参数资料
型号: LTC3704IMS#PBF
厂商: Linear Technology
文件页数: 20/28页
文件大小: 0K
描述: IC REG CTRLR INV PWM CM 10-MSOP
标准包装: 50
PWM 型: 电流模式
输出数: 1
频率 - 最大: 1MHz
占空比: 97%
电源电压: 2.5 V ~ 36 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)
包装: 管件
LTC3704
APPLICATIO S I FOR ATIO
L 1 = L 2 =
2 ? Δ I L 1 ? f
=
? 0 . 5 = 5 . 2 μ H
I LSAT ( MIN ) ≥ – ? 1 +
? χ ? 1
?
?
? ? I O ( MAX ) ?
= 1 . 2 ? 2 . 0 ?
= 4 . 8 A
regulator feedback loop acts on the resulting error amp
output signal to return V O to its steady-state value. During
this recovery time, V O can be monitored for overshoot or
ringing that would indicate a stability problem.
A second, more severe transient can occur when connect-
ing loads with large (> 1 μ F) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C O , causing a nearly instantaneous drop in V O . No
regulator can deliver enough current to prevent this prob-
lem if the load switch resistance is low and it is driven
quickly. The only solution is to limit the rise time of the
switch drive in order to limit the inrush current di/dt to the
load.
Design Example: A 5V to 15V Input, –5V at 2A Output
Positive-to-Negative Converter
The design example presented here will be for the circuit
V IN ( MIN )
? D MAX
5
2 ? 0 . 8 ? 300 k
The minimum saturation current for this inductor is:
2 1 – D MAX
1
1 – 0 . 5
The inductor chosen is a BH Electronics part # 510-1009,
which has an open circuit parallel inductance of 4.56 μ H
and a maximum dc current rating of 6.5A.
5. For the power MOSFET,
? 1 + ? ? I O ( MAX ) ? ρ Τ
shown in Figure 1. The input voltage range is 5V to 15V,
and the output is -5V. The maximum load current is 2A at
an input voltage of 5V (3A peak), and 3A at an input voltage
of 15V (5A peak).
R DS ( ON ) ≤ V SENSE ( MAX ) ?
? 2 ?
D MAX – 1
? χ ?
D MAX =
= = 50 %
1. The maximum duty cycle of the main switch is:
V OUT – 5
V OUT ? V IN ( MIN ) – 10
2. Pulse-Skip operation is chosen, so the MODE/SYNC pin
At the maximum duty cycle of 50%, the maximum SENSE
pin voltage is reduced to 130mV due to slope compensa-
tion, as shown in Figure 11. Assuming a maximum
junction temperature of 125 ° C for the power MOSFET,
ρ Τ = 1.5, and
is connected to the INTV CC pin.
3. The operating frequency is chosen to be 300kHz to
R DS ( ON ) ≤ 0 . 130 ?
0 . 5 – 1
– 1 . 2 ? 2 . 0 ? 1 . 5
= 18 . 1 m Ω
Δ I L 1 = ? χ ? I O ( MAX ) ?
Δ I L 1 = 0 . 4 ? 2 . 0 ?
= 0 . 8 A
I D ( PEAK ) = ? 1 + ? ? I O ( MAX ) = 6 A
reducethesizeoftheinductors.FromFigure5,theresistor
from the FREQ pin to ground is 80.6k.
4. A total inductor ripple current of 40% of the maximum
is chosen, so the inductor ripple current is:
D MAX
1 – D MAX
0 . 5
1 – 0 . 5
For a standard 1:1 coupled inductor, the inductance is
therefore:
The MOSFET chosen was Siliconix/Vishay’s Si4884, which
has a maximum R DS(ON) = 16.5m Ω at V GS = 4.5V at 25 ° C.
The minimum BV DSS = 30V and the maximum gate charge
is Q G = 20nC.
6. The output diode must withstand a reverse voltage of
V IN(MAX) – V O = 20V and a continuous current of
I O(MAX) = 5.0A (peak output current at V IN = 15V). The peak
current in the diode is:
? χ ?
? 2 ?
The power dissipated in this diode at full load is:
3704fb
20
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