参数资料
型号: LTC1436ACGN-PLL#TRPBF
厂商: Linear Technology
文件页数: 11/28页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 24-SSOP
标准包装: 2,500
PWM 型: 电流模式
输出数: 1
频率 - 最大: 138kHz
占空比: 99%
电源电压: 3.5 V ~ 30 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: 0°C ~ 70°C
封装/外壳: 24-SSOP(0.154",3.90mm 宽)
包装: 带卷 (TR)
LTC1436A
LTC1436A-PLL/LTC1437A
OPERATIO
Power-On Reset
(Refer to Functional Diagram)
The AUX block can be used as a comparator having its
The POR pin is an open drain output which pulls low when
the main regulator output voltage is out of regulation.
When the output voltage rises to within 7.5% of regula-
tion, a timer is started which releases POR after 2 16
(65536) oscillator cycles. In shutdown, the POR output is
pulled low.
Auxiliary Linear Regulator
The auxiliary linear regulator in the LTC1436A/LTC1437A
controls an external PNP transistor for operation up to
500mA. An internal AUXFB resistive divider set for 12V
operation is invoked when AUXDR pin is above 9.5V to
allow 12V VPP supplies to be easily implemented. When
AUXDR is below 8.5V an external feedback divider may be
used to set other output voltages. Taking the AUXON pin
low shuts down the auxiliary regulator providing a conve-
nient logic controlled power supply.
inverting input tied to the internal 1.19V reference. The
AUXDR pin is used as the output and requires an external
pull-up to a supply less than 8.5V in order to inhibit the
invoking of the internal resistive divider.
INTV CC /DRV CC /EXTV CC Power
Power for the top and bottom MOSFET drivers and most
of the other LTC1436A/LTC1437A circuitry is derived from
the INTV CC pin. The bottom MOSFET driver supply DRV CC
pin is internally connected to INTV CC in the LTC1436A and
externally connected to INTV CC in the LTC1437A. When
the EXTV CC pin is left open, an internal 5V low dropout
regulator supplies INTV CC power. If EXTV CC is taken above
4.8V, the 5V regulator is turned off and an internal switch
is turned on to connect EXTV CC to INTV CC . This allows the
INTV CC power to be derived from a high efficiency external
source such as the output of the regulator itself or a
secondary winding, as described in the Applications Infor-
mation section.
APPLICATIO N S I N FOR M ATIO N
The basic LTC1436A application circuit is shown in Figure
1, High Efficiency Step-Down Converter. External compo-
nent selection is driven by the load requirement, and
R SENSE =
100mV
I MAX
begins with the selection of R SENSE . Once R SENSE is
known, C OSC and L can be chosen. Next, the power
MOSFETs and D1 are selected. Finally, C IN and C OUT are
selected. The circuit shown in Figure 1 can be configured
for operation up to an input voltage of 28V (limited by the
external MOSFETs).
R SENSE Selection For Output Current
R SENSE is chosen based on the required output current.
The LTC1436A/LTC1437A current comparator has a maxi-
mum threshold of 150mV/R SENSE and an input common
mode range of SGND to INTV CC . The current comparator
threshold sets the peak of the inductor current, yielding a
maximum average output current I MAX equal to the peak
value less half the peak-to-peak ripple current ? I L .
Allowing a margin for variations in the LTC1436A/
The LTC1436A/LTC1437A work well with R SENSE values
≥ 0.005 ? .
C OSC Selection for Operating Frequency
The LTC1436A/LTC1437A use a constant frequency
architecture with the frequency determined by an external
oscillator capacitor C OSC . Each time the topside MOSFET
turns on, the voltage on C OSC is reset to ground. During the
on-time, C OSC is charged by a fixed current plus an
additional current which is proportional to the output
voltage of the phase detector V PLLLPF (LTC1436A-PLL/
LTC1437A). When the voltage on the capacitor reaches
1.19V, C OSC is reset to ground. The process then repeats.
The value of C OSC is calculated from the desired operating
frequency. Assuming the phase-locked loop has no exter-
nal oscillator input (V PLLLPF = 0V):
LTC1437A and external component values yields:
14367afb
11
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