A8904SLP Allegro Microsystems Inc, A8904SLP Datasheet - Page 13

• Manufacturer Part Number: A8904SLP
• Description: IC CTRLR/DRVR DC MOTOR 28TSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8904SLP

• Applications: DC Motor Driver, Brushless (BLDC), 3 Phase
• Number Of Outputs: 1
• Current - Output: ±1.4A
• Voltage - Load: 4 V ~ 14 V
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A8904
between the TACH and REF signal. If the TACH signal goes low
before the REF signal then an ERROR FAST is produced and if
the TACH signal goes low after the REF signal then an ERROR
SLOW is produced. The error signal generated enables the ap-
propriate current source (see diagram next page) to either charge
or discharge the fi lter components on the FILTER terminal.
rent control in the windings via the transconductance stage (see
diagram next page). The output current is sensed through an
internal sense resistor, R
A speed error signal is created by integrating the differences
The FILTER voltage is then used to provide linear cur-
Speed error signals
S
. The voltage across the sense resistor
3-Phase Brushless DC Motor Controller/Driver
Functional Description (cont’d)
is compared to the lowest of either one-tenth of the voltage at
the FILTER terminal, minus the fi lter threshold voltage, or to the
maximum current limit reference.
be introduced by disabling the frequency-lock loop circuitry
(D24 = 1).
where R
V
G = 1, when D28 = 0 and gain = 500 mA/V or
G = 2, when D28 = 1 and gain = 250 mA/V.
shaped via the fi lter components that are introduced at the FIL-
TER terminal.
(D3 & D4) provides output current limit protection. This feature
is particularly useful where high transient currents are experi-
enced, e.g., during start-up. Once normal running conditions are
reached, the current limit can be appropriately reduced. Note that
the current limit is scaled according to the g
tor or index pulses, can be used to create the TACH signal, rather
than the internally generated once-around scheme. The external
signal is applied to the SECTOR DATA terminal and the serial
port bit (D19 = 1) must be programmed to enable this feature.
FILTERTH
Alternatively, external control of the FILTER terminal can
The transconductance function is defi ned as:
The closed loop control response of the overall system is
Clamping the current to a level defi ned by the serial port
Sector mode. An external tachometer signal, such as sec-
S
I
is nominally 200 m,
is approximately 1.85 V,
OUT
= (V
with Back EMF Sensing
FILTER
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
– V
FILTERTH
) / (10 x R
m
value selected.
S
x G)
12