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參數(shù)資料
| 型號： | ISL6232CAZA-T |
| 廠商： | INTERSIL CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Efficiency System Power Supply Controller for Notebook Computers |
| 中文描述： | 2 A DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | ROHS COMPLIANT, PLASTIC, QSOP-28 |
| 文件頁數(shù)： | 21/25頁 |
| 文件大?。?/td> | 746K |
| 代理商： | ISL6232CAZA-T |
21
FN9116.0
April 18, 2005
Input Capacitor Selection
The input capacitors must meet the input ripple current
(I
RMS
) requirement imposed by the switching current. The
ISL6232 dual switching regulators operate at the same
switching frequency with out of phase. This interleaves the
current pulses drawn by the two regulators and have no
overlap time at normal operation. The input RMS current is
much smaller when compared with both regulators operating
in phase or operating at different switching frequencies. The
input RMS current varies with load and the input voltage.
The maximum input capacitor RMS current for a single buck
regulator is given by:
when V
IN
= 2V
OUT
(D = 50%), I
rms
has maximum current of
I
OUT
/2. The ESR of the input capacitor is important for
determining capacitor power dissipation. All the power (I
2rms
x ESR) heats up the capacitor and reduces efficiency. Non-
tantalum chemistries (ceramic, polymer such as POSCAP, or
SPCAP) are preferred due to their low ESR and resilience to
power-up surge currents. Choose input capacitors that
exhibit less than +10°C temperature rise at the RMS input
current for optimal circuit longevity.
MOSFET Selection
The synchronous buck regulator has the input voltage from
either AC adapter output or battery output. The maximum
AC adapter output voltage does not exceed 24V while the
maximum battery voltage does not exceed 17V for a 4 series
Li-Ion battery cell battery pack. Therefore, a 30V logic
MOSFET should be used.
The high side MOSFET must be able to dissipate the
conduction losses plus the switching losses. The input
voltage of the synchronous regulator is equal to the AC
adapter output voltage or battery voltage. The maximum
efficiency is achieved by selecting a high side MOSFET that
has the conduction losses equal to the switching losses.
Ensure that the ISL6232 LGATE gate driver can supply
sufficient gate current to prevent it from conduction,
otherwise, cross-conduction problems may occur.
Conduction is due to the injected current into the drain-to-
gate parasitic capacitor (Miller capacitor C
gd
) caused by the
voltage rising rate at phase node during the moment of the
high-side MOSFET turn-on. Reasonably slowing turn-on
speed of the high-side MOSFET by connecting a resistor
between the BOOT pin and gate drive supply source, and
high sink current capability of the low-side MOSFET gate
driver, helps reduce the possibility of cross-conduction.
For the high-side MOSFET, the worst-case conduction
losses occur at the minimum input voltage:
The optimum efficiency occurs when the switching losses
equal the conduction losses. However, it is difficult to
calculate the switching losses in the high-side MOSFET
since it must allow for difficult-to-quantify factors that
influence the turn-on and turn-off times. These factors
include the MOSFET internal gate resistance, gate charge,
threshold voltage, stray inductance, and the pull-up and pull-
down resistance of the gate driver. The following switching
loss calculation provides a rough estimate.
where Q
gd
: drain-to-gate charge, Q
rr
: total reverse recovery
charge of the body-diode in low side MOSFET, I
LV
: inductor
valley current, I
LP
:is Inductor peak current, I
g,sink
and
I
g
,
source
are the peak gate-drive source/sink current of Q1.
To achieve low switching losses requires low drain-to-gate
charge Q
gd
. Generally, the lower the drain-to-gate charge,
the higher the on-resistance. Therefore, there is a trade-off
between the on-resistance and drain-to-gate charge. Good
MOSFET selection is based on the Figure of Merit (FOM),
which is the product of the total gate charge and on-
resistance. Usually, the smaller the value of FOM, the higher
the efficiency for the same application.
For the low-side MOSFET, the worst-case power dissipation
occurs at minimum output voltage and maximum input
voltage:
Choose a low-side MOSFET that has the lowest possible
on-resistance with a moderate-sized package, like SO-8,
and one that is reasonably priced. The switching losses are
not an issue for the low side MOSFET because it operates at
zero-voltage-switching.
Choose an Schottky diode, in parallel with the low side
MOSFET Q2, with a forward voltage drop low enough to
prevent the low-side MOSFET Q2 body-diode from turning
on during the dead time. This also reduces the power loss in
the high-side MOSFET associated with the reverse recovery
of the low-side MOSFET Q2 body diode. As a general rule,
select a diode with a DC current rating equal to one-third of
the load current. One option is to choose a combined
MOSFET with the Schottky diode in a single package. The
integrated packages may work better in practice because
there is less stray inductance due to short connection. This
Schottky diode is optional and may be removed if efficiency
loss can be tolerated.
Loop Compensation Design
ISL6232 uses constant frequency peak current mode control
architecture to achieve fast loop transient response. An
accurate current sensing resistor in series with the output
I
rms
I
OUT
V
V
---------------------------------------------------------
V
–
(
)
IN
=
(EQ. 16)
P
Q1 Conduction
V
IN
---------------
I
OUT
2
R
DSON
=
(EQ. 17)
P
Q1 Switching
1
2
--
V
IN
I
LV
f
s
Q
g source
------------------------
1
2
--
V
IN
I
LP
f
s
Q
g
,
k
sin
-----------------
Q
rr
V
IN
f
s
+
+
=
(EQ. 18)
P
Q2
1
V
IN
---------------
–
I
OUT
2
R
DSON
=
(EQ. 19)
ISL6232
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| ISL6232CAZ-T | 制造商:Intersil Corporation 功能描述:LEAD-FREE HI EFFICIENCY SYSTEM PWR SUPPLY CONTR FOR NOTEBOOK - Tape and Reel |
| ISL6232EVAL1 | 功能描述:EVALUATION BOARD 1 ISL6232 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:- 產(chǎn)品培訓模塊:Obsolescence Mitigation Program 標準包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓撲結構:升壓 頻率 - 開關:3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| ISL6235 | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:Advanced Triple PWM Only Mode and Dual Linear Power Controller for Portable Applications |
| ISL6235CA | 制造商:Rochester Electronics LLC 功能描述:SYSTEM ELECTRONICS REGULATOR FOR LCD-PC - Bulk |
| ISL6235CA-T | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
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