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參數(shù)資料
| 型號： | LM2599T-ADJ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator, with Features |
| 中文描述： | 7.5 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, PZFM7 |
| 封裝： | TO-220, 7 PIN |
| 文件頁數(shù)： | 18/31頁 |
| 文件大小： | 812K |
| 代理商： | LM2599T-ADJ |
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Block Diagram
Application Information
PIN FUNCTIONS
+V
(Pin 1)— This is the positive input supply for the IC
switching regulator. A suitable input bypass capacitor must
be present at this pin to minimize voltage transients and to
supply the switching currents needed by the regulator.
Ground
(Pin 4)— Circuit ground.
Output
(Pin 2)— Internal switch. The voltage at this pin
switches between approximately (+V
IN
V
SAT
) and approxi-
mately 0.5V, with a duty cycle of V
OUT
/V
IN
. To minimize
coupling to sensitive circuitry, the PC board copper area con-
nected to this pin should be kept to a minimum.
Feedback
(Pin 6)— Senses the regulated output voltage to
complete the feedback loop.
Shutdown /Soft-start
(Pin 7)— This dual function pin pro-
vides the following features: (a) Allows the switching regula-
tor circuit to be shut down using logic level signals thus drop-
ping the total input supply current to approximately 80 μA.
(b) Adding a capacitor to this pin provides a soft-start feature
which minimizes startup current and provides a controlled
ramp up of the output voltage.
Error Flag
(Pin 3)— Open collector output that provides a
low signal (flag transistor ON) when the regulated output
voltage drops more than 5% from the nominal output volt-
age. On start up, Error Flag is low until V
reaches 95% of
the nominal output voltage and a delay time determined by
the Delay pin capacitor. This signal can be used as a reset to
a microprocessor on power-up.
Delay
(Pin 5)— At power-up, this pin can be used to provide
a time delay between the time the regulated output voltage
reaches 95% of the nominal output voltage, and the time the
error flag output goes high.
Special Note
If any of the above three features (Shutdown
/Soft-start, Error Flag, or Delay) are not used, the respective
pins should be left open.
EXTERNAL COMPONENTS
SOFT-START CAPACITOR
C
— A capacitor on this pin provides the regulator with a
Soft-start feature (slow start-up). When the DC input voltage
is first applied to the regulator, or when the Shutdown
/Soft-start pin is allowed to go high, a constant current (ap-
proximately 5 μA begins charging this capacitor). As the ca-
pacitor voltage rises, the regulator goes through four operat-
ing regions (See the bottom curve in Figure 13).
1. Regulator in Shutdown.
When the SD /SS pin voltage is
between 0V and 1.3V, the regulator is in shutdown, the out-
put voltage is zero, and the IC quiescent current is approxi-
mately 85 μA.
2. Regulator ON, but the output voltage is zero.
With the
SD /SS pin voltage between approximately 1.3V and 1.8V,
the internal regulator circuitry is operating, the quiescent cur-
rent rises to approximately 5 mA, but the output voltage is
still zero. Also, as the 1.3V threshold is exceeded, the
Soft-start capacitor charging current decreases from 5 μA
down to approximately 1.6 μA. This decreases the slope of
capacitor voltage ramp.
3. Soft-start Region.
When the SD /SS pin voltage is be-
tween 1.8V and 2.8V (
@
25C), the regulator is in a Soft-start
condition. The switch (Pin 2) duty cycle initially starts out
very low, with narrow pulses and gradually get wider as the
capacitor SD /SS pin ramps up towards 2.8V. As the duty
cycle increases, the output voltage also increases at a con-
trolled ramp up. See the center curve in Figure 13 The input
supply current requirement also starts out at a low level for
DS012582-30
FIGURE 12.
L
www.national.com
18
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