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参数资料
| 型号： | LM4510SDX/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | LM4510 Synchronous Step-Up DC/DC Converter with True Shutdown Isolation; Package: LLP; No of Pins: 10; Qty per Container: 4500/Reel |
| 中文描述： | 1.8 A SWITCHING REGULATOR, 1200 kHz SWITCHING FREQ-MAX, DSO10 |
| 封装： | 3 X 3 MM, 0.80 MM HEIGHT, LEAD FREE, LLP-10 |
| 文件页数： | 3/16页 |
| 文件大小： | 2467K |
| 代理商： | LM4510SDX/NOPB |
Synchronous boost converter is shown in Figure 3. At the start
of each cycle, the oscillator sets the driver logic and turns on
the NMOS power device and turns off the PMOS power de-
vice.
Cycle 1 Description
Refer to Figure 4. NMOS switch turn-on
→ Inductor current
increases and flows to GND.
PMOS switch turn-off
→ Isolate VOUT from SW → Output ca-
pacitor supplies load current.
30031015
FIGURE 4. Equivalent Circuit During Cycle 1
During operation, EAMP output voltage (V
COMP) increases for
larger loads and decreases for smaller loads. When the sum
of the ramp compensation and the sensed NMOS current
reaches a level determined by the EAMP output voltage, the
PWM COMP resets the logic, turning off the NMOS power
device and turning on the PMOS power device.
Cycle 2 Description
Refer to Figure 5. NMOS Switch turn-off
→ PMOS Switch turn-
on
→ Inductor current decreases and flows through PMOS
→ Inductor current recharges output capacitor and supplies
load current.
30031016
FIGURE 5. Equivalent Circuit During Cycle 2
After the switching period the oscillator then sets the driver
logic again repeating the process.
ON/OFF CONTROL
The LM4510 shuts down when the EN pin is low. In this mode
the feedback resistors and the load are disconnected from the
input in order to avoid leakage current flow and to allow the
output voltage to drop to 0V.
The LM4510 turns on when EN is high. There is an internal
pull-down resistor on the EN pin so the device is in a normally
off state.
SHORT CIRCUIT PROTECTION
When V
OUT goes down to VIN–0.7V (typ.), the device stops
switching due to the short-circuit protection circuitry and the
short-circuit output current is limited to I
INIT_CHARGE.
FEEDBACK FAULT PROTECTION
The LM4510 features unique Feedback Fault Protection to
maximize safety when the feedback resistor is not properly
connected to a circuit or the feedback node is shorted directly
to ground.
Feedback fault triggers V
OUT monitoring. During monitoring,
if V
OUT reaches a protection level, the device shuts down.
When the feedback network is reconnected and V
OUT is lower
than the OFF threshold level of Feedback Fault Protection,
V
OUT monitoring stops. VOUT is then regulated by the control
loop.
INPUT UNDER-VOLTAGE LOCK-OUT
The LM4510 has dedicated circuitry to protect the IC and the
external components when the battery voltage is lower than
the preset threshold. This under-voltage lock-out with hys-
teresis prevents malfunctions during startup or abnormal
power off.
THERMAL SHUTDOWN
If the die temperature exceeds 150°C (typ.), the thermal pro-
tection circuitry shuts down the device. The switches remain
off until the die temperature is reduced to approximately
140°C (typ.).
Application Information
ADJUSTING OUTPUT VOLTAGE
The output voltage is set using the feedback pin and a resistor
voltage divider (R
F1, RF2) connected to the output as shown
in the Typical Application Circuit.
The ratio of the feedback resistors sets the output voltage.
R
F2 Selection
First of all choose a value for R
F2 generally between 10 k
and 25 k
.
R
F1 Selection
Calculate R
F1 using the following equation:
Table 1 gives suggested component values for several typical
output voltages.
TABLE 1. Suggested Component Values for Different Output Voltages
Output Voltage (V)
R
F2 (k)
R
F1 (k)
R
C (k)
C
C1 (nF)
16
20.5
240
46.4
2.2
12
20.5
174
46.4
2.2
5
20.5
60.4
46.4
2.2
3.3
20.5
33
46.4
2.2
11
www.national.com
LM4510
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