- 您现在的位置：买卖IC网 > PDF目录1840 > MAX1844EEP+T (Maxim Integrated Products)IC REG CTRLR BUCK PWM CM 20-QSOP PDF资料下载
参数资料
| 型号： | MAX1844EEP+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 20-QSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 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： | -40°C ~ 85°C |
| 封装/外壳： | 20-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
Current-Limit Circuit (ILIM)
The current-limit circuit employs a unique “ valley ” cur-
rent-sensing algorithm (Figure 4). If the magnitude of the
+5V
V IN
current-sense voltage at CS is above the current-limit
threshold, the PWM is not allowed to initiate a new cycle.
The actual peak current is greater than the current-limit
threshold by an amount equal to the inductor ripple cur-
rent. Therefore, the exact current-limit characteristic and
maximum load capability are a function of the sense
resistance, inductor value, and battery voltage.
There is also a negative current limit that prevents exces-
sive reverse inductor currents when V OUT is sinking cur-
rent. The negative current-limit threshold is set to
MAX1844
BST
DH
LX
5 ?
approximately 120% of the positive current limit and
therefore tracks the positive current limit when ILIM is
adjusted.
The current-limit threshold is adjusted with an external
resistor-divider at ILIM. A 1μA (min) divider current is
recommended. The current-limit threshold adjustment
range is from 25mV to 300mV. In the adjustable mode,
the current-limit threshold voltage is precisely 1/10 the
voltage seen at ILIM. The threshold defaults to 100mV
when ILIM is connected to V CC . The logic threshold for
switchover to the 100mV default value is approximately
V CC - 1V.
Carefully observe the PC board layout guidelines to
ensure that noise and DC errors do not corrupt the cur-
rent-sense signal seen by CS. Mount or place the IC
close to the low-side MOSFET and sense resistor with
short, direct traces, making a Kelvin sense connection to
the sense resistor.
In Figure 1, the Schottky diode (D1) provides a current
path parallel to the Q2/R SENSE current path. Accurate
current sensing demands D1 to be off while Q2 con-
ducts. Avoid large current-sense voltages that, com-
bined with the voltages across Q2, would allow D1 to
conduct. If very large sense voltages are used, connect
D1 in parallel with Q2.
MOSFET Gate Drivers (DH, DL)
The DH and DL drivers are optimized for driving moder-
ate-sized high-side, and larger low-side power
MOSFETs. This is consistent with the low duty factor
seen in the notebook environment, where a large V BATT -
V OUT differential exists. An adaptive dead-time circuit
monitors the DL output and prevents the high-side FET
from turning on until DL is fully off. There must be a low-
resistance, low-inductance path from the DL driver to the
MOSFET gate for the adaptive dead-time circuit to work
Figure 5. Reducing the Switching-Node Rise Time
properly; otherwise, the sense circuitry in the MAX1844
will interpret the MOSFET gate as “ off ” while there is
actually still charge left on the gate. Use very short, wide
traces measuring no more than 20 squares (50 to 100
mils wide if the MOSFET is 1 inch from the MAX1844).
The dead time at the other edge (DH turning off) is deter-
mined by a fixed 35ns (typ) internal delay.
The internal pulldown transistor that drives DL low is
robust, with a 0.5 ? (typ) on-resistance. This helps pre-
vent DL from being pulled up during the fast rise-time of
the inductor node, due to capacitive coupling from the
drain to the gate of the low-side synchronous-rectifier
MOSFET. However, for high-current applications, there
are still some combinations of high- and low-side FETs
that will cause excessive gate-drain coupling, which can
lead to efficiency-killing, EMI-producing shoot-through
currents. This is often remedied by adding a resistor in
series with BST, which increases the turn-on time of the
high-side FET without degrading the turn-off time
(Figure 5).
POR, UVLO, and Soft-Start
Power-on reset (POR) occurs when V CC rises above
approximately 2V, resetting the fault latch and soft-start
counter, and preparing the PWM for operation. Until V CC
reaches 4.2V, V CC undervoltage lockout (UVLO) circuitry
inhibits switching. DL is held low if overvoltage protec-
tion is disabled, and held high if overvoltage protection is
enabled. See the Output Overvoltage Protection section.
When V CC rises above 4.2V, an internal digital soft-start
timer begins to ramp up the maximum allowed current
limit. The ramp occurs in five steps: 20%, 40%, 60%,
80%, and 100%; 100% current is available after 1.7ms
±50%.
14
______________________________________________________________________________________
相关PDF资料 |
PDF描述 |
|---|---|
| MAX1845EEI+ | IC REG CTRLR BUCK PWM CM 28-QSOP |
| MAX1847EEE+T | IC REG CTRLR FLYBK INV CM 16QSOP |
| MAX1853EXT-T | IC REG SWITCHED CAP INV SC70-6 |
| MAX1856EUB | IC PS PWM SLIC SYNCH 10-UMAX |
| MAX1857EUA47+ | IC REG LDO 4.75V/ADJ .5A 8-UMAX |
相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1844EGP | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1844EGP+ | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1844EGP-T | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1844ETP | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1844ETP+ | 功能描述:电流型 PWM 控制器 Step-Down Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
发布紧急采购，3分钟左右您将得到回复。