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LTC1326C-2.5 Datasheet(PDF) 9 Page - Linear Technology |
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LTC1326C-2.5 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page 9 LTC1326/LTC1326-2.5 During a supply induced reset condition, the ability of the PBR pin to force a soft reset condition on the SRST pin is disabled. In other words SRST will remain high. If the PBR pin is held low, both during and after a supply induced reset (low RST), the RST pin will remain low until 200ms after the PBR goes high. Power Detect/Gate Drive The LTC1326/LTC1326-2.5 for the most part are powered internally from the VCC3 pin. The exception is at the gate drive of the output FET on the RST pin. On the input to this FET is power detection circuitry used to detect and drive the gate from either the 3.3V input pin (VCC3) or the 5V input pin (VCC5) on the LTC1326 or the 2.5V input pin (VCC25) on the LTC1326-2.5. The gate drive is derived from the pin with the highest potential. This ensures the part pulls the RST pin low as soon as either input pin is ≥ 1V. Early versions of the LTC1326 did not have the power detect/gate drive circuitry. These early versions were powered off of VCC3 alone. Consult factory for date codes concerning this circuitry change. All date codes of the LTC1326-2.5 have the power detect/gate drive circuits. Dual and Single Supply Monitor Operation The VCC3, VCC5 and VCCA inputs may be individually disabled by the following override techniques which allow the LTC1326 or LTC1326-2.5 to be used as a dual or single supply monitor. LTC1326 Override Functions The VCCA pin, if unused, can be tied to either VCC3 or VCC5. This is an obvious solution since the trip points for VCC3 and VCC5 will always be greater than the trip point for VCCA. The VCC5 input trip point is disabled if its voltage is equal to the voltage on VCC3 ±25mV and the voltage on VCC5 is less than 4.15V. In this manner the part will behave as a 3.3V monitor and the VCC5 reset will be disabled. The VCC5 trip point is reenabled when the voltage on VCC5 is equal to the voltage on VCC3 ±25mV and the two inputs are greater than approximately 4.15V. In this manner the LTC1326 can function as a 5V monitor with the 3.3V monitor disabled. When monitoring either 3.3V or 5V with VCC3 strapped to VCC5, (see Figure 1) the LTC1326 determines which is the appropriate range. The LTC1326 handles this situation as shown in Figure 2. Above 1V and below VRT3, RST is held low. From VRT3 to approximately 4.15V the LTC1326 assumes 3.3V supply monitoring and RST is deasserted. Above approximately 4.15V the LTC1326 operates as a 5V monitor. In most systems the 5V supply will pass through the 3.1V to 4.15V region in <200ms during power-up, and the RST output will behave as desired. Table 1 summarizes the state of RST and RST at various operating voltages with VCC3 = VCC5. APPLICATIO S I FOR ATIO Table 1. Override Truth Table (VCC3 = VCC5) INPUTS (VCC3 = VCC5 = VCC) RST RST 0V ≤ VCC ≤ 1V — — 1V ≤ VCC ≤ VRT3 01 VRT3 ≤ VCC ≤ 4.15V 1 0 4.15V ≤ VCC ≤ VRT5 01 VRT5 ≤ VCC 10 Figure 2. RST Voltage vs Supply Voltage 1 2 3 4 8 7 6 5 VCC3 VCC5 VCCA GND PBR SRST RST RST LTC1326 SYSTEM RESET R2 1326/2.5 F01 R1 ADJUSTABLE SUPPLY 3.3V OR 5V 4.7k Figure 1 SUPPLY VOLTAGE (V) 0 3 4 5 4 1326/2.5 F02 2 1 0 1 2 3 5 VCC3 = VCC5 = VCCA = 0V TO 5V 4.7k PULL-UP FROM RST TO VCC3 |
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Similar Description - LTC1326C-2.5 |
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