STMicroelectronics AN2836 Modern motion control applications need more flexibility that can be addressed Datasheet

AN2836
Application note
L6225, L6226, L6227 dual full-bridge drivers
1
Introduction
Modern motion control applications need more flexibility that can be addressed only with
specialized IC products. The L6225, L6226, L6227 are dual full-bridge driver ICs specifically
developed to drive a wide range of motors. These ICs are one-chip, cost-effective solutions
that include several unique circuit design features. These features allow the devices to be
used in many applications including DC and stepper motor driving. The principal aim of this
development project was to produce easy-to-use, fully-protected power ICs. In addition
several key functions such as protection circuit and PWM current control drastically reduce
the number of external components to meet requirements for many different applications.
The L6225, L6226, L6227 are highly integrated, mixed-signal power ICs that allow the user
to easily design a control system for two-phase bipolar stepper motors, multiple DC motors
and a wide range of inductive loads. Figure 1 to Figure 3 show the block diagrams of the
L6225, L6226, L6227 . Each IC integrates eight power DMOS plus other added features for
safe operation and flexibility. The L6227 also features a constant tOFF PWM current control
technique (synchronous mode) for each of the two full bridges
July 2009
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Contents
AN2836
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Main differences between L6225, L6226, L6227 . . . . . . . . . . . . . . . . . . . 8
4
Designing an application with L6225, L6226, L6227 . . . . . . . . . . . . . . 10
4.1
Current ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2
Voltage ratings and operating range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3
Choosing the bulk capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4
Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5
Sensing resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.6
Charge pump external components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.7
Sharing the charge pump circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.8
Reference voltage for PWM current control (L6227 only) . . . . . . . . . . . . 17
4.9
Input logic pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.10
EN pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.11
Programmable off-time monostable (L6227 only) . . . . . . . . . . . . . . . . . . 20
4.12
Off-time selection and minimum on-time (L6227 only) . . . . . . . . . . . . . . . 22
4.12.1
4.13
Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.14
Adjusting the overcurrent detection trip point (L6226 only) . . . . . . . . . . . 27
4.15
Paralleling two full bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.16
5
Slow decay mode (L6227 only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.15.1
Paralleling two full bridges to get a single full bridge . . . . . . . . . . . . . . . 29
4.15.2
Paralleling the four half bridges to get a single half bridge . . . . . . . . . . 32
Power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.16.1
Maximum output current vs. selectable devices . . . . . . . . . . . . . . . . . . 34
4.16.2
Power dissipation and thermal analysis with PractiSPINTM software . . 35
Application example (L6227) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Appendix A Demonstration boards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
A.1
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PractiSPINTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
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Contents
A.2
EVAL6225PD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
A.2.1
A.3
Important notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
EVAL6227PD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
A.3.1
Important notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
A.4
EVAL6226QR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.5
EVAL6227QR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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List of tables
AN2836
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
4/57
RSENSE recommended values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Application data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Motor data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
EVAL6225PD part list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
EVAL6227PD part list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
EVAL6226QR part list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
EVAL6226QR part list. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
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AN2836
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
L6225 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
L6226 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
L6227 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Supply voltage of high-side gate drivers versus supply voltage . . . . . . . . . . . . . . . . . . . . . 10
Currents and voltages during the deadtime at a phase change . . . . . . . . . . . . . . . . . . . . . 11
Voltage at the two outputs during the deadtime at a phase change . . . . . . . . . . . . . . . . . . 11
Typical application and layout suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Two situations that must be avoided . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Charge pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Sharing the charge pump circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Obtaining a variable voltage through a PWM output of a µC . . . . . . . . . . . . . . . . . . . . . . . 18
Logic input pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ENA and ENB input pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PWM current control circuitry (L6227 only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PWM output current regulation waveforms (L6227 only) . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Typical off-time vs. COFF for several values of ROFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Minimum on-time vs. COFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Slow decay mode output stage configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
PWM controller loses the current regulation due to minimum on-time (L6227 only) . . . . . 24
PWM controller loses the current regulation due to minimum on-time (L6227 only) - detail24
L6225 and L6227 overcurrent detection simplified circuitry . . . . . . . . . . . . . . . . . . . . . . . . 24
L6226 overcurrent detection simplified circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Overcurrent operation: timing 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Overcurrent operation: timing 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Typical disable time vs. CEN for several values of REN . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Typical delay time vs. CEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Output current detection threshold versus RCL value (L6226 only) . . . . . . . . . . . . . . . . . . 28
Adjusting the OCD threshold through an external reference voltage (L6226 only). . . . . . . 28
VS and SENSE pins maximum sourced current handling. . . . . . . . . . . . . . . . . . . . . . . . . . 29
VS and SENSE pins maximum sinked current handling . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
L6225 parallel connection with lower overcurrent threshold . . . . . . . . . . . . . . . . . . . . . . . 30
L6226 parallel connection with lower overcurrent threshold . . . . . . . . . . . . . . . . . . . . . . . 31
L6227 parallel connection with lower overcurrent threshold . . . . . . . . . . . . . . . . . . . . . . . 31
L6225 parallel connection for higher current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
L6226 parallel connection for higher current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
L6225 paralleling the four half bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
L6226 paralleling the four half bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
IC dissipated power versus output current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Maximum output current vs. selectable devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Power dissipation and thermal analysis with PractiSPINTM software . . . . . . . . . . . . . . . . . 36
Application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
PractiSPINTM PC software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
PractiSPINTM ST7 demonstration board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
EVAL6225PD board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
EVAL6225PD electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
EVAL6225PD component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
EVAL6225PD top layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
EVAL6225PD bottom layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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List of figures
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
Figure 54.
Figure 55.
Figure 56.
Figure 57.
Figure 58.
Figure 59.
Figure 60.
Figure 61.
Figure 62.
Figure 63.
6/57
AN2836
EVAL6227PD board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
EVAL6227PD electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
EVAL6227PD component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
EVAL6227PD top layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
EVAL6227PD bottom layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
EVAL6226QR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
EVAL6226QR component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
EVAL6226QR top layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
EVAL6226QR bottom layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
EVAL6226QR electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
EVAL6226QR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
EVAL6227QR component placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
EVAL6227QR top layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
EVAL6227QR bottom layer layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
EVAL6227QR electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Doc ID 15084 Rev 1
AN2836
2
References
References
1.
"A New Fully Integrated Stepper Motor Driver IC", Proceedings of PCIM 2001,
September 2001, Intertech Communication
2.
"Stepper Motor Driving" (AN235)
3.
"Controlling Voltage Transients in Full bridge Driver Applications" (AN280)
4.
"A New High Power IC Surface Mount Package Family" (AN668)
5.
"L6205, L6206, L6207 dual full bridge drivers" (AN1762).
Doc ID 15084 Rev 1
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Main differences between L6225, L6226, L6227
3
AN2836
Main differences between L6225, L6226, L6227
The L6225, L6226 and L6227 are DMOS dual full-bridge ICs.
The L6225 (see Figure 1) includes logic for CMOS/TTL interface, a charge pump that
provides auxiliary voltage to drive the high-side DMOS, non-dissipative overcurrent
protection circuitry on the high-side DMOS, with a fixed trip point set at 2.8 A (see
Section 4.13), overtemperature protection, undervoltage lockout for reliable startup.
In addition, the L6226 (see Figure 2) gives the possibility of adjusting the trip point of the
overcurrent protection for each of the two full bridges (through two external resistors), and
its internal open-drain MOSFETs (see Section 4.13) are not internally connected to EN pins
but to separate OCD pins, allowing easier external diagnostics and overcurrent management.
The L6227 (see Figure 3) has an overcurrent protection function with a fixed trip point set at
2.8 A and internal open-drain MOSFETs connected to EN pins, as the L6225, but it also
integrates two PWM current controllers for each of the two full bridges (see Section 4.11).
Figure 1.
L6225 block diagram
6"//4
6#0
6"//4
6"//4
6"//4
6
6
63!
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8/57
Doc ID 15084 Rev 1
AN2836
Main differences between L6225, L6226, L6227
Figure 2.
L6226 block diagram
6"//4
6"//4
6"//4
6"//4
6
6
63!
#(!2'%
05-0
6#0
02/'#,!
/#$!
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6
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Figure 3.
L6227 block diagram
6"//4
6#0
6"//4
6"//4
6"//4
6
6
63!
#(!2'%
05-0
/#$!
