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参数资料
| 型号： | LM2630MTC-ADJX |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封装： | PLASTIC, TSSOP-20 |
| 文件页数： | 14/14页 |
| 文件大小： | 373K |
| 代理商： | LM2630MTC-ADJX |
or until the inductor current reaches zero; when this occurs,
the zero cross detector will disable the low-side driver to turn
off the low-side switch. The zero cross detector is disabled in
FPWM mode.
For any peak current mode step-down converter, a compen-
sation ramp is needed to avoid subharmonic oscillations
when the duty cycle is higher than 50%. For the LM2630, this
compensation ramp is internally set to equal the maximum
down slope of the current amplifier output:
Where n = 5 is the gain of the current sense amplifier. The
maximum output voltage equals 6V. Also, a 10 H inductor
and a 0.025
Ω sense resistor are assumed to determine the
internal compensation ramp. Different values of inductor and
sense resistor can be used as long as the resulted M
DOWN (=
n x R
SEN x VOUT/L) is less than MC.
PULSE-SKIPPING MODE AT LIGHT LOAD
Pulse-skipping mode can be enabled by pulling PFWM pin
low. This mode decreases switching frequency at light loads
to reduce the switching frequency related losses. If PFWM is
set at low, the controller goes into the pulse-skipping mode
when the sensed inductor current goes below the 25 mV
threshold set by the pulse-skipping comparator. In the pulse-
skipping mode, the high-side switch only turns on at the
beginning of a clock cycle when the voltage at the feedback
pin falls below the reference voltage. Once the switch is on,
it stays on until the sensed current rises to the 25 mV thresh-
old
FAST TRANSIENT RESPONSE
When the output voltage fails to exceed 97% of the nominal
level, the low voltage regulation(LREG) comparator will set
the PWM logic to turn the high-side switch on at maximum
duty cycle. This improves transient response since it bypass-
es the error amplifier and PWM comparator. During start-up,
the LREG is disabled.
BOOST HIGH-SIDE GATE DRIVE
A flying capacitor is used to bootstrap the power supply for
the high-side driver as illustrated in Figure 1. The boost ca-
pacitor is charged from an internal voltage rail (about 5.5V)
through an internal diode when the synchronous rectifier (low-
side MOSFET) is on, and then boosts up the high-side gate
voltage to turn high-side MOSFET on at the beginning of next
cycle. The internal diode connecting between the VIN pin and
the CBOOT pin reduces the count of external components.
For low input voltage application (Vin < 5V), some external
charge pump circuitry can be used to boost the gate voltage
in order to reduce conduction loss. Details will be discussed
in the Application Circuits Section.
SUPPLY VOLTAGE FOR THE LM2630
When 5V is available, it is recommended to connect LM2630
V
IN (pin13) to 5V. This can improve efficiency (see the second
figure in Typical Performance Characteristics), and also re-
duce power dissipation inside the IC. Since the 5V supply is
only used to power the LM2630 (including the gate charge for
the external MOSFETs), it only requires a small amount of
current.
REFERENCE
The 1.238V reference is of ±2.4% accuracy over temperature.
A 220 pF capacitor is recommended between the V
REF pin
and ground. The load at the V
REF pin should not exceed
100A.
FREQUENCY CONTROL PIN (FADJ) AND SYNC PIN
With the FADJ pin open, the switching frequency is 200 kHz.
The frequency can be increased by connecting a resistor be-
tween FADJ and ground. The device can also be synchro-
nized with an external CMOS or TTL logic clock in the range
from 200 kHz to 400 kHz. It is recommended to connect the
SYNC pin to ground if not used.
PROTECTIONS
The current limit comparator provides the cycle-by-cycle cur-
rent limit function by turning off the high-side MOSFET when-
ever the sensed current reaches 110 mV. A second level of
current limit is accomplished by the 80% low voltage detector:
if the load pulls the output voltage down below 80% of the
nominal value, the device will turn off the high-side MOSFET
and turn on the low-side MOSFET in a latched condition. This
protection feature is disabled during startup. The latched con-
dition can be reset by shutting the device down and then
powering it up. Built-in input undervoltage lockout circuit will
keep most of the internal function blocks off until the input
voltage rises to about 3.5V.
SOFT START
A capacitor at the SS pin provides the soft start feature. When
the regulator is first powered up, or when the SD pin goes
high, a 10A current source charges up the SS capacitor from
the 0.6V clamping voltage. The switch duty cycle starts with
narrow pulses and gradually get wider as the SS pin voltage
ramps up to about 1.3V, above which the duty cycle will be
controlled by the maximum current limit until the output volt-
age rises to the nominal value and the regulator starts to
operate in the normal current mode PWM control. The
LM2630 use a digital counter, referenced to the oscillator fre-
quency, to set the soft start timeout. The timeout is dependent
on the switching frequency (timeout = 4096/F
S). If the output
voltage doesn't move within the ±3% window of the nominal
value during this period, the device will latch itself off.
POWER GOOD
The LM2630 provides a power good signal by monitoring the
voltage at the FB pin and compared the feedback voltage with
the V
REF voltage. Once the output voltage exceeds the ±9%
window of the nominal value, the PGOOD pin goes low, and
stays low until the output voltage returns to the ±3% window
of the nominal value.
Design Procedure
Guidelines for selecting external components are discussed
in this section.
INDUCTOR SELECTION
The most critical parameters for the inductor are the induc-
tance, peak current and the dc resistance. The inductance is
related to the switching frequency and the ripple current:
Higher switching frequency allows smaller inductor, but re-
duces the efficiency. A higher value of ripple current reduces
inductance, but increase the conductance loss, core loss,
current stress for the inductor and switch devices, and re-
quires a bigger output capacitor for the same output voltage
9
www.national.com
100120 Version 9 Revision 2
Print Date/Time: 2011/08/25 17:11:52
LM2630
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2630MTCX-ADJ | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LM2630MTCX-ADJ/NOPB | 制造商:Texas Instruments 功能描述:DC DC Cntrlr Single-OUT Step Down 4.5V to 30V Input 20-Pin TSSOP T/R |
| LM2631 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Synchronous Step-Down Power Supply Controller |
| LM2631MTC-ADJ | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Current-Mode SMPS Controller |
| LM2633 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Advanced Two-Phase Synchronous Triple Regulator Controller for Notebook CPUs |
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