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February 1999
PBL 3771/1 Precision Stepper Motor Driver
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.
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.
V CC
V
- +
CC
R S
Q M A1
+ -
Logic
M B1
P
PBL 3771/1
V MM1
+ -
V MM2 M B2
- +
+ -
Phase 2
CD2 V R2
C2
GND
E2
28-pin PLCC package 22-pin plastic DIP package 24-pin SO package
Figure 1. Block diagram.
1
PB
L
S R
Q
37
RC
71
/1
Logic
M A2
B L
L B1 P 71/ 37
37
Phase 1
CD 1 V R1
C1
E1
71
/1
PBL 3771/1
Maximum Ratings
Parameter Pin no. (DIL) Symbol Min Max Unit
Voltage Logic supply Motor supply Logic inputs Comparator inputs Reference inputs Current Motor output current Logic inputs Analog inputs Oscillator charging current Temperature Operating junction temperature Storage temperature** ** Circuit only. The packaging can handle max 60C
11 3, 20 7, 8, 15, 16 10, 13 9, 14 1, 4, 19, 22 7, 8, 15, 16 10, 13 12
VCC VMM VI VC VR IM II IA IRC TJ TS
0 0 -0.3 -0.3 -0.3 -700 -10 -10
7 45 6 VCC 7.5 +700
V V V V V mA mA mA mA C C
5 -40 -55 +150 +150
Recommended Operating Conditions
Parameter Symbol Min Typ Max Unit
Logic supply voltage Motor supply voltage Motor output current *** Junction temperature **** Rise time logic inputs Fall time logic inputs Oscillator timing resistor
VCC VMM IM TJ tr tf RT
4.75 10 -650 -20
5
2
15
5.25 40 650 +125 2 2 20
V V mA C s s kohms
*** In microstepping mode, "sine/cosine" drive where I1 = 650 * cos() and I2 = 650 * sin() mA, otherwise 500 mA/channel both channels fully on. ****See operating temperature chapter.
Phase 1 7
CD 1 V R1 8 9
C1 10
E1 2
Pin numbers refer to DIL-package
PBL 3771/1
I CC VCC V 11
- + CC
| V MA - V MB |
R S Q 4
+ -
M A1 M B1 V MM1 V MM2 M B2 M A2
IM I OL I MM
Logic
1
t on 50 %
t off
3
15 kW +
RT
-
20
- +
22 Logic S R Q 19
t VE V
CH
I RC
RC
12
+ -
td
3 300 pF
VCC CT Phase 2 II I IH I IL IA VI VIH VIL VA VR VCH VC
820 pF
16
15
14
13 C2 IC IA
5, 6, 17, 18 GND
21 E2
CD2 V R2
1 kW
RC
VE
VM VMA
V MM
t
CC
RS
fs = t + t on off
1
ton D= ton + t off
Figure 2. Definitions of symbols.
2
Figure 3. Definition of terms.
PBL 3771/1
Electrical Characteristics
Electrical characteristics over recommended operating conditions, unless otherwise noted. -20C - TJ - +125C.
Parameter Ref. Symbol fig. Conditions Min Typ Max Unit
General Supply current Total power dissipation
ICC PD
Turn-off delay Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current Reference Inputs Input resistance Input current Turn-off voltage Comparator Inputs Threshold voltage | VCH1 - VCH2 | mismatch Input current
td
3
VMM = 40 V, IM1= 450 mA, IM2= 0 mA. Notes 2, 3. VMM = 40 V, IM1 = IM2 = 318 mA. Notes 2, 3. Ta = +25C, dVC/dt 50 mV/s. Note 3. 2.0 VI = 2.4 V VI = 0.4 V Ta = +25C Ta = +25C, VR = 2.5 V. 20 RC = 1 kohms, VR = 2.5 V RC = 1 kohms 430 -10 IM = 500 mA VMM = 41 V, VE = VR = 0 V, VC = VCC IM = 500 mA IM = 500 mA VMM = 41 V, VE = VR = 0 V, VC = VCC IM = 500 mA
38 1.4 1.6 1.0
50 1.6 1.8 1.5
mA W W s
VIH VIL IIH IIL RR IR VTO VCH VCH,diff IC
0.8 20 -0.4 5 0.5 29 450 1
V V A mA kohms mA mV mV mV A V A V V A V kHz
1.0 38 470 1
Motor Outputs Lower transistor saturation voltage Lower transistor leakage current Lower diode forward voltage drop Upper transistor saturation voltage Upper transistor leakage current Upper diode forward voltage drop Chopper Oscillator Chopping frequency fs 3
1.00 1.10 1.20 1.00 25.0 26.5
1.20 300 1.25 1.35 300 1.25 28.0
CT = 3300 pF, RT = 15 kohms
Thermal Characteristics
Parameter Ref. Symbol fig. Conditions Min Typ Max Unit
Thermal resistance
RthJ-BW RthJ-A RthJ-BW RthJ-A RthJ-BW RthJ-A
13 13 13 13 13 13
DIL package. DIL package. Note 2. PLCC package. PLCC package. Note 2. SO package. SO package. Note 2.