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Designing an application with L6225, L6226, L6227
AN2836
4
Designing an application with L6225, L6226, L6227
4.1
Current ratings
With MOSFET (DMOS) devices, unlike bipolar transistors, current under short-circuit
conditions is, at first approximation, limited by the RDS(on) of the DMOS themselves and
could reach very high values. L6225, L6226, L6227 OUT pins and the two VSA and VSB pins
are rated for a maximum of 1.4 Arms and 2.8 A peak (typical values), corresponding to a
total (for the whole IC) 2.8 Arms (5.6 A peak). These values are meant to avoid damaging
metal structures, including the metallization on the die and bond wires. In practical
applications, though, maximum allowable current is less than these values, due to power
dissipation limits (see Section 4.16). The devices have a built-in overcurrent detection
(OCD) that provides protection against short circuits between the outputs and between an
output and ground (see Section 4.13).
4.2
Voltage ratings and operating range
The L6225, L6226, L6227 require a single supply voltage (VS), for the motor supply. Internal
voltage regulators provide the 5 V and 10 V required for the internal circuitry. The operating
range for VS is 8 to 52 V. To prevent working from an undesirable low supply voltage an
undervoltage lockout (UVLO) circuit shuts down the device when the supply voltage falls
below 5.5 V. To resume normal operating conditions, VS must then exceed 6.3 V. The
hysteresis is provided to avoid false intervention of the UVLO function during fast VS
ringings. It should be noted, however, that RDS(on) of the DMOS is a function of the VS
supply voltage. Actually, when VS is less than 10 V, RDS(on) is adversely affected, and this is
particularly true for the high-side DMOS that are driven from VBOOT supply. This supply is
obtained through a charge pump from the internal 10 V supply, which tends to reduce its
output voltage when VS goes below 10 V. Figure 4 shows the supply voltage of the high-side
gate drivers (VBOOT - VS) versus the supply voltage (VS).
Figure 4.
Supply voltage of high-side gate drivers versus supply voltage
6 "//4
;6=
6 3
63 ;6=
!-V
Note that VS must be connected to both VSA and VSB since the bootstrap voltage (at VBOOT
pin) is the same for the two H-bridges. The integrated DMOS have a rated drain-source
breakdown voltage of 60 V. However VS should be kept below 52 V, since in normal working
conditions the DMOS see a Vds voltage that exceeds VS supply. In particular, during a
phase change (when each output of the same H-bridge switches from VS to GND or vice
versa, for example to reverse the current in the load) at the beginning of the deadtime (when
all the DMOS are off) the SENSE pin sees a negative spike due to a non-negligible parasitic
10/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
inductance of the PCB path from the pin to GND. This spike is followed by a stable negative
voltage due to the drop on RSENSE. One of the two OUT pins of the bridge sees a similar
behavior, but with a slightly larger voltage due to the forward recovery time of the integrated
freewheeling diode and the forward voltage drop across it (see Figure 5). Typical duration of
this spike is 30 ns. At the same time, the other OUT pin of the same bridge sees a voltage
above VS, due to the PCB inductance and voltage drop across the high-side (integrated)
freewheeling diode, as the current reverses direction and flows into the bulk capacitor. It
turns out that the highest differential voltage can be observed between the two OUT pins of
the same bridge, during the deadtime at a phase change, and this must always be kept
below 60 V [3].
Figure 5.
Currents and voltages during the deadtime at a phase change
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Figure 6 shows the voltage waveforms at the two OUT pins referring to an application, with a
peak output current of 1.4 A, VS = 52 V, RSENSE = 0.33 Ω, TJ = 25 °C (approximately) and a
good PCB layout. Below ground spike amplitude is –2.65 V for one output, the other OUT
pin is at about 57 V. In these conditions, total differential voltage reaches almost 60 V, which
is the absolute maximum rating for the DMOS. Keeping differential voltage between two
output pins belonging to the same full bridge within rated values is a must that can be
accomplished with proper selection of bulk capacitor value and equivalent series resistance
(ESR), according to current peaks and chopping style and adopting good layout practices to
minimize PCB parasitic inductances (see below) [3].
Figure 6.
Voltage at the two outputs during the deadtime at a phase change
/UT /UT !-V
Doc ID 15084 Rev 1
11/57
Designing an application with L6225, L6226, L6227
4.3
AN2836
Choosing the bulk capacitor
Since the bulk capacitor, placed between VS and GND pins, is charged and discharged
during the IC operation, its AC current capability must be greater than the RMS value of the
charge/discharge current. In case of PWM current regulation, the current flows from the
capacitor to the IC during the on-time (tON) and from the IC (implementing a fast decay
current recirculation technique) or from the power supply (implementing a slow decay
current recirculation technique) to the capacitor during the off-time (tOFF). The RMS value of
the current flowing into the bulk capacitor depends on peak output current, output current
ripple, switching frequency, duty cycle and chopping style. It also depends on power supply
characteristics. A power supply with poor high-frequency performances (or long, inductive
connections to the IC) causes the bulk capacitor to be recharged slowly: the higher the
current control switching frequency, the higher the current ripple in the capacitor. RMS
current in the capacitor, however, does not exceed the RMS output current. Bulk capacitor
value (C) and the ESR determine the amount of voltage ripple on the capacitor itself and on
the IC. In slow decay, neglecting the deadtime and output current ripple, and assuming that
during the on-time the capacitor is not recharged by the power supply, the voltage at the end
of the on-time is:
Equation 1
t
ON
V –I
⋅ ⎛ ESR + -----------⎞ ,
S OUT ⎝
C ⎠
so the supply voltage ripple is:
Equation 2
I
t
ON
⋅ ⎛ ESR + -----------⎞
OUT ⎝
C ⎠
where IOUT is the output current. With fast decay, instead, recirculating current recharges
the capacitor, causing the supply voltage to exceed the nominal voltage. This can be very
dangerous if the nominal supply voltage is close to the maximum recommended supply
voltage (52 V). In fast decay the supply voltage ripple is about:
Equation 3
I
t
+t
ON OFF-⎞
⋅ ⎛ 2 ⋅ ESR + ------------------------------OUT ⎝
⎠
C
always assuming that the power supply does not recharge the capacitor, and neglecting the
output current ripple and the deadtime. Usually (if C > 100 µF) the capacitance role is much
less than the ESR, then supply voltage ripple can be estimated as:
Equation 4
I OUT ⋅ ESR
in slow decay
2 ⋅ I OUT ⋅ ESR
in fast decay
Equation 5
12/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
For example, if a maximum ripple of 500 mV is allowed and IOUT = 1 A, the capacitor ESR
should be lower than:
Equation 6
0.5V
ESR < ------------ = 500mΩ
1A
In slow decay
1 0.5V
ESR < --- ⋅ ------------ = 250mΩ
2 1A
In fast decay
Equation 7
Actually, current sunk by the VSA and VSB pins of the device is subject to higher peaks due
to the reverse recovery charge of the internal freewheeling diodes. The duration of these
peaks is, though, very short, and can be filtered using a small value (100÷200 nF), good
quality ceramic capacitors, connected as close as possible to the VSA, VSB and GND pins of
the IC. The bulk capacitor will be chosen with maximum operating voltage 25% greater than
the maximum supply voltage, considering also power supply tolerances. For example, with a
48 V nominal power supply, with 5% tolerance, maximum voltage is 50.4 V, then operating
voltage for the capacitor should be at least 63 V.
4.4
Layout considerations
Working with devices that combine high power switches and control logic in the same IC,
special attention has to be paid to the PCB layout. In extreme cases, power DMOS
commutation can induce noise that could cause improper operation in the logic section of
the device. Noise can be radiated by high dV/dt nodes or high dI/dt paths, or conducted
through GND or supply connections. Logic connections, especially high-impedance nodes
(actually all logic inputs, see further), must be kept far from switching nodes and paths. With
the L6225, L6226, L6227, in particular, external components for the charge pump circuitry
should be connected together through short paths, since these components are subject to
voltage and current switching at relatively high frequency (600 kHz). The primary means to
minimize conducted noise is to have a good GND layout (see Figure 7).
Figure 7.
