APA2018 datasheet(13/19 Pages) ANPEC

13 / 19 page

Rev. A.5 - Apr., 2016

APA2018

www.anpec.com.tw

Function Descriptions

∆IL is inversely proportional to L. Minimize ∆IL is as much

as necessary for a specific application. Increase the in-

ductance to reduce the ripple current. Do not use greater

than 4.7

µH, as this prevents the boost converter from

responding to fast output current changes properly. If

using above 3.3

µH, and then use at least 10µF capaci-

tance on PVDD to ensure boost converter stability.

The typical inductor value range for the APA2018 is 2.2

µH

to 3.3

µH. Select an inductor with less than 0.5Ω dc

resistance, DCR. Higher DCR reduces total efficiency

due to an increase in voltage drop across the inductor.

Thermal protection

Boost Converter Capacitor Selection

The value of the boost capacitor is determined by the

minimum value of working capacitance required for sta-

bility and the maximum voltage ripple allowed on PVDD

in the application. Working capacitance refers to the avail-

able capacitance after derating the capacitor value for

DC bias, temperature, and aging. Do not use any com-

ponent with a working capacitance less than 6.8

µF. This

corresponds to a 10

µF/16V capacitor or a 10µF/10V

capacitor.

Do not use above 22

µF capacitance as it will reduce the

boost converter response time to large output current

transients.

Equation 3 shows the relationship between the boost

capacitance, C, to load current, load voltage, ripple voltage,

input voltage, and switching frequency (IPVDD, PVDD,

∆V, VBAT, and fBOOST respectively).

Insert the maximum allowed ripple voltage into Equation

3 and solve for C. The 1.5 multiplier accounts for capaci-

tance loss due to applied dc voltage and temperature for

X5R and X7R ceramic capacitors.

Short Circuit Auto-recovery

When a short circuit event happens, the APA2018 goes to

low duty cycle mode and tries to reactivate itself every 1.8

seconds. The auto-recovery will continue until the short

circuit event stops. This feature protects the device with-

out affecting the device's long term reliability.

(

)

PVDD

VBAT

PVDD

BOOST

PVDD

∫

∆

−

The over-temperature circuit limits the junction tempera-

ture of the APA2018. When the junction temperature ex-

ceeds T

J = +170

oC, a thermal sensor turns off the output

buffer, allowing the devices to cool. The thermal sensor

allows the amplifier to start-up after the junction tempera-

ture down about 140 oC. The thermal protection designed

with a 30oC hysteresis lowers the average T

J during con-

tinuous thermal overload conditions, increasing lifetime

of the IC.

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