RT8004 RICHTEK [Richtek Technology Corporation], RT8004 Datasheet - Page 13

• Manufacturer Part Number: RT8004
• Description: 3A, 4MHz, Synchronous Step-Down Regulator
• Manufacturer: RICHTEK [Richtek Technology Corporation]

As an example, consider the RT8004 in dropout at an
input voltage of 3.3V, a load current of 3A and an ambient
temperature of 70°C. From the typical performance graph
of switch resistance, the R
at 70°C is approximately 97mΩ. Therefore, power
dissipated by the part is :
P
For the TSSOP package, the θ
junction temperature of the regulator is :
T
Which is below the maximum junction temperature of
125°C. Note that at higher supply voltages, the junction
temperature is lower due to reduced switch resistance
(R
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V
equal to ΔI
resistance of C
discharge C
by the regulator to return V
During this recovery time, V
overshoot or ringing that would indicate a stability problem.
The COMP pin external components and output capacitor
shown in Typical Application Circuit will provide adequate
compensation for most applications.
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of RT8004.
DS8004-03
D
J
A ground plane is recommended. If a ground plane layer
is not used, the signal and power grounds should be
segregated with all small-signal components returning
to the GND pin at one point that is then connected to
the PGND pin close to the IC. The exposed pad should
be connected to GND.
Connect the terminal of the input capacitor(s), C
close as possible to the PVDD pin. This capacitor
provides the AC current into the internal power
MOSFETs.
DS(ON)
= 70°C+(0.873W) (47°C/W) = 111°C
= (I
LOAD
).
LOAD
)
2
OUT
September 2007
(R
(ESR), where ESR is the effective series
DS(ON)
generating a feedback error signal used
OUT
. ΔI
OUT
) = (3A)
LOAD
immediately shifts by an amount
DS(ON)
OUT
2
also begins to charge or
OUT
(97mΩ) = 0.873W
to its steady-state value.
of the P-Channel switch
JA
can be monitored for
is 47°C/W. Thus the
IN
, as
LX node is with high frequency voltage swing and should
be kept small area. Keep all sensitive small-signal nodes
away from LX node to prevent stray capacitive noise
pick-up.
Flood all unused areas on all layers with copper.
Flooding with copper will reduce the temperature rise
of power components. You can connect the copper areas
to any DC net (PVIN, SVIN, V
any other DC rail in your system).
Connect the FB pin directly to the feedback resistors.
The resistor divider must be connected between V
and GND.
OUT
, PGND, SGND, or
RT8004
www.richtek.com
OUT
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