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參數(shù)資料
| 型號： | AP-211 |
| 廠商： | California Micro Devices Corporation |
| 英文描述： | Instantly Available PCI Card Power Management |
| 中文描述： | 即時可用的PCI卡電源管理 |
| 文件頁數(shù)： | 5/7頁 |
| 文件大?。?/td> | 631K |
| 代理商： | AP-211 |
9/99
5
215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
CALIFORNIA MICRO DEVICES
AP-211
Typical Applications
Cold-Start Behavior
A cold-start situation occurs when a PC is powered ON.
Typically, power supplies take milliseconds to reach their
nominal voltage. Both the 5V and 3.3V voltage sources are
ramping up together. As soon as the 5V source reaches the
regulator_enable
4.25V threshold, the regulator turns ON.
At that time the output capacitor begins to rapidly charge
and pulls a large transient current which can easily exceed
values of 1 ampere. It is, therefore, very important to take
into consideration the parasitic series resistances and parasitic
inductance between the supply voltage V
cc
and the device.
The voltage seen by the device is given by:
V
CCIN
= V
CC
- (R
S
x I) - (R
t
x I) - (L
t
x d
I
/ d
t
)
where, V
cc
is the power supply voltage,
R
s
is the power supply output impedance,
R
is the interconnect series resistance (between supply
and the CMPWR150), and
L
is the trace (line) inductance (between supply and
the CMPWR150).
Clearly a large, rapidly changing current will create a significant
change in V
, and if the input level drops below the
regulator_disable
4.1V threshold, the regulator will turn OFF.
The input level will then start to rise back toward 5V, turning
the regulator back ON. This results in an unstable state (motor
boating) where the regulator turns on and off until the output
capacitor is finally charged to the 3.3V level.
Input Capacitor
To minimize the unstable state effect, an input capacitor is
required in close proximity to the V
input pin. When a
transition occurs from V
to V
, the capacitor is used as a
charge reservoir to provide current to the load as well. This is
especially critical when the output capacitor is not yet charged
at power-up, or when the output level is much lower than
Figure 7.
Power Regulator Circuit
3.3V. In this case, the device will go into current limiting
until VOUT goes back to its nominal level. A large Tantalum
capacitor of 10
μ
F or greater is recommended.
Output Capacitor
During power transitions, a previously charged capacitor will
provide the current to the load until the regulator or the
auxiliary supply take over. A larger Tantalum capacitor at the
output will improve this transition, and a value of 10
μ
F or
greater is recommended.
High Frequency Capacitors
Additionally ceramic chip capacitors can be placed next to
both inputs and output pins to reduce the high frequency
noise. A value of 0.1
μ
F is recommended.
Supply Transient Characteristics
A resistive load of 6.8
is used, setting a load current of
485mA at 3.3V.
V
CC
power-up 0V to 5V (cold-start) with V
AUX
open circuit
Ch1: V
CC
, offset 4.1V
Ch2: V
Ch3: DRIVE
Figure 8 shows V
approaching the enable threshold during
a 0V to 5V initial power-up transition (or cold-start). V
is
left open. When V
reaches the 4.3V enable threshold,
the regulator turns ON. The large in-rush current caused
by the uncharged output capacitor generates a voltage drop
of about 230mV on the V
pin. The 250mV hysteresis
ensures the regulator remains enabled during the transient.
Figure 8
1
2
5
CM PWR-150
3.3V Vaux
3.3V output
3
nc
Vcc
Drive
Gnd
Vout
4
To
PCI
bus
5V main
P-channel MOSFET
10
μ
F
+
0.1
μ
F
10
μ
F
+
0.1
μ
F
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