AAT1112IWP-0.6-T1 查看數據表（PDF） - Analog Technology Inc

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AAT1112IWP-0.6-T1

1.5A, 1.4MHz Step-Down Converter

Analog Technology Inc 

AAT1112

1.5A, 1.4MHz Step-Down Converter

The internal voltage loop compensation also limits

the minimum output capacitor value to 10µF. This is

due to its effect on the loop crossover frequency

(bandwidth), phase margin, and gain margin.

Increased output capacitance will reduce the

crossover frequency with greater phase margin.

Adjustable Output Resistor Selection

The output voltage on the AAT1112 is programmed

with external resistors R1 and R2. To limit the bias

current required for the external feedback resistor

string while maintaining good noise immunity, the

minimum suggested value for R2 is 59kΩ.

Although a larger value will further reduce quies-

cent current, it will also increase the impedance of

the feedback node, making it more sensitive to

external noise and interference. Table 1 summa-

rizes the resistor values for various output voltages

with R2 set to either 59kΩ for good noise immunity

or 221kΩ for reduced no load input current.

VOUT (V)

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.8

1.85

2.0

2.5

3.0

3.3

R2 = 59kΩ

R1 (kΩ)

19.6

29.4

39.2

49.9

59.0

68.1

78.7

88.7

118

124

137

187

237

267

R2 = 221kΩ

R1 (kΩ)

75

113

150

187

221

261

301

332

442

464

523

715

887

1000

Table 1: AAT1112 Resistor Values for Various

Output Voltages.

Thermal Calculations

There are three types of losses associated with

the AAT1112 step-down converter: switching loss-

es, conduction losses, and quiescent current loss-

es. Conduction losses are associated with the

RDS(ON) characteristics of the power output switch-

ing devices. Switching losses are dominated by

the gate charge of the power output switching

devices. At full load, assuming continuous conduc-

tion mode (CCM), a simplified form of the losses is

given by:

PTOTAL

=

IO2

·

(RDS(ON)H

·

VO

+ RDS(ON)L

VIN

·

[VIN

-

VO])

+ (tsw · FS · IO + IQ) · VIN

IQ is the step-down converter quiescent current.

The term tsw is used to estimate the full load step-

down converter switching losses.

For the condition where the step-down converter is

in dropout at 100% duty cycle, the total device dis-

sipation reduces to:

PTOTAL = IO2 · RDS(ON)H + IQ · VIN

Since RDS(ON), quiescent current, and switching

losses all vary with input voltage, the total losses

should be investigated over the complete input

voltage range.

Given the total losses, the maximum junction tem-

perature can be derived from the θJA for the

TDFN3-12 and TSOPJW-12 packages, which is

50°C/W and 160°C/W respectively.

TJ(MAX) = PTOTAL · ΘJA + TAMB

14

1112.2007.01.1.1

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