参数资料
型号: MAX8794ETB/V+T
厂商: Maxim Integrated Products
文件页数: 11/13页
文件大小: 0K
描述: IC REG DDR 3A LV 10TDFN
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 2,500
应用: 转换器,DDR
输入电压: 1.1 V ~ 3.6 V
输出数: 1
输出电压: 0.5 V ~ 1.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 10-WFDFN 裸露焊盘
供应商设备封装: 10-TDFN-EP(3x3)
包装: 带卷 (TR)
Low-Voltage DDR Linear Regulator
For a step-voltage change at REFIN, the rate of change
of the output voltage is limited by the total output
SAFE OPERATING REGION
capacitance, 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 during dynamic transitions. With the
additional capacitance, the REFIN voltage slews
between the two set points with a time constant given
by R EQ x C REFIN , where R EQ is the equivalent parallel
resistance seen by the slew capacitor.
Operating Region and Power Dissipation
The maximum power dissipation of the MAX8794
3.5
3.0
2.5
2.0
1.5
1.0
0.5
DROPOUT VOLTAGE
LIMITED
MAXIMUM CURRENT LIMIT
T A = 0°C TO +70°C
V IN(MAX) - V OUT(MIN)
depends on the thermal resistance of the 10-pin TDFN
package and the circuit board, the temperature differ-
ence between the die and ambient air, and the rate of
airflow. The power dissipated in the device is:
0
0
T A = +100°C
0.5 1.0 1.5 2.0 2.5 3.0
INPUT-OUTPUT DIFFERENTIAL VOLTAGE (V)
3.5
P SRC = I SRC x (V IN – V OUT )
P SINK = I SINK x V OUT
The resulting maximum power dissipation is:
Figure 5. Power Operating Region—Maximum Output Current
vs. Input-Output Differential Voltage
V DROPOUT = R DS(ON) x I OUT
P DIS ( MAX ) =
T J(MAX ) - T A
θ JC + θ CA
For low output-voltage applications, the sink current is
limited by the output voltage and the R DS(ON) of the
MOSFET.
where T J(MAX) is the maximum junction temperature
(+150°C), T A is the ambient temperature, θ JC is the
thermal resistance from the die junction to the package
case, and θ CA 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
backside pad, and use wide input and output traces.
When 1in 2 of copper is connected to the device, the
maximum allowable power dissipation of a 10-pin TDFN
package is 1951mW. The maximum power dissipation is
derated by 24.4mW/°C above T A = +70°C. Extra copper
on the PCB increases thermal mass and reduces ther-
mal resistance of the board. Refer to the MAX8794 eval-
uation kit for a layout example.
The MAX8794 delivers 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 differen-
tial (dropout voltage) determines the lowest usable sup-
ply voltage. Because the MAX8794 uses an n-channel
pass transistor, the dropout voltage is a function of the
drain-to-source on-resistance (R DS(ON) = 0.25 ? max)
multiplied by the load current (see the Typical
Operating Characteristics):
Input Capacitor Selection
Bypass IN to PGND with a 10μF or greater ceramic
capacitor. Bypass V CC 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 addi-
tional bulk capacitance (polymer or tantalum) and dis-
tributed ceramic capacitors.
Output Capacitor Selection
The MAX8794 output stability is independent of the out-
put capacitance for C OUT from 10μF to 220μF.
Capacitor ESR between 2m ? and 50m ? is needed to
maintain stability. Within the recommended capaci-
tance and ESR limits, the output capacitor should be
chosen to provide good transient response:
? I OUT(P-P) x ESR = ? V OUT(P-P)
where ? I OUT(P-P) is the maximum peak-to-peak load-
current step (typically equal to the maximum source
load plus the maximum sink load), and ? V OUT(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 MAX8794 or discharged to ground,
improving efficiency.
______________________________________________________________________________________
11
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