Typical application and layout suggestions
AM01627v1
Doc ID 15084 Rev 1
13/57
Designing an application with L6225, L6226, L6227
AN2836
High-current GND tracks (i.e. the tracks connected to the sensing resistors) must be
connected directly to the negative terminal of the bulk capacitor. A good quality, highfrequency bypass capacitor is also required (typically a 100 nF÷200 nF ceramic would
suffice), since electrolytic capacitors show a poor high frequency performance. Both bulk
electrolytic and high-frequency bypass capacitors have to be connected with short tracks to
VSA, VSB and GND. On the L6225, L6226, L6227 GND pins are the logic GND, since only
the quiescent current flows through them. Logic GND and power GND should be connected
together in a single point, the bulk capacitor, to keep noise in the power GND from affecting
logic GND. Specific care should be paid layouting the path from the SENSE pins through the
sensing resistors to the negative terminal of the bulk capacitor (power ground). These tracks
must be as short as possible in order to minimize parasitic inductances that can cause
dangerous voltage spikes on the SENSE and OUT pins (see Section 4.2: Voltage ratings
and operating range). For the same reason the capacitors on VSA, VSB and GND should be
very close to the GND and supply pins. Refer to Section 4.5: Sensing resistors for
information on selecting the sense resistors. Traces connected to VSA, VSB, SENSEA,
SENSEB, and the four OUT pins must be designed with adequate width, since high currents
are flowing through these traces, and layer changes should be avoided. Should a layer
change prove necessary, multiple and large via holes have to be used. A wide GND copper
area can be used to improve heat removal, thus reducing thermal resistance.
Figure 8 shows two typical situations that must be avoided. An important consideration
about the location of the bulk capacitors is the ability to absorb the inductive energy from the
load, without allowing the supply voltage to exceed the maximum rating. The diode shown in
Figure 8 prevents the recirculation current from reaching the capacitors and results in a high
voltage on the IC pins that can damage the device. Having a switch or a power connection
that can disconnect the capacitors from the IC, while there is still current in the motor, also
results in a high-voltage transient since there is no capacitance to sink the recirculation
current.
Figure 8.
Two situations that must be avoided
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14/57
Doc ID 15084 Rev 1
AN2836
4.5
Designing an application with L6225, L6226, L6227
Sensing resistors
Each motor winding current flows through the corresponding sensing resistor, causing a
voltage drop that can be used by the logic (integrated in the L6227; an external logic can be
used with L6225 and L6226) to control the peak value of the load current. Two issues must
be taken into account when choosing the RSENSE value:
The sensing resistor dissipates energy and provides dangerous negative voltages on the
SENSE pin during the current recirculation. For this reason the resistance of this component
should be kept low.
The voltage drop across RSENSE is compared with a reference voltage (on Vref pin) by the
internal comparator (L6227 only): the lower the RSENSE value, the higher the peak current
error due to noise on the Vref pin and to the input offset of the current sense comparator.
Small values of RSENSE must be avoided.
A good compromise is to calculate the sensing resistor value so that the voltage drop,
corresponding to the peak current in the load (Ipeak), is about 0.5 V: RSENSE = 0.5 V / Ipeak.
It should be clear that the sensing resistor must absolutely be non-inductive in order to avoid
dangerous negative spikes on the SENSE pins. Wire-wound resistors cannot be used here,
while metallic film resistors are recommended for their high peak current capability and low
inductance. For the same reason the connections between the SENSE pins, C6, C7, VSA,
VSB and GND pins (see Figure 7) must be made as short as possible (see also Section 4.4:
Layout considerations).
The average power dissipated by the sensing resistor is:
●
Fast decay recirculation: PR ≈ Irms2 · RSENSE
●
Slow decay recirculation: PR ≈ Irms2 · RSENSE · D
where D is the duty cycle of the PWM current control and Irms is the RMS value of the load
current.
Nevertheless, the sensing resistor power rating should be chosen, taking into account the
peak value of the dissipated power:
Equation 8
2
P R ≈ I pk ⋅ R SENSE
where Ipk is the peak value of the load current.
Using multiple resistors in parallel helps to obtain the required power rating with standard
resistors, and reduces the inductance.
The RSENSE tolerance reflects on the peak current error: 1% resistors should be preferred.
Table 1 shows the RSENSE recommended values (for a 0.5 V drop) and power ratings for
typical examples of current peak values.
Doc ID 15084 Rev 1
15/57
Designing an application with L6225, L6226, L6227
Table 1.
4.6
AN2836
RSENSE recommended values
Ipk
RSENSE value [Ω]
RSENSE power rating [W]
0.25
2
0.125
0.5
1
0.25
1
0.5
0.5
Alternatives
2 X 1 Ω, 0.25 W
paralleled
Charge pump external components
An internal oscillator, with its output at the CP pin, switches from GND to 10 V with a typical
frequency of 600 kHz (see Figure 9).
Figure 9.
Charge pump
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When the oscillator output is at ground, C5 is charged by VS through D2. When it rises to
10, D2 is reverse biased and the charge flows from C5 to C8 through D1, so the VBOOT pin,
after a few cycles, reaches the maximum voltage of VS + 10 V - VD1 - VD2, which supplies
the high-side gate drivers.
With a differential voltage between VS and VBOOT of about 9 V and both the bridges
switching at 50 kHz, the typical current drawn by the VBOOT pin is 1.85 mA.
Care must be taken in establishing the PCB layout of the C5, D1, D2 connections in order to
minimize interferences with the rest of the circuit (see also Section 4.4). Recommended
values for the charge pump circuitry are:
●
D1, D2: 1N4148
●
C5: 10 nF 100 V ceramic
●
C8: 220 nF 25 V ceramic
Due to the high charge pump frequency, fast diodes are required. Connecting the cold side
of the bulk capacitor (C8) to VS instead of GND, the average current in the external diodes
during operation is less than 10 mA. At IC power-up the current in the external diodes is
less than 200 mA. The reverse voltage of the charge pump diodes is about 10 V in all
16/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
conditions. The 1N4148 diodes withstand about 200 mA DC (1 A peak), and the maximum
reverse voltage is 75 V, so they should fit for the majority of applications.
4.7
Sharing the charge pump circuitry
If more than one device is used in the application, it's possible to use the charge pump from
one L6225, L6226 or L6227 to supply the VBOOT pins of several ICs. The unused CP pins on
the slave devices are left unconnected, as shown in Figure 10. A 100 nF capacitor (C8)
should be connected to the VBOOT pin of each device. Supply voltage pins (VS) of the
devices sharing the charge pump must be connected together.
The higher the number of devices sharing the same charge pump, the lower the differential
voltage available for the gate drive (VBOOT - VS), causing a higher RDS(on) for the high-side
DMOS, thus higher dissipating power.
Better performance can also be obtained using a 33 nF capacitor for C5 and using Schottky
diodes (for example BAT47 are recommended).
Sharing the same charge pump circuitry for more than 3÷4 devices is not recommended,
since it reduces the VBOOT voltage increasing the high-side MOS on-resistance and thus
power dissipation.
Figure 10. Sharing the charge pump circuitry
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4.8
Reference voltage for PWM current control (L6227 only)
The L6227 has two analog inputs, VREFA and VREFB, connected to the internal sense
comparators, to control the peak value of the motor current through the integrated PWM
circuitry. In typical applications these pins are connected together, in order to obtain the
same current in the two motor windings. A fixed reference voltage can be easily obtained
through a resistive divider from an available 5 V voltage rail (maybe the one supplying the
µC or the rest of the application) and GND.
A very simple way to obtain a variable voltage without using a DAC is to low-pass filter a
PWM output of a µC (see Figure 11).
Doc ID 15084 Rev 1
17/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 11. Obtaining a variable voltage through a PWM output of a µC
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Assuming that the PWM output swings from 0 to 5 V, the resulting voltage is:
Equation 9
V
ref
5V ⋅ D
⋅R
μC
DIV= -------------------------------------------R
+R
LP
DIV
where DµC is the duty cycle of the PWM output of the µC.
Assuming that the µC output impedance is lower than 1 kΩ, with RLP = 56 kΩ, RDIV = 15 kΩ,
CLP = 10 nF and a µC PWM switching from 0 to 5 V at 100 kHz, the low-pass filter time
constant is about 0.12 ms and the remaining ripple on the Vref voltage is about 20 mV. Using
higher values for RLP, RDIV and CLP reduces the ripple, but the reference voltage takes more
time to vary after changing the duty cycle of the µC PWM, and too high values of RLP also
increase the impedance of the Vref net at low frequencies, causing a poor noise immunity.
As sensing resistor values are typically kept small, a small noise on the Vref input pins might
cause a considerable error in the output current. It's then recommended to decouple these
pins with ceramic capacitors of some tens of nF, placed very close to the Vref and GND pins.
