參數(shù)資料
型號(hào)： SC2440TETRT
廠商： Semtech Corporation
英文描述： 2.5 MHz Dual Switching Regulator with Integrated 2A Switches
中文描述： 2.5 MHz雙開(kāi)關(guān)穩(wěn)壓器集成甲開(kāi)關(guān)
文件頁(yè)數(shù)： 10/26頁(yè)
文件大?。?/td> 643K
代理商： SC2440TETRT
10
2005 Semtech Corp.
www.semtech.com
SC2440
POWER MANAGEMENT
Applications Information
Minimum On Time Consideration
The operating duty cycle of a step-down switching
regulator with diode rectifier in continuous-conduction
mode (CCM) is given by
CESAT
V
D
IN
D
OUT
V
V
V
V
+
D
+
=
(2)
where V
is the switch saturation voltage and V
D
is
voltage drop across the rectifying diode.
Duty cycle decreases with increasing
OUT
IN
V
V
ratio. In peak
current-mode control, the PWM modulating ramp is the
sensed current ramp of the power switch. This current
ramp is absent unless the switch is turned on. The
intersection of this ramp with the output of the voltage
feedback error amplifier determines the switch pulse
width. The propagation delay time required to
immediately turn off the switch after it is turned on is
the minimum switch on time (T
ON(MIN)
). Closed-loop
measurement of the SC2440 with low
IN
OUT
V
V
ratios shows
that the minimum on time is about 105ns at room
temperature. T
also exhibits a slight positive
temperature coefficient (Figure 6). The power switch in
the SC2440 is either not turned on at all or for at least
T
ON(MIN)
. If the required switch on time (=f
than the minimum on time, the regulator will either skip
cycles or it will jitter.
D) is shorter
Example: Determine the maximum operating frequency
of a dual 12V to 1.0V and 12V to 3.3V switching
regulator using the SC2440.
Assuming that V
= 0.45V, V
= 0.25V and V
= 13.2V
(10% high line), the corresponding duty ratios, D
and
D
, of the 1.0V and 3.3V converters can be calculated
using (2).
45
.
1
D
1
=
+
11
.
25
.
45
.
2
13
+
=
28
.
25
.
45
.
2
13
45
.
3
+
D
2
=
+
=
If the ambient temperature can be as high as 85
°
C, then
the maximum operating frequencies of the 1.0V and the
3.3V converters will be
KHz
920
ns
120
D
1
=
and
MHz
3
=
ns
120
D
2
respectively.
Channel frequency should be set below 920KHz to allow
margin for load transient.
Minimum Off Time Limitation
The PWM latch in Figure 2 is reset every period by the
clock. The clock also turns off the power transistor to
refresh the bootstrap capacitor. This minimum off time
limits the attainable duty cycle of the regulator at a given
switching frequency. Measurement shows that the power
transistor needs to be turned off for at least 120ns every
switching period to properly reset the latch and to refresh
the bootstrap capacitor. For a step-down converter, D
V
increases with increasing
IN
OUT
V
ratio. If the required duty
cycle is higher than the attainable maximum, then the
Figure 6. Variation of Minimum On Time with
Temperature.
Minimum On Time vs Temperature
80
90
100
110
120
130
-40
-20
0
20
40
60
80
100
Temperature (°C)
T
O
相關(guān)PDF資料
PDF描述
SC2441A 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441AEVB 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441ATETRT 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441 Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441EVB Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC2441 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441A 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441A_09 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441AEVB 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
SC2441ATETRT 制造商:Semtech Corporation 功能描述:
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