LP38691, LP38693

SNVS321K – JANUARY 2005 – REVISED APRIL 2013

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TANTALUM

Solid Tantalum capacitors have good temperature stability: a high quality Tantalum will typically show a

capacitance value that varies less than 10-15% across the full temperature range of -40°C to +125°C. ESR will

vary only about 2X going from the high to low temperature limits.

REVERSE VOLTAGE

A reverse voltage condition will exist when the voltage at the output pin is higher than the voltage at the input pin.

the input to output voltage becomes reversed. A less common condition is when an alternate voltage source is

connected to the output.

There are two possible paths for current to flow from the output pin back to the input during a reverse voltage

condition.

than the programmed output voltage, the control circuit will drive the gate of the pass element to the full ON

condition. In this condition, reverse current will flow from the output pin to the input pin, limited only by the

1000

μF in this manner will not damage the device as the current will rapidly decay. However, continuous

reverse current should be avoided. When the Enable pin is low this condition will be prevented.

2. The internal PFET pass element has an inherent parasitic diode. During normal operation, the input voltage

value where the control circuity is alive, or the Enable pin is low (LP38693 only), and the output voltage is

more than 500 mV (typical) above the input voltage the parasitic diode becomes forward biased and current

flows from the output pin to the input pin through the diode. The current in the parasitic diode should be

limited to less than 1A continuous and 5A peak.

If used in a dual-supply system where the regulator output load is returned to a negative supply, the output

pin must be diode clamped to ground to limit the negative voltage transition. A Schottky diode is

recommended for this protective clamp.

PCB LAYOUT

Good PC layout practices must be used or instability can be induced because of ground loops and voltage drops.

The input and output capacitors must be directly connected to the input, output, and ground pins of the regulator

using traces which do not have other currents flowing in them (Kelvin connect).

pins. The regulator ground pin should be connected to the external circuit ground so that the regulator and its

capacitors have a "single point ground".

It should be noted that stability problems have been seen in applications where "vias" to an internal ground plane

were used at the ground points of the IC and the input and output capacitors. This was caused by varying ground

potentials at these nodes resulting from current flowing through the ground plane. Using a single point ground

technique for the regulator and it’s capacitors fixed the problem. Since high current flows through the traces

in series with the input and output capacitors.

WSON MOUNTING

The NGG0006A (No Pullback) 6-Lead WSON package requires specific mounting techniques which are detailed

in the TI AN-1187 Application Report. Referring to the section PCB Design Recommendations (Page 5), it should

be noted that the pad style which should be used with the WSON package is the NSMD (non-solder mask

defined) type. Additionally, it is recommended the PCB terminal pads to be 0.2 mm longer than the package

pads to create a solder fillet to improve reliability and inspection.

that the device can meet all specifications at the rated current.

The thermal dissipation of the WSON package is directly related to the printed circuit board construction and the

amount of additional copper area connected to the DAP.

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