Note that the Vref pins cannot be left unconnected, while, if connected to GND, zero current
is not guaranteed due to the voltage offset in the sense comparator. The best way to cut
down the IC power consumption and clear the load current is to pull down the EN pins. With
very small reference voltage, PWM integrated circuitry can lose control of the current due to
the minimum allowed duration of tON (see Section 4.11).
4.9
Input logic pins
IN1A, IN2A, IN1B, IN2B are CMOS/TTL compatible logic input pins. The input comparator
has been configured with hysteresis to ensure the required noise immunity. Typical values
for turn-on and turn-off thresholds are Vth,ON = 1.8 V and Vth,OFF = 1.3 V. As shown in
Figure 12, these pins are ESD-protected (2 kV human-body electro-static discharge), and
can be directly connected to the logic outputs of a µC. A series resistor is generally not
recommended, as it could help inducted noise to disturb the inputs. All logic pins enforce a
specific behavior and cannot be left unconnected.
18/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 12. Logic input pins
6
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4.10
EN pins
The ENA, ENB pins are, actually, bi-directional. As an input, with a comparator similar to the
other logic input pins (TTL/CMOS with hysteresis), they control the state of the power
DMOS. When each of the two pins is at a low logic level, all the power DMOS of the
corresponding H-bridge (A or B) are turned off. In L6225 and L6227 the EN pins are also
connected to the two corresponding open-drain outputs of the protection circuits that pull the
pins to GND if overcurrent in the corresponding H-bridge or overtemperature conditions
exist. In L6226 the open-drain outputs are on separate pins, OCDA and OCDB, allowing
easier external diagnostics and overcurrent management. For this reason, with L6225 and
L6227 (and L6226 if EN pins are connected to DIAG pins), EN pins must be driven through
a series resistor of 2.2 kΩ minimum (for 5 V logic), to allow the voltage at the pin to be pulled
below the turn-off threshold.
A capacitor (CEN in Figure 13) connected between each EN pin and GND is also
recommended, to reduce the RMS value of the output current when overcurrent conditions
persist (see Section 4.13). The EN pin must not be left unconnected.
Figure 13. ENA and ENB input pins
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Doc ID 15084 Rev 1
19/57
Designing an application with L6225, L6226, L6227
4.11
AN2836
Programmable off-time monostable (L6227 only)
The L6227 includes a constant off-time PWM current controller for each of the two bridges.
The current control circuit senses the bridge current by sensing the voltage drop across an
external sense resistor connected between the source of the two lower power MOSFET
transistors and ground, as shown in Figure 14. As the current in the load builds up, the
voltage across the sense resistor increases proportionally. When the voltage drop across
the sense resistor becomes greater than the voltage at the reference input (VREFA or
VREFB), the sense comparator triggers the monostable, switching the low-side MOSFET
off. The low-side MOSFET remains off for the time set by the monostable and the motor
current recirculates in the upper path. When the monostable times out, the bridge again
turns on. Since the internal deadtime, used to prevent cross conduction in the bridge, delays
the turn- on of the power MOSFET, the effective off-time is the sum of the monostable time
plus the deadtime.
Figure 14. PWM current control circuitry (L6227 only)
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Figure 15 shows the typical operating waveforms of the output current, the voltage drop
across the sensing resistor, the RC pin voltage and the status of the bridge. Immediately
after the low-side power MOSFET turns on, a high peak current flows through the sensing
resistor due to the reverse recovery of the freewheeling diodes. The L6227 provides a 1 µs
blanking time tBLANK that inhibits the comparator output so that this current spike cannot
prematurely re-trigger the monostable.
20/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 15. PWM output current regulation waveforms (L6227 only)
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Figure 16 shows the magnitude of the OFF time tOFF versus COFF and ROFF values. It can
be approximately calculated from the equations:
●
tRCFALL = 0.6 · ROFF · COFF
●
tOFF = tRCFALL + tDT = 0.6 · ROFF · COFF + tDT
where ROFF and COFF are the external component values and tDT is the internally generated
deadtime with:
●
20 kΩ ≤ ROFF ≤ 100 kΩ
●
0.47 nF ≤ COFF ≤ 100 nF
●
tDT = 1 µs (typical value)
Therefore:
●
tOFF(MIN) = 6.6 µs
●
tOFF(MAX) = 6ms
These values allow a sufficient range of tOFF to implement the drive circuit for most motors.
The capacitor value chosen for COFF also affects the rise time tRCRISE of the voltage at the
pin RCA (or RCB). The rise time tRCRISE is only an issue if the capacitor is not completely
charged before the next time the monostable is triggered. Therefore, the on-time tON, which
depends on motor and supply parameters, has to be longer than tRCRISE in order to allow a
good current regulation by the PWM stage. Furthermore, the on-time tON cannot be shorter
than the minimum on-time tON(MIN).
Equation 10
t
>t
= 1.5μs (typ. value)
⎧ ON ON ( MIN )
⎨
⎩t ON > t RCRISE – t DT
Equation 11
t RCRISE = 600 ⋅ C OFF
Doc ID 15084 Rev 1
21/57
Designing an application with L6225, L6226, L6227
4.12
AN2836
Off-time selection and minimum on-time (L6227 only)
Figure 17 also shows the lower limit for the on-time tON for having a good PWM current
regulation capacity. It has to be said that tON is always longer than tON(MIN) because the
device imposes this condition, but it can be shorter than tRCRISE - tDT. In this last case the
device continues to work, but the off-time tOFF is no longer constant.
So, a small COFF value gives more flexibility for the applications (allows shorter on-time and,
therefore, higher switching frequency), but the smaller the value for COFF, the more
influential the noise on the circuit performance.
Figure 16. Typical off-time vs. COFF for several Figure 17. Minimum on-time vs. COFF
values of ROFF
Coff [nF]
4
1 . 10
R = 100 k Ω
100
R = 47 k Ω
3
R = 20 k Ω
to n ( m in ) [ u s]
to f f [ u s]
1 . 10
100
10
1
0.1
1
10
10
1
100
Coff [nF]
1
10
100
Coff [nF]
AM01636v1
4.12.1
0.1
AM01637v1
Slow decay mode (L6227 only)
Figure 18 shows the operation of the bridge in the slow decay mode. At the start of the off
time, the lower power MOSFET is switched off and the current recirculates around the upper
half of the bridge. Since the voltage across the coil is low, the current decays slowly. After
the deadtime the upper power MOSFET is operated in the synchronous rectification mode.
When the monostable times out, the lower power MOSFET is turned on again after a delay
set by the deadtime to prevent cross conduction.
22/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 18. Slow decay mode output stage configurations
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In some conditions (short off-time, very low regulated current, high motor winding L / R) the
system may need an on-time shorter than 1.5 µs in which case the PWM current controller
can lose the regulation.
Figure 19 shows the operation of the circuit in this condition. When the current first reaches
the threshold, the bridge is turned off for a fixed time and the current decays. During the
following on-time, the current increases above the threshold, but the bridge cannot be
turned off until the minimum 1.5 µs on-time expires. Since the current increases more in
each on-time than it decays during the off-time, it keeps growing during each cycle, with a
steady state asymptotic value set by the duty cycle and load DC resistance. The resulting
peak current is:
Equation 12
D
I pk = V S ⋅ -----------------R LOAD
where D = tON / (tON + tOFF) is the duty cycle and RLOAD is the load DC resistance.
Doc ID 15084 Rev 1
23/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 20. PWM controller loses the current
Figure 19. PWM controller loses the current
regulation due to minimum on-time
regulation due to minimum on-time
(L6227 only) - detail
(L6227 only)
!-V
4.13
!-V
Overcurrent protection
To implement an overcurrent protection, a dedicated overcurrent detection (OCD) circuitry
(see Figure 21 and 22 for a simplified schematic) senses the current in each high side.
Power DMOS are actually made of thousands of individual identical cells, each carrying a
fraction of the total flowing current. The current sensing element, connected in parallel to the
power DMOS, is made only of a few such cells, having a 1:N ratio compared to the power
DMOS. The total drain current is split between the output and the sense element according
to the cell ratio. Sensed current is, then, a small fraction of the output current and does not
contribute significantly to power dissipation.
Figure 21. L6225 and L6227 overcurrent detection simplified circuitry
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24/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 22. L6226 overcurrent detection simplified circuitry
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This sensed current is compared to an internally-generated reference (adjustable through
the external resistors RCLA and RCLB for L6226) to detect an overcurrent condition. An
internal open-drain MOSFET turns on when the sum of the currents in the bridges 1A and
2A or 1B and 2B reaches the threshold (2.8 A typical value for L6225 and L6227; adjustable
through the external resistors RCLA and RCLB for L6226). In L6225 and L6227 the open
drain is internally connected to the EN pins. With L6226 the OCD pins should be connected
to the EN pins to allow the protection to function. To ensure an overcurrent protection,
connect these pins to an external RC network (see Figure 21 and 22).
