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參數(shù)資料
| 型號(hào)： | LMS5213M7X-2.8 |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS |
| 中文描述： | 三端固定電壓調(diào)節(jié)器 |
| 文件頁(yè)數(shù)： | 7/8頁(yè) |
| 文件大?。?/td> | 221K |
| 代理商： | LMS5213M7X-2.8 |
Application Information
The LMS5213 is a low dropout, linear regulator designed
primarily for battery-powered applications. The LMS5213
can be used with low cost ceramic capacitors, typical value
of 0.47μF.
As illustrated in the simplified schematics, the LMS5213
consists of a 1.25V reference, error amplifier, P-channel
pass transistor and internal feedback voltage diode. The
1.25V reference is connected to the input of the error amp.
The error amp compares this reference with the feedback
voltage. If the feedback voltage is lower than the reference,
the pass transistor gate is pulled lower allowing more current
to pass and increasing the output voltage. If the feedback
voltage is too high, the pass transistor gate is pulled up
allowing less current to pass to the output. The output volt-
age is fedback through the resistor divider. Additional blocks
include short circuit current protection and thermal protec-
tion.
The LMS5213 features an 80mA P-channel MOSFET tran-
sistor. This provides several advantages over similar designs
using PNP pass transistors including longer battery life.
The P-channel MOSFET requires no base drive, which re-
duces quiescent current considerably. PNP based regulators
waste considerable amounts of current in dropout when the
pass transistor saturates. They also have high base drive
currents under large loads. The LMS5213 does not suffer
from these problems and consumes only the specified qui-
escent current under light and heavy loads.
External Capacitors
Like any low-dropout regulators, the LMS5213 requires ex-
ternal capacitors for regulator stability. The LMS5213 is spe-
cially designed for portable applications requiring minimum
board space and the smallest components.
A 0.1μF capacitor should be placed from V
to GND if there
is more than 10 inches of wire between the input and AC
filter or when a battery is used as the input. This capacitor
must be located a distance of not more than 1cm from the
input pin and returned to a clean analog ground.
The LMS5213 is designed to work with small ceramic output
capacitors. Ceramic capacitors ranging between 0.47μF to
4.7μF are the smallest and least expensive.
No-Load Stability
The LMS5213 will remain stable and in regulation with
no-load (other than the internal voltage divider). This is
especially important in CMOS RAM keep-alive applications.
Enable Input
The LMS5213 is shut off by pulling the V
pin below 0.6V;
all internal circuitry is powered off and the quiescent current
is typically 1μA. Pulling the V
high above 2V re-enables
the device and allows operation. If the shut down feature is
not used, the V
pin should be tied to V
IN
to keep the
regulator output on all the time.
Thermal Behavior
The LMS5213 regulator has internal thermal shutdown to
protect the device from over heating. Under all operating
conditions, the maximum junction temperature of the
LMS5213 must be below 125C. Maximum power dissipation
can be calculated based on the output current and the
voltage drop across the part. The maximum power dissipa-
tion is
P
D(MAX)
= (T
J(MAX)
- T
A
)/
θ
JA
θ
is the junction-to-ambient thermal resistance, 478C/W
for the LMS5213 in the SC70 package. T
is the maximum
ambient temperature T
is the maximum junction tem-
perature of the die, 125C
When operating the LMS5213 at room temperature, the
maximum power dissipation is 209 mW.
The actual power dissipated by the regulator is
P
D
= (V
IN
-V
OUT
) I
L
+ V
IN
I
GND
The figure below shows the voltage and currents, which are
present in the circuit.
Substituting P
, determined above, for P
and solving
for the operating condition that are critical to the application
will give the maximum operating conditions for the regulator
circuit. To prevent the device from entering thermal shut-
down, maximum power dissipation cannot be exceeded.
Fixed Voltage Regulator
The LMS5213 offers a smaller system solution that is ideal
for general-purpose voltage regulation in any handheld
device.
DS200109-22
FIGURE 1. Power Dissipation Diagram
DS200109-20
FIGURE 2. Single-Cell Regulator
L
www.national.com
7
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