RT9026
10
DS9026-07 September 2011www.richtek.com
Application Information
RT9026 is a 3A sink/source tracking termination regulator.
It is specifically designed for low-cost and low-external
component count system such as notebook PC
applications. The RT9026 possesses a high speed
operating amplifier that provides fast load transient response
and only requires a 10μF ceramic input capacitor and two
10μF ceramic output capacitor.
VTTREF Regulator
VTTREF is a reference output voltage with source/sink
current capability up to 10mA. To ensure stable operation
0.1μF ceramic capacitor between VTTREF and GND is
recommended.
S3, S5 Logic Control
The S3 and S5 terminals should be connected to SLP_S3
and SLP_S5 signals respectively. Both VTTREF and VTT
are turned on at normal state (S3 = High, S5 = High). In
standby state (S3 = Low, S5 = High) VTTREF is kept
alive while VTT is turned off and left high impedance. Both
VTT and VTTREF outputs are turned off and discharged
to ground through internal MOSFETs during shutdown
state (S5 = low).
Capacitor Selection
Good bypassing is recommended from VLDOIN to GND
to help improve AC performance. A 10μF or greater input
capacitor located as close as possible to the IC is
recommended. The input capacitor must be located at a
distance of less than 0.5 inches from the VLDOIN pin of
the IC.
Adding a ceramic capacitor 1μF close to the VIN pin and
it should be kept away from any parasitic impedance from
the supply power.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
P
D(MAX)
= ( T
J(MAX)
− T
A
) / θ
JA
Where T
J(MAX)
is the maximum operation junction
temperature, T
A
is the ambient temperature and the θ
JA
is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
the RT9026, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance θ
JA
is layout
dependent. The thermal resistance θ
JA
for WDFN-10L 3x3
is 70°C/W, for SOP-8 (Exposed Pad) is 75°C/W and for
MSOP-10 (Exposed Pad) is 86°C/W on the standard
JEDEC 51-7 four layers thermal test board. The maximum
power dissipation at T
A
= 25°C can be calculated by
following formula :
P
D(MAX)
= (125°C − 25°C) / (70°C/W) = 1.429W for
WDFN-10L 3x3 packages
P
D(MAX)
= (125°C − 25°C) / (75°C/W) = 1.333W for
SOP-8 (Exposed Pad) packages
P
D(MAX)
= (125°C − 25°C) / (86°C/W) = 1.163W for
MSOP-10 (Exposed Pad) packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
J(MAX)
and thermal
resistance θ
JA
. For RT9026 packages, the Figure 3 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
STATE S3 S5 VTTREF VTT
Normal H H ON ON
Standby L H ON OFF(high-Z)
Shutdown L L
OFF
dischar
e
OFF
dischar
e
Table 2. S3 and S5 Control
For stable operation, the total capacitance of the cerarnic
capcitor at the VTT output terminal must not be larger
than 30μF. The RT9026 is designed specifically to work
with low ESR ceramic output capacitor in space saving
and performance consideration. Larger output capacitance
can reduce the noise and improve load transient response,
stability and PSRR. The output capacitor should be located
near the VTT output terminal pin as close as possible.