Figure 23 and 24 show the device operating in overcurrent condition (short to ground).
When an overcurrent is detected, the internal open-drain MOSFET pulls the EN pin to GND,
switching off all 4 power DMOS of the bridge and allowing the current to decay. Under a
persistent overcurrent condition, like a short to ground or a short between two output pins,
the external RC network on the EN pin (see Figure 21 and 22) reduces the RMS value of the
output current by imposing a fixed disable time after each overcurrent occurrence. The
values of REN and CEN are selected to ensure proper operation of the device under a shortcircuit condition. When the current flowing through the high-side DMOS reaches the OCD
threshold (2.8 A typ. for L6225 and L6227, adjustable for L6226), after an internal
propagation delay (tOCD(ON)) the open drain starts discharging CEN. When the EN pin
voltage falls below the turn-off threshold (VTH(OFF)), all the power DMOS turn off after the
internal propagation delay (tD(OFF)EN). The current begins to decay as it circulates through
the freewheeling diodes. Since the DMOS are off, there is no current flowing through them
and no current to sense, so the OCD circuit, after a short delay (tOCD(OFF)), switches the
internal open-drain device off, and REN can charge CEN. When the voltage at the EN pin
reaches the turn-on threshold (VTH(ON)), after the tD(ON)EN delay, the DMOS turns on and
the current restarts. Even if the maximum output current is very high, the external RC
network provides a disable time (tDISABLE) to ensure a safe RMS value (see Figure 23 and
24).
Doc ID 15084 Rev 1
25/57
Designing an application with L6225, L6226, L6227
Figure 23. Overcurrent operation: timing 1
AN2836
Figure 24. Overcurrent operation: timing 2
!-V
!-V
The maximum value reached by the current depends on its slew rate, thus on the state of
the short-circuit, the supply voltage, and on the total intervention delay (tDELAY). It can be
noticed that after the first current peak, the maximum value reached by the output current
becomes lower, because the capacitor on the EN pins is discharged starting from a lower
voltage, resulting in a shorter tDELAY.
The following approximate relations estimate the disable time and the first OCD intervention
delay after the short-circuit (worst case).
The time the device remains disabled is:
Equation 13
where:
Equation 14
VEN(LOW) is the minimum voltage reached by the EN pin, and can be estimated by the
relation:
Equation 15
VEN ( LOW ) = VTH ( OFF ) ⋅ e
−
t D ( OFF ) EN + t OCD ( OFF )
ROPDR ⋅C EN
The total intervention time is:
Equation 16
t DELAY = tOCD (ON ) + t EN ( FALL ) + t D (OFF ) EN
where
26/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Equation 17
tEN(FALL) = ROPDR ⋅ CEN ⋅ ln
VDD
VTH(OFF)
tOCD(OFF), tOCD(ON), tD(ON)EN, tD(OFF)EN, and ROPDR are device intrinsic parameters, VDD is
the pull-up voltage applied to REN.
The external RC network, CEN in particular, must be chosen in order to obtain a reasonably
fast OCD intervention (short tDELAY) and a safe disable time (long tDISABLE).
Figure 25 and 26 show both tDISABLE and tDELAY as a function of CEN: at least 100 µs for
tDISABLE are recommended, keeping the delay time below 1÷2 µs at the same time.
The internal open drain can also be turned on if the device experiences an overtemperature
(OVT) condition. The OVT causes the device to shut down when the die temperature
exceeds the OVT threshold (TJ >165 °C typ.). Since the OVT is also connected directly to
the gate drive circuits (see Figure 1 to Figure 3), all the power DMOS shut down, even if the
EN pin voltage is still over Vth(OFF). When the junction temperature falls below the OVT
turn-off threshold (150 °C typ.), the open drain turns off, CEN is recharged up to VTH(ON)
and then the power DMOS are turned back on.
Figure 25. Typical disable time vs. CEN for
several values of REN
R E N = 2 2 0 kΩ
3
1 .1 0
R E N = 1 0 0 kΩ
Figure 26. Typical delay time vs. CEN
C
EN
C
EN
[n F ]
10
R E N = 4 7 kΩ
R E N = 3 3 kΩ
t DELAY [µs]
t DISABLE [µs]
R E N = 1 0 kΩ
100
1
10
1
1
10
C
EN
100
0 .1
[n F ]
1
10
AM01645v1
4.14
100
[n F ]
AM01646v1
Adjusting the overcurrent detection trip point (L6226 only)
The L6226 allows the user to set the overcurrent detection threshold separately for the two
full bridges connecting two resistors (RCL) to pins PROGCLA and PROGCLB. The OCD
threshold (ISOVER) follows the equations:
●
ISOVER = 2.8 A ±30% at -25 °C < Tj < 125 °C if RCL = 0 Ω (PROGCL connected to
GND)
●
---------------- ±10% at -25 °C < Tj < 125 °C
ISOVER = 11050
R
CL
if 5 kΩ < RCL < 40 kΩ
Figure 27 shows the OCD threshold versus the RCL value in the range from 5 kΩ to 40 kΩ.
Doc ID 15084 Rev 1
27/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 27. Output current detection threshold versus RCL value (L6226 only)
, 3/ 6% 2
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The overcurrent detection threshold can also be adjusted through an external reference
voltage, as shown in Figure 28. The external reference voltage source should be able to sink
current (about 300 µA maximum). Moreover, if the supply voltage is provided to the L6226
before VEXT, and its EN pins are at a high logic level, the device starts working with minimum
OCD threshold (actually the capacitor placed at the bottom of RCL allows a short startup
time with a higher OCD threshold). VEXT can also be obtained through a PWM output of a
µC, adding a series resistor to obtain a low-pass filter.
The OCD threshold (ISOVER) follows the equation:
●
( 1.2V – Vext )
------------------------------------------------------- ±10%, at -25 °C < Tj < 125 °C if 0.25 A < ISOVER < 2.25 A
ISOVER = 9208.3
R
CL
Figure 28. Adjusting the OCD threshold through an external reference voltage
(L6226 only)
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28/57
Doc ID 15084 Rev 1
AN2836
4.15
4.15.1
Designing an application with L6225, L6226, L6227
Paralleling two full bridges
Paralleling two full bridges to get a single full bridge
The outputs of L6225, L6226, L6227 can be paralleled to increase the output current
capability or reduce the power dissipation in the device at a given current level. It must be
noted, however, that the internal wire bond connections from the die to the power or sense
pins of the package must carry current in both of the associated half bridges (see Figure 29
and 30). When the two halves of one full bridge (for example OUT1A and OUT2A) are
connected in parallel, the peak current rating is not increased since the total current must
still flow through one bond wire on the power supply or sense pin. In addition, the
overcurrent detection senses the sum of the current in the upper devices of each bridge (A
or B), so connecting the two halves of one bridge in parallel does not increase the
overcurrent detection threshold.
Figure 29. VS and SENSE pins maximum sourced current handling
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Figure 30. VS and SENSE pins maximum sinked current handling
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Doc ID 15084 Rev 1
29/57
Designing an application with L6225, L6226, L6227
AN2836
This configuration has to be used when two separate loads are driven, since the ICs have
only two ENABLE inputs, one for the full bridge A and the other for the bridge B. In this case
pulling to GND one of the two ENABLE pins disables only one load (see Figure 31 to 33).
This configuration can also be used if a 2.8 A OCD threshold is desired (instead of 5.6 A).
Half-bridge 1 and the half-bridge 2 of the bridge A are connected in parallel and the same is
done for the bridge B as shown in Figure 31 to 33. In this configuration, the peak current for
each half bridge is still limited by the bond wires for the supply and sense pins so the
dissipation in the device is reduced, but the peak current rating is not increased. Using this
configuration with L6226, two separate resistors connected to pins PROGCLA and
PROGCLB must be used. With L6227, two separate RC networks should be used on the RC
pins. When two different loads are driven (see Figure 33) by the two equivalent half bridges,
two separate sensing resistors are needed, while if the two equivalent half bridges drive two
separate loads, they must be connected from the OUT pins to VS (see Figure 33) to make
the PWM current control work properly.
In this configuration, the resulting bridge has the following characteristics (typical values).
