参数资料
型号: LTC3252EDE#TRPBF
厂商: Linear Technology
文件页数: 7/12页
文件大小: 0K
描述: IC REG BUCK SWITCHED CAP 12DFN
标准包装: 2,500
类型: 降压(降压),切换电容(充电泵)
输出类型: 可调式
输出数: 2
输出电压: 0.9 V ~ 1.6 V
输入电压: 2.7 V ~ 5.5 V
PWM 型: Burst Mode?
频率 - 开关: 1MHz ~ 1.6MHz
电流 - 输出: 250mA
同步整流器:
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 12-WFDFN 裸露焊盘
包装: 带卷 (TR)
供应商设备封装: 12-DFN(4x3)
LTC3252
OPERATIO
(Refer to Simplified Block Diagram)
Unlike conventional buck converters, the LTC3252’s inter-
nal oscillator is designed to produce a clock pulse whose
period is random on a cycle-by-cycle basis but fixed
between 1MHz and 1.6MHz. This has the benefit of spread-
ing the switching noise over a range of frequencies, thus
significantly reducing the peak noise. Figures 1 and 2
show how the spread spectrum feature of the LTC3252
significantly reduces the peak harmonic noise and virtu-
ally elliminates harmonics compared to a conventional
buck converter.
Spread spectrum operation is always enabled but is most
effective when the LTC3252’s outputs are out of Burst
Mode operation and the oscillator is running continuously
(see the Low Current Burst Mode Operation section).
Low Current Burst Mode Operation
To improve efficiency at low output currents, a Burst Mode
operation function is included in the LTC3252. An output
current sense is used to detect when the required output
current of both outputs drop below an internally set
Figure 1. Conventional Buck Input Noise
threshold (30mA typ). When this occurs, the part shuts
down the internal oscillator and goes into a low current
operating state. The LTC3252 will remain in the low
current operating state until either output has dropped
enough to require another burst of current. The LTC3252
resumes continuous operation when the load on one or
both outputs exceeds the internally set threshold. Unlike
traditional charge pumps where the burst current is highly
dependant on many factors (i.e., supply, switch strength,
capacitor selection, etc.), the LTC3252’s burst current is
set by the burst threshold and hysteresis. This means that
the output ripple voltage in Burst Mode operation is
relatively consistent and is typically about 12mV with a
4.7 μ F output capacitor on a 1.5V output. The ripple voltage
amplitude is a direct function of the output capacitor size.
Burst Mode operation ripple voltage does increase slightly
at lower output voltages due to the increase in loop gain.
Users can counteract output voltage ripple increase through
the use of a slightly larger output capacitor. See Recom-
mended Output Capacitance guidelines of Figure 3.
Figure 2. LTC3252 Input Noise
3252f
7
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