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LTC2903A Datasheet(PDF) 10 Page - Linear Technology |
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LTC2903A Datasheet(HTML) 10 Page - Linear Technology |
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10 / 16 page  10 LTC2903-1 29031f APPLICATIO S I FOR ATIO Power-Up The LTC2903-1 issues a logic low on the RST output when an input supply voltage resides below the prescribed threshold voltage. Ideally, the RST logic output would remain low with the input supply voltage down to zero volts. Most supervisors lack pull-down capability below 1V. The LTC2903-1 power supply supervisors incorporate a new low voltage pull-down circuit that can hold the RST line low with as little as 200mV of input supply voltage on V1, V2 or V3. The pull-down circuit helps maintain a low impedance path to ground, reducing the risk of floating the RST node to undetermined voltages. Such voltages may trigger external logic causing erroneous reset operation(s). Furthermore, a mid-scale voltage could cause external circuits to operate in the middle of their voltage transfer characteristic, consuming more quiescent current than normal. These conditions could cause serious system reliability problems. When V1, V2 and V3 are ramped simultaneously, the reset pull-down current increases up to three times the current that may be pulled with a single input. Figure 1 demon- strates the reset pin current sinking ability for single supply and triple supply-tracking applications. Figure 2 shows a detailed view of the reset pin voltage with a 10k pull-up resistor to V1. The LTC2903-1 supervisors derive their internal supply voltage (VCC) automatically from the greater voltage on the V1 and V2 inputs. With all supply inputs above threshold, the quiescent current drawn from VCC is 20µA (typ). Supply Monitoring The LTC2903-1 accurately monitors four inputs in a small 6-lead SOT-23 package. The low voltage reset output includes an integrated 200ms reset delay timer. The reset line pulls high 200ms after all voltage inputs exceed their respective thresholds. The reset output remains low dur- ing power-up, power-down and brownout conditions on any of the voltage inputs. For applications requiring an adjustable trip threshold, use the V4 input on the LTC2903-A1. Connect the tap point on an external resistive divider (R1, R2) placed between the positive voltage being sensed and ground, to the high impedance input on V4. The LTC2903-A1 compares the voltage on the V4 pin to the internal 0.5V reference. Figure 3 shows a generic setup for the positive adjustable application. Figure 3. Setting the Positive Adjustable Trip Point VCC (V) 10 1000 10000 0 0.8 1.2 29031 F01 1 0.4 0.2 1.0 0.6 100 V1 = V2 = V3 V1 ONLY TA = 25°C VRST = 0.3VCC Figure 1. RST Pull-Down Current vs VCC V1 (V) 0 0 0.1 0.3 0.4 0.5 0.7 0.1 0.5 0.7 39031 F02 0.2 0.6 0.4 0.9 1.0 0.2 0.3 0.6 0.8 TA = 25°C V1 ONLY COMPETITION PART V1 = V2 = V3 – + 0.5V 29031 F03 V4 VTRIP R1 1% LTC2903-A1 R2 1% + – Figure 2. RST Output Voltage with a 10k Pull-Up to V1 (Enlarged Area of Detail) |
Similar Part No. - LTC2903A |
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Similar Description - LTC2903A |
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