MLX16305 Datasheet, PDF (14/29 Pages) Melexis Microelectronic Systems – Interlock switch sensor interface IC

MLX16305
Interlock switch sensor interface IC
10. Current mode (CM)
The high accuracy of the MLX16305 can be used
• to define clear boundaries of voltages. These boundaries will allow straightforward classification
of the state of current modulated switches.
• to measure industry standard current modulated sensors (for instance with the MLX90308,
MLX90314)
10.1. Current to Voltage conversion principle
The current ISENSE, supplied by the voltage regulator, is copied on the RREF pin with a 10:1 ratio. This
current is converted into voltage information via the external RREF resistor. An additional offset current is
forced on Rref. This results in a voltage over the RREF resistor of
• V_RREF = (I_SENSE / 10 + I_OFFSET) * R_REF
This V_RREF is then copied on the MEASOUT pin with a factor of 0.9, i.e.:
• V_MEASOUT = V_RREF * 0.9
10.2. The actual measurement
In current mode 2 type of measurements can be distinguished:
1) Offset measurement
While the voltage regulator is disabled, the contribution of the internal offset current can be measured.
• V_MEASOUT (Vreg is disabled) = V_{MEASOUT_IOFFSET}
2) Actual Isense measurement
When a channel is selected and ENABLE is set high, the Isense of the selected channel will be copied on
top of the offset current onto RREF.
• V_{MEASOUT _}(Vreg Enabled) = V_{MEASOUT_ENABLED}
From this we can derive
• V_{CALC_ISENSE} = V_{MEASOUT_ENABLED} - V_{MEASOUT_IOFFSET}
Remarks:
• The current is always copied directly from the voltage regulator. Therefore as soon as ENABLE
has gone high to fix which channel is supplied (MUX_SUP is fixed), then MUX_SENSE becomes
don’t care!
3901016305
Rev. 005
Page 14 of 29
Data Sheet
Oct/06