The TPS7H3024 has a built-in
hysteresis current of
24μA with an accuracy of ±
3% (with R
HYS = 49.9kΩ). The hysteresis
current is approximately equivalent to V
HYS/R
HYS. A tolerance of
0.1% for the R
HYS resistor is recommended as the tolerance ultimately affects
the accuracy of the hysteresis current. This current is mirrored internally across all
SENSEx inputs. This hysteresis current becomes active when the SENSEx voltage is greater
than the threshold voltage (
599.7mV ±
1%, refer to
Equation 12 and
Figure 8-5). This current (I
HYS_SENSEx) multiplied by the R
TOPx resistance
induces a voltage (V
HYS_SENSEx) that is added to the SENSEx node. This
effectively boost (or increments) the node voltage (in this case V
SENSEx).
When the VOUTx voltage is
falling and becomes lower than VOUT_FALLx, the voltage is considered
as:
- Not in regulation: for an
undervoltage channel (UV).
- In regulation: for an overvoltage
channel (OV).
The hysteresis voltage is defined
as:
Equation 13.
Where:
- IHYS_SENSEx = 24 ×
10–6 Amps (or 24μA)
- RTOPx units are in
Ohms (Ω)
The falling voltage
threshold can be calculated as:
Equation 14.
Using
Equation 9 and Equation 14
Equation 15.
Where:
- VTH_SENSEx is the
nominal sense threshold voltage of 0.599V
- IHYS_SENSEx = 24 ×
10–6 Amps (or 24μA)
- RTOPx and
RBOTTOMx units are in Ohms (Ω)
The VOUTx_FALL
error can be calculated as:
Equation 16.
Equation 16 is obtained using the derivative method and under the assumptions that all variables
are uncorrelated and both resistors have the same tolerance
Where the equation terms are:
Equation 17.
Equation 18.
Equation 19.
Equation 20.
Where:
- RTOL is the
resistors tolerance (same for top and bottom resistors) as numeric value.
For example, for 0.1% tolerance resistors, we use 0.001.
- VTH_SENSEx_ACC is
the SENSEx threshold accuracy as numeric value (in this case 0.01).
- IHYS_SENSEx_ACC is
the hysteresis current accuracy as numeric value (in this case 0.03).
- VTH_SENSEx is the
nominal sense threshold voltage of 0.599V.
- IHYS_SENSEx = 24 ×
10–6 Amps (or 24μA).
- RTOPx and
RBOTTOMx units are in Ohms (Ω).
Using Equation 15 and Equation 16 we can calculate the falling voltage range as:
Equation 21.
Figure 8-6, shows a conceptual diagram of the rising and falling voltage, the diagram also
shows the errors on this voltage due to VTH accuracy, IHYS
accuracy, and the resistive divider tolerances. At the system level, take into
account errors for a robust design.