参数资料
| 型号： | NCP5214MNR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 24/32页 |
| 文件大小： | 0K |
| 描述： | IC CTLR NOTEBOOK DDR PWR 22-DFN |
| 产品变化通告： | Product Discontinuation 01/Oct/2008 |
| 标准包装： | 2,500 |
| 应用： | 控制器，DDR |
| 输入电压： | 4.5 V ~ 24 V |
| 输出数： | 2 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 22-VFDFN 裸露焊盘 |
| 供应商设备封装： | 22-DFN（6x5） |
| 包装： | 带卷 (TR) |
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NCP5214
tss [
0.8 Css
VDDQ is finished. The C ss will continue to charge up until
it reaches about 2.5 V to 3.0 V.
The soft?start time t ss can be programmed by the
soft?start capacitor according to the following equation:
(eq. 40)
Iss
Ceramic capacitors with low tolerance and low
temperature coefficient, such as B, X5R, X7R ceramic
capacitors are recommended to be used as the C SS . Ceramic
capacitors with Y5V temperature characteristic are not
recommended.
Soft?Start of VTT Active Terminator
The VTT source current limit is used as a constant
current source to charge up the VTT output capacitor
during VTT soft?start. Besides, the VTT source current
limit is reduced to about 1.0 A for 128 internal clock cycles
to minimize the inrush current during VTT soft?start.
Therefore, the VTT soft?start time t SSVTT can be estimated
to VTTGND with at least a 10 m F capacitor if external
voltage source is used.
Design Example
A design example of a VDDQ bulk converter with the
following design parameters is shown below:
DDR2 VDDQ bulk converter design parameters:
1. Input voltage range: 7.0 V to 20 V.
2. Nominal V OUT : 1.8 V.
3. Static tolerance: 2% ( " 36 mV).
4. Transient tolerance: " 100 mV.
5. Maximum output current: 10 A
(I VDDQ(max) = 8.0 A, I VTT(max) = 2.0 A).
6. Load transient step: 1.0 A to 8.0 A.
7. Switching frequency: 400 kHz.
8. Bandwidth: 100 kHz.
9. Soft?start time: 400 m s.
a. Calculate input capacitor rms ripple current rating and
voltage rating:
1.836 V * 1.836 V 2 + 4.2 A
by the equation:
tSSVTT [
COUTVTT VTT
ILIMVTSS
(eq. 41)
ICIN(RMS) w 10 A
8.0 V 8.0 V
(eq. 42)
where C OUTVTT is the capacitance of VTT output capacitor
VCIN(rating) w 20
1.25 V + 25 V
(eq. 43)
and I LIMVTSS is the VTT soft?start source current limit.
Boost Supply Diode and Capacitor
An external diode and capacitor are used to generate the
boost voltage for the supply of the high?side gate driver of
the bulk regulator. Schottky diode with low forward
voltage should be used to ensure higher floating gate drive
Therefore, two 10 m F 25 V ceramic capacitors with 1210
size in parallel are used.
b. Calculate inductance, rated current and DCR of
inductor:
First, suppose ripple current is 0.3 times the maximum
output current, such that:
voltage can be applied across the gate and the source of the
high?side MOSFET. A Schottky diode with 30 V reverse
L w
(20 V?1.836 V)
0.3 10 A 20 V
1.836 V
400 kHz
+ 1.39 m H (eq. 44)
L v
+ 2.56 m H
voltage and 0.5 A DC current ratings can be used as the
boost supply diode for most applications. A 0.1 m F to
0.22 m F ceramic capacitor should be sufficient as the boost
capacitor.
VTTI Input Power Supply for VTT and VTTR
Both VTT and VTTR are supplied by VTTI for sourcing
current. VTTI is normally connected to the VDDQ output
for optimum performance. If VTTI is connected to VDDQ,
no bypass capacitor is required to add to VTTI since the
bulk capacitor at VDDQ output is sufficiently large.
Besides, the maximum load current of VDDQ is the sum of
Second, the overshoot requirement at load release is then
considered and supposes two 220 m F capacitors in parallel
are used as an initially guess, such that:
440 m F ((100 mV ) 1.836 V)2?(1.836 V)2)
7 A ) 0.3 2 7 A 2
(eq. 45)
Thus, inductors with standard inductance values of
1.5 m H, 1.8 m H and 2.2 m H can be used. As a trade?off
between smaller overshoot and better efficiency, the
average value of 1.8 m H inductor is selected.
Then, the maximum rated DC current is calculated by:
I VDDQ(max) and I VTT(max) when making electrical design
and components selection of the VDDQ buck regulator.
IL(rated) + 1.2
10 A )
(20 V?1.836 V) 1.836 V
2 1.8 m H 400 kHz 20
VTTI can also be connected to an external voltage source.
However, extra power dissipation will be generated from
+ 13.39 A
(eq. 46)
the internal VTT high?side MOSFET and more
heatsinking is required if the external voltage is higher than
VDDQ. Whereas, the headroom will be limit by the R DS(on)
of the VTT linear regulator high?side MOSFET, and the
Therefore, inductor with maximum rated DC current of
14 A or larger can be used.
Finally, the DCR of inductor is 2.0 m W per m H of
inductance as a rule of thumb, then:
DCR + 2 m W
maximum VTT output current with VTT within regulation
window will also be reduced if the external voltage is lower
1 m H
1.8 m H + 3.6 m W
(eq. 47)
than VDDQ. Besides, the VTTI pin input must be bypassed
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