参数资料
| 型号： | NCP3122MNTXG |
| 厂商： | ON Semiconductor |
| 文件页数： | 17/42页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 2A DL 32QFN |
| 产品变化通告： | NCP312x Soft Start Charge 6/Nov/2008 |
| 标准包装： | 4,000 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 可调至 0.8V |
| 输入电压： | 4.5 V ~ 15 V |
| 频率 - 开关： | 200kHz ~ 2.2MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-VFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 32-QFN（5x5） |
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NCP3122
The peak reverse voltage is equal to the maximum input
voltage. The peak conducting current is clamped by the
current limit of the NCP3122. Use of Schottky barrier diodes
reduces diode reverse recovery input current spikes. For
because the diode conduction interval is much longer than
that of the transistor. Converter efficiency will be improved
if the voltage drop across the diode is lower. The average
current can be calculated from:
switching regulators operating at low duty cycles, it is
beneficial to use rectifying diodes with somewhat higher
RMS current ratings (thus lower forward voltages). This is
Table 3. Schottky Diode Example
I D(AVG) +
I LOAD V IN * V OUT
V IN
Part Number
Description
V RRM min
V F max
I O(rec) max
Package
Web
[V]
[V]
[A]
MBRS2040LT3G
MBRS230LT3G
MBRS240LT3G
SS24T3G
MBRA340T3G
MBRS330T3G
2 A, 40 V Low V f Schottky Rectifier
2 A, 30 V Low V f Schottky Rectifier
2 A, 40 V Low V f Schottky Rectifier
2 A, 40 V Schottky Rectifier
3 A, 40 V Schottky Rectifier
3 A, 30 V Schottky Rectifier
40
30
40
40
40
30
0.43
0.49
0.43
0.5
0.45
0.5
2
2
2
2
3
3
SMB
SMB
SMB
SMB
SMA
SMC
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www.onsemi.com
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www.onsemi.com
The worst case of the diode average current occurs during
maximum load current and maximum input voltage. The
rectifying diodes should be placed close to the SW pin to
avoid the possibility of ringing due to trace inductance.
ESR CIN is the effective series resistance of the input
capacitance.
The input capacitor voltage ripple depends on the C IN
capacitor value. Therefore, the input capacitor can be
@ OUT @ 1 * OUT
Input Capacitor
The input current to the step down converter is
discontinuous. The input capacitor has to maintain the DC
estimated by:
C IN +
I LOAD
f SW @ D V IN
V V
V IN V IN
V OUT ) V D
V IN ) V D * V DSAT
@ 1 * OUT @ ESR )
D V OUT +
I RMS +
input voltage and to sustain the ripple current produced by
internal MOSFET switching. For stable operation of the
switch mode converter, a low ESR capacitor is needed to
prevent large voltage transients from appearing at the input.
Therefore, ceramic capacitors are preferred, but the circuit
works in a stable manner also with electrolytic capacitors. It
must be located near the regulator and use short leads. Also,
paralleling ceramic capacitors will increase the regulator
stability.
The RMS value of the input capacitor current ripple is:
I RMS + I LOAD D(1 * D)
The duty cycle is:
D +
where:
V D is the voltage drop across the rectifying diode and
V DSAT is the switch saturation voltage on the power
MOSFET.
The equation reaches its maximum value with duty cycle
= 0.5, where:
I LOAD
2
Losses in the input capacitor can be calculated using the
following equation:
Output Capacitor
The output capacitor filters output inductor ripple current
and provides low impedance for load current changes. The
principle consideration for the output capacitor is the ripple
current induced by the switches through the inductor. It
supplies the current to the load in DCM or during load
transient and filters the output voltage ripple. For low output
ripple voltage and good stability, low ESR output capacitors
are recommended. The inductor ripple current acting against
the ESR of the output capacitor is the major contributor to
the output ripple voltage.
An output capacitor has two main functions: it filters the
output and provides regulator loop stability.
The ESR of the output capacitor and the peak ? to ? peak
value of the inductor ripple current are the main factors
contributing to the output ripple voltage value.
The output voltage ripple is given by the following
equation:
V OUT V 1
f SW @ L V IN 8 @ f SW @ C OUT
where:
ESR is the equivalent series resistance of the output
capacitor.
The output capacitor value can by expressed by:
where:
P CIN + I RMS 2 @ ESR CIN
C OUT +
D I L
8 @ f SW @ D V OUT * D I L @ ESR
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17
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