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參數(shù)資料
| 型號(hào)： | MAX1565 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply |
| 中文描述： | 小型、高效率、5路輸出數(shù)碼相機(jī)電源 |
| 文件頁數(shù)： | 20/26頁 |
| 文件大?。?/td> | 512K |
| 代理商： | MAX1565 |
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M
If we select L = 4.7μH and f
OSC
= 440kHz, P
SLOPE
=
V
IN
/(
π
L) = 214kHz, so choose f
C
= 40kHz and calculate C
C
:
C
C
= (V
FB
/V
OUT
)(R
LOAD
/R
CS
)(gm/2
π
f
C
)
= (1.25/1.5)(4.3/0.6) x (135μS/(6.28 x 40kHz)
= 3.2nF
Choose 3.3nF. Now select R
C
such that transient droop
requirements are met. For example, if 4% transient
droop is allowed, the input to the error amplifier moves
0.04 x 1.25V, or 50mV. The error amp output drives
50mV x 135μS, or 6.75μA across R
C
to provide tran-
sient gain. Since the current-sense transresistance is
0.6V/A, the value of R
C
that allows the required load
step swing:
R
C
= 0.6 I
IND(PK)
/6.75μA
In a step-down DC-to-DC converter, if L
IDEAL
is used,
output current relates to inductor current by:
I
IND(PK)
= 1.25 I
OUT
Thus, for a 250mA output load step with V
IN
= 3.35V
and V
OUT
= 1.5V:
R
C
= (1.25 x 0.6 x 0.25)/6.75μA = 27.8k
Choose 27k
. Note that the inductor does not limit the
response in this case since it can ramp at (V
IN
-
V
OUT
)/4.7μH, or (3.35 - 1.5)/4.7μH = 394mA/μs.
The output filter capacitor is then chosen so that the
C
OUT
R
LOAD
pole cancels the R
C
C
C
zero:
C
OUT
R
LOAD
= R
C
C
C
For example:
C
OUT
= 27k
x 3.3nF/4.3 = 20.7μF
Choose 22μF. If the output filter capacitor has signifi-
cant ESR, a zero occurs at:
Z
ESR
= 1/(2
π
C
OUT
R
ESR
)
If Z
ESR
> f
C
, it can be ignored, as is typically the case
with ceramic output capacitors. If Z
ESR
is less than f
C
,
it should be cancelled with a pole set by capacitor C
P
connected from COMPSD to GND:
C
P
= C
OUT
R
ESR
/R
C
If C
P
is calculated to be < 10pF, it can be omitted.
Auxiliary Controller Component Selection
External MOSFET
All MAX1565 auxiliary controllers drive external logic-
level N-channel MOSFETs. Significant MOSFET selec-
tion parameters are:
1) On-resistance (R
DS(ON)
)
2) Maximum drain-to-source voltage (VDS(MAX))
3) Total gate charge (Q
G
)
4) Reverse transfer capacitance (CRSS)
DL_ swings between OUTSU and GND. Use a MOSFET
with on-resistance specified at or below the main output
voltage. The gate charge, Q
G
, includes all capacitance
associated with charging the gate and helps to predict
MOSFET transition time between on and off states.
MOSFET power dissipation is a combination of
on-resistance and transition losses. The on-resistance
loss is:
P
RDSON
= D I
L2
R
DS(ON)
where D is the duty cycle, I
L
is the average inductor
current, and R
DS(ON)
is MOSFET on-resistance. The
transition loss is approximately:
P
TRANS
= (V
OUT
I
L
f
OSC
t
T
)/3
where V
OUT
is the output voltage, I
L
is the average
inductor current, f
OSC
is the switching frequency, and
t
T
is the transition time. The transition time is approxi-
mately Q
G
/I
G
, where Q
G
is the total gate charge, and
I
G
is the gate drive current (typically 0.5A). The total
power dissipation in the MOSFET is:
P
MOSFET
= P
RDSON
+ P
TRANS
Diode
For most auxiliary applications, a Schottky diode rectifies
the output voltage. The Schottky diode
’
s low forward volt-
age and fast recovery time provide the best performance
in most applications. Silicon signal diodes (such as
1N4148) are sometimes adequate in low-current
(<10mA) high-voltage (>10V) output circuits where the
output voltage is large compared to the diode forward
voltage.
Auxiliary Compensation
The auxiliary controllers employ voltage-mode control
to regulate their output voltage. Optimum compensa-
tion somewhat depends on whether the design uses
continuous or discontinuous inductor current.
Small, High-Efficiency, Five-Channel
Digital Still Camera Power Supply
20
______________________________________________________________________________________
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| MAX1565ETJ | Small, High-Efficiency, Five-Channel Digital Still Camera Power Supply |
| MAX1566-MAX1567 | Six-Channel, High-Efficiency, Digital Camera Power Supplies |
| MAX156ACNG | 8-/4-Channel ADCs with Simultaneous T/Hs and Reference |
| MAX156BCNG | 8-/4-Channel ADCs with Simultaneous T/Hs and Reference |
| MAX156BENG | 8-/4-Channel ADCs with Simultaneous T/Hs and Reference |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1565ETJ | 功能描述:PMIC 解決方案 5Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1565ETJ+ | 功能描述:PMIC 解決方案 5Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1565ETJ+T | 功能描述:PMIC 解決方案 5Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1565ETJ-T | 功能描述:PMIC 解決方案 5Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-24 封裝:Reel |
| MAX1565EVKIT | 制造商:Maxim Integrated Products 功能描述:SMALL, HIGH-EFFICIENCY, FIVE-CHANNEL DSC - Bulk |
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