参数资料
| 型号： | CS5157HGDR16G |
| 厂商： | ON Semiconductor |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR BUCK SYNC 5BIT 16-SOIC |
| 产品变化通告： | Product Obsolescence 24/Jan/2011 |
| 标准包装： | 1 |
| 应用： | 控制器，Intel Pentium? II |
| 输入电压： | 4.25 V ~ 20 V |
| 输出数： | 2 |
| 输出电压： | 1.3 V ~ 2.05 V，2.1 V ~ 3.5 V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-SOIC |
| 包装： | 剪切带 (CT) |
| 其它名称： | CS5157HGDR16GOSCT |
CS5157H
capacitive load they present to the controller IC. For the
typical application where V CC1 = V CC2 = 12 V and 5.0 V is
used as the source for the regulator output current, the
where:
COFF +
Perioid
(1 * duty cycle)
4848.5
following gate drive is provided;
VGATE(H) + 12 V * 5.0 V + 7.0 V, VGATE(L) + 12 V
Period +
1
switching frequency
(see Figure 19.)
Schottky Diode for Synchronous MOSFET
A Schottky diode may be placed in parallel with the
synchronous MOSFET to conduct the inductor current upon
turn off of the switching MOSFET to improve efficiency.
The CS5157H reference circuit does not use this device due
to it’s excellent design. Instead, the body diode of the
synchronous MOSFET is utilized to reduce cost and
conducts the inductor current. For a design operating at
200 kHz or so, the low non?overlap time combined with
Schottky forward recovery time may make the benefits of
this device not worth the additional expense (see Figure 8,
channel 2). The power dissipation in the synchronous
MOSFET due to body diode conduction can be estimated by
the following equation:
M 1.00 m s
Power + VBD
ILOAD
conduction time
switching frequency
Trace 3 = V GATE(H) (10 V/div.)
Math 1 = V GATE(H) ? 5.0 V IN
Trace 4 = V GATE(L) (10 V/div.)
Trace 2? Inductor Switching Nodes (5.0 V/div.)
Where V BD = the forward drop of the MOSFET body
diode. For the CS5157H demonstration board as shown in
Figure 8;
Figure 19. CS5157H Gate Drive Waveforms Depicting
Power + 1.6 V
13 A
100 ns
233 kHz + 0.48 W
Rail to Rail Swing
The most important aspect of MOSFET performance is
RDS ON , which effects regulator efficiency and MOSFET
thermal management requirements.
The power dissipated by the MOSFETs may be estimated
as follows;
Switching MOSFET:
Power + ILOAD2 RDSON duty cycle
Synchronous MOSFET:
This is only 1.3% of the 36.4 W being delivered to the
load.
Input and Output Capacitors
These components must be selected and placed carefully
to yield optimal results. Capacitors should be chosen to
provide acceptable ripple on the input supply lines and
regulator output voltage. Key specifications for input
capacitors are their ripple rating, while ESR is important for
output capacitors. For best transient response, a combination
Power + ILOAD2
Duty Cycle =
RDSON
(1 * duty cycle)
of low value/high frequency and bulk capacitors placed
close to the load will be required.
VOUT ) (ILOAD RDSON OF SYNCH FET)
VIN ) (ILOAD RDSON OF SYNCH FET)
* (ILOAD RDSON OF SWITCH FET)
Output Inductor
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the
inductor value will decrease output voltage ripple, but
degrade transient response.
Off Time Capacitor (C OFF )
The C OFF timing capacitor sets the regulator off time:
THERMAL MANAGEMENT
TOFF + COFF
4848.5
Thermal Considerations for Power
Thermal Impedance +
When the V FFB pin is less than 1.0 V, the current charging
the C OFF capacitor is reduced. The extended off time can be
calculated as follows:
TOFF + COFF 24, 242.5
Off time will be determined by either the T OFF time, or the
time out timer, whichever is longer.
The preceding equations for duty cycle can also be used
to calculate the regulator switching frequency and select the
MOSFETs and Diodes
In order to maintain good reliability, the junction
temperature of the semiconductor components should be
kept to a maximum of 150 ° C or lower. The thermal
impedance (junction to ambient) required to meet this
requirement can be calculated as follows:
TJUNCTION(MAX) * TAMBIENT
Power
C OFF timing capacitor:
http://onsemi.com
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