Covers value selection and details relating to the current-sense and current-limit device pins (RILIM, RSNS, SNS/CS) on TI high-side switches, including accuracy, temperature drift, and using the sense output for closed-loop control or open-load detection.
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Device Type |
Question |
Answer |
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HSS |
How do I calculate the RILIM resistor value and understand the actual current limit range? |
Use TI's H_HB_HC_ICLPDISS_calculator.xlsm. Enter your target current limit to get the theoretical RILIM, then enter your chosen standard resistor value and tolerance. Accuracy varies: ±20% at low settings, ±3% at higher settings. Formula: ICL = (RILIM × VCL) / KCL — see datasheet for device-specific VCL and KCL constants. Use 0.1–0.5% resistors to keep gain error below 1%. Sources: |
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HSS |
How do I scale the RSNS resistor when operating at low supply voltage (e.g., 6V cold crank)? |
At low VBB, standard RSNS values (calculated for 12V) push ISNSFH out of spec. Constraint: VBB − ISNSFH × (RSNS + 200) > 0.7. At VBB=6V with ISNSFH=4–5.3mA, RSNS(max) ≈ 800Ω. Always recalculate RSNS for the lowest expected supply voltage in your application. Source: |
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HSS |
How accurate is the integrated current sense output, and can I use it for closed-loop control? |
Typically ±3–5% at rated conditions, no external shunt required. Accuracy degrades at very low current and temperature extremes. Usable for closed-loop control (e.g., seat heater power-based temperature regulation). Calibrate at operating temperature for highest accuracy; use the K_SNS tempco from the datasheet for thermal compensation. Sources: |
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HSS |
How does the SNS pin work, and how do I select the RSNS and RILIM resistors? |
SNS pin outputs a current proportional to load current via internal sense ratio K_SNS (e.g., 1µA per 1mA of load). VSNS = I_LOAD × K_SNS × RSNS. RILIM programs the overcurrent trip: RILIM = V_ILIM_REF / (K_SNS × I_LIMIT). Use 0.1–0.5% tolerance resistors. Check RSNS maximum in the datasheet — too large a value clamps the SNS pin and trips current limit early at low loads.
Related figure: SLVAG11 (Basics of High-Side Switches and Controllers), Figure 3-4 “Basic High-Side Switch Current Sense Implementation” shows the sense-MOSFET current mirror and RSNS/ADC path described above — ti.com/lit/pdf/slvag11. Sources: |
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HSS |
Why does my measured VSNS voltage differ from what the datasheet formula predicts? |
Most common causes:
Verify VSNS at steady state = I_LOAD × K_SNS × RSNS at measured TJ before concluding a device issue. Sources: |
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HSS |
Can I use a high-side switch to limit load current down to the milliamp range? |
Yes, but minimum programmable current limit for most TPS1H/TPS2H parts is hundreds of mA. For sub-100mA limiting, the integrated current limit is unreliable. Instead, place a high-accuracy current-sense amplifier (e.g., INA228) downstream and implement software current limiting in the MCU, using the HSS purely for protection and switching. Sources: |
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HSS |
How do I use the SNS output to detect load changes or open-load events without a full ADC? |
The SNS pin current feeds a window comparator or an RSNS-to-GPIO threshold for binary detection. With switch ON and no load, SNS current is near zero, pulling VSNS below threshold — indicating open load. For granular tracking, ±3–5% linearity enables proportional current readout with only RSNS gain-setting — one MCU ADC channel is sufficient. The TPS272C45 datasheet includes a worked example for detecting quantized load steps (e.g., 1-lamp vs. 2-lamp). Sources: |
