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LTC4211CMS Datasheet(PDF) 10 Page - Linear Technology |
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LTC4211CMS Datasheet(HTML) 10 Page - Linear Technology |
10 / 36 page 10 LTC4211 4211f PI FU CTIO S RESET (Pin 1/Pin 1): An open-drain N-channel MOSFET whose source connects to GND (Pin 4/Pin 5). This pin pulls low if the voltage at the FB pin (Pin 5/Pin 6) falls below the FB pin threshold (1.236V). During the start-up cycle, the RESET pin goes high impedance at the end of the second timing cycle after the FB pin goes above the FB threshold. This pin requires an external pull-up resistor to VCC. If an undervoltage lockout condition occurs, the RESET pin pulls low independently of the FB pin to prevent false glitches. ON (Pin 2/Pin 2): An active high signal used to enable or disable LTC4211 operation. COMP1’s threshold is set at 1.236V and its hysteresis is set at 80mV. If a logic high signal is applied to the ON pin (VON > 1.316V), the first timing cycle begins if an overvoltage condition does not exist on the GATE pin (Pin 6/Pin 7). If a logic low signal is applied to the ON pin (VON < 1.236V), the GATE pin is pulled low by an internal 200 µA current sink. The ON pin can also be used to reset the electronic circuit breaker. If the ON pin is cycled low and then high following a circuit breaker trip, the internal circuit breaker is reset, and the LTC4211 begins a new start-up cycle. TIMER (Pin 3/Pin 4): A capacitor connected from this pin to GND sets the LTC4211’s system timing. The LTC4211’s initial and second start-up timing cycles and its internal “power good” delay time are defined by this capacitor. GND (Pin 4/Pin 5): Device Ground Connection. Connect this pin to the system’s analog ground plane. FB (Pin 5/Pin 6): The FB (Feedback) pin is an input to the COMP2 comparator and monitors the output supply volt- age through an external resistor divider. If VFB < 1.236V, the RESET pin pulls low. An internal glitch filter at COMP2’s output helps prevent negative voltage transients from triggering a reset condition. If VFB > 1.239V, the RESET pin goes high after one timing cycle. GATE (Pin 6/Pin 7): The output signal at this pin is the high side gate drive for the external N-channel FET pass transistor. (8-Lead Package/10-Lead Package) As shown in the Block Diagram, an internal charge pump supplies a 10 µA gate current and sufficient gate voltage drive to the external FET for supply voltages from 2.5V to 16.5V. The internal charge-pump and zener clamps at the GATE pin determine the gate drive voltage ( ∆VGATE = VGATE – VCC). The charge pump produces a minimum 4V of ∆VGATE for supplies in the range of 2.5V < VCC < 4.75V. For VCC > 4.75V, the ∆VGATE is limited by zener clamp Z1 connecting between GATE and VCC pins. The ∆VGATE is typically at 12V and with guaranteed minimum value of 10V. For VCC > 15V, the zener clamp Z2 sets the limitation for ∆VGATE. Z2 clamps the gate voltage to ground to 26V typically. The minimum Z2’s clamp voltage is 23V. This effectively sets ∆VGATE to 8V minimum. SENSE (Pin 7/Pin 8): Circuit Breaker Set Pin. With a sense resistor placed in the power path between VCC and SENSE, the LTC4211’s electronic circuit breaker trips if the voltage across the sense resistor exceeds the thresholds set internally for the SLOW COMP and the FAST COMP, as shown in the Block Diagram. The threshold for the SLOW COMP is VCB(SLOW) = 50mV, and the electronic circuit breaker trips if the voltage across the sense resistor exceeds 50mV for 20 µs. The SLOW COMP delay is fixed in the S8/MS8 version and adjustable in the MS version of the LTC4211. To adjust the SLOW COMP’s delay, please refer to the section on Adjusting SLOW COMP’s Response Time. Under transient conditions where large step current changes can and do occur over shorter periods of time, a second (fast) comparator instead trips the electronic circuit breaker. The threshold for the FAST COMP is set at VCB(FAST) = 150mV, and the circuit breaker trips if the voltage across the sense resistor exceeds 150mV for more than 300ns. The FAST COMP’s delay is fixed in the LTC4211 and cannot be adjusted. To disable the electronic circuit breaker, connect the VCC and SENSE pins together. VCC (Pin 8/Pin 9): This is the positive supply input to the LTC4211. The LTC4211 operates from 2.5V < VCC < 16.5V, and the supply current is typically 1mA. An internal undervoltage lockout circuit disables the device until the voltage at VCC exceeds 2.3V. |
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