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參數(shù)資料
| 型號： | MAX1856 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | 數(shù)字信號處理 |
| 英文描述： | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA |
| 中文描述： | 寬輸入范圍、可同步的、PWM SLIC電源 |
| 文件頁數(shù)： | 11/18頁 |
| 文件大小： | 594K |
| 代理商： | MAX1856 |
M
Wide Input Range, Synchronizable,
PWM SLIC Power Supply
______________________________________________________________________________________
11
100kHz to 500kHz frequency, which is set by a resistor
(R
OSC
) connected from FREQ to GND. The relationship
between f
OSC
and R
OSC
is:
Thus, a 250kHz operating frequency, for example, is
set with R
OSC
= 200k
. At higher frequencies, the
magnetic components will be smaller. Peak currents
and, consequently, resistive losses will be lower at the
higher switching frequency. However, core losses, gate
charge currents, and switching losses increase with
higher switching frequencies.
Rising clock edges on SYNC/
SHDN
are interpreted as
synchronization input. If the sync signal is lost while
SYNC/
SHDN
is high, the internal oscillator takes over at
the end of the last cycle, and the frequency is returned
to the rate set by R
OSC
. If the signal is lost with
SYNC/
SHDN
low, the IC waits for 50μs before shutting
down. This maintains output regulation even with inter-
mittent sync signals. When an external sync signal is
used, Idle Mode switchover at the 15mV current-sense
threshold is disabled so that Idle Mode only occurs at
very light loads. Also, R
OSC
should be set for a fre-
quency 15% below the SYNC clock rate:
Setting the Output Voltage
Set the output voltage using two external resistors form-
ing a resistive divider to FB between the output and
REF. First select a value for R3 between 3.3k
and
100k
. R1 is then given by:
For a dual output as shown in Figure 1, a split feedback
technique is recommended. Since the feedback volt-
age threshold is 0, the total feedback current is:
Since the feedback resistors are connected to the ref-
erence, I
TOTAL
must be <400μA so that V
REF
is guaran-
teed to be in regulation (see
Electrical Characteristics
Table
). Therefore, select R3 so the total current value is
between 200μA and 250μA as shown in Figure 1. To
ensure that the MAX1856 regulates both outputs with
the same degree of accuracy over load, select the
feedback resistors (R1 and R2) so their current ratio
(I
R1
:I
R2
) equals the output power ratio (P
OUT1
:P
OUT2
)
under full load:
Once R3 and the dual feedback currents (I
R1
and I
R2
)
are determined from the two equations above, use the
following two equations to determine R1 and R2:
Selecting the Transformer
The MAX1856 PWM controller works with economical
off-the-shelf transformers. The transformer selection
depends on the input-to-output voltage ratio, output
current capacity, duty cycle, and oscillator frequency.
Table 1 shows recommended transformers for the typi-
cal applications, and Table 2 gives some recommend-
ed suppliers.
Transformer Turns Ratio
The transformer turns ratio is a function of the input-to-
output voltage ratio and maximum duty cycle. Under
steady-state conditions, the change in flux density dur-
ing the on-time must equal the return change in flux
density during the off-time (or flyback period):
For example, selecting a 50% duty cycle for the stan-
dard application circuit (Figure 1) and a +12V input
voltage, the -72V output requires a 1:6 turns ratio, and
the -24V output requires a 1:2 turns ratio. Therefore, a
transformer with a 1:2:2:2 turns ratio was selected.
Primary inductance
The average input current at maximum load can be cal-
culated as:
where
η
= efficiency. For V
OUT
= -24V, I
OUT(MAX)
=
400mA, and V
IN(MIN)
= 10.8V as shown in Figure 1, this
I
V
V
IN DC
(
OUT OUT MAX
η
IN MIN
(
)
(
)
)
=
V t
N
V
N
P
OUT OFF
S
=
I
V
R
and I
V
R
R
OUT
1
R
OUT
1
1
2
2
2
=
=
I
I
V
V
I
R
R
OUT OUT
OUT
2
OUT
1
2
1
1
2
=
I
I
I
V
R
TOTAL
R
R
REF
3
=
+
=
1
2
R
R
V
V
OUT
REF
1
3
=
R
M
kHz
kHz
(
OSC SYNC
(
OSC
)
.
)
=
×
50
0 85
R
M
kHz
kHz
(
OSC
OSC
=
×
50
)
相關PDF資料 |
PDF描述 |
|---|---|
| MAX1856EUB | Replaced by TMS320C6202B : Fixed-Point Digital Signal Processor 352-FCBGA 0 to 0 |
| MAX1864 | Fixed-Point Digital Signal Processor 352-FCBGA |
| MAX1864-MAX1865 | Fixed-Point Digital Signal Processor 384-FC/CSP |
| MAX1865 | Fixed-Point Digital Signal Processor 352-FCBGA |
| MAX1864UEEE | xDSL/Cable Modem Triple/Quintuple Output Power Supplies |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1856EUB | 功能描述:電信線路管理 IC RoHS:否 制造商:STMicroelectronics 產品:PHY 接口類型:UART 電源電壓-最大:18 V 電源電壓-最小:8 V 電源電流:30 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風格:SMD/SMT 封裝 / 箱體:VFQFPN-48 封裝:Tray |
| MAX1856EUB+ | 功能描述:電信線路管理 IC Synchronizable PWM SLIC Power Supply RoHS:否 制造商:STMicroelectronics 產品:PHY 接口類型:UART 電源電壓-最大:18 V 電源電壓-最小:8 V 電源電流:30 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風格:SMD/SMT 封裝 / 箱體:VFQFPN-48 封裝:Tray |
| MAX1856EUB+T | 功能描述:電信線路管理 IC Synchronizable PWM SLIC Power Supply RoHS:否 制造商:STMicroelectronics 產品:PHY 接口類型:UART 電源電壓-最大:18 V 電源電壓-最小:8 V 電源電流:30 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風格:SMD/SMT 封裝 / 箱體:VFQFPN-48 封裝:Tray |
| MAX1856EUB-T | 功能描述:電信線路管理 IC RoHS:否 制造商:STMicroelectronics 產品:PHY 接口類型:UART 電源電壓-最大:18 V 電源電壓-最小:8 V 電源電流:30 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風格:SMD/SMT 封裝 / 箱體:VFQFPN-48 封裝:Tray |
| MAX1856EVKIT | 功能描述:電源管理IC開發(fā)工具 Evaluation Kit for the MAX1856 RoHS:否 制造商:Maxim Integrated 產品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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