参数资料
型号: LTC3809IMSE-1#PBF
厂商: Linear Technology
文件页数: 11/24页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 10-MSOP
标准包装: 50
PWM 型: 电流模式
输出数: 1
频率 - 最大: 600kHz
占空比: 100%
电源电压: 2.75 V ~ 9.8 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: 10-TFSOP,10-MSOP(0.118",3.00mm 宽)裸露焊盘
包装: 管件
LTC3809-1
OPERATION
Dropout Operation
(Refer to Functional Diagram)
where A is a constant determined by the state of the IPRG
When the input supply voltage (V IN ) approaches the output
voltage, the rate of change of the inductor current while the
external P-channel MOSFET is on (ON cycle) decreases.
This reduction means that the P-channel MOSFET will
remain on for more than one oscillator cycle if the inductor
current has not ramped up to the threshold set by the
EAMP on the I TH pin. Further reduction in the input supply
voltage will eventually cause the P-channel MOSFET to be
turned on 100%; i.e., DC. The output voltage will then be
determined by the input voltage minus the voltage drop
across the P-channel MOSFET and the inductor.
Undervoltage Lockout
pin. Floating the IPRG pin selects A = 1; tying IPRG to
V IN selects A = 5/3; tying IPRG to GND selects A = 2/3.
The maximum value of V ITH is typically about 1.98V, so
the maximum sense voltage allowed across the external
P-channel MOSFET is 125mV, 85mV or 204mV for the
three respective states of the IPRG pin.
However, once the controller’s duty cycle exceeds 20%,
slope compensation begins and effectively reduces the
peak sense voltage by a scale factor (SF) given by the
curve in Figure 1.
The peak inductor current is determined by the peak sense
voltage and the on-resistance of the external P-channel
MOSFET:
To prevent operation of the P-channel MOSFET below
safe input voltage levels, an undervoltage lockout is
incorporated in the LTC3809-1. When the input supply
voltage (V IN ) drops below 2.25V, the external P- and
N-channel MOSFETs and all internal circuits are turned
off except for the undervoltage block, which draws only
a few microamperes.
Peak Current Sense Voltage Selection
and Slope Compensation (IPRG Pin)
When the LTC3809-1 controller is operating below 20%
I PK =
Δ V SENSE(MAX )
R DS ( ON )
110
100
90
80
70
60
50
40
duty cycle, the peak current sense voltage (between the
V IN and SW pins) allowed across the external P-channel
MOSFET is determined by:
30
20
10
0
0
10 20 30 40 50 60 70 80 90 100
Δ V SENSE ( MAX ) = A ? ITH
V
– 0 . 7 V
10
DUTY CYCLE (%)
38091 F01
Figure 1. Maximum Peak Current vs Duty Cycle
38091fc
11
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