參數(shù)資料
型號(hào)： SC403MLTRT
廠商： Semtech
文件頁(yè)數(shù)： 16/32頁(yè)
文件大小： 741K
描述： IC REG DL BCK/LINEAR SYNC 32MLPQ
標(biāo)準(zhǔn)包裝： 1
系列： EcoSpeed®, SmartDrive™
拓?fù)洌?/td> 降壓（降壓）同步（1），線性（LDO）（1）
功能： 任何功能
輸出數(shù)： 2
頻率 - 開(kāi)關(guān)： 1MHz
電壓/電流 - 輸出 1： 可調(diào)至 0.75V，6A
電壓/電流 - 輸出 2： 可調(diào)至 0.75V，200mA
帶 LED 驅(qū)動(dòng)器： 無(wú)
帶監(jiān)控器： 無(wú)
帶序列發(fā)生器： 是
電源電壓： 3 V ~ 28 V
工作溫度： -40°C ~ 85°C
安裝類(lèi)型： 表面貼裝
封裝/外殼： 32-VFQFN 裸露焊盤(pán)
供應(yīng)商設(shè)備封裝： 32-MLPQ（5x5）
包裝： 標(biāo)準(zhǔn)包裝
其它名稱(chēng)： SC403MLDKR
SC403
16
One-Shot Timer and Operating Frequency
One-shot timer operation is shown in Figure 2. The FB
Comparator output goes high when V
FB
 is less than the
internal 750mV reference. This feeds into the gate drive
and turns on the high-side MOSFET, and starts the one-
shot timer. The one-shot timer uses an internal compara-
tor and a capacitor. One comparator input is connected to
V
OUT
, the other input is connected to the capacitor. When
the on-time begins, the internal capacitor charges from
zero volts through a current which is proportional to V
IN
.
When the capacitor voltage reaches V
OUT
, the on-time is
completed and the high-side MOSFET turns off.
Gate
Drives
FB Comparator
One-Shot
Timer
On-time = K x R
TON
 x (V
OUT
/V
IN
)
V
OUT
V
IN
FB
750mV
Q1
Q2
L
C
OUT
 
V
IN
ESR
+
V
OUT
V
LX
FB
DH
DL
R
TON
+
-
Figure 2  On-Time Generation
This method automatically produces an on-time that is
proportional to V
OUT
 and inversely proportional to V
IN
.
Under steady-state conditions, the switching frequency
can be determined from the on-time by the following
equation.
IN
ON
OUT
SW
V
T
V
f
The SC403 uses an external resistor to set the on-time
which indirectly sets the frequency. The on-time can be
programmed to provide an operating frequency from
200kHz to 1MHz using a resistor between the TON pin and
ground. The resistor value is selected by the following
equation.
OUT
IN
ON
TON
V
pF
25
V
)
ns
10
t
(
R
The maximum R
TON
 value allowed is shown by the follow-
ing equation.
A
5
.
1
10
V
R
MIN
_
IN
MAX
_
TON
Immediately after the on-time, the DL (drive signal for the
low side FET) output drives high to turn on the low-side
MOSFET. DL has a minimum high time of ~320ns, after
which DL continues to stay high until one of the following
occurs:
VFB falls below the 750mV reference
The zero cross detector senses that the voltage
on the LX node is below ground. Power save is
activated eight switching cycles after a zero
crossing is detected.
TON limitations and V
DD
 Supply Voltage
For V
DD
 below 4.5V, the TON accuracy may be limited by
the input voltage.
The original R
TON
 equation is accurate if V
IN
 satisfies the
relationship over the entire V
IN
 range, as follows.
   V
IN
  < (V
DD
 - 1.6V) x 10
If V
IN
 exceeds (V
DD
 - 1.6V) x 10, for all or part of the V
IN
range, the R
TON
 equation is not accurate. In all cases where
V
IN
 > (V
DD
 - 1.6V) x 10, the R
TON
 equation must be modified,
as follows.
OUT
DD
ON
TON
V
25pF
10
1.6V)
(V
10ns)
(T
R
Note that when V
IN
 > (V
DD
 - 1.6V) x 10 , the actual on-time
is fixed and does not vary with V
IN
. When operating in this
condition, the switching frequency will vary inversely with
V
IN
 rather than approximating a fixed frequency.
 V
OUT
 Voltage Selection
The switcher output voltage is regulated by comparing
V
OUT
 as seen through a resistor divider at the FB pin to the
internal 750mV reference voltage, see Figure 3.
R
1
To FB pin
R
2
V
OUT
Figure 3  Output Voltage Selection
"
"
Applications Information (continued)
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