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參數(shù)資料
| 型號： | LTC1539IGW |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual High Efficiency, Low Noise, Synchronous Step-Down Switching Regulators |
| 中文描述： | 2 A SWITCHING CONTROLLER, 400 kHz SWITCHING FREQ-MAX, PDSO36 |
| 封裝： | 0.300 INCH, PLASTIC, SSOP-36 |
| 文件頁數(shù)： | 20/32頁 |
| 文件大?。?/td> | 451K |
| 代理商： | LTC1539IGW |
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20
LTC 1538-AUX/LTC 1539
APPLICATIO
S I
FOR
ATIO
U
W
U
U
With the addition of an external PNP pass device, a linear
regulator capable of supplying up to 0.5A is created. As
shown in Figure 11a, the base of the external PNP con-
nects to the AUXDR pin together with a pull-up resistor.
The output voltage V
OAUX
at the collector of the external
PNP is sensed by the AUXFB pin.
The input voltage to the auxiliary regulator can be taken
from a secondary winding on the primary inductor as
shown in Figure 11a. In this application, the SFB1 pin
regulates the input voltage to the PNP regulator (see SFB1
Pin Operation) and should be set to approximately 1V to
2V above the required output voltage of the auxiliary
regulator. A Zener clamp diode may be required to keep the
secondary winding resultant output voltage under the 28V
AUXDR pin specification when the primary is heavily
loaded and the secondary is not.
The AUXFB pin is the feedback point of the regulator. An
internal resistor divider is available to provide a 12V output
by simply connecting AUXFB directly to the collector of the
external PNP. The internal resistive divider is switched in
when the voltage at AUXFB goes above 9.5V with 1V built-
in hysteresis. For other output voltages, an external resis-
tive divider is fed back to AUXFB as shown in Figure 11b.
The output voltage V
OAUX
is set as follows:
R
R
=
V
12V AUX DR
OAUX
When used as a voltage comparator as shown in Figure
11c, the auxiliary block has a noninverting characteristic.
When AUXFB drops below 1.19V, the AUXDR pin will be
pulled low. A minimum current of 5
μ
A is required to pull up
the AUXDR pin to 5V when used as a comparator output in
order to counteract a 1.5
μ
A internal pull-down current source.
V
V
OAUX
=
+
<
≥
119
.
1
8
7
8V AUX DR<8.5V
12V
Efficiency Considerations
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. Efficiency can be expressed as:
Efficiency = 100% – (L1 + L2 + L3 + ...)
AUXDR
AUXFB
SFB1
LTC1538-AUX/
LTC1539
AUXON
+
+
1538 F11b
V
SEC
SECONDARY
WINDING
1:N
ON/OFF
V
OAUX
R6
10
μ
F
R5
R8
R7
R6
R5
V
SEC
= 1.19V
> (V
OAUX
+ 1V)
1 +
(
)
Figure 11b. 5V Output Auxiliary Regulator Using
External Feedback Resistors
Figure 11a. 12V Output Auxiliary Regulator
Using Internal Feedback Resistors
LTC1538-AUX/
LTC1539
AUXON
AUXDR
AUXFB
SFB1
+
+
1538 F11a
V
SEC
SECONDARY
WINDING
1:N
ON/OFF
V
OAUX
12V
R6
10
μ
F
R5
R6
R5
V
SEC
= 1.19V
> 13V
1 +
(
)
Figure 11c. Auxiliary Comparator Configuration
–
+
AUXON
AUXFB
ON/OFF
INPUT
V
PULL-UP
<
7.5V
AUXDR
OUTPUT
1538 F11c
1.19V REFERENCE
LTC1538-AUX/LTC1539
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