ZXBM1016
Issue 1 - February 2007 6 www.zetex.com
© Zetex Semiconductors plc 2007
Control input
The device is controlled from a voltage applied to the SPD pin input. This control voltage can be
derived from an externally generated PWM signal. This signal is converted to a voltage in a
conventional integrator external to the device. Alternatively an external thermistor network can
be used to generate the voltage.
Tail-end current control
To minimize the current at the end of a commutation cycle, the tail current, a proprietary circuit
technique is provided. A number of pins are used to give control over the function. The current is
controlled using the internal PWM function and this acts together with the PWM speed control,
the current control and the start-up function.
Start-up function
The device has a controlled start function prior to the device going into the tail-end current control
mode. This allows the motor to start up at its minimum speed before being allowed to accelerate
to the speed defined by the voltage on the SPD pin.
Device protection
Two levels of protection are provided for fault conditions. The first level of protection is the
conventional lock function. If the motor is stopped or stalled for any reason the motor will enter
the locked rotor condition. In this locked rotor condition the motor speed is set to minimum speed
and the ZXBM1016 will attempt to restart the motor at periodic intervals.
A second level of protection is provided by a current monitor function. An external 100m⍀ sense
resistor is used to detect the current and this is compared with a preset voltage on the SetTh pin.
If the current attempts to rise above the threshold voltage the internal PWM circuit will back-off
the power being delivered to the coil to ensure the maximum is not exceeded.
Pin functional description
H+ - Positive Hall input
H- - Negative Hall input
The rotor position is detected by a Hall sensor, with the output applied to the H+ and H- pins. This
sensor can be either a 4 pin 'naked' Hall device or of the 3 pin buffered switching type. For a 4 pin
device the differential Hall output signal is connected to the H+ and H- pins. For a single-ended
buffered Hall sensor the Hall device output is attached to the H+ pin, with a pull-up attached if
needed. The H- pin has an external potential divider attached to hold the pin at a voltage that is
half of the output swing of the Hall sensor. When H+ is high in relation to H-, Ph2 is the active
drive.
H-Bias - Hall bias output voltage
This is a 1.75V nominal voltage source used to bias a differential unbuffered Hall sensor when
that type is being utilized.
ThRef - External network reference
This is a reference voltage of nominal 5V and is used by external networks to set up the SPD and
S
MIN
pins control voltages.
It is designed for the ability to 'source' current and therefore it will not 'sink' any current from a
higher voltage. The total current drawn from the pin by the minimum speed potential divider
network and any other voltage setting network should not exceed 10mA.
