參數(shù)資料
型號(hào): LM2700MTX-ADJ
廠(chǎng)商: NATIONAL SEMICONDUCTOR CORP
元件分類(lèi): 穩(wěn)壓器
英文描述: 600kHz/1.25MHz, 2.5A, Step-up PWM DC/DC Converter
中文描述: 4.3 A SWITCHING REGULATOR, 1500 kHz SWITCHING FREQ-MAX, PDSO14
封裝: TSSOP-14
文件頁(yè)數(shù): 11/17頁(yè)
文件大小: 478K
代理商: LM2700MTX-ADJ
Operation
(Continued)
The phase margin can also be improved by adding C
C2
as
discussed earlier in the section. The equation for A
is
given below with additional equations required for the calcu-
lation:
mc
)
0.072fs (in V/s)
where R
is the minimum load resistance, V
is the maxi-
mum input voltage, g
is the error amplifier transconduc-
tance found in the Electrical Characteristics table, and R
D-
SON
is the value chosen from the graph ’R
vs. V
IN
’ in
the Typical Performance Characteristics section.
Application Information
Layout Considerations
The LM2700 uses two separate ground connections, PGND
for the driver and NMOS power device and AGND for the
sensitive analog control circuitry. The AGND and PGND pins
should be tied directly together at the package. The feed-
back and compensation networks should be connected di-
rectly to a dedicated analog ground plane and this ground
plane must connect to the AGND pin. If no analog ground
plane is available then the ground connections of the feed-
back and compensation networks must tie directly to the
AGND pin. Connecting these networks to the PGND can
inject noise into the system and effect performance.
The input bypass capacitor C
, as shown in Figure 3 must
be placed close to the IC. This will reduce copper trace
resistance which effects input voltage ripple of the IC. For
additional input voltage filtering, a 100nF bypass capacitor
can be placed in parallel with C
, close to the V
pin, to
shunt any high frequency noise to ground. The output ca-
pacitor, C
, should also be placed close to the IC. Any
copper trace connections for the C
capacitor can in-
crease the series resistance, which directly effects output
voltage ripple. The feedback network, resistors R
and
R
, should be kept close to the FB pin, and away from the
inductor, to minimize copper trace connections that can in-
ject noise into the system. Trace connections made to the
inductor and schottky diode should be minimized to reduce
power dissipation and increase overall efficiency. For more
detail on switching power supply layout considerations see
Application Note AN-1149: Layout Guidelines for Switching
Power Supplies
20012331
FIGURE 3. 600 kHz operation, 8V output
L
www.national.com
11
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