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| 型号： | MAX1897ETP+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 24/33页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 20-TQFN |
| 标准包装： | 2,500 |
| 系列： | Quick-PWM™ |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 550kHz |
| 电源电压： | 4.5 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 85°C |
| 封装/外壳： | 20-WQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
Input Capacitor Selection
The input capacitor must meet the ripple current
requirement (I RMS ) imposed by the switching currents.
The MAX1887/MAX1897 multiphase slave controllers
operate out-of-phase (MAX1897 POL = V CC or float),
staggering the turn-on times of each phase. This mini-
mizes the input ripple current by dividing the load cur-
rent among independent phases:
the minimum power dissipation occurs where the resis-
tive losses equal the switching losses.
Choose a low-side MOSFET that has the lowest possi-
ble on-resistance (R DS(ON) ), comes in a moderate-
sized package (i.e., one or two SO-8s, DPAK or
D 2 PAK), and is reasonably priced. Make sure that the
DL gate driver can supply sufficient current to support
the gate charge and the current injected into the para-
I RMS = ? LOAD ? ?
?
?
? η ? ? V IN
? I ? ? V OUT ( V IN ? V OUT )
?
?
?
sitic gate-to-drain capacitor caused by the high-side
MOSFET turning on; otherwise, cross-conduction prob-
lems may occur.
MOSFET Power Dissipation
? V
? ? I
?
PD ( N H Re sistive ) = ? OUT ? ? LOAD ? R DS ( ON )
for out-of-phase operation.
When operating the MAX1897 in-phase (POL = GND),
the high-side MOSFETs turn on simultaneously, so
input capacitors must support the combined input rip-
ple currents of each phase:
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET (N H ), the worst-
case power dissipation due to resistance occurs at the
minimum input voltage:
2
? V IN ? ? η ?
I RMS = I LOAD ?
?
?
? V OUT ( V IN ? V OUT )
? V IN
?
?
?
Generally, a small high-side MOSFET is desired to
reduce switching losses at high input voltages.
However, the R DS(ON) required to stay within package
for in-phase operation.
For most applications, nontantalum chemistries (ceram-
ic, aluminum, or OS-CON) are preferred because of
their resistance to inrush surge currents typical of sys-
tems with a mechanical switch or connector in series
with the input. If the MAX1887/MAX1897 is operated as
the second stage of a two-stage power-conversion sys-
tem, tantalum input capacitors are acceptable. In either
configuration, choose an input capacitor that exhibits
less than +10 ° C temperature rise at the RMS input cur-
rent for optimal circuit longevity.
Power MOSFET Selection
Most of the following MOSFET guidelines focus on the
power-dissipation often limits how small the MOSFET
can be. Again, the optimum occurs when the switching
losses equal the conduction (R DS(ON) ) losses. High-
side switching losses don ’ t usually become an issue
until the input is greater than approximately 15V.
Calculating the power dissipation of the high-side
MOSFET (N H ) due to switching losses is difficult since it
must allow for difficult quantifying factors that influence
the turn-on and turn-off times. These factors include the
internal gate resistance, gate charge, threshold volt-
age, source inductance, and PC board layout charac-
teristics. The following switching-loss calculation
provides only a very rough estimate and is no substi-
tute for breadboard evaluation, preferably including
verification using a thermocouple mounted on N H :
( V IN ( MAX ) )
challenge of obtaining high load-current capability
when using high-voltage (>20V) AC adapters. Low-cur-
rent applications usually require less attention.
The high-side MOSFET (N H ) must be able to dissipate
PD ( N H
Switching ) =
2
C RSS f SW I LOAD
I GATE η
? V IN
? fSW switching-loss equation. If the high-side
the resistive losses plus the switching losses at both
V IN(MIN) and V IN(MAX) . Calculate both of these sums.
Ideally, the losses at V IN(MIN) should be roughly equal
to losses at V IN(MAX) , with lower losses in between. If
the losses at V IN(MIN) are significantly higher than the
losses at V IN(MAX) , consider increasing the size of N H .
Conversely, if the losses at V IN(MAX) are significantly
higher than the losses at V IN(MIN) , consider reducing
the size of N H . If V IN does not vary over a wide range,
where C RSS is the reverse transfer capacitance of N H
and I GATE is the peak gate-drive source/sink current
(1A typ).
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the C
2
MOSFET chosen for adequate R DS(ON) at low battery
voltages becomes extraordinarily hot when biased from
24
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| MAX1898EUB41 | 功能描述:电池管理 Linear Charger for 1-Cell Li+ Battery RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
| MAX1898EUB41+ | 功能描述:电池管理 Linear Charger for 1-Cell Li+ Battery RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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| MAX1898EUB41-T | 功能描述:电池管理 Linear Charger for 1-Cell Li+ Battery RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
| MAX1898EUB42 | 功能描述:电池管理 Linear Charger for 1-Cell Li+ Battery RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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