参数资料
型号: LT3439EFE#PBF
厂商: Linear Technology
文件页数: 5/12页
文件大小: 0K
描述: IC REG PSH-PLL CTRLR ISO 16TSSOP
标准包装: 95
类型: 推挽式控制器,隔离式
输出数: 1
输入电压: 2.8 V ~ 17.5 V
频率 - 开关: 20kHz ~ 250kHz
电流 - 输出: 1A
同步整流器:
工作温度: -40°C ~ 125°C
安装类型: 表面贴装
封装/外壳: 16-TSSOP(0.173",4.40mm)裸露焊盘
包装: 管件
供应商设备封装: 16-TSSOP-EP
产品目录页面: 1331 (CN2011-ZH PDF)
LT3439
BLOCK DIAGRA
T1
D1
V OUT
V IN
?
?
?
?
D2
C OUT
11
13
3
14
SHDN V IN
LT3439
COLA
COLB
LDO
REGULATOR
T
FF
Q
SLEW
CONTROL
OUTPUT
DRIVERS
INTERNAL V CC
QB
R T
7
R T
C T
6
5
C T
SYNC
OSCILLATOR
10
GND
4
R SL
+
R SENSE
16
PGND
1
3439 BD
R SL
OPERATIO
Push-Pull Topology
The push-pull DC transformer topology is a very straight-
forward switching power supply. The two switches are
turned on out of phase at 50% duty cycles. During the
switch on time, V IN is applied across the primary side of
the transformer. The voltage on the secondary side of the
transformer is simply V IN times the turns ratio. The diodes
rectify the secondary voltage and generate the output
voltage. The output capacitor is for hold-up and filtering.
Some of the topology’s advantages are: 1) Stepping up or
down the input voltage can easily be done by setting the
turns ratio. 2) The transformer provides isolation between
the input and output. 3) Each switch cycle applies V IN
across the transformer in opposite polarities. Therefore,
the transformer core never saturates and a separate reset
circuit is not necessary.
The push-pull topology is not without its concerns. An
imbalance in the two sides of the transformer can
eventually cause the transformer to saturate. Also, dur-
ing the turn-off of the switches, the leakage inductance
causes a large undesirable voltage spike. The LT3439
slew control feature addresses both of these concerns
and is discussed in the Applications Information section.
Slew Control
Control of voltage and current slew rate is maintained via
two feedback loops. One loop controls the output switch
collector voltage dV/dt and the other loop controls the
emitter current dI/dt. Output slew control is achieved by
comparing the two currents generated by these slewing
events to a current set by the external resistor R SL . The two
control loops work together to provide a smooth transition
from voltage slew control to current slew control.
Internal Regulator
Most of the control circuitry operates from an internal 2.4V
low dropout regulator that is powered from V IN . V IN can
sn3439 3439fs
5
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