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參數(shù)資料
| 型號： | MAX1737EVKIT |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | MAX1737 Evaluation Kit |
| 中文描述： | MAX1737評估板 |
| 文件頁數(shù)： | 16/18頁 |
| 文件大?。?/td> | 234K |
| 代理商： | MAX1737EVKIT |
M
Stand-Alone Switch-Mode
Lithium-Ion Battery-Charger Controller
16
______________________________________________________________________________________
0.5
×
I
CHG
. If the input to output voltage ratio is such
that the PWM controller will never work at 50% duty
cycle, then the worst-case capacitor current will occur
where the duty cycle is nearest 50%.
The impedance of the input capacitor is critical to pre-
venting AC currents from flowing back into the wall cube.
This requirement varies depending on the wall cube’s
impedance and the requirements of any conducted or
radiated EMI specifications that must be met. Aluminum
electrolytic capacitors are generally the least costly, but
are usually a poor choice for portable devices due to
their large size and low equivalent series resistance
(ESR). Tantalum capacitors are better in most cases, as
are high-value ceramic capacitors. For equivalent size
and voltage rating, tantalum capacitors will have higher
capacitance and ESR than ceramic capacitors. This
makes it more critical to consider RMS current and
power dissipation when using tantalum capacitors.
The output filter capacitor is used to absorb the induc-
tor ripple current. The output capacitor impedance
must be significantly less than that of the battery to
ensure that it will absorb the ripple current. Both the
capacitance and ESR rating of the capacitor are impor-
tant for its effectiveness as a filter and to ensure stabili-
ty of the PWM circuit. The minimum output capacitance
for stability is:
where C
OUT
is the total output capacitance, V
REF
is the
reference voltage (4.2V), V
BATT
is the maximum battery
voltage (typically 4.2V per cell), and V
DCIN(MIN)
is the
minimum source input voltage.
The maximum output capacitor ESR allowed for stability
is:
R
V
REF
where R
ESR
is the output capacitor ESR and R
CS
is the
current-sense resistor from CS to BATT.
Setting the Timers
The MAX1737 contains four timers: a prequalification
timer, fast-charge timer, full-charge timer, and top-off
timer. Connecting a capacitor from TIMER1 to GND
and TIMER2 to GND sets the timer periods. The
TIMER1 input controls the prequalification, full-charge,
and top-off times, while TIMER2 controls fast-charge
timeout. The typical timeouts for a 1C charge rate are
set to 7.5 minutes for the prequalification timer, 90 min-
utes for the fast-charge timer, 90 minutes for the full-
charge timer, and 45 minutes for the top-off timer by
connecting a 1nF capacitor to TIMER1 and TIMER2.
Each timer period is directly proportional to the capaci-
tance at the corresponding pin. See the
Typical
Operating Characteristics.
Compensation
Each of the three regulation loops—the input current
limit, the charging current limit, and the charging volt-
age limit—can be compensated separately using the
CCS, CCI, and CCV pins, respectively.
The charge-current loop error amp output is brought
out at CCI. Likewise, the source-current error amplifier
output is brought out at CCS; 47nF capacitors to
ground at CCI and CCS compensate the current loops
in most charger designs. Raising the value of these
capacitors reduces the bandwidth of these loops.
The voltage-regulating loop error amp output is brought
out at CCV. Compensate this loop by connecting a
capacitor in parallel with a series resistor-capacitor
(RC) from CCV to GND. Recommended values are
shown in Figure 1.
Applications Information
MOSFET Selection
The MAX1737 uses a dual N-channel external power
MOSFET switch to convert the input voltage to the
charging current or voltage. The MOSFET must be
selected to meet the efficiency and power-dissipation
requirements of the charging circuit, as well as the tem-
perature rise of the MOSFETs. The MOSFET character-
istics that affect the power dissipation are the
drain-source on-resistance (R
DS(ON)
) and the gate
charge. In general, these are inversely proportional.
To determine the MOSFET power dissipation, the oper-
ating duty cycle must first be calculated. When the
charger is operating at higher currents, the inductor
current will be continuous (the inductor current will not
drop to 0A) and, in this case, the high-side MOSFET
duty cycle (D) can be approximated by the equation:
and the synchronous-rectifier MOSFET duty cycle (D
′
)
will be 1 - D or:
V
V
′ ≈
D
V
DCIN
BATT
DCIN
D
V
V
BATT
DCIN
≈
R
V
ESR
CS
BATT
<
×
C
V
V
V
×
V
f
R
OUT
REF
BATT
DCIN MIN
×
BATT
CS
>
+
1
(
)
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| MAX1739EEP+T | 功能描述:顯示驅(qū)動器和控制器 CCFL Backlight Controller RoHS:否 制造商:Panasonic Electronic Components 工作電源電壓:2.7 V to 5.5 V 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Reel |
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