11 40 9 35 13 42
C/W C/W C/W C/W C/W C/W
Notes 1. All voltages are with respect to ground. Currents are positive into, negative out of specified terminal. 2. 3. 4. All ground pins soldered onto a 20 cm2 PCB copper area with free air convection. Not covered by final test program. Switching duty cycle D = 30%, fS = 26.5 kHz. 3
PBL 3771/1
MB1 1
NC 1 MB1 2 E1 3 VMM1 4 MA1 5 GND 6 GND 7 Phase1 8 CD1 9 VR1 10 C1 11 Vcc 12
24 NC 23 MB2 22 E2 21 VMM2
22 21 20 19 18
MB2
3 GND 2 GND 1 GND 28 GND 26 CD 2 4 MA2
E1 2 V MM1 3 MA1 4 GND 5 GND 6 Phase 1 7 CD1 8 VR1 9 C 1 10 VCC 11
E2 V MM2 MA2 GND GND Phase 2 CD2 VR2
V MM2 5 E2 6 M B2 7 M B1 8 GND 9 E1 10 VMM1 11
27 Phase 2
25 V R2 24 C 2 23 RC
PBL 3771/1 SO
20 MA2 19 GND 18
GND
PBL 3771/1N
17 16 15 14 13 12
PBL 3771/1QN
22 VCC 21 C 1 20 V R1 19 CD1
17 Phase2 16 CD2 15 VR2 14 C2 13 RC
MA1 12
GND 13
GND 14
GND 15
GND 16
GND 17
C2 RC
Figure 4. Pin configuration.
Pin Description
Refer to figure 4.
SO DIP PLCC Symbol Description
2 3 4 5 6,7, 18,19 8 9 10 11
1 2 3 4 5,6, 17,18 7 8 9 10
8 10 11 12 1-3,9, 13-17,28 18 19 20 21
MB1 E1 VMM1 MA1 GND
Phase1 CD1 VR1 C1
12 13 14
11 12 13
22 23 24
VCC RC C2
Motor output B, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Common emitter, channel 1. This pin connects to a sensing resistor to ground. Motor supply voltage, channel 1, 10 to 40 V. VMM1 and VMM2 should be connected together. Motor output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Ground and negative supply. Note: these pins are used thermally for heat-sinking. Make sure that all ground pins are soldered onto a suitably large copper ground plane for efficient heat sinking. Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Current 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." Reference voltage, channel 1. Controls the threshold voltage for the comparator and hence the output current. Input resistance is typically 2.5 kohms, 20%. Comparator 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. Logic voltage supply, nominally +5 V. 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. Comparator 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. Reference voltage, channel 2. Controls the threshold voltage for the comparator and hence the output current. Input resistance is typically 2.5 kohms, 20%. Current 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." Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. Motor output A, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. Motor supply voltage, channel 2, 10 to 40 V. VMM1 and VMM2 should be connected together. Common emitter, channel 2. This pin connects to a sensing resistor to ground. Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
15 16 17 20 21 22 23
14 15 16 19 20 21 22
25 26 27 4 5 6 7
VR2 CD2 Phase2 MA2 VMM2 E2 MB2
4
Phase1 18
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 discharge 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.
