参数资料
型号: LTC1436AEGN#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS
中文描述: 2 A SWITCHING CONTROLLER, 400 kHz SWITCHING FREQ-MAX, PDSO24
封装: 0.150 INCH, PLASTIC, SSOP-24
文件页数: 13/28页
文件大小: 493K
代理商: LTC1436AEGN#PBF
20
LTC1436A
LTC1436-PLL-A/LTC1437A
14367afb
APPLICATIONS INFORMATION
WU
U
Figure 11a. 12V Output Auxiliary Regulator Using
Internal Feedback Resistors
The minimum on-time for the LTC1436A/LTC1437A in a
properly configured application is less than 300ns but
increases at low ripple current amplitudes (see Figure 12).
If an application is expected to operate close to the
minimum on-time limit, an inductor value must be chosen
that is low enough to provide sufficient ripple amplitude to
meet the minimum on-time requirement. To determine the
proper value, use the following procedure:
1. Calculate on-time at maximum supply, tON(MIN) =
(1/f)(VOUT/VIN(MAX)).
2. Use Figure 12 to obtain the peak-to-peak inductor ripple
current as a percentage of IMAX necessary to achieve
the calculated tON(MIN).
3. Ripple amplitude
IL(MIN) = (% from Figure 12) (IMAX)
where IMAX = 0.1/RSENSE.
4. LMAX = t
VV
I
ON MIN
IN MAX
OUT
L MIN
()
Choose an inductor less than or equal to the calculated
LMAX to ensure proper operation.
1436 F11a
VSEC = 1.19V 1 +
> 13V
R6
R5
()
ON/OFF
VSEC
SECONDARY WINDING
R6
R5
10
F
1:N
VOAUX
12V
AUXDR
LTC1436A
LTC1437A
AUXFB
AUXON
+
SFB
+
Figure 11c. Auxiliary Comparator Configuration
+
AUXON
AUXFB
ON/OFF
INPUT
VPULL-UP < 8.5V
AUXDR
OUTPUT
1436 F11c
1.19V REFERENCE
LTC1436A
LTC1437A
Figure 11b. 5V Output Auxiliary Regulator Using
External Feedback Resistors
ON/OFF
VSEC
SECONDARY WINDING
R6
R5
R8
R7
1436 F11b
10
F
1:N
VOAUX
AUXDR
LTC1436A
LTC1437A
AUXFB
AUXON
VSEC = 1.19V 1 +
R6
R5
()
VOAUX = 1.19V 1 +
R8
R7
()
+
SFB
+
Minimum On-Time Considerations
Minimum on-time, tON(MIN), is the smallest amount of
time that the LTC1436A/LTC1437A are capable of turning
the top MOSFET on and off again. It is determined by
internal timing delays and the gate charge required to turn
on the top MOSFET. Low duty cycle applications may
approach this minimum on-time limit. If the duty cycle
falls below what can be accommodated by the minimum
on-time, the LTC1436A/LTC1437A will begin to skip cycles.
The output voltage will continue to be regulated, but the
ripple current and ripple voltage will increase. Therefore
this limit should be avoided.
Figure 12. Minimum On-Time vs Inductor Ripple Current
Because of the sensitivity of the LTC1436A/LTC1437A
current comparator when operating close to the minimum
on-time limit, it is important to prevent stray magnetic flux
generated by the inductor from inducing noise on the
current sense resistor, which may occur when axial type
cores are used. By orienting the sense resistor on the
radial axis of the inductor (see Figure 13), this noise will be
minimized.
INDUCTOR RIPPLE CURRENT (% OF IMAX)
0
200
MINIMUM
ON-TIME
(ns)
250
300
350
400
RECOMMENDED
REGION FOR MIN
ON-TIME AND
MAX EFFICIENCY
10
20
30
40
1435A F12
50
60
70
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