STWBC2-HP datasheet(13/96 Pages) STMICROELECTRONICS

13 / 96 page

Table 6. VIN current monitor operating parameters

Parameter

Value

Multiplication factor from V(VIN_SNS_P, VIN_SNS_N) to ADC mux

x 4.1

LPF

160Hz 2nd order

2.1.4.5

Bridge current monitor (Bridge_I)

The Bridge Current Sense stage provides a voltage proportional to the filtered value of current flowing in

RBRG_SNS to the ADC MUX. Since the sense resistor RBRG_SNS is placed at the bridge GND node, a

synchronous rectification is indirectly applied on the sensed voltage.

The current flowing in the sense resistor can be positive or negative; the zero cross detector is a simple

comparator (ZCD COMP) providing the polarity of the current flowing in RBRG_SNS.

The required 2nd order low pass filter (1 ms LPF) is implemented by means of external passive components as

shown in the figure below (requirement is T=1ms ±10%).

Figure 16. Bridge current monitor

Table 7. Bridge current monitor operating parameters

Parameter

Condition

Value

Multiplication factor from V(BRG_ISNS_P, BRG_ISNS_N) to ADC mux

Gain = 0

x 4

Gain = 1

x 8

Gain = 2

x 16

Gain = 3

x 32

2.1.4.6

Ring voltage monitor (Ring_V)

The tank ring voltage is AC coupled with the STWBC2-HP using an RC circuit. As RNG_SNS pin is maintained at

a fixed voltage, the ring voltage is converted in current flowing in the RNG_SNS pin thanks to the resistor:

IRNG_SNS=VRINGR

The current to voltage amplifier (IV) converts the input current in voltage. It rectifies also the signal.

The peak-to-peak detector tracks the positive and negative peaks of the ring signal.

The RNG_FT_S pin is driven by the rectified signal from IV converter or from the peak-to-peak detector. An

external 1 ms low pass filter is connected to the RNG_FT_S pin.

The output of the external low pass filter is connected to the RNG_FT_R pin. This signal is internally routed to the

ADC mux Ring_V input.

STWBC2-HP

Analog AFE functions

DS13825 - Rev 1.0

page 13/96

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