参数资料
型号: LT3434EFE
厂商: Linear Technology
文件页数: 17/24页
文件大小: 0K
描述: IC REG BUCK ADJ 3A 16TSSOP
标准包装: 95
类型: 降压(降压)
输出类型: 可调式
输出数: 1
输出电压: 1.25 V ~ 54 V
输入电压: 3.3 V ~ 60 V
PWM 型: 电流模式,混合
频率 - 开关: 200kHz
电流 - 输出: 3A
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
LT3434
APPLICATIO S I FOR ATIO
output voltage is less than 3.3V it is recommended that an
alternate boost supply is used. The boost diode can be
connected to the input (Figure 7b) but care must be taken
to prevent the boost voltage (V BOOST = V IN ? 2) from
exceeding the BOOST pin absolute maximum rating. The
additional voltage across the switch driver also increases
power loss and reduces efficiency. If available, an inde-
pendent supply can be used to generate the required
BOOST voltage (Figure 7c). Tying BOOST to V IN or an
independent supply may reduce efficiency but it will re-
duce the minimum V IN required to start-up with light
loads. If the generated BOOST voltage dissipates too
much power at maximum load, the BOOST voltage the
LT3434 sees can be reduced by placing a Zener diode in
series with the BOOST diode (Figure 7a option).
OPTIONAL
A 0.68 μ F boost capacitor is recommended for most appli-
cations. Almost any type of film or ceramic capacitor is
suitable but the ESR should be <1 ? to ensure it can be fully
recharged during the off time of the switch. The capacitor
value is derived from worst-case conditions of 4700ns on
time, 65mA boost current and 0.7V discharge ripple. The
boost capacitor value could be reduced under less de-
manding conditions but this will not improve circuit opera-
tion or efficiency. Under low input voltage and low load
conditions a higher value capacitor will reduce discharge
ripple and improve start-up operation.
SHUTDOWN FUNCTION AND UNDERVOLTAGE
LOCKOUT
The SHDN pin on the LT3434 controls the operation of the
IC. When the voltage on the SHDN pin is below the 1.2V
shutdown threshold the LT3434 is placed in a “zero”
supply current state. Driving the SHDN pin above the
V IN
V IN BOOST
LT3434
GND
SW
V OUT
shutdown threshold enables normal operation. The SHDN
pin has an internal sink current of 3 μ A.
In addition to the shutdown feature, the LT3434 has an
undervoltage lockout function. When the input voltage is
V BOOST – V SW = V OUT
V BOOST(MAX) = V IN + V OUT
(7a)
below 2.4V, switching will be disabled. The undervoltage
lockout threshold doesn’t have any hysteresis and is
mainly used to insure that all internal voltages are at the
correct level before switching is enabled. If an undervolt-
V IN
V IN BOOST
age lockout function with hysteresis is needed to limit
LT3434
GND SW
V OUT
input current at low V IN to V OUT ratios refer to Figure 8 and
the following:
V UVLO = R 1 ? SHDN + + I SHDN SHDN
? + V
V OUT ( R 1 )
V IN
V BOOST – V SW = V IN
V BOOST(MAX) = 2V IN
(7b)
V IN BOOST
LT3434
GND
SW
V BOOST – V SW = V DC
D SS
V DC
V OUT
3434 F07
? V V SHDN ?
? R 3 R 2 ?
V HYST =
R 3
R1 should be chosen to minimize quiescent current during
normal operation by the following equation:
V BOOST(MAX) = V DC + V IN
(7c)
Figure 7. BOOST Pin Configurations
R 1 =
V IN – 2 V
( 1 . 5 ) ( I SHDN ( MAX )
)
3434fb
17
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