- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385522 > MAX1802 (Maxim Integrated Products, Inc.) Digital Camera Step-Down Power Supply PDF資料下載
參數(shù)資料
| 型號： | MAX1802 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Digital Camera Step-Down Power Supply |
| 中文描述： | 數(shù)碼相機(jī)降壓型電源 |
| 文件頁數(shù)： | 21/28頁 |
| 文件大?。?/td> | 469K |
| 代理商： | MAX1802 |
第1頁第2頁第3頁第4頁第5頁第6頁第7頁第8頁第9頁第10頁第11頁第12頁第13頁第14頁第15頁第16頁第17頁第18頁第19頁第20頁當(dāng)前第21頁第22頁第23頁第24頁第25頁第26頁第27頁第28頁
M
Digital Camera Step-Down
Power Supply
______________________________________________________________________________________
21
the N-channel turn-off current (equal to 17mV/R
DSN
).
Choose R
DSN
value between R
DSP
and 3R
DSP
to keep
the N-channel turn-off current low for optimal efficiency.
If a lower R
DSN
is used, connect a Schottky diode from
PGNDM to LXM for better efficiency (see
Diode
Selection
).
For the main converter, the external gate drive swings
between the voltage at VDDM and GND. For the auxil-
iary controllers, the external gate drive swings between
the voltage at VDDC and GND. Use a MOSFET whose
on-resistance is specified at or below the minimum
gate drive voltage swing, and make sure that the maxi-
mum voltage swing does not exceed the maximum
gate-source voltage specification of the MOSFET. The
gate charge, Q
g
, includes all capacitance associated
with gate charging and helps to predict the transition
time required to drive the MOSFET between on and off
states. The power dissipated in the MOSFET is due to
R
DS(ON)
and transition losses. The R
DS(ON)
loss is:
P
1
≈
D I
L
2R
DS(ON)
where D is the duty cycle, I
L
is the average inductor
current, and R
DS(ON)
is the on-resistance of the MOS-
FET. The transition loss is approximately:
where V
SWING
is V
OUT
for the auxiliary controllers or
V
IN(MAX)
for the main and core converters, I
L
is the
average inductor current, f
OSC
is the converter switch-
ing frequency, and t
T
is the transition time. The transi-
tion time is approximately Q
g
/ I
G
, where Q
g
is the total
gate charge, and I
G
is the gate drive current (0.4A typ).
The total power dissipation in the MOSFET is
P
MOSFET
= P
1
+ P
2
.
Diode Selection
The main and core converters use synchronous recti-
fiers and thus do not require a diode. However, if the
external N-channel synchronous rectifier has low on-
resistance (less than the P-channel on-resistance), the
high N-channel turn-off current results in lower efficien-
cy. In that case, connect a Schottky diode, rated for
maximum output current, from PGNDM to LXM to
improve efficiency.
The auxiliary controllers require external rectifiers. For
low-output-voltage applications, use a Schottky diode
to rectify the output voltage because of the diode
’
s low
forward voltage and fast recovery time. Schottky diodes
exhibit significant leakage current at high reverse volt-
ages and high temperatures. Thus, for high-voltage,
high-temperature applications, use ultra-fast junction
rectifiers.
Compensation Design
Each DC-DC converter has an internal transconduc-
tance error amplifier whose output is used to compen-
sate the control loop. Typically, a series resistor and
capacitor are inserted from COMP_ to GND to form a
pole-zero pair. The external inductor, the output capac-
itor, the compensation resistor and capacitor, and for
the main converter, the external P-channel MOSFET,
govern control-loop stability. The inductor and output
capacitor are usually chosen in consideration of perfor-
mance, size, and cost, but the compensation resistor
and capacitor are chosen to optimize control-loop sta-
bility. The component values in the circuit of Figure 1
yield stable operation over a broad range of input/out-
put voltages and converter switching frequencies.
Follow the procedures below for optimal compensation.
In the following descriptions, Bode plots are used to
graphically describe the loop response of the convert-
ers over frequency. The Bode plot shows loop gain and
phase vs. frequency. A single pole results in a -20dB
per decade slope and a -90
°
phase shift, and a single
zero results in a +20dB per decade slope and a +90
°
phase shift. The stability of the system can be deter-
mined by the phase margin (how far from 0
°
the loop
phase is when the response drops to 0dB) and gain
margin (how far below 0dB the gain is when the phase
reaches 0
°
). The system is stable for phase margins
>30
°
, and a phase margin of 45
°
is preferred. The gain
margin should be at least 10dB.
Main Converter
The main converter uses current mode to regulate the
output voltage by forcing the required current through
the inductor. Since the P-channel MOSFET operates
with constant drain-source on-resistance (R
DSP
), the
voltage across the MOSFET is proportional to the
inductor current. The converter current-sense amplifier
measures the
“
on
”
MOSFET drain-source voltage to
determine the inductor current for regulation. The gain
through the current-sense amplifier (measured across
the MOSFET) is A
VCSM
= 9.3V/V. The voltage-divider
attenuates the loop gain by A
VDV
= V
REF
/ V
OUT
, and
the gain DC voltage of the error amplifier is A
VEA
=
2000V/V. The controller forces the peak inductor cur-
rent (I
L
) such that:
I
L
R
DSP
A
VCSM
= V
OUT
A
VDV
A
VEA
or
I
L
= V
OUT
A
VDV
A
VEA
/ (A
VCSM
R
DSP
)
P
V
3
SWING L OSC T
2
≈
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1802EHJ | Digital Camera Step-Down Power Supply |
| MAX1804 | External Four-Input Feedback Integrator for Power Supplies |
| MAX1804EUB | External Four-Input Feedback Integrator for Power Supplies |
| MAX1809 | 3A, 1MHz, DDR Memory Termination Supply |
| MAX1809EEE | 3A, 1MHz, DDR Memory Termination Supply |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1802EHJ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1802EHJ+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1802EHJ+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1802EHJ-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1804EUB | 功能描述:電流和電力監(jiān)控器、調(diào)節(jié)器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:Current Regulators 電源電壓-最大:48 V 電源電壓-最小:5.5 V 工作溫度范圍:- 40 C to + 150 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:HPSO-8 封裝:Reel |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。