TPS717 datasheet(12/42 Pages) TI

12 / 42 page

OUT

GND

Current

Limit

Thermal

Shutdown

UVLO

1.20-V

Band Gap

250 kW

0.8 V

360 kW

640 kW

3.3 MW

TPS717

SBVS068H – FEBRUARY 2006 – REVISED JANUARY 2015

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Functional Block Diagrams (continued)

Figure 32. Adjustable Voltage Version

7.3 Feature Description

7.3.1 Internal Current Limit

The TPS717xx 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 output voltage. For reliable operation, do

not operate the device in a current-limit state for extended periods of time.

The PMOS pass element in the TPS717xx has a built-in body diode that conducts current when the voltage at

OUT exceeds the voltage at IN. This current is not limited, so if extended reverse voltage operation is

anticipated, external limiting may be appropriate.

7.3.2 Shutdown

The enable pin (EN) is active high and compatible with standard and low voltage, TTL-CMOS levels. When

shutdown capability is not required, EN can be connected to IN.

7.3.3 Startup and Noise Reduction Capacitor

Fixed voltage versions of the TPS717xx use a quick-start circuit to fast-charge the noise reduction capacitor,

CNR, if present (see Figure 31). This circuit allows the combination of very low output noise and fast start-up

times. The NR pin is high impedance, so a low-leakage CNR capacitor must be used; most ceramic capacitors

are appropriate in this configuration.

Note that for fastest startup, apply VIN first, then the enable pin (EN) driven high. If EN is tied to IN, startup is

somewhat slower. Refer to Figure 29 in Typical Characteristics. The quick-start switch is closed for approximately

135

μs. To ensure that CNR is fully charged during the quick-start time, use a 0.01-μF or smaller capacitor.

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TPS717 Datasheet(PDF) 12 Page - Texas Instruments