●
Equivalent device: full bridge
●
RDS(on) HS + RDS(on) LS 0.73 Ω typ. value at TJ = 25°C
●
1.4 A max RMS load current
●
2.8 A OCD threshold
Figure 31. L6225 parallel connection with lower overcurrent threshold
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30/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 32. L6226 parallel connection with lower overcurrent threshold
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Figure 33. L6227 parallel connection with lower overcurrent threshold
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For some applications the recommended configuration is half bridge 1 of bridge A paralleled
with the half-bridge 1 of the bridge B, and the same for the half-bridges 2 as shown in
Figure 34 and 35.
Figure 34. L6225 parallel connection for higher current
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Doc ID 15084 Rev 1
31/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 35. L6226 parallel connection for higher current
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This configuration cannot be used with L6227, because of its internal PWM current
controllers that work separately for bridge A and bridge B. Using this configuration with the
L6227 may damage the device.
In this configuration the resulting bridge has the following characteristics (typical values):
●
Equivalent device: full bridge
●
RDS(on) HS + RDS(on) LS 0.73 Ω typ. value at TJ = 25 °C
●
2.8 A max RMS load current
●
5.6 A OCD threshold
It should be noted that using two separate loads for the two equivalent half bridges the
maximum current cannot be sourced or sinked simultaneously by the two equivalent half
bridges (for example to drive two separate loads), due to the 2.8 A maximum current limit for
the VS and SENSE pins (see Figure 29 and 30). When a single load is driven (see Figure 34
and 35), the RCLA and RCLB resistors connected to the PROGCL pins of L6226 should have
the same value.
4.15.2
Paralleling the four half bridges to get a single half bridge
It is also possible to parallel the four half bridges to obtain a simple half bridge as shown in
Figure 36 and 37.
This configuration cannot be used with L6227, because of its internal PWM current
controllers that work separately for bridge A and bridge B. Using this configuration with the
L6227 may damage the device.
The resulting half bridge has the following characteristics (typical values):
●
Equivalent device: half bridge
●
RDS(on) HS + RDS(on) LS 0.36 Ω typ. value at TJ = 25 °C
●
2.8 A max RMS load current
●
5.6 A OCD threshold
When the L6226 is used in this configuration, RCLA and RCLB resistors connected to
PROGCL pins must have the same value.
32/57
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 36. L6225 paralleling the four half bridges
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Figure 37. L6226 paralleling the four half bridges
!-V
4.16
Power management
Even when operating at current levels well below the maximum ratings of the device, the
operating junction temperature must be kept below 125 °C.
Figure 38 shows the IC dissipated power versus the RMS load current, in the case of:
●
a single IC driving two loads (for instance 2 DC motors or a two-phase stepper motor)
●
or a single IC, with two full bridges paralleled (see Section 4.15: Paralleling two full
bridges) driving one load (for instance 1 DC motor or one phase of a two-phase stepper
motor) and assuming the supply voltage is 24 V.
Doc ID 15084 Rev 1
33/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 38. IC dissipated power versus output current
!-V
4.16.1
Maximum output current vs. selectable devices
Figure 39 shows a comparison of performance between different devices of the
powerSPINTM family, for different packages and in a parallel configuration, with the following
assumptions:
34/57
●
Each equivalent full bridge drives a load
●
Supply voltage: 24 V; switching frequency: 30 kHz
●
Tamb = 25 °C, TJ = 125 °C
●
Maximum RDS(on) (taking into account process spread) has been considered, at 125 °C
●
Maximum quiescent current IQ (taking into account process spread) has been
considered
●
PCB is an FR4 with a dissipating copper surface on the top side of 6 cm2 (with a
thickness of 35 µm) for SO and PowerDIP packages (D, N suffixes)
●
PCB is an FR4 with a dissipating copper surface on the top side of 6 cm2 (with a
thickness of 35 µm), 16 via holes and a ground layer for the PowerSO package (PD
suffix)
●
For each device configuration (on the x-axis) the y-axis shows the maximum output
(load) current
●
2 x ‘device’ means that the two loads are driven by two equivalent full bridges obtained
by paralleling two full bridges for each of the two ICs used. The current reported in
Figure 39 is the maximum output current of an equivalent full bridge (a paralleled IC).
Doc ID 15084 Rev 1
AN2836
Designing an application with L6225, L6226, L6227
Figure 39. Maximum output current vs. selectable devices
,OAD CURRENT
;!=
4.16.2
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Power dissipation and thermal analysis with PractiSPINTM software
The PractiSPINTM software includes a power dissipation and thermal analysis section that
helps in calculating the IC power dissipation and estimating its junction temperature, through
a simulation.
This section is intended to help to give a fast evaluation of the device, package and
dissipating copper area required by the user’s application, and to be a good starting point for
designing an application (from the power dissipation and thermal point of view). Software
results, especially thermal results, need to be confirmed on the bench.
The input data for simulation are divided in three sections:
a)
Application data: to select the motor characteristics and its configuration, the
driving parameters and the analysis type (steady state, single pulse or repeated
pulse analysis).
b)
Device data: to choose the device part number and to edit some available IC
parameters.
c)
PCB data: to select the package, the PCB dissipating charcteristics and ambient
temperature.
The output data include the waveforms of temperature and current profile, the estimated IC
power dissipation and junction temperature.
For more details on the formulas used in the software, please refer to the "Help" menu of
“Power Dissipation and Thermal Analysis”.
Doc ID 15084 Rev 1
35/57
Designing an application with L6225, L6226, L6227
AN2836
Figure 40. Power dissipation and thermal analysis with PractiSPINTM software
AM01660v1
36/57
Doc ID 15084 Rev 1
AN2836
5
Application example (L6227)
Application example (L6227)
Table 2.
Table 3.
Application data
Application data
Value
Rotation speed
300 rpm (fCK=1 kHZ)
Winding peak current
0.5 A
Maximum ripple
50 mA
Supply voltage
24 V ± 5 %
Sequence
Wave mode
OFF time
15 µs
Motor data
Motor data
Value
Winding resistance
6.6 Ω
Winding inductance
7.9 mH
Step angle
1.8° / step
Maximum BEMF at 300 rpm
15 V
The bulk capacitor needs to withstand at least 24 V + 5% + 25% ≅ 32 V. A 50 V capacitor is
used. Allowing a voltage ripple of 200 mV, the capacitor ESR should be lower than 200 mV /
0.5 A = 400 mΩ. The AC current capability should be about 0.5 A.
Providing a reference voltage of 0.5 V, a sensing resistor of 1 Ω is needed.
Loading the input data on the power dissipation and thermal analysis section, the resulting
switching frequency is 11.9 kHz. The on-time is tON = (1 / fSW) - tOFF ≅ 70 µs, which is far
from the minimum allowed (1.5 µs), so slow decay can be used. The duty cycle is D ≅ 78%.
The sense resistors’ power rating is about PR ≅ Irms2 · RSENSE · D ≅ 0.25 W. A
1 Ω - 0.25 W - 1% resistor is used. The charge pump uses recommended components
(1N4148 diodes and ceramic capacitors).
R = 18 kΩ, C = 1.2 nF are connected to the RC pins, obtaining tOFF ≅ 16 µs. On the EN pins
5.6 nF capacitors have been placed, and the pins are driven by the µC through 100 kΩ
resistors. With these values, in case of short-circuit between two OUT pins or an OUT pin
and GND, the powerDMOS turns off after about 1 µs, and tDISABLE ≅ 240 µs.
Doc ID 15084 Rev 1
37/57
Application example (L6227)
AN2836
Figure 41. Application example
AM01661v1
With wave drive selected, the dissipating power is about 0.8 W. If the ambient temperature is
about 50 °C, with 4 cm2 of copper area on the PCB and a SO24 package, the estimated
junction temperature is about 94°C. Using more copper area or a PowerDIP package
reduces the junction temperature.
38/57
Doc ID 15084 Rev 1
AN2836
Demonstration boards
Appendix A
A.1
Demonstration boards
PractiSPINTM
PractiSPINTM is an evaluation and demonstration system that can be used with the
powerSPINTM family of devices. A graphical user interface (GUI) program (see Figure 42)
runs on an IBM-PC under windows and communicates with a common ST7-based interface
board (see Figure 43) through the RS232 serial port. The ST7 interface board is connected
to a device-specific board (target board) via a standard 34-pin ribbon cable interface.
