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LM2734Z 데이터시트(PDF) 9 Page - Texas Instruments |
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LM2734Z 데이터시트(HTML) 9 Page - Texas Instruments |
9 / 32 page LM2734 VIN BOOST SW GND L D1 D2 D3 R3 C4 VBOOST CBOOST VZ V IN C IN V OUT C OUT LM2734Z www.ti.com SNVS334E – JANUARY 2005 – REVISED APRIL 2013 R3 will then be given by R3 = (VIN - VZENER) / (1.25 x IBOOST + IZENER) (10) For example, let VIN = 10V, VZENER = 5V, VD2 = 0.7V, IZENER = 1mA, and duty cycle D = 50%. Then IBOOST = (0.5 + 0.5) x (5 - 0.7) mA = 4.3mA (11) R3 = (10V - 5V) / (1.25 x 4.3mA + 1mA) = 787 Ω (12) Figure 12. Boost Voltage Supplied from the Shunt Zener on VIN ENABLE PIN / SHUTDOWN MODE The LM2734Z has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is applied to EN, the part is in shutdown mode and its quiescent current drops to typically 30nA. Switch leakage adds another 40nA from the input supply. The voltage at this pin should never exceed VIN + 0.3V. SOFT-START This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s reference voltage ramps from 0V to its nominal value of 0.8V in approximately 200µs. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. OUTPUT OVERVOLTAGE PROTECTION The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control switch is turned off, which allows the output voltage to decrease toward regulation. UNDERVOLTAGE LOCKOUT Undervoltage lockout (UVLO) prevents the LM2734Z from operating until the input voltage exceeds 2.74V(typ). The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until VIN drops below 2.3V(typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. CURRENT LIMIT The LM2734Z uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a current limit comparator detects if the output switch current exceeds 1.7A (typ), and turns off the switch until the next switching cycle begins. Copyright © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2734Z |
유사한 부품 번호 - LM2734Z_15 |
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유사한 설명 - LM2734Z_15 |
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