LP2966

SNVS028E – APRIL 2000 – REVISED APRIL 2013

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The primary source of noise in low-dropout regulators is the internal reference. In CMOS regulators, noise has a

low frequency component and a high frequency component, which storngly depend on the silicon area and

quiescent current. Noise can be reduced in two ways: by increasing the transistor area or by increasing the

current drawn by the internal reference. Increasing the area will increase the die size and decreases the chance

of fitting the die into a small package. Increasing the current drawn by the internal reference increases the total

supply current (ground pin current) of the IC. Using an optimized trade-off of ground pin current and die size,

LP2966 achieves low noise performance with low quiescent current in an VSSOP-8 package.

Short-Circuit Foldback Protection

In the presence of a short or excessive load current condition, the LP2966 uses an internal short circuit foldback

mechanism that regulates the maximum deliverable output current. A strong negative temperature coefficient is

designed into the circuit to enable extremely higher peak output current capability (in excess of 400mA per output

at room temperature, see TYPICAL PERFORMANCE CHARACTERISTICS ). Thus, a system designer using the

LP2966 can achieve higher peak output current capability in applications where the LP2966 internal junction

temperature is kept below 125°C. Refer to APPLICATIONS INFORMATION on calculating the maximum output

current capability of the LP2966 for your application.

Error Flag Operation

The LP2966 produces a logic low signal at the Error Flag pin (ERROR) when the corresponding output drops out

of regulation due to low input voltage, current limiting, or thermal limiting. This flag has a built in Hysteresis. The

timing diagram in Figure 32 shows the relationship between the ERROR and the output voltage. In this example,

the input voltage is changed to demonstrate the functionality of the Error Flag.

Figure 32. Error Flag Operation

The internal error flag comparators have open drain output stages. Hence, the ERROR pins should be pulled

high through a pull up resistor. Although the ERROR pin can sink current of 1mA, this current adds to the battery

drain. Hence, the value of the pull up resistor should be in the range of 100k

Ω to 1MΩ. The ERROR pins must

be connected to ground if this function is not used. It should also be noted that when the shutdown pins are

pulled low, the ERROR pins are forced to be invalid for reasons of saving power in shutdown mode.

Shutdown Operation

The two LDO regulators in the LP2966 have independent shutdown. A CMOS Logic level signal at the shutdown

(SD) pin will turn-off the corresponding regulator. Pins SD1 and SD2 must be actively terminated through a

100k

Ω pull-up resistor for a proper operation. If these pins are driven from a source that actively pulls high and

low (such as a CMOS rail to rail comparator), the pull-up resistor is not required. These pins must be tied to Vin if

not used.

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