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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.2.0 Nov.16, 2011

AX6604/5

Current Limit

Each channel of AX6604/5 includes a fold back current limiter. It monitors and controls

the pass transistor’s gate voltage, estimates the output current, and limits the output current

within 250mA.

Thermal Shutdown Protection

Thermal Shutdown protection limits total power dissipation of AX6604/5. When the

junction temperature exceeds TJ = +150°C, a thermal sensor turns off the pass transistor,

allowing the IC to cool down. The thermal sensor turns the pass transistor on again after the

junction temperature cools down by 40°C, resulting in a pulsed output during continuous

thermal shutdown conditions.

Thermal shutdown protection is designed to protect the AX6604/5 in the event of fault

conditions. For continuous operation, the absolute maximum operating junction temperature

rating of TJ = +125°C should not be exceeded.



APPLICATION INFORMARION

Like any low-dropout regulator, the AX6604/5 requires input and output decoupling

capacitors. The device is specifically designed for portable applications requiring minimum

board space and smallest components. These capacitors must be correctly selected for

good performance (see Capacitor Characteristics Section). Please note that linear regulators

with a low dropout voltage have high internal loop gains which require care in guarding

against oscillation caused by insufficient decoupling capacitance.

Input Capacitor

An input capacitance of 1μF is required between input pin and ground directly (the amount

of the capacitance may be increased without limit). The input capacitor must be located less

than 1cm from the device to assure input stability. A lower ESR capacitor allows the use of less

capacitance, while higher ESR type (like aluminum electrolytic) requires more capacitance.

Capacitor types (aluminum, ceramic and tantalum) can be mixed in parallel, but the total

equivalent input capacitance/ ESR must be defined as above to stable operation. There are no

requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must

be considered when selecting the capacitor to ensure the capacitance will be 1μF over the entire

operating temperature range.

Output Capacitor

The AX6604/5 is designed specifically to work with very small ceramic output

capacitors. A ceramic capacitor (temperature characteristics X7R, X5R) in 1μF is suitable for

the AX6604/5 application. The recommended minimum capacitance for the device is 1μF,

X5R or X7R dielectric ceramic, between VOUT and GND for stability, but it may be

increased without limit. Higher capacitance values help to improve transient. The output

capacitor's ESR is critical because it forms a zero to provide phase lead which is required for

loop stability.