Diodes ZXBM1021 - Manual (Page 9)

ZXBM1021
Document number: DS36322 Rev. 2 - 2
9 of 25
www.diodes.com
April 2014
© Diodes Incorporated
ZXBM1021
Functional Descriptions
(cont.)
Sense – Current Control Sense
This pin is used by the current sensing circuit to monitor the current taken by the motor windings. The signal comes from a sense resistor in the
low-side ground return of the external H-bridge driver.
SetTh – Current Control Threshold Voltage
This pin is used by the current sensing circuit as the reference voltage for the voltage on the sense pin to be compared against. If the voltage on
the sense pin starts to exceed the voltage set on this pin the current control circuitry starts to back off the output drive PWM duty and thus
reducing the current being supplied to the motor coil.
SetThRef – SetTh and Start-up Reference
This pin is derived from an internal start-up circuit and is used as the source voltage for the potential divider network attached to the SetTh pin.
Under running conditions this voltage will be typically ThRef-0.1V. However, during start up the voltage ramps up from 0V to ThRef-0.1V at a rate
determined by the capacitor on the C
LCK
pin giving a gradual release of current limit from 0 to nominal setting. ThRef-0.1V is equal to 4.9V
typical.
This low power pin is capable of supplying a maximum of 200µA. It should only be used to supply the potential divider network attached to the
SetTh pin.
Ph1Lo and Ph2Lo – Low-Side External H-Bridge Drive Output
Ph1Lo and Ph2Lo outputs drive the low side of the external power device H-bridge that in turn drives the single phase winding. These outputs
provide both the commutation and PWM waveforms. The outputs are active pull-up and active pull-down to help faster switching off when driving
MOSFET devices with a high gate capacitance. When in the high state the outputs will provide up to 100mA of drive into the base or gates of
external transistors as shown in the typical application circuit shown on the front page.
When in the low state the active phase drive is again capable of sinking up to 100mA to aid turn off times during PWM operation. When the
phase is inactive the output is held low by a 7.5k Ω internal pull-down resistor.
Ph1Hi and Ph2Hi – High-Side External H-Bridge Driver
Ph1Hi and Ph2Hi are the high side outputs to the external H-bridge and are open collector outputs capable of sinking 50mA. This signal provides
commutation only to the H-bridge.
V+OP – Phase Outputs Supply Voltage
This pin is the supply to the Phase outputs Ph1Lo and Ph2Lo only. This pin can be connected to V
CC
pin directly or through a resistor. For
external Bipolar power devices the resistor on V+OP is used to control the current into the transistor base and its value is chosen accordingly.
For external MOSFET power devices, the pin can be used to slow down the turn-on speed of the low-side MOSFETS. Slowing down the turn-on
speed of low side switches helps to prevent parasitic turn-on of the high-side switches and thus helping to prevent shoot-through during turn-on
of low-side switches. The gate resistor connected at Ph1Lo and Ph2Lo plus the resistor on V+OP controls the turn on speed of the MOSFET.
The turn-off of speed of the MOSFETS is controlled by the gate resistor only.
V
CC
– IC Supply voltage
This provides the supply for the device's internal circuitry except Ph1Lo and Ph2Lo output stages, which are supplied from the V+OP pin.
For 12V fans this can be supplied directly from the Fan Motor supply. For fans likely to run in excess of the 18V maximum rating for the device
this will be supplied from an external regulator such as a Zener diode or low drop out regulator.
GND – Supply Return
This is the device supply ground return pin and will generally be the most negative supply pin to the fan.