LM9070

SNVS130E – DECEMBER 1999 – REVISED APRIL 2013

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Figure 22. Control Logic Not Used

Conventional load dump protection is built in to withstand up to +60V and

−50V transients. A 1 kΩ resistor in

series with the ON/OFF and Keep-Alive inputs are recommended to provide the same level of transient

protection for these pins if required. Protection against reverse polarity battery connections is also built in. With a

reversed battery the output of the LM9070 will not go more negative than one diode drop below ground. This will

prevent damage to any of the 5V load circuits.

For applications where the control logic is not required the logic pins should be configured as shown in Figure 22.

A separate device, called the LM9071, can be used. The LM9071 is available in a 5-lead TO-220 package and

does not provide control logic functions, but still retains all of the protection features of the LM9070.

RESET FLAG

Excessive loading of the output to the point where the output voltage drops by 300 mV to 500 mV will signal a

On power-up and recovery from a fault condition the delay capacitor is used to hold the micro in a reset condition

for a programmable time interval to allow the system operating voltages and

clock to stabilize before executing code. The typical delay time interval can be estimated using the following

equation:

(1)

INPUT STABILITY

Low dropout voltage regulators which utilize a PNP power transistor usually exhibit a large increase in current

transistor. To significantly minimize this increase in current the LM9070 detects when the PNP enters saturation

and reduces the operating current.

This reduction in input current can create a stability problem in applications with higher load current (> 100 mA)

where the input voltage is applied through a long length of wire, which in effect adds a significant amount of

inductance in series with the input. The drop in input current may create a positive input voltage transient which

may take the PNP out of saturation. If the input voltage is held constant at the threshold where the PNP is going

in and out of saturation, an oscillation may be created.

This is only observed where significant series inductance is present in the input supply line and when the rise

and fall time of the input supply is very slow. If the application and removal of the input voltage changes at a rate

greater than 500 mV/

quickly for an oscillation to be established.

MICROPROCESSOR SYSTEM REGULATOR WITH KEEP-ALIVE INTERVAL AT TURN-OFF

Figure 23 illustrates a system application circuit utilizing both of the logic control inputs of the LM9070. Closing

the ON/OFF switch powers ON the system. Once powered, the system controller sets the Keep-Alive line low.

The NPN transistor is used only to signal the controller that the ON/OFF switch has been opened and the system

is to be turned OFF. Upon detecting this high level at the ON/OFF Sense input line, the controller can then

perform a power down routine. The system will remain fully powered until the controller commands total shut

down by taking the Keep-Alive line high. The system then shuts OFF and reverts to a very low current drain

standby condition until switched back on.

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