The TPS7H4011 features a VSNS+ and VSNS- pin to enable differential remote sensing. Therefore, the effective voltage seen by the error amplifier is (VSNS+) − (VSNS-) (which is defined as VSENSE for simplicity). As shown in Figure 8-1, this can be particularly useful when powering an FPGA due to the high currents and potentially large parasitic resistances (indicated in blue). R_parasitic1 represents the parasitic resistance in the high current input voltage path powering the FPGA. This is compensated for by using a sense line from the point of load to the top of the feedback resistor divider. R_parasitic2 represents the parasitic resistance in the high current ground path. This is accounted for by connecting a sense line from the local ground to the VSNS- pin. Some FPGAs have sense lines that may utilized for this purpose. If there is no sense line, the VSNS- pin may be connected near the FPGA ground pin itself.

Figure 8-1 FPGA Remote Sense Example

Figure 8-2 shows the more generalized case for remote sensing.

Figure 8-2 Remote Sense Diagram

During steady state operation, VSENSE will be equal to the reference voltage, V_REF (0.6V typical). By appropriately setting the resistor divider for VSNS+ and by connecting VSNS- to the remote ground, the output voltage value across the load, V_LOAD, can be set using Equation 1. TI recommends 1% tolerance or better resistors. Start with a 10kΩ for R_{FB_TOP} and use Equation 1 to calculate R_{FB_BOT}. To improve efficiency at light loads, consider using larger value resistors. If the values are too high, the regulator is more susceptible to noise and voltage errors.

where

• V_REF = 0.6V (typ)
• V_OUT(set) = voltage set point; this is the voltage regulated across the load

When utilizing the differential sensing feature, VSNS- is connected to the remote ground, and any voltage at the remote ground will offset the reference voltage on the non-inverting input to the error amplifier the corresponding amount (V_EA+ = V_REF + PGND_REMOTE). This offset at the error amplifier will then command a different output, VOUT_LOCAL. This output voltage will ensure the programmed voltage is seen across the load itself, V_LOAD. Therefore, it should be noted that V_{OUT_LOCAL} will likely be a higher voltage in order to regulate V_LOAD to the desired value.

If differential sensing is not required, connect VSNS- to GND. Then V_REF will appear on the non-inverting input of the error amplifier. In this configuration, the behavior is the same as standard, non-differential feedback. Therefore, only R_parasitic1 is accounted for, not R_parasitic2.

VSNS+ is a high impedance input with minimal leakage current. For proper operation, VSNS- outputs a small bias current of approximately 10μA. Therefore, this current will result in a small voltage drop across R_{parasitic_VSNS-} and R_parasitic2. This voltage drop adds a small error term to the VSNS- pin; however, if these parasitic resistances are minimized, the error term is generally negligible.

This remote sensing architecture is capable of sensing offsets between the remote and local ground of ±100mV. Therefore, the difference between PGND_LOCAL and PGND_REMOTE must be under 100mV.