RT8023GQW Richtek USA Inc, RT8023GQW Datasheet - Page 14

• Manufacturer Part Number: RT8023GQW
• Description: IC CONV STP-DWN W/2 LDO 24WQFN
• Manufacturer: Richtek USA Inc

Specifications of RT8023GQW

• Topology: Step-Down (Buck) Synchronous (1), Linear (LDO) (2)
• Function: Any Function
• Number Of Outputs: 3
• Frequency - Switching: 1.2MHz
• Voltage/current - Output 1: 0.8 V ~ 5 V, 1.5A
• Voltage/current - Output 2: 0.8 V ~ 5 V, 700mA
• Voltage/current - Output 3: 0.8 V ~ 5 V, 350mA
• W/led Driver: No
• W/supervisor: No
• W/sequencer: Yes
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

RT8023
Application Information
For Buck Converter Part
The Typical Application Circuit shows the basic RT8023
application circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by C
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔI
and decreases with higher inductance.
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal.
For the ripple current selection, the value of ΔI
will be a reasonable starting point. The largest ripple current
occurs at the highest V
current stays below the specified maximum, the inductor
value should be chosen according to the following
equation :
Inductor Core Selection
The inductor type must be selected once the value for L
is known. Generally speaking, high efficiency converters
can not afford the core loss found in low cost powdered
iron cores. So, the more expensive ferrite or
mollypermalloy cores will be a better choice. The selected
inductance rather than the core size for a fixed inductor
value is the key for actual core loss. As the inductance
increases, core losses decrease. Unfortunately, increase
of the inductance requires more turns of wire and therefore
the copper losses will increase.
Ferrite designs are preferred at high switching frequency
due to the characteristics of very low core losses. So,
design goals can focus on the reduction of copper loss
and the saturation prevention.
www.richtek.com
14
L =
Δ
I =
L
⎡
⎢
⎣
f
⎡
⎢
⎣
× Δ
V
V
f L
OUT
×
OUT
I
L(MAX)
⎤ ⎡
⎥ ⎢
⎦ ⎣
IN
×
and C
⎤ ⎡
⎥ ⎢
⎦ ⎣
1
×
−
V
1
OUT
V
OUT
−
IN
V
IN
.
IN(MAX)
V
. To guarantee that the ripple
⎤
⎥
⎦
OUT
L
increases with higher V
⎤
⎥
⎦
L
= 0.4(I
MAX
IN
)
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded. The previous situation results in an
abrupt increase in inductor ripple current and consequent
output voltage ripple.
Do not allow the core to saturate!
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy materials
are small and do not radiate energy. However, they are
usually more expensive than the similar powdered iron
inductors. The rule for inductor choice mainly depends
on the price vs. size requirement and any radiated field/
EMI requirements.
C
The input capacitance, C
trapezoidal current at the source of the top MOSFET. To
prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
This formula has a maximum at V
I
commonly used for design because even significant
deviations do not offer much relief.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
The selection of C
series resistance (ESR) to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for C
Loop stability can be checked by viewing the load transient
response as described in a later section.
The output ripple, ΔV
I
RMS
RMS
Δ
IN
V
and C
OUT
OUT
= I
= I
OUT(MAX)
OUT
selection to ensure that the control loop is stable.
≤ Δ
OUT
/2. This simple worst-case condition is
I ESR
L
⎡
⎢
⎣
Selection
OUT
V
V
OUT
+
is determined by the required effective
IN
OUT
8fC
, is determined by :
1
OUT
V
V
OUT
IN,
IN
DS8023-02 February 2011
⎤
⎥
⎦
is needed to filter the
−
1
IN
= 2V
OUT
, where