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參數(shù)資料
| 型號： | AAT2504 |
| 廠商： | Advanced Analogic Technologies, Inc. |
| 英文描述： | Adjustable 3-Channel Regulator |
| 中文描述： | 可調(diào)節(jié)的3通道穩(wěn)壓器 |
| 文件頁數(shù)： | 14/22頁 |
| 文件大?。?/td> | 948K |
| 代理商： | AAT2504 |
AAT2504
Adjustable 3-Channel Regulator
14
2504.2007.06.1.0
Output Capacitor
The output capacitor limits the output ripple and
provides holdup during large load transitions. A
4.7μF to 10μF X5R or X7R ceramic capacitor typi-
cally provides sufficient bulk capacitance to stabi-
lize the output during large load transitions and has
the ESR and ESL characteristics necessary for low
output ripple.
The output voltage droop due to a load transient is
dominated by the capacitance of the ceramic out-
put capacitor. During a step increase in load cur-
rent, the ceramic output capacitor alone supplies
the load current until the loop responds. Within two
or three switching cycles, the loop responds and
the inductor current increases to match the load
current demand. The relationship of the output volt-
age droop during the three switching cycles to the
output capacitance can be estimated by:
Once the average inductor current increases to the
DC load level, the output voltage recovers. The
above equation establishes a limit on the minimum
value for the output capacitor with respect to load
transients.
The internal voltage loop compensation also limits
the minimum output capacitor value to 4.7μF. This
is due to its effect on the loop crossover frequency
(bandwidth), phase margin, and gain margin.
Increased output capacitance will reduce the
crossover frequency with greater phase margin.
Adjustable Output Resistor Selection
The output voltage on the step-down converter is
programmed with external resistors R2 and R6. To
limit the bias current required for the external feed-
back resistor string while maintaining good noise
immunity, the minimum suggested value for R6 is
59k
Ω
. Although a larger value will further reduce
quiescent current, it will also increase the imped-
ance of the feedback node, making it more sensitive
to external noise and interference. Table 2 summa-
rizes the resistor values for various output voltages
with R6 set to either 59k
Ω
for good noise immunity
or 221k
Ω
for reduced no load input current.
With enhanced transient response for extreme
pulsed load application, an external feed-forward
capacitor (C1 in Fig.3) can be added.
Table 2: Step-Down Converter Resistor Values
for Various Output Voltages.
Thermal Calculations
There are three types of losses associated with the
AAT2504 step-down converter: switching losses,
conduction losses, and quiescent current losses.
Conduction losses are associated with the R
DS(ON)
characteristics of the power output switching
devices. Switching losses are dominated by the gate
charge of the power output switching devices. At full
load, assuming continuous conduction mode (CCM),
a simplified form of the LDO losses is given by:
P
TOTAL
I
O
2
· (R
DSON(HS)
· V
O
+ R
DSON(LS)
· [V
IN
- V
O
])
V
IN
=
+ (t
sw
· F · I
O
+ I
Q
) · V
IN
R6 = 59k
Ω
R2 (k
Ω
)
0
6.65
13.3
19.6
26.1
32.4
39.2
59.0
61.9
71.5
105
124
137
158
R6 = 221k
Ω
R2 (k
Ω
)
0
24.3
48.7
73.2
97.6
124
147
221
232
274
392
464
511
590
V
OUT
(V)
0.9*
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
2.8
3.0
3.3
C
OUT
=
3
·
Δ
I
LOAD
V
DROOP
·
F
S
* For the 0.9V output, R6 is open.
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| AAT2505IWP-AQ-T1 | 制造商:ANALOGICTECH 制造商全稱:Advanced Analogic Technologies 功能描述:Dual Channel, Step-Down Converter/Linear Regulator |
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