21
V CC (+5 V)
+ 0.1 m F 0.1 m F
V MM
10 m F
11 V 7 8 9
3
CC
3 V
MM1
20 V
MM2
Phase 1 CD1 V R1 Phase 2 CD 2 V R2 RC GND 12 5, 6, 17, 18
MA1
4
MB1
1 19
PBL 3771/1
MA2
16 15
Rs
14
MB2 C1 10
1 kW
22
E1 2
C2 13
1 kW
E2 21
STEPPER MOTOR
Motor Current
+5 V 15 kW
3 300 pF
820 pF 1.0 W RS
820 pF 1.0 W RS
Pin numbers refer to DIL package.
GND (V MM )
1
2
3
GND (V CC )
Time
FAST Current Decay SLOW Current Decay
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.
5
PBL 3771/1
External components The voltage across the sensing resistor is fed back to the comparator via a lowpass 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 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 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.
V CC (+5 V)
+ 0.1 F 0.1 F
V MM
10 F
5 14 D0 V DD Sign1 CD1 7 To P 15 16 6 17 22 1 D7 V 3 4 2 7 8 9 Phase 1 CD1 V R1 Phase 2 CD 2 V R2 RC GND 12 +5 V 15 k
3 300 pF
11
CC
3 V
MM1
20 V
MM2
MA1
4
PBM 3960/1
A0 A1 WR CS RESET V Ref
DA1 Sign2 CD2
MB1
1 19
PBL 3771/1
MA2
20 19 21
16 15 14
+2.5V
V SS 18
DA2
MB2 C1 10
1 k
22
E1 2
C2 13
1 k
E2 21
5, 6, 17, 18
STEPPER MOTOR
820 pF 1.0 RS
820 pF 1.0 RS
Pin numbers refer to DIL package.
GND (V MM)
GND (V CC )
Figure 7. Microstepping system with PBM 3960 /1 and PBL 3771/1.
6
PBL 3771/1
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 m) permits the circuit to operate with a maximum of 320 mA output current, both channels driving, at ambient temperatures up to +70C. 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 +160C. Operating temperature. The max recommended operating temperature is 125C. 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) Tj = 25C
1.0 .8
1.2 1.0 .8
VCE Sat (V)
Tj = 125C
Tj = 25C
.6
.4 .2
.6
Tj = 125C
.4 .2
0
0
.10
.20
.30
.40
.50
.60
0
.10
.20
.30
.40
.50
.60
IM (A)
I M (A)
Figure 8. Typical upper diode voltage drop vs. recirculating current.
Figure 9. Typical source saturation voltage vs. output current.
Vd (V) Tj = 25C
1.0 .8
VCE Sat (V)
1.0 .8
Tj = 25C
Tj = 125C
.6
.6
Tj = 125C
.4 .2
.4 .2
00
.10
.20
.30
.40
.50
.60
0
.10
.20
.30
.40
.50
.60
I M (A)
I M (A)
Figure 10. Typical lower diode voltage drop vs. recirculating current.
PD (W)
Figure 11 Typical sink saturation voltage vs. output current.
3.0
VMM = 36V
2.0
VMM = 14V
1.0
00
.10
.20
.30
.40
.50
.60
Max allow power dis
I M (A)
Figure 12. Power dissipation vs. motor current, both channels driven, Ta = 25C.
7
PBL 3771/1
Thermal resistance [C/W]
80
70
60
22-pin DIP 24-pin SO
50
40
30
20 5 10 15 20 25 30 35
PCB copper foil area [cm 2 ]
PLCC package DIP package
28-pin PLCC
Figure 13. Thermal Resistance vs. PC Board copper area and suggested layout.
Best for high speed Best for high torque
PBL 3771/1
PBL 3771/1
Figure 14. Connection of unipolar motors.
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.
Ordering Information
Package Part No.
DIP Tube PLCC Tube PLCC Tape & Reel SO tube SO Tape & Reel
PBL 3771/1NS PBL 3771/1QNS PBL 3771/1QNT PBL 3771/1SOS PBL 3771/1SOT
Specifications subject to change without notice. 1522-PBL 3771/1 Uen. Rev B (c) Ericsson Components AB 1999
Ericsson Components AB SE-164 81 Kista-Stockholm, Sweden Telephone: +46 8 757 50 00 8

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