-decay mode, only one
of the lower transistors in the H-bridge
(those closest to the negative supply) is
switched on and off, while one of the
upper transistors is held constantly on.
During turn-off, the current recirculates
through the upper transistor (which one
depends on current direction) and the
corresponding free-wheeling diode
connected to VMM, see figure 5.
In fast current decay mode, both the
upper and lower transistors are
switched. During the off-time, the
freewheeling current is opposed by the
supply voltage, causing a rapid dis-
charge of energy in the winding.
Fast current decay may be required in
half- and microstepping applications
when rapid changes of motor current are
necessary. Slow current decay,
however, gives less current ripple, and
should always be selected, if possible, to
mini-mize core losses and switching
noise.
Applications Information
Current control
The output current to the motor winding
is mainly determined by the voltage at
the reference input and the value of the
sensing resistor, RS.
Chopping frequency, winding
inductance, and supply voltage will affect
the current level, but to much less
extent. Fast current decay setting will
produce somewhat lower (average)
current than slow current decay. The
peak current through the sensing
resistor (and motor winding) can be
expressed as:
IM,peak = 0.18 • (VR / RS) [A]
i.e., with a recommended value of 1 ohm
for the sensing resistor, RS, a 2.5 V
reference voltage will produce an output
current of approximately 450 mA. To
improve noise immunity on the VR input,
the control range may be increased to
5 volts if RS is correspondingly changed
to 2 ohms.
3
21
R
s
7
8
9
16
15
14
Phase
CD
V
Phase
CD
V
1
1
2
2
R1
R2 ECECGND
RC
PBL 3771/1
15 kW
3 300 pF
1.0 W 1.0 W
M
M
M
M
A1
B1
A2
B2
VCC VV
MM1 MM2
+5 V
4
1
19
22
11 3 20
12 5, 6,
17, 18 213 21
10
11
22
R
S
STEPPER
MOTOR
V
MM
Pin numbers refer
to DIL package.
GND (V )
1 kW 1 kW
820 pF 820 pF
RS
0.1 mF 0.1 mF
+
10 mF
V (+5 V)
CC
GND
(V )
CC MM
PBL 3771/1
6
External components
The voltage across the sensing resistor
is fed back to the comparator via a low-
pass filter section, to prevent erroneous
switching due to switching transients.
The recommended filter component
values, 1 kohm and 820 pF, are suitable
for a wide range of motors and
operational conditions.
Since the low-pass filtering action
introduces a small delay of the signal to
the comparator, peak voltage across the
sensing resistor, and hence the peak
motor current, will reach a slightly higher
level than the threshold, VC, set by the
reference voltage
(VC = 450 mV @VR = 2.5 V).
The time constant of the low-pass filter
may therefore be reduced to minimize
the delay and optimize low-current
performance, especially if a low (12 V)
supply voltage is used. Increasing the
time constant may result in unstable
switching.
The frequency of the clock oscillator is
set by the R-C combination at pin RC.
The recommended values give a
nominal frequency of 26.5 kHz. A lower
occur if the chopping duty cycle exceeds
approximately 50%. To avoid this, it is
necessary to choose a motor with a low
winding resistance. Low winding
resistance means less inductance and
will therefore enable higher stepping
rates, however it also means less torque
capability. A compromise has to be
made.
Choose a motor with the lowest
possible winding resistance that still
gives the required torque and use as
high supply voltage as possible without
exceeding the maximum recommended
40 V. Check that the chopping duty cycle
does not exceed 50% at maximum
current.
Since the PBL 3771/1 produces a
regulated, constant output current it is
not necessary to use a motor that is
rated at the same voltage as the actual
supply voltage. Only rated current needs
to be considered. Typical motors to be
used together with the PBL 3771/1 have
voltage ratings of 5 to 12 V, while the
supply voltage usually ranges from 24 to
40 V.
Figure 7. Microstepping system with PBM 3960 /1 and PBL 3771/1.
D0
D7
A0
A1
WR
CS
RESET
VV
PBM 3960/1
21
2
19
4
20
3
18
5
1
15
6
22
16
17
7
14
To
µP
+2.5V
Sign
CD
DA
1
1
1
Sign
CD
DA
2
2
2
SS
VDD
Ref
7
8
9
16
15
14
Phase
CD
V
Phase
CD
V
1
1
2
2
R1
R2 ECECGND
RC
PBL 3771/1
15 kΩ
3 300 pF
1.0 Ω1.0 Ω
M
M
M
M
A1
B1
A2
B2
VCC VV
MM1 MM2
+5 V
4
1
19
22
11 3 20
12 5, 6,
17, 18 213 21
10
11
22
R
S
STEPPER
MOTOR
V
MM
Pin numbers refer
to DIL package.
