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參數(shù)資料
| 型號(hào)： | FAN5233MTC |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Analog IC |
| 中文描述： | SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封裝： | TSSOP-24 |
| 文件頁數(shù)： | 9/15頁 |
| 文件大小： | 388K |
| 代理商： | FAN5233MTC |
PRODUCT SPECIFICATION
FAN5233
REV. 1.0.6 1/22/02
9
Functional Description
The FAN5233 is a high efficiency and high precision DC/DC
controller for notebook and other portable applications. It
provides all of the voltages necessary for system electronics:
5V, 3.3V, 12V, and 5V-ALWAYS. Utilization of both input
and output voltage feedback in a current-mode control
allows for fast loop response over a wide range of input and
output variations. Current sense based on MOSFET R
DS,on
gives maximum efficiency, while also permitting the use of a
sense resistor for high accuracy.
3.3V and 5V Architecture
The 3.3V and 5V switching regulator outputs of the
FAN5233 are generated from the unregulated input voltage
using synchronous buck converters. Both high side and low-
side MOSFETs are N-channel.
The 3.3V and 5V switchers have pins for current sensing and
for setting of output over-current threshold using MOSFET
R
DS,on
. Each converter has a pin for voltage-sense feedback,
a pin that shuts down the converter, and a pin for generating
the boost voltage to drive the high-side MOSFET.
If the 5V switcher is not used, connect SDN5 (pin 17) to
SGND (pin 14). If the 3.3V switcher is not used, connect
SDN3.3 (pin 11) to SGND (pin 14).
The following discussion of the FAN5233 design will be
done with reference to Figures 1 through 4, showing the
internal block diagram of the IC.
3.3V and 5V PWM Current Sensing
Peak current sensing is done on the low side driver because
of the very low duty-cycle on the high side MOSFET. The
current is sampled 50ns after turn on and the value is held for
current feedback and over-current limit.
3.3V and 5V PWM Loop Compensation
The 3.3V and 5V control loops of the FAN5233 function as
voltage mode with current feedback for stability. They each
have an independent voltage feedback pin, as shown in Fig-
ure 1. They use voltage feed-forward to guarantee loop rejec-
tion of input voltage variation: that is to say that the PWM
(pulse width modulation) ramp amplitude is varied as a func-
tion of the input voltage. Compensation of the control loops
is done entirely internally using current-mode feedback com-
pensation. This scheme allows the bandwidth and phase mar-
gin to be almost independent of output capacitance and ESR.
3.3V and 5V PWM Current Limit
The 3.3V and 5V converters each sense the voltage across
their own low-side MOSFET to determine whether to enter
current limit. If an output current in excess of the current
limit threshold is measured then the converter enters a pulse
skipping mode where Iout is equal to the over-current (OC)
set limit. After 8 clock cycles then the regulator is latched off
(HSD and LSD off). This is the likely scenario in the case of
a "soft" short. If the short is "hard" it will instantly
trigger the under-voltage protection which again will latch
the regulator off (HSD and LSD off) after a 2μs delay.
Selection of a current-limit set resistor must include the
tolerance of the current-limit trip point, the MOSFET on
resistance and temperature coefficient, and the ripple current,
in addition to the maximum output current.
Example: Maximum DC output current on the 5V is 5A,
input voltage is 16V, the MOSFET R
DS,on
is 17m
, and the
inductor is 5μH at a current of 5A. Because of the low
R
DS,on
, the low-side MOSFET will have a maximum tem-
perature (ambient + self-heating) of only 75°C, at which its
R
DS,on
increases to 20m
.
Peak current is DC output current plus peak ripple current:
where T is the maximum period, V
O
is output voltage, VIN is
input voltage and L is the inductance. This current generates
a voltage on the low-side MOSFET of 7A 20m
= 140mV.
The current limit threshold is typically 150mV (worst-case
135mV) with R2 = 1K
, and so this value is suitable. R2
could be increased a further 10% if additional noise margin
is deemed necessary.
Precision Current Limit
Precision current limiting can be achieved by placing a
discrete sense resistor between the source of the low-side
MOSFET and ground.
In this case, current limit accuracy is set by the tolerance of
the IC, +10%.
Figure 4. Using a Precision Current Sense Resistor
Shutdown (SDWN)
The SDWN pin turns off all 4 converters (+5V, +3.3V, and
+12V, 5V-ALWAYS) and puts the FAN5233 into a low-
power mode (Shutdown mode).
This mode of operation implies the use of a push button
switch between SDWN and Vin. Pushing the button allows
I
pk
I
DC
VIN
------------2L
V
–
(
T
V
O
VIN
+
5A
-16V
5V
–
2.5
μ
H
(
)
4μsec
16V
+
6.4A
=
=
=
HSD
SW
LSD
ISEN
GND
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| FAN5233MTCX | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 PWM Buck Controller adjustable RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5234 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Dual Mobile-Friendly PWM / PFM Controller |
| FAN5234_10 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Dual Mobile-Friendly PWM / PFM Controller |
| FAN5234MTC | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5234MTC_Q | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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