AAT4250 データシートの表示（PDF） - Analog Technology Inc

部品番号

コンポーネント説明

一致するリスト

AAT4250

Slew Rate Controlled Load Switch

Analog Technology Inc 

AAT4250

Slew Rate Controlled Load Switch

For maximum current, refer to the following equation:

IOUT(MAX) < ( PD(MAX) / RDS)1/2

For example, if VIN = 5V, RDS(MAX)=224mΩ and TA

= 25°C, IOUT(MAX) = 1.7A. If the output load current

were to exceed 1.7A or if the ambient temperature

were to increase, the internal die temperature will

increase, and the device will be damaged.

Higher peak currents can be obtained with the

AAT4250. To accomplish this, the device thermal

resistance must be reduced by increasing the heat

sink area or by operating the load switch in a duty

cycle manner. Duty cycles with peaks less than

2ms in duration can be considered using the

method below.

High Peak Output Current Applications

Some applications require the load switch to oper-

ate at a continuous nominal current level with short

duration high current peaks. Refer to the IDM spec-

ification in the Absolute Maximum table to ensure

the AAT 4250’s maximum pulsed current rating is

not exceeded. The duty cycle for both output cur-

rent levels must be taken into account. To do so,

first calculate the power dissipation at the nominal

continuous current level, and then add in the addi-

tional power dissipation due to the short duration

high current peak scaled by the duty factor.

For example, a 4V system using an AAT4250 oper-

ates at a continuous 100mA load current level and

has short 2A current peaks, as in a GSM applica-

tion. The current peak occurs for 576µs out of a

4.61ms period.

First, the current duty cycle is calculated:

% Peak Duty Cycle: X/100 = 576µs/4.61ms

% Peak Duty Cycle = 12.5%

The load current is 100mA for 87.5% of the 4.61ms

period and 2A for 12.5% of the period. Since the

Electrical Characteristics do not report RDS MAX for 4

volts operation, it must be calculated approximated

by consulting the chart of RDSON vs. VIN. The Rds

reported for 5 volt RDS can be scaled by the ratio

seen in the chart to derive the Rds for 4 volt VIN:

175mΩ x 120mΩ/115mΩ = 183mΩ. Derated for

temperature: 183mΩ x (1 + .002800 x (125°C -

25°C)) = 235mΩ . The power dissipation for a

100mA load is calculated as follows:

PD(MAX) = I2OUT x RDS

PD(100mA) = (100mA)2 x 235mΩ

PD(100mA) = 2.35mW

PD(87.5%D/C) = %DC x PD(100mA)

PD(87.5%D/C) = 0.875 x 2.35mW

PD(87.5%D/C) = 2.1mW

The power dissipation for 100mA load at 87.5%

duty cycle is 2.1mW. Now the power dissipation for

the remaining 12.5% of the duty cycle at 2A is cal-

culated:

PD(MAX) = I2OUT x RDS

PD(2A) = (2A)2 x 235mΩ

PD(2A) = 940mW

PD(12.5%D/C) = %DC x PD(2A)

PD(12.5%D/C) = 0.125 x 940mW

PD(12.5%D/C) = 117.5mW

The power dissipation for 2A load at 12.5% duty

cycle is 117mW. Finally, the two power figures are

summed to determine the total true power dissipa-

tion under the varied load.

PD(total) = PD(100mA) + PD(2A)

PD(total) = 2.1mW + 117.5mW

PD(total) = 120mW

The maximum power dissipation for the AAT4250

operating at an ambient temperature of 85°C is

267mW. The device in this example will have a

total power dissipation of 120mW. This is well with

in the thermal limits for safe operation of the

device, in fact, at 85°C, the AAT4250 will handle a

2A pulse for up to 28% duty cycle. At lower ambi-

ent temperatures the duty cycle can be further

increased.

4250.2001.12.0.94

9

Share Link: