AOZ1213

Rev. 1.3 November 2009

www.aosmd.com

Page 8 of 16

Protection Features

The AOZ1213 has multiple protection features to prevent

system circuit damage under abnormal conditions.

Over Current Protection (OCP)

The sensed inductor current signal is also used for over

current protection. Since the AOZ1213 employs peak

current mode control, the COMP pin voltage is

proportional to the peak inductor current. The COMP pin

voltage is limited to be between 0.4V and 2.5V internally.

The peak inductor current is automatically limited cycle

by cycle.

The cycle by cycle current limit threshold is internally set.

When the load current reaches the current limit

threshold, the cycle by cycle current limit circuit turns off

the high side switch immediately to terminate the current

duty cycle. The inductor current stop rising. The cycle by

cycle current limit protection directly limits inductor peak

current. The average inductor current is also limited due

to the limitation on peak inductor current. When cycle by

cycle current limit circuit is triggered, the output voltage

drops as the duty cycle decreasing.

The AOZ1213 has internal short circuit protection to

protect itself from catastrophic failure under output short

circuit conditions. The FB pin voltage is proportional to

the output voltage. Whenever FB pin voltage is below

0.3V, the short circuit protection is triggered. To prevent

current limit running away, when comp pin voltage is

higher than 2.1V, the short circuit protection is also

triggered. When the above conditions happen, PWM

turns off immediately, after about 1mS the converter

restarts via a soft start scheme. The short circuit

protection process repeats until the short circuit condition

disappears.

Power-On Reset (POR)

A power-on reset circuit monitors the input voltage.

When the input voltage exceeds 4.0V, the converter

starts operation. When input voltage falls below 3.7V,

the converter will stop switching.

Linear Regulator

The AOZ1213 contains an error amplifier which can be

configured as a linear regulator controller. By adding an

external follower (NPN or NMOS) and divider resistors as

shown in Figure 1, the FB2 and LDRV pins can be

configured as a controller for a Low Dropout Regulator.

The LDRV pin source capability come from LDO inside

which is capable more than 10mA of base current to the

external NPN transistor.

The FB2 voltage is monitored by an Under Voltage

Protection circuit, which shutdown LDRV output when

FB2 voltage is under 0.6V.

Thermal Protection

An internal temperature sensor monitors the junction

temperature. It shuts down the internal control circuit and

high side NMOS if the junction temperature exceeds

145°C. The regulator will restart automatically under the

control of soft-start circuit when the junction temperature

decreases to 100°C.

Application Information

The basic AOZ1213 application circuit is shown in

Figure 1. Component selection is explained below.

Buck Regulator Design

Input Capacitor

steady input voltage and filter out the pulsing input

current. The voltage rating of input capacitor must be

greater than maximum input voltage plus ripple voltage.

The input ripple voltage can be approximated by

equation below:

Since the input current is discontinuous in a buck

converter, the current stress on the input capacitor is

another concern when selecting the capacitor. For a buck

circuit, the RMS value of input capacitor current can be

calculated by:

if let m equal the conversion ratio:

The relationship between the input capacitor RMS

current and voltage conversion ratio is calculated and

shown in Figure 2 on the next page. It can be seen that

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