MAX1510ETB データシートの表示（PDF） - Maxim Integrated

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MAX1510ETB

Low-Voltage DDR Linear Regulators

Maxim Integrated 

MAX1510/MAX17510

Low-Voltage DDR Linear Regulators

For a step voltage change at REFIN, the rate of change

of the output voltage is limited by the total output capaci-

tance, the current limit, and the load during the transition.

Adding a capacitor across REFIN and AGND filters noise

and controls the rate of change of the REFIN voltage dur-

ing dynamic transitions. With the additional capacitance,

the REFIN voltage slews between the two set points with

a time constant given by REQ x CREFIN, where REQ is the

equivalent parallel resistance seen by the slew capacitor.

Operating Region and Power Dissipation

The maximum power dissipation of the MAX1510/

MAX17510 depends on the thermal resistance of the 10-

pin TDFN package and the circuit board, the temperature

difference between the die and ambient air, and the rate

of airflow. The power dissipated in the device is:

PSRC = ISRC x (VIN - VOUT)

PSINK = ISINK x VOUT

The resulting maximum power dissipation is:

PDIS(MAX)

=

TJ(MAX) - TA

θ JC + θCA

where TJ(MAX) is the maximum junction temperature

(+150°C), TA is the ambient temperature, θJC is the

thermal resistance from the die junction to the package

case, and θCA is the thermal resistance from the case

through the PCB, copper traces, and other materials to

the surrounding air. For optimum power dissipation, use a

large ground plane with good thermal contact to the back-

side pad, and use wide input and output traces.

When 1 square inch of copper is connected to the device,

the maximum allowable power dissipation of a 10-pin

TDFN package is 1951mW. The maximum power dissipa-

tion is derated by 24.4mW/°C above TA = +70°C. Extra

copper on the PCB increases thermal mass and reduces

thermal resistance of the board. Refer to the MAX1510

evaluation kit for a layout example.

The devices deliver up to 3A and operates with input

voltages up to 3.6V, but not simultaneously. High output

currents can only be achieved when the input-output

differential voltages are low (Figure 5).

Dropout Operation

A regulator’s minimum input-to-output voltage differ-

ential (dropout voltage) determines the lowest usable

supply voltage. Because the devices use an n-channel

pass transistor, the dropout voltage is a function of the

drain-to-source on-resistance (RDS(ON) = 0.25Ω max)

multiplied by the load current (see the Typical Operating

Characteristics):

VDROPOUT = RDS(ON) x IOUT

SAFE OPERATING REGION

3.5

DROPOUT VOLTAGE

3.0 LIMITED

MAXIMUM CURRENT LIMIT

2.5

1s RMS

LIMIT

2.0

TA = 0°C TO +70°C

100s RMS

1.5

LIMIT

VIN(MAX) - VOUT(MIN)

1.0

0.5

TA = +100°C

0

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

INPUT-OUTPUT DIFFERENTIAL VOLTAGE (V)

Figure 5. Power Operating Region—Maximum Output Current

vs. Input-Output Differential Voltage

For low output-voltage applications, the sink current is

limited by the output voltage and the RDS(ON) of the

MOSFET.

Input Capacitor Selection

Bypass IN to PGND with a 10μF or greater ceramic capaci-

tor. Bypass VCC to AGND with a 1μF ceramic capacitor

for normal operation in most applications. Typically, the

LDO is powered from the output of a step-down controller

(memory supply) that has additional bulk capacitance

(polymer or tantalum) and distributed ceramic capacitors.

Output Capacitor Selection

The MAX1510/MAX17510 output stability is independent

of the output capacitance for COUT from 10μF to 220μF.

Capacitor ESR between 2mΩ and 50mΩ is needed to

maintain stability. Within the recommended capacitance

and ESR limits, the output capacitor should be chosen to

provide good transient response:

ΔIOUT(P-P) x ESR = ΔVOUT(P-P)

where ΔIOUT(P-P) is the maximum peak-to-peak load cur-

rent step (typically equal to the maximum source load plus

the maximum sink load), and ΔVOUT(P-P) is the allowable

peak-to-peak voltage tolerance.

Using larger output capacitance can improve efficiency in

applications where the source and sink currents change

rapidly. The capacitor acts as a reservoir for the rapid

source and sink currents, so no extra current is supplied

by the MAX1510/MAX17510 or discharged to ground,

improving efficiency.

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