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TPS73515QDRBRQ1 Datasheet(PDF) 9 Page - Texas Instruments |
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TPS73515QDRBRQ1 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 26 page TPS735-Q1 www.ti.com SBVS252A – OCTOBER 2014 – REVISED JANUARY 2015 7.3 Feature Description 7.3.1 Internal Current-Limit The TPS735-Q1 internal current-limit helps protect the regulator during fault conditions. During current-limit, the output sources a fixed amount of current that is largely independent of the output voltage. For reliable operation, do not operate the device in current-limit for extended periods of time. The PMOS pass element in the TPS735-Q1 family of devices has a built-in body diode that conducts current when the voltage at the OUT pin exceeds the voltage at the IN pin. This current is not limited, so if extended reverse voltage operation is anticipated, external limiting can be appropriate. 7.3.2 Shutdown The enable pin (EN) is active high and is compatible with standard and low-voltage TTL-CMOS levels. When shutdown capability is not required, the EN pin can be connected to the IN pin. 7.3.3 Dropout Voltage The TPS735-Q1 family of devices uses a PMOS pass transistor to achieve low dropout. When (VIN – VOUT) is less than the dropout voltage (VDO), the PMOS pass device is in the linear region of operation and the input-to- output resistance (R(IN/OUT)) of the PMOS pass element. VDO scales with the output current because the PMOS device behaves like a resistor in dropout. As with any linear regulator, PSRR and transient response are degraded when (VIN – VOUT) approaches dropout. This effect is shown in the Typical Characteristics section (see Figure 8 through Figure 10). 7.3.4 Startup and Noise Reduction Capacitor Fixed voltage versions of the TPS735-Q1 family of devices use a quick-start circuit to fast-charge the noise reduction capacitor, CNR, if present (see the Functional Block Diagram section). This architecture allows the combination of very-low output noise and fast startup times. The NR pin is high impedance so a low-leakage CNR capacitor must be used. Most ceramic capacitors are appropriate in this configuration. A high-quality, COG-type (NPO) dielectric ceramic capacitor is recommended for CNR when used in environments where abrupt changes in temperature can occur. Note that for fastest start-up, apply VIN first, then drive the enable pin (EN) high. If the EN pin is tied to the IN pin, start-up is somewhat slower. Refer to the Typical Application section (see Figure 17 and Figure 18). The quick- start switch is closed for approximately 135 μs. To ensure that CNR is charged during the quick-start time, use a capacitor with a value of no more than 0.01 μF. 7.3.5 Transient Response As with any regulator, increasing the size of the output capacitor reduces overshoot and undershoot magnitude but increases the transient response duration. In the adjustable version, adding CFB between the OUT and FB pins improves stability and transient response performance. The transient response of the TPS735-Q1 family of devices is enhanced by an active pulldown that engages when the output overshoots by approximately 5% or more when the device is enabled. When enabled, the pull-down device behaves like a 400- Ω resistor to ground. 7.3.6 Undervoltage Lockout (UVLO) The TPS735-Q1 family of devices uses an undervoltage lockout circuit to keep the output shut off until the internal circuitry is operating properly. The UVLO circuit has a deglitch feature so that the UVLO typically ignores undershoot transients on the input if the transients are less than 50 μs in duration. 7.3.7 Minimum Load The TPS735-Q1 family of devices is stable and well-behaved with no output load. To meet the specified accuracy, a minimum load of 500 μA is required. Below 500 μA and at junction temperatures near 125°C, the output can drift up enough to cause the output pulldown to turn on. The output pulldown limits voltage drift to 5% (typically) but ground current can increase by approximately 50 μA. In most applications, the junction does not reach high temperatures at light loads because very little power is dissipated. Therefore, the specified ground current is valid at no load in most applications. Copyright © 2014–2015, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: TPS735-Q1 |
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