参数资料
| 型号： | SC4525DSETRT |
| 厂商： | Semtech |
| 文件页数： | 9/21页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A 8SOIC |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1 V ~ 16.74 V |
| 输入电压： | 3 V ~ 18 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 65kHz ~ 350kHz |
| 电流 - 输出： | 3A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 105°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm Width）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 8-SOIC-EP |
| 其它名称： | SC4525DSEDKR |
SC4525D
Applications Information
Operation
The SC4525D is a 350kHz fixed frequency, peak current-
mode, step-down switching regulator with an integrated
3.9A power NPN transistor. With the peak current-mode
control, the double reactive poles of the output LC filter
are reduced to a single real pole by the inner current
loop. This simplifies loop compensation and achieves fast
transient response with a simple Type-2 compensation
network.
As shown in Figure 2, the switch collector current is
sensed with an integrated 3.53m W sense resistor. The
sensed current is summed with a slope-compensating
ramp before it is compared with the transconductance
error amplifier (EA) output. The PWM comparator trip
point determines the switch turn-on pulse width. The
current-limit comparator ILIM turns off the power switch
when the sensed signal exceeds the 8mV current-limit
threshold.
Driving the base of the power transistor above the
input power supply rail minimizes the power transistor
saturation voltage and maximizes efficiency. An external
bootstrap circuit (formed by the capacitor C and the
diode D in Figure ) generates such a voltage at the BST
pin for driving the power transistor.
the internal bias circuit of the SC4525D turns on and the
SC4525D draws 2mA from V IN . The .9μA charging current
turns off and the 2.4μA current source I C in Figure 3 slowly
charges the soft-start capacitor.
The error amplifier EA in Figure 2 has two non-inverting
inputs. The non-inverting input with the lower voltage
predominates. One of the non-inverting inputs is biased
to a precision V reference and the other non-inverting
input is tied to the output of the amplifier A . Amplifier A
produces an output V = 2(V SS/EN - .2V). V is zero and COMP
is forced low when V SS/EN is below .2V. During start up,
the effective non-inverting input of EA stays at zero until
the soft-start capacitor is charged above .2V. Once V SS/
EN exceeds .2V, COMP is released. The regulator starts to
switch when V COMP rises above 0.4V. If the soft-start interval
is made sufficiently long, then the FB voltage (hence the
output voltage) will track V during start up. V SS/EN must be
at least .83V for the output to achieve regulation. Proper
soft-start prevents output overshoot. Current drawn from
the input supply is also well controlled.
Overload / Short-Circuit Protection
Table 2 lists various fault conditions and their
corresponding protection schemes in the SC4525D.
Table 2: Fault conditions and protections
Shutdown and Soft-Start
The SS/EN pin is a multiple-function pin. An external
capacitor (4.7nF to 22nF) connected from the SS pin to
ground sets the soft-start and overload shutoff times of
the regulator (Figure 3). The effect of V SS/EN on the SC4525D
is summarized in Table .
Table 1: SS/EN operation modes
Condition
IL>ILimit, V FB >0.8V
IL>ILimit, V FB <0.8V
VSS/EN Falling
SS/EN<1.9V
Tj>160C
Cause of Fault
Over current
Over current
Persistent over current
or short circuit
Over temperature
Protective Action
Cycle-by-cycle limit at
programmed frequency
Cycle-by-cycle limit with
frequency foldback
Shutdown, then retry
(Hiccup)
Shutdown
SS/EN
<0.2V
0.4V to 1.2V
1.2V to 2.15V
>2.15V
Mode
Shutdown
Not switching
Switching & hiccup disabled
Switching & hiccup armed
Supply Current
18uA @ 5Vin
2mA
Load dependent
As summarized in Table , overload shutdown is disabled
during soft-start (V SS/EN <2. 5V). In Figure 3, the reset input
of the overload latch B 2 will remain high if the SS/EN
voltage is below 2. 5V. Once the soft-start capacitor is
charged above 2. 5V, the output of the Schmitt trigger
Pulling the SS/EN pin below 0.2V shuts off the regulator
and reduces the input supply current to 8μA (V IN = 5V).
When the SS/EN pin is released, the soft-start capacitor
is charged with an internal .9μA current source (not
shown in Figure 3). As the SS/EN voltage exceeds 0.4V,
B goes high, the reset input of B 2 goes low and hiccup
becomes armed. As the load draws more current from
the regulator, the current-limit comparator ILIM (Figure
2) will eventually limit the switch current on a cycle-by-
cycle basis. The over-current signal OC goes high, setting
9
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