Depending on the target device, the PractiSPINTM can drive a stepper motor, 1 or 2 DC
motors or a brushless DC (BLDC) motor, setting significant parameters such as speed,
current, voltage, direction, acceleration and deceleration rates from a user friendly graphic
interface, and programming a sequence of movements.
The software also allows evaluating the power dissipated by the selected device and, for a
given package and dissipating copper area on the PCB, estimates the junction temperature
of the device.
Figure 42. PractiSPINTM PC software
AM01662v1
Doc ID 15084 Rev 1
39/57
Demonstration boards
AN2836
Figure 43. PractiSPINTM ST7 demonstration board
!-V
A.2
EVAL6225PD
A demonstration board has been produced to help the evaluation of the device in a
PowerSO package. It implements a typical application with several added components.
Figure 45 shows the electrical schematic of the board. Table 1 gives the part list.
Table 4.
EVAL6225PD part list
Part reference
40/57
Value
Description
CN1, CN2, CN3, CN4
2-pole
Connector
CN5
34-pole
Connector
C1
220 nF/100 V
Ceramic or polyester capacitor
C2
220 nF/100 V
Ceramic or polyester capacitor
C3
100 µF/63 V
Capacitor
C4
10 nF/100 V
Ceramic capacitor
C5
10 µF/16 V
Capacitor
C6, C7
5.6 nF
Capacitor
C11
100 nF
Capacitor
C8, C10
470 pF
Capacitor
C9, C12
68 nF
Capacitor
C13
2.2 nF
Capacitor
D1
BAT46SW
Diode
D3
BZX79C5V1 5.1 V
Zener diode
JP1
3-pole
Jumper
R1
0Ω
Resistor
R2
700 Ω 0.6 Ω
Resistor
R13
10 kΩ
Resistor
R3, R4, R5, R6
100 kΩ
Resistor
Doc ID 15084 Rev 1
AN2836
Demonstration boards
Table 4.
EVAL6225PD part list (continued)
Part reference
Value
Description
R7, R9, R10, R12
1 Ω 0.4 Ω
Resistor
R18, R14
1 kΩ
Resistor
R15, R19
20 kΩ
Resistor
R16, R20
2.2 kΩ
Resistor
R17, R21
5 kΩ
Trimmer
R22
12 kΩ
Resistor
R23
50 kΩ
Trimmer
U1
L6225PD
L6225PD
U2
L6506D
L6506D
JP2, JP3, JP4, JP5, JP6
2-pole
Jumper
The demonstration board provides external connectors for the supply voltage, an external
5V reference for the logic inputs, four outputs for the motor and a 34-pin connector to control
the main functions of the board through an external µC board or the PractiSPINTM tool. The
board also accommodates the L6506 PWM current controller. R23 sets the PWM operating
frequency. If the L6506 does not need to be used, simply connect the two VREF inputs to a
voltage high enough to keep current control inactive.
The PractiSPINTM tool is composed of a graphic interface software running on a PC that
connects with the hardware based on the ST7 µC, which contains upgradable firmware. This
tool allows a fast and easy evaluation of the powerSPINTM family of devices, allowing to
drive DC, BLDC and stepper motors, depending on the target device. The practiSPIN
connected to the EVAL6225PD can drive DC motors and inductive loads, allowing output
voltage and current settings.
The PC software also provides a power dissipation and thermal analysis section, intended
to help give a fast evaluation of the device, package and dissipating copper area required by
the user’s application, and to be a good starting point for designing an application (from the
power dissipation and thermal point of view).
Running the demonstration board in standalone mode, instead, R17 and R21 set the
reference voltage separately for the two bridges, while R16, C9 and R20, C12 are low-pass
filters which provide an external reference voltage by a PWM output of a µC (see also the
microstepping section in the AN2839). Using external VREF inputs, R15, R17, R19, R21 can
be disconnected through JP4 and JP5, unless the PractiSPINTM ST7 demonstration board
is used. This board, in fact, is provided with an offset cancellation circuitry trimmable
through a potentiometer (see PractiSPINTM documentation). Closing JP2 and JP3 is
recommended for safe overcurrent protection.
The 5 V voltage for logic inputs and for references (VrefA and VrefB) is obtained from R2, D3.
Depending on the supply voltage, the value of resistor R2 should be changed in order to
ensure a correct biasing of D3.
The jumper JP1 allows choosing the 5 V voltage from the internal Zener diode network or
pin 11 of CN5 (for example an external µC board can provide 5 V to the demonstration
board). Also a CN2 connector can be used to provide an external 5 V voltage to the board
(in that case R2, D3 should be disconnected). CN2, or pin 1 of CN5, can also be used to
provide a 5 V voltage to external circuits (as, for example, the PractiSPINTM ST7 board). In
Doc ID 15084 Rev 1
41/57
Demonstration boards
AN2836
this case the current that can be drawn from the board depends on the supply voltage and
on the value of R2.
Figure 46 to 48 show the placement of the components and the two-layer layout of the
L6225PD demonstration board. A large GND area has been used, to guarantee minimal
noise and good power dissipation for the device.
Figure 44. EVAL6225PD board
2
2
*0
*0
2
*0
2
*0
*0
!-V
A.2.1
42/57
Important notes
●
JP1: closed in INT position for use with PractiSPINTM ST7 board
●
R17, R21: set the maximum current obtainable through practiSPIN (see PractiSPINTM
documentation)
●
R2 : recommended to be changed to adequate value (depending on supply voltage) to
obtain 5 V across D3
●
JP2, JP3 : closed for safe overcurrent protection
●
JP4, JP5 : closed for use with PractiSPINTM ST7 board
●
JP6: open for use with PractiSPINTM ST7 board.
Doc ID 15084 Rev 1
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Demonstration boards
Figure 45. EVAL6225PD electrical schematic
!-V
43/57
Demonstration boards
AN2836
Figure 46. EVAL6225PD component placement
!-V
Figure 47. EVAL6225PD top layer layout
!-V
Figure 48. EVAL6225PD bottom layer layout
!-V
44/57
Doc ID 15084 Rev 1
AN2836
A.3
Demonstration boards
EVAL6227PD
A demonstration board has been produced to help the evaluation of the device in a
PowerSO package. It implements a typical application with several added components.
Figure 50 shows the electrical schematic of the board. Table 5 gives the part list.
Table 5.
EVAL6227PD part list
Part name
Value
Description
CN1, CN2, CN3, CN4
2-pole
Connector
CN5
34-pole
Connector
C1
220 nF/100 V
Ceramic or polyester capacitor
C2
220 nF/100 V
Ceramic or polyester capacitor
C3
100 µF/63 V
Capacitor
C4
10 nF/100 V
Ceramic capacitor
C5
10 µF/16 V
Capacitor
C6, C7
5.6 nF
Capacitor
C8, C9
68 nF
Capacitor
C10, C11
820 pF
Capacitor
D1
BAT46SW
Diode
D3
BZX79C5V1 5.1 V
Zener diode
JP1
3-pole
Jumper
JP2, JP3, JP4, JP5, JP6
2-pole
Jumper
R1
0Ω
Resistor
R2
3.17 kΩ 0.6 Ω
Resistor
R3, R4
100 kΩ
Resistor
R5, R16
20 kΩ
Resistor
R6, R7
100 kΩ
Trimmer
R8, R17
2.2 kΩ 0.4 Ω
Resistor
R9, R11, R12, R14
0.4 Ω 1 Ω
Resistor
R18, R15
5 kΩ
Trimmer
U1
L6227PD
L6227PD
The demonstration board provides external connectors for the supply voltage, an external 5
V reference for the logic inputs, four outputs for the motor and a 34-pin connector to control
the main functions of the board through an external µC board or the PractiSPINTM tool.
The PractiSPINTM tool is composed of a graphic interface software running on a PC that
connects with the hardware based on the ST7 µC, which contains upgradable firmware. This
tool allows a fast and easy evaluation of the powerSPINTM family of devices, allowing to
drive DC, BLDC and stepper motors, depending on the target device. The PractiSPINTM
connected to the EVAL6227PD can drive DC motors and inductive loads, allowing output
voltage and current settings.
Doc ID 15084 Rev 1
45/57
Demonstration boards
AN2836
The PC software also provides a power dissipation and thermal analysis section, intended
to help give a fast evaluation of the device, package and dissipating copper area required by
the user’s application, and to be a good starting point for designing an application (from the
power dissipation and thermal point of view).