GND (V )
1 kΩ1 kΩ
820 pF 820 pF
RS
0.1 µF 0.1 µF
+
10 µF
V (+5 V)
CC
GND
(V )
CC MM
frequency will result in higher current
ripple and may cause audible noise from
the motor, while increasing the
frequency results in higher switching
losses and possibly increased iron
losses in the motor.
The sensing resistor, RS, should be
selected for maximum motor current.
The relationship between peak motor
current, reference voltage and the value
of RS is described under “Current
control” above. Be sure not to exceed
the maximum output current which is
650 mA per channel (or 500 mA per
channel, both channels fully on, see
“Recommended Operating Conditions”).
Motor selection
The PBL 3771/1 is designed for bipolar
motors, i.e., motors that have only one
winding per phase. A unipolar motor,
having windings with a center tap, can
also be used, see figure 14.
The chopping principle in the
PBL 3771/1 is based on a constant
frequency and a varying duty cycle. This
scheme imposes certain restrictions on
motor selection. Unstable chopping can
PBL 3771/1
7
P
D
(W)
0 .10 .20 .30 .40 .50 .60
I
M
(A)
0
1.0
2.0
3.0
V
MM
= 14V
V
MM
= 36V
General
Phase inputs. A logic HIGH on a Phase
input gives positive current flowing out
from MA into MB. A logic LOW gives a
current in the opposite direction.
Slow/fast current decay. A logic HIGH
on the CD input gives slow current
decay, a logic LOW gives fast current
decay.
Heat sinking. Soldering the four center
pins onto a free PCB copper area of 20
cm2 (approx. 1.8" x 1.8", copper foil
thickness = 35 µm) permits the circuit to
operate with a maximum of 320 mA
output current, both channels driving, at
ambient temperatures up to +70°C.
Consult figures 12 and 13 in order to
determine the necessary copper area for
heat sinking if higher currents are
required.
Thermal shutdown. The circuit is
equipped with a thermal shutdown
function that reduces the output current
at chip temperatures above +160°C.
Operating temperature. The max re-
commended operating temperature is
125°C. This gives an estimated lifelength
of about 5 years at continous drive, A
change of ±10° would increase/decrease
the lifelength of the circuit with about 5
years.
Vd (V)
0 .10 .20 .30 .40 .50 .60
IM (A)
0
.2
.4
.6
.8
1.0 Tj = 25°C
Tj = 125°C
Tj = 25°C
Tj = 125°C
VCE Sat (V)
0 .10 .20 .30 .40 .50 .60
IM (A)
.2
.4
.6
.8
1.0
1.2
Figure 9. Typical source saturation
voltage vs. output current.
Figure 8. Typical upper diode voltage
drop vs. recirculating current.
Figure 10. Typical lower diode voltage
drop vs. recirculating current. Figure 11 Typical sink saturation voltage
vs. output current.
V
d
(V)
0 .10 .20 .30 .40 .50 .60
I
M
(A)
0
.2
.4
.6
.8
1.0
T
j
= 25°C
T
j
= 125°C
.2
.4
.6
.8
1.0
V
CE Sat
(V)
0 .10 .20 .30 .40 .50 .60
I
M
(A)
T
j
= 25°C
T
j
= 125°C
Figure 12. Power dissipation vs. motor current, both channels driven, T
a = 25°C.
Max allow power dis
PBL 3771/1
8
Ericsson Components AB
SE-164 81 Kista-Stockholm, Sweden
Telephone: +46 8 757 50 00
Figure 14. Connection of unipolar motors.
Specifications subject to change without
notice.
1522-PBL 3771/1 Uen. Rev B
© Ericsson Components AB 1999
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. These products are
sold only according to Ericsson Components' general
conditions of sale, unless otherwise confirmed in
writing.
Thermal resistance [°C/W]
PCB copper foil area [cm ]
2
80
70
60
50
40
30
20 5101520 30 3525
PLCC package
DIP package
Best for high speed
PBL 3771/1
Best for high torque
PBL 3771/1
Figure 13. Thermal Resistance vs. PC Board copper area and suggested layout.
Ordering Information
Package Part No.
DIP Tube PBL 3771/1NS
PLCC Tube PBL 3771/1QNS
PLCC Tape & Reel PBL 3771/1QNT
SO tube PBL 3771/1SOS
SO Tape & Reel PBL 3771/1SOT
24-pin SO
22-pin
DIP
28-pin
PLCC
