LM337H datasheet(16/28 Pages) TI1

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LM137, LM337-N

SNVS778E – MAY 1999 – REVISED JANUARY 2016

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9 Power Supply Recommendations

The input supply to the LM137 and LM337-N must be kept at a voltage level such that its maximum input to

output differential voltage rating is not exceeded. The minimum dropout voltage must also be met with extra

headroom when possible to keep the LM137 and LM337-N in regulation. TI recommends an input capacitor,

especially when the input pin is placed more than 4 inches away from the power-supply filter capacitor.

10 Layout

10.1 Layout Guidelines

Some layout guidelines must be followed to ensure proper regulation of the output voltage with minimum noise.

Traces carrying the load current must be wide to reduce the amount of parasitic trace inductance and the

feedback loop from VOUT to ADJ must be kept as short as possible. To improve PSRR, a bypass capacitor can

be placed at the ADJ pin and must be placed as close as possible to the IC. In cases when VIN shorts to ground,

an external diode must be placed from VIN to VOUT to divert the surge current into the output capacitor and

protect the IC. Similarly, in cases when a large bypass capacitor is placed at the ADJ pin and VOUT shorts to

ground, an external diode must be placed from VOUT to ADJ to provide a path for the bypass capacitor to

discharge. These diodes must be placed close to the corresponding IC pins to increase their effectiveness.

10.2 Layout Example

Figure 18. Layout Example (SOT-223)

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