Running the demonstration board in standalone mode, instead, R15 and R18 set the
reference voltage separately for the two bridges, while R8, C8 and R17, C9 are low-pass
filters which provide an external reference voltage by a PWM output of a µC (see also the
microstepping section in the AN2839). Using external VREF inputs, R5, R15, R16, R18
should be disconnected, unless the practiSPIN ST7 demonstration board is used. This
board, in fact, is provided with an offset cancellation circuitry trimmable through a
potentiometer (see PractiSPINTM documentation).
R6, C10 and R7, C11 are used to set the off-time of the two channels of the IC.
Closing JP2 and JP3 is recommended for safe overcurrent protection.
The 5 V voltage for logic inputs and for references (VrefA and VrefB) is obtained from R2 and
D3. Depending on the supply voltage, the value of resistor R2 should be changed in order to
ensure a correct biasing of D3.
The jumper JP1 allows choosing the 5 V voltage from the internal Zener diode network or
pin 11 of CN5 (for example an external µC board can provide 5 V to the demonstration
board). Also a CN2 connector can be used to provide an external 5 V voltage to the board
(in that case R2, D3 should be disconnected). CN2, or pin 1 of CN5, can also be used to
provide a 5V voltage to external circuits (as, for example, the PractiSPINTM ST7 board). In
this case the current that can be drawn form the board depends on the supply voltage and
on the value of R2.
Figure 51 to Figure 53 show the placement of the components and the two-layer layout of
the L6227PD demonstration board. A large GND area has been used, to guarantee minimal
noise and good power dissipation for the device.
Figure 49. EVAL6227PD board
*0
*0
2
2
2
*0
!-V
46/57
Doc ID 15084 Rev 1
AN2836
A.3.1
Demonstration boards
Important notes
●
JP1 : closed in INT position for use with PractiSPINTM ST7 board
●
R15, R18 : set the maximum current obtainable through PractiSPINTM (see
PractiSPINTM documentation)
●
R2 : recommended to be changed to adequate value (depending on supply voltage) to
obtain 5 V across D3
●
JP2, JP3 : closed for safe overcurrent protection
●
JP4, JP5: closed for use with PractiSPINTM ST7 board
●
JP6: open for use with PractiSPINTM ST7 board
Doc ID 15084 Rev 1
47/57
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Figure 50. EVAL6227PD electrical schematic
!-V
AN2836
Demonstration boards
Figure 51. EVAL6227PD component placement
!-V
Figure 52. EVAL6227PD top layer layout
!-V
Figure 53. EVAL6227PD bottom layer layout
!-V
Doc ID 15084 Rev 1
49/57
Demonstration boards
A.4
AN2836
EVAL6226QR
A demonstration board has been produced to help the evaluation of the device in the QFN
package. The board implemets a typical application that can be used as a reference design
to drive a two-phase bipolar stepper motor up to 1 A DC, multiple DC motors and a wide
range of inductive loads.
Thanks to the small footprint of L6226Q (QFN 5x5 mm 32 leads), the PCB is very compact
(27x24.5 mm).
Figure 58 shows the electrical schematic of the board. Table 6 gives the part list.
Table 6.
EVAL6226QR part list
Part reference
Part value
Part description
C1
220 nF/25 V
Capacitor
C2
220 nF/63 V
Capacitor
C3
10 nF/25 V
Capacitor
C4
100 µF/63 V
Capacitor
C5, C6
5.6 nF
Capacitor
D1
BAT46SW
Diodes
R1, R2, R3, R4
100 kΩ 5% 0.25 W
Resistor
R5, R6
10 kΩ 1% 0.25 W
Resistor
R9, R10
0.4 Ω 1 W
Resistor
U1
L6226Q
Dual full bridge in VFQFPN5x5
Figure 54. EVAL6226QR
!-V
The INx input pins drive the corresponding half bridge. When low logic level is applied, the
low-side MOSFET is switched on whereas a high logic level turns on the high-side
MOSFET.
Pins ENA and ENB are used to implement overcurrent and thermal protection by connecting
them respectively to the outputs DIAGA and DIAGB.
50/57
Doc ID 15084 Rev 1
AN2836
Demonstration boards
The output current detection threshold is selectable by a resistor connected between the IC
dedicated pins and ground.
D1, C1 and C3 establish a charge pump circuit, which generates the supply voltage for the
high-side integrated MOSFETs. Due to voltage and current switching at relatively high
frequency, these components are connected together through short paths in order to
minimize induced noise on other circuitries.
R1, R2 and C5, C6 are used by the overcurrent protection integrated circuitry (disable time
tDISABLE is about 200 µs and delay time tDELAY about 1 µs with the values in Table 6).
R5 and R6 are used to set the output current detection threshold at about 1.1 A typical
value.
Figure 55 and 57 show the placement of the components and the two-layer layout of the
EVAL6226QR reference design board. A GND area has been used to improve the IC power
dissipation.
Figure 55. EVAL6226QR component placement
!-V
Figure 56. EVAL6226QR top layer layout
Figure 57. EVAL6226QR bottom layer layout
!-V
Doc ID 15084 Rev 1
!-V
51/57
Demonstration boards
AN2836
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A.5
EVAL6227QR
A demonstration board has been produced to help the evaluation of the device in a QFN
package. The board implemets a typical application that can be used as a reference design
to drive a two-phase bipolar stepper motor up to 1 A DC, multiple DC motors and a wide
range of inductive loads.
Thanks to the small footprint of L6227Q (QFN 5x5 mm 32 leads), the PCB is very compact
(27x32 mm).
Figure 63 show the electrical schematic of the board. Table 7 gives the part list.
52/57
Doc ID 15084 Rev 1
AN2836
Demonstration boards
Table 7.
EVAL6226QR part list
Part reference
Part value
Part description
C1
220 nF/25 V
Capacitor
C2
220 nF/63 V
Capacitor
C3
10 nF/25 V
Capacitor
C4
100 µF/63 V
Capacitor
C5, C6
5.6 nF
Capacitor
C7, C10
820 pF
Capacitor
C8, C9
220 nF
Capacitor
D1
BAT46SW
Diodes
R1, R2, R3, R4, R7, R8, R9,
R10
100 kΩ 5% 0.25 W
Resistor
R5, R6
10 kΩ 1% 0.25 W
Resistor
R11, R13
20 kΩ 5% 0.25 W
Resistor
R12, R14
2 kΩ 1% 0.25 W
Resistor
R20, R21
0.4 Ω 1 W
Resistor
U1
L6227Q
Dual full bridge in VFQFPN5x5
Figure 59. EVAL6226QR
!-V
The INx input pins drive the corresponding half bridge. When low logic level is applied the
low-side MOSFET is switched on whereas a high logic level turns on the high-side
MOSFET.
To perform the PWM current control an analog reference voltage should be provided to each
channel of the driver. A fixed reference voltage can be easily obtained through a resistive
divider from an external voltage rail and GND (maybe the one supplying the µC or the rest of
the application).
Otherwise a very simple way to obtain a variable voltage without using a DAC is to low-pass
filter a PWM output of a µC.
Doc ID 15084 Rev 1
53/57
Demonstration boards
AN2836
D1, C1 and C3 establish a charge pump circuit, which generates the supply voltage for the
high-side integrated MOSFETs. Due to voltage and current switching at relatively high
frequency, these components are connected together through short paths in order to
minimize induced noise on other circuitries.
R1, R2 and C5, C6 are used by the overcurrent protection integrated circuitry (disable time
tDISABLE is about 200 µs and delay time tDELAY about 1 µs with the values in Table 7).
R5, C7 and R6, C10 are used to set the off-time tOFF of the two PWM channels at about
50 µs. The off-time should be adjusted according to the motor electrical characteristics and
supply voltage, changing R5, C7 and R6, C10 values.
R11, R12, C8 and R13, R14, C9 are low-pass filters which provide an external reference
voltage through a PWM output of a µC.
Figure 60 to 62 show the placement of the components and the two-layer layout of the
EVAL6227QR reference design board. A GND area has been used to improve the IC power
dissipation.
Figure 60. EVAL6227QR component placement
!-V
Figure 61. EVAL6227QR top layer layout
Figure 62. EVAL6227QR bottom layer layout
!-V
54/57
Doc ID 15084 Rev 1
!-V
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Doc ID 15084 Rev 1
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AN2836
Demonstration boards
Figure 63. EVAL6227QR electrical schematic
!-V
55/57
Revision history
AN2836
Revision history
Table 8.
56/57
Document revision history
Date
Revision
22-Jul-2009
1
Changes
Initial release
Doc ID 15084 Rev 1
AN2836
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