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参数资料
| 型号： | LM1572MTCX-ADJ/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.2 A SWITCHING REGULATOR, 570 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | TSSOP-16 |
| 文件页数： | 11/17页 |
| 文件大小： | 583K |
| 代理商： | LM1572MTCX-ADJ/NOPB |
Pin Description (Continued)
V
IN (Pins 3,4) - This is the input supply to the power stage
(connected to the Drain of the switching MOSFET). To aid
thermal dissipation from the die, two pins are used for this
function. Both these pins must be connected together, very
close to the IC, onto a large PCB copper plane.
SW (Pins 5,6) - This is the Source of the internal switching
MOSFET and forms the ’switching node’ of the buck con-
verter. These two pins should be connected together on the
PCB close to the IC. The length of the trace from this node to
the cathode of the catch diode, and from the anode of the
diode to the IC ground must be kept very small. The maxi-
mum inductance connected to the switching node (for any
application) is recommended to be 15H. See the Inductor
Selection procedure for more details.
GND (Pins 7,9,13,14) - This is the Ground for the IC and for
the input and output rails of the buck converter. To aid
thermal dissipation from the die, four pins are used for this
function. Connect as many as possible of these ground pins
together, close to the IC onto a large PCB copper plane. A
two-sided PCB with one side serving as a ’ground plane’ is
strongly recommended. The ground pins must then connect
to the ground plane very close to the IC through several vias.
The vias also serve to transfer heat to the other side of the
board for better thermal management.
SD (Pin 8) - Shutdown/Standby/UVLO Pin. This pin actually
has two thresholds. If it is taken below 2.38V (typical), the
switch turns off and the output of the converter falls to
zero.This is the ’standby mode’. The internal circuitry of the
IC remains active, continuing to draw about 2.3mA from the
input. If the voltage on this pin is lowered below 1V (typical),
the IC enters ’shutdown mode’ drawing only 26 A from the
input. Above 2.38V, the switching action resumes, and so
this pin can also be used to set an undervoltage lockout
threshold (UVLO) for the input rail. If this pin is not intended
to be used actively, it can be left floating to allow continuous
switching. The voltage on this pin should not exceed 7V to
avoid damage.
NC (Pins 10,11) - No Internal Connection.
SS (Pin 12) - Softstart pin. A small capacitor connected from
this pin to ground programs the amount of softstart. This
capacitor charges up by means of an internal 4.5A current
source, during power-up, and also whenever the output of
the converter is enabled. The allowed duty cycle increases
slowly as the capacitor charges, reaching the maximum
allowed when the voltage on this pin approaches 2V. The
capacitor continues to charge, finally reaching 6V, at which
level it is internally clamped. This pin is internally forced to
ground (to discharge the softstart capacitor and to reset the
softstart function) whenever the shutdown pin is taken below
2.38V. If the softstart feature is not required, the softstart pin
can be left floating.
FB (Pin 15) - This is the feedback pin for the IC and is used
to set the output of the converter to regulate to the desired
value. For the fixed voltage part this pin is normally con-
nected directly to the output. For the adjustable part, a
resistive divider is used between the output and ground, so
that the voltage on this pin is 2.42V when the output is at the
required level. For fixed voltage parts, the internal divider
draws about 0.5mA, a consideration possibly affecting the
choice of the bootstrap capacitor (see description of Pin 1
above).
COMP (Pin 16) - This is the output of the error transconduc-
tance amplifier and is used for frequency compensation of
the feedback loop. A small capacitor from this pin to ground
(about 3.3nF to 6.8nF) provides the simplest loop compen-
sation, but a series resistor-capacitor combination (R be-
tween 1k to 1.5k) may also be used to improve the phase
margin/crossover frequency of the loop. The voltage on this
pin is at about 1V at very light loads. Under very heavy loads
or under output short-circuit, the voltage on this pin clamps
to 2V, and the converter enters protective foldback. The IC
automatically recovers from this mode when the load is
reduced.
LM1572
www.national.com
3
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