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LTC2934ITS8-2-TRPBF Datasheet(PDF) 8 Page - Linear Technology |
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LTC2934ITS8-2-TRPBF Datasheet(HTML) 8 Page - Linear Technology |
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8 / 12 page  LTC2934 8 2934f APPLICATIONS INFORMATION Figure 3. RST vs VCC with 10k Pull-Up R3 is easily obtained from: R3 = RSUM – R1 – R2 = 8.1M – 1.87M – 130k = 6.1M The closest 1% value is 6.04M. Plugging the standard values back into the equations yields the design values for the falling power-fail and reset voltages: VPF = 1.720V, VR = 1.608V Figure 2 demonstrates how the inputs can be biased to monitor two voltages (V1, V2). In this example, four resistors are required. Calculate each divider ratio for the desired falling threshold (VFT) using: RnB RnA V V V V FT TH FT = − = − 1 04 1 . In Figure 2, PFO is tied back to the MR input, making the state of the RST output dependent upon both V1 and V2. If V1 and V2 are both above the configured falling threshold plus hysteresis, RST is allowed to pull high. If independent operation of the status outputs is desired, simply omit the PFO to MR connection. Selecting Output Logic Style The LTC2934 status outputs are available in two options: open-drain (LTC2934-1) or active pull-up (LTC2934-2). The open-drain option (LTC2934-1) allows the outputs to be pulled up to a user defined voltage with a resistor. The open-drain pull-up voltage may be greater than VCC (5.5V maximum), which is not always possible with inferior battery supervisors, due to internal diode clamps. When the status outputs are low, power is dissipated in the pull-up resistors. Recommended resistor values lie in the range between 10k and 470k. Figure 3 demonstrates typical LTC2934-1 RST output behavior. The active pull-up option (LTC2934-2) eliminates the need for external pull-up resistors on the status outputs. Integrated pull-up devices pull the outputs up to VCC. Actively pulled up outputs may not be driven above VCC. Some applications require the RST and/or PFO outputs to be valid with VCC down to ground. Active pull-up handles this requirement with the addition of an external resistor from the output to ground. The resistor provides a path for leakage currents, preventing the output from floating to undetermined voltages when connected to high impedance (such as CMOS logic inputs). The resistor value should be small enough to provide effective pull-down without excessively loading the pull-up circuitry. A 100k resistor from output to ground is satisfactory for most applications. When the status outputs are high, power is dissipated in the pull-down resistors. Figure 4 demonstrates typical LTC2934-2 RST output behavior. Figure 4. RST vs VCC ADJ PFI LTC2934 V1 V2 R1B R2B R2A R1A RST PFO MR Figure 2. Dual Voltage Monitoring VCC (V) 0 2.0 2.5 3.0 1.5 1.0 12 0.5 1.5 2.5 3 3.5 0.5 0 3.5 2934 F03 EXTERNALLY CONFIGURED FOR 3V FALLING THRESHOLD LTC2934-1 VCC (V) 0 2.0 2.5 3.0 1.5 1.0 12 0.5 1.5 2.5 3 3.5 0.5 0 3.5 2934 F04 EXTERNALLY CONFIGURED FOR 3V FALLING THRESHOLD LTC2934-2 |
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Similar Description - LTC2934ITS8-2-TRPBF |
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