参数资料
型号: LT3437HFE#TRPBF
厂商: Linear Technology
文件页数: 18/28页
文件大小: 0K
描述: IC REG BUCK ADJ 0.5A 16TSSOP
标准包装: 2,500
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: 500mA
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: 带卷 (TR)
供应商设备封装: 16-TSSOP-EP
LT3437
APPLICATIO S I FOR ATIO
These requirements result in the use of a Schottky type
diode. DC switching losses are minimized due to its low
forward voltage drop, and AC behavior is benign due to its
OPTIONAL
lack of a significant reverse recovery time. Schottky diodes
are generally available with reverse voltage ratings of 60V,
and even 100V, and are price competitive with other types.
V IN
V IN BOOST
LT3437
GND SW
V OUT
The use of so-called “ultrafast” recovery diodes is gener-
ally not recommended. When operating in continuous
mode, the reverse recovery time exhibited by “ultrafast”
diodes will result in a slingshot type effect. The power
internal switch will ramp up V IN current into the diode in an
attempt to get it to recover. When the diode has finally
turned off, some tens of nanoseconds later, the V SW node
V BOOST – V SW = V OUT
V BOOST(MAX) = V IN + V OUT
(6a)
voltage ramps up at an extremely high dV/dt, perhaps 5V
to even 10V/ns! With real world lead inductances, the V SW
V IN
V IN BOOST
LT3437
node can easily overshoot the V IN rail. This can result in
GND
SW
V OUT
poor RFI behavior, and if the overshoot is severe enough,
damage the IC itself.
V BOOST – V SW = V IN
V BOOST(MAX) = 2V IN
BOOST PIN
For most applications, the boost components are a 0.1 μ F
capacitor and a BAS21 diode. The anode is typically
(6b)
connected to the regulated output voltage, to generate a
voltage approximately V OUT above V IN to drive the output
stage (Figure 6a). However, the output stage discharges
the boost capacitor during the on time of the switch. The
V IN
V IN BOOST
LT3437
GND SW
D SS
V DC
V OUT
output driver requires at least 2.5V of headroom through-
out this period to keep the switch fully saturated. If the
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 6b), 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 6c). Tying BOOST to V IN or an
independent supply may reduce efficiency, but it will
reduce 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
LT3437 sees can be reduced by placing a Zener diode in
series with the BOOST diode (Figure 6a option).
3437 F06
V BOOST – V SW = V DC
V BOOST(MAX) = V DC + V IN
(6c)
Figure 6. BOOST Pin Configurations
A 0.1 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, 11mA boost current and 0.7V discharge
ripple. The boost capacitor value could be reduced under
less demanding conditions, but this will not improve
circuit operation or efficiency. Under low input voltage and
low load conditions, a higher value capacitor will reduce
discharge ripple and improve start-up operation.
3437fc
18
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