RT8023GQW Richtek USA Inc, RT8023GQW Datasheet - Page 15
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RT8023GQW
Manufacturer Part Number
RT8023GQW
Description
IC CONV STP-DWN W/2 LDO 24WQFN
Manufacturer
Richtek USA Inc
Datasheet
1.RT8023GQW.pdf
(19 pages)
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
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
RT8023GQW
Manufacturer:
INTERSIL
Quantity:
36 710
The output ripple will be highest at maximum input voltage
since ΔI
placed in parallel may be needed to meet the ESR and
RMS current handling requirement. Dry tantalum, special
polymer, aluminum electrolytic and ceramic capacitors are
all available in surface mount packages. Special polymer
capacitors offer very low ESR value. However, it provides
lower capacitance density than other types. Although
Tantalum capacitors have the highest capacitance density,
it is important to only use types that pass the surge test
for use in switching power supplies. Aluminum electrolytic
capacitors have significantly higher ESR. However, it can
be used in cost-sensitive applications for ripple current
rating and long term reliability considerations. Ceramic
capacitors have excellent low ESR characteristics but can
have a high voltage coefficient and audible piezoelectric
effects. The high Q of ceramic capacitors with trace
inductance can also lead to significant ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, V
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at V
part.
Output Voltage Programming
The resistive divider allows the FB pin to sense a fraction
of the output voltage as shown in Figure2.
DS8023-02 February 2011
IN
L
increases with input voltage. Multiple capacitors
. At best, this ringing can couple to the output
Figure 2. Setting the Output Voltage
RT8023
GND
FB
IN
large enough to damage the
V
OUT
R1
R2
For adjustable voltage mode, the output voltage is set by
an external resistive divider according to the following
equation :
Where V
Efficiency Consideration
The efficiency of a switching regulator is equal to the output
power divided by the input power times 100%. It is often
useful to analyze individual losses to determine what is
limiting the efficiency and which change would produce
the most improvement. The efficiency can be expressed
as :
Efficiency = 100 − (L1 + L2 + L3 + …..)
Where L1, L2, etc., are the individual losses as a
percentage of input power, although all dissipative
elements in the circuit produce losses, V
current and I
the losses.
The V
loss at a very low load current whereas the I
dominates the efficiency loss at medium to high load
current. In a typical efficiency plot, the efficiency curve at
very low load currents can be misleading since the actual
power lost is of no consequence.
1. The V
including the DC bias current as given in the electrical
characteristics and the internal main switch and
synchronous switch gate charge currents. The gate charge
current results from switching the gate capacitance of the
internal power MOSFET switches. Each time the gate is
switched from high to low to high again, a packet of charge
ΔQ moves from V
The value of ΔQ/Δt is the current out of V
larger than the DC bias current. In continuous mode,
I
Where Q
and bottom switches. Both the DC bias and gate charge
losses are proportional to V
significant at higher supply voltages.
V
GATECHG
OUT
IN
= V
quiescent current loss dominates the efficiency
IN
REF
= f(Q
T
REF
and Q
quiescent current appears due to two factors
is the internal reference voltage (0.8V typ.).
2
R losses are two main sources for most of
T
⎛
⎜
⎝
+ Q
1
B
+
IN
are the gate charges of the internal top
R2
R1
B
)
to ground.
⎞
⎟
⎠
IN
and their effects will be more
RT8023
IN
www.richtek.com
that is typically
IN
quiescent
2
R loss
15