参数资料
型号: LTC3722IGN-1#PBF
厂商: Linear Technology
文件页数: 18/28页
文件大小: 0K
描述: IC REG CTRLR DIV ISO PWM 24SSOP
标准包装: 55
PWM 型: 电流模式,全桥
输出数: 1
频率 - 最大: 1MHz
占空比: 98.5%
电源电压: 3.8 V ~ 10.3 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 24-SSOP(0.154",3.90mm 宽)
包装: 管件
LTC3722-1/LTC3722-2
OPERATION
DC MAX
(2 ? V OUT )
f SW
= 150kHz
R SLOPE = V O ?
= 3.3V ?
3.Slopecompensationisrequiredformostpeakcurrent
mode controllers in order to prevent subharmonic
oscillation of the current control loop. In general, if the
system duty cycle exceeds 50% in a fixed frequency,
continuous current mode converter, an unstable con-
dition exists within the current control loop. Any
perturbation in the current signal is amplified by the
PWM modulator resulting in an unstable condition.
Some common manifestations of this include alternate
pulse nonuniformity and pulse width jitter. Fortunately,
this can be addressed by adding a corrective slope to
the current sense signal or by subtracting the same
slope from the current command signal (error am-
plifier output). In theory, the current doubler output
configuration does not require slope compensation
since the output inductor duty cycles only approach
50%. However, transient conditions can momentarily
cause higher duty cycles and therefore, the possibility
for unstable operation.
Transformer turns ratio (N) =
V IN(MIN) ? = 5
R CS = 0.05Ω
f SW = 300kHz, i.e., transformer f =
2
R CS
(2 ? L ? f SW ? 74μA ? N)
0.05
2 ? 2.2μH ? 300k ? 74μA ? 5
R SLOPE = 338Ω, choose the next higher standard value
to account for tolerances in I SLOPE , R CS , N and L.
V(C T ) CURRENT
R SLOPE
R CS
SLOPE
The exact amount of required slope compensation is
easily programmed by the LTC3722-1/LTC3722-2 with
the addition of a single external resistor (see Figure 9).
The LTC3722-1/LTC3722-2 generates a current that
is proportional to the instantaneous voltage on C T ,
(33μA/V(C T )). Thus, at the peak of C T , this current is
approximately 74μA and is output from the CS pin. A
resistor connected between CS and the external current
sense resistor sums in the required amount of slope
compensation. The value of this resistor is dependent
on several factors including minimum V IN , V OUT , switch-
ing frequency, current sense resistor value and output
inductor value. An illustrative example with the design
equation for current doubler secondary follows.
C T
LTC3722
BRIDGE
I=
33k CS
ADDED
33k
CURRENT SENSE
WAVEFORM 372212 F09
Figure 9. Slope Compensation Circuitry
Example:
V IN = 36V to 72V
V OUT = 3.3V
I OUT = 40A
L = 2.2μH
372212fb
18
For more information www.linear.com/LTC3722
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