MAX8794ETB+T Maxim Integrated Products, MAX8794ETB+T Datasheet - Page 11

• Manufacturer Part Number: MAX8794ETB+T
• Description: IC DDR LINEAR REG 10-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8794ETB+T

• Applications: Converter, DDR
• Voltage - Input: 1.1 ~ 3.6 V
• Number Of Outputs: 1
• Voltage - Output: 0.5 ~ 1.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

For a step-voltage change at REFIN, the rate of change
of the output voltage is limited by the total output
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
resistance seen by the slew capacitor.
The maximum power dissipation of the MAX8794
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:
The resulting maximum power dissipation is:
where T
(+150°C), T
thermal resistance from the die junction to the package
case, and θ
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
maximum allowable power dissipation of a 10-pin TDFN
package is 1951mW. The maximum power dissipation is
derated by 24.4mW/°C above T
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).
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
multiplied by the load current (see the Typical
Operating Characteristics ):
Operating Region and Power Dissipation
EQ
x C
J(MAX)
2
of copper is connected to the device, the
REFIN
CA
A
P
P
DIS MAX
is the ambient temperature, θ
SRC
is the thermal resistance from the case
is the maximum junction temperature
P
, where R
(
______________________________________________________________________________________
SINK
= I
)
SRC
= I
=
SINK
EQ
x (V
T
θ
J MAX
(
JC
is the equivalent parallel
IN
A
x V
Dropout Operation
Low-Voltage DDR Linear Regulator
= +70°C. Extra copper
+
DS(ON)
– V
)
OUT
θ
-
OUT
CA
T
A
)
= 0.25Ω max)
JC
is the
For low output-voltage applications, the sink current is
limited by the output voltage and the R
MOSFET.
Bypass IN to PGND with a 10µF or greater ceramic
capacitor. Bypass V
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.
The MAX8794 output stability is independent of the out-
put capacitance for C
Capacitor ESR between 2mΩ and 50mΩ is needed to
maintain stability. Within the recommended capaci-
tance and ESR limits, the output capacitor should be
chosen to provide good transient response:
where ∆I
current step (typically equal to the maximum source
load plus the maximum sink load), and ∆V
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.
Figure 5. Power Operating Region—Maximum Output Current
vs. Input-Output Differential Voltage
OUT(P-P)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
∆I
0
V
OUT(P-P)
0
DROPOUT
DROPOUT VOLTAGE
LIMITED
INPUT-OUTPUT DIFFERENTIAL VOLTAGE (V)
0.5
is the maximum peak-to-peak load-
SAFE OPERATING REGION
Output Capacitor Selection
CC
1.0
Input Capacitor Selection
T
x ESR = ∆V
A
= +100 ° C
= R
to AGND with a 1µF ceramic
1.5
OUT
T
MAXIMUM CURRENT LIMIT
A
= 0 ° C TO +70 ° C
DS(ON)
2.0
V
from 10µF to 220µF.
IN(MAX)
2.5
OUT(P-P)
x I
- V
OUT(MIN)
OUT
3.0
DS(ON)
3.5
OUT(P-P)
of the
11
is