SLA7042 查看數據表（PDF） - Allegro MicroSystems
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SLA7042 Datasheet PDF : 8 Pages
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SLA7042M AND SLA7044M
MICROSTEPPING,
UNIPOLAR PWM, HIGH-CURRENT
MOTOR CONTROLLER/DRIVERS
REFERENCE/ENABLE INPUT
The serial DATA input port is enabled (active low) by
the REFERENCE/ENABLE input when VREF/EN is between
0.4 V and 2.5 V. With VREF/EN greater than VDD - 1 V, the
serial DATA input port is disabled, the outputs are OFF,
and the controller/driver will not be affected by changes at
the DATA, CLOCK, or STROBE inputs.
With VREF/EN between 0.4 V and 2.5 V, the output
current limit is a linear function of VREF and the step
reference current ratio.
IOUT ≈
VREF
3 • RS
• SRCR
In a typical (SLA7042M) application where VDD = 5 V,
a VREF/EN between 0.4 V and 2.5 V, and a maximum
allowable load current of 1.2 A, the maximum value of RS
is 0.69 Ω and IOUTmin is 0.11 A when SRCR is 100%
(DATA input = 111X).
POWER DISSIPATION CALCULATIONS
The SLA7042/44M normally do not require special
heat sinking except under unusual circumstances (two
phases operating near maximum output current and TA
>65°C). However, as with all power drivers, the basic
constituents of power dissipation should be evaluated.
Conduction losses (internal power dissipation) include:
(a) FET output power dissipation (IOUT2 • rDS(on) or
IOUT • VDS(ON)),
(b) FET body diode power dissipation (VSD • IOUT), and
(c) control circuit power dissipation (VDD • IDD).
PACKAGE RATINGS/DERATING FACTORS
Thermal calculations must also consider the tempera-
ture effects on the output FET ON resistance. The appli-
cable thermal ratings for the 18-lead power-tab SIP PMCM
package are:
RθJA = 28°C/W (junction to ambient with no heat sink)
or 4.5 W at +25°C and a derating factor of -36 mW/°C
for operation above +25°C.
RθJM = 5°C/W (junction to mounting surface).
TEMPERATURE EFFECTS ON FET rDS(on)
Analyzing safe, reliable operation includes a concern
for the relationship of NMOS ON resistance to junction
temperature. Device package power calculations must
include the increase in ON resistance (producing higher
output ON voltages) caused by higher operating junction
temperatures. Figure 5 provides a normalized ON resis-
tance curve, and all thermal calculations should consider
increases from the given +25°C limits, which may be
caused by internal heating during normal operation.
2.5
2.0
1.5
1.0
0.5
0
-40
0
+40
+80
+120
JUNCTION TEMPERATURE in °C
+160
Dwg. GK-017
FIGURE 5.␣ NORMALIZED ON RESISTANCE
vs TEMPERATURE
The power MOSFET outputs of these devices are
similar to the International Rectifier type IRL510
(SLA7042M) and IRL520 (SLA7044M). These devices
feature an excellent combination of fast switching, rugged-
ized device design, low on-resistance, and cost effective-
ness.
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