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LTC2908CDDB-B1 Datasheet(PDF) 8 Page - Linear Integrated Systems |
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LTC2908CDDB-B1 Datasheet(HTML) 8 Page - Linear Integrated Systems |
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8 / 16 page  8 LTC2908 sn2908 2908fs APPLICATIO S I FOR ATIO Supply Monitoring The LTC2908 is a low power, high accuracy, six input supply monitoring circuit with two adjustable inputs. The reset delay is set to a nominal of 200ms with an internal capacitor, eliminating the need for an external timing capacitor. All input voltages must be above predetermined thresh- olds for the reset not to be invoked. The LTC2908 asserts the reset output during power-up, power-down and brown- out conditions on any one of the voltage inputs. Ultralow Voltage Pull-Down on RST The LTC2908 issues a logic low on the RST output when any one of the inputs falls below its threshold. 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 LTC2908 power supply supervisor incorporates a novel low voltage pull-down circuit that can hold the RST line low with as little as 200mV of input supply voltage on V1 and/or V2 (see Figures 1 and 2). The pull-down circuit helps maintain a low impedance path to ground, reducing the risk of the RST node from floating to an indeterminate voltage. Such an indeterminate voltage may trigger external logic causing erroneous reset operation(s). Furthermore, a mid-scale voltage level could cause external circuits to operate in the middle of their voltage transfer character- istic, consuming more quiescent current than normal. These conditions could cause serious system reliability problems. Power-Up During power-up, RST starts asserting low as soon as there is at least 200mV on V1 and/or V2. The RST pull- down capability is a function of V1 and V2 as shown in the Typical Performance Characteristics. The greater of V1, V2 is the internal supply voltage (VCC) that powers the other internal circuitry. Once all the VX inputs rise above their thresholds, an internal timer is started. After the internal timer counts a 200ms delay time, RST weakly pulls high to VCC. Power-Down On power-down, once any of the VX inputs drop below their threshold, RST asserts logic low. VCC of at least 0.5V guarantees a logic low of 0.15V at RST. SUPPLY VOLTAGE, VCC (V) 0.01 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 G16 VCC = V1 = V2 V3 = V4 = VADJ1 = VADJ2 = GND RST AT 150mV RST AT 50mV SUPPLY VOLTAGE, VCC (V) 0.01 0.1 1 10 0 0.4 0.6 0.8 0.001 0.2 1 2908 G17 VCC = V1 V2 = V3 = V4 = VADJ1 = VADJ2 = GND RST AT 150mV RST AT 50mV Figure 1. RST Pull-Down Current (IRST) vs Supply Voltage (VCC) with Dual Channel Supply Figure 2. RST Pull-Down Current (IRST) vs Supply Voltage (VCC) with Single Channel Supply |
Similar Part No. - LTC2908CDDB-B1 |
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Similar Description - LTC2908CDDB-B1 |
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