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参数资料
| 型号： | MAX889TESA+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 7/8页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHD CAP INV ADJ 8SOIC |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 切换式电容器（充电泵），反相 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | -2.5 V ~ -5.5 V |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 2MHz |
| 电流 - 输出： | 200mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 8-SOIC |
High-Frequency, Regulated,
200mA, Inverting Charge Pump
Adjust the output voltage to a negative voltage from
C OUT ≥ ?
-2.5V to -V IN with external resistors R1 and R2 as
shown in Figures 1 and 4. FB servos to GND. Choose
R1 to be 100k ? or less. Calculate R2 for the desired
? 15.5 ? ? R1 ?
? ? ?
? f MIN ? ? R1 + R2 ?
I OUT
output voltage:
V OUT = -V REF (R2 / R1)
where C OUT is the output capacitor value, and f MIN is the
minimum oscillator frequency in the Electrical
R2 = R1 (V OUT / -V REF )
where V REF can be either V IN or a positive reference
source.
Typically, choose a voltage-divider current of at least
Characteristics table.
To ensure stability for regulated output mode, suitable
output capacitor ESR should be determined by the follow-
ing equation:
?? ? 1 +
R ESR ≤ ?
? ?
?
?
R1 ?
30μA to minimize the effect of FB input current and
capacitance:
R1 ≤ V REF / 30μA
? 19.2 x 10 -3 ? ?
I OUT
R2 ?
?
R2 < -V OUT / 30μA
Capacitor Selection
The appropriate capacitors used with the MAX889
depend on the switching frequency. Table 1 provides
suggested values for C IN , C FLY , and C OUT .
Surface-mount ceramic capacitors are preferred for
C IN , C OUT , and C FLY due to their small size, low cost,
and low ESR. To ensure proper operation over the
entire temperature range, choose ceramic capacitors
with X7R (or equivalent) low-temperature-coefficient
(tempco) dielectrics. See Table 2 for a list of suggested
capacitor suppliers.
The output capacitor stores the charge transferred from
the flying capacitor and services the load between
oscillator cycles. A good general rule is to make the
output capacitance at least five-times greater than the
flying capacitor.
Output voltage ripple is largely dependent on C OUT .
Choosing a low-ESR capacitor of sufficient value is impor-
tant in minimizing the peak-to-peak output voltage ripple,
which is approximated by the following equation:
Power Dissipation
The power dissipated in the MAX889 depends on the
input voltage, output voltage, and output current. Device
power dissipation is accurately described by:
P DISS = I OUT (V IN - (-V OUT )) + (I Q ? V IN )
where I Q is the device quiescent current. P DISS must be
less than the package dissipation rating (see Absolute
Maximum Ratings ). Pay particular attention to power dis-
sipation limits when generating small negative voltages
from large positive input voltages.
Layout Considerations
The MAX889 ’ s high oscillator frequencies demand
good layout techniques that ensure stability and help
maintain the output voltage under heavy loads. Take
the following steps to ensure optimum layout:
1) Mount all components as close together as possible.
2) Place the feedback resistors R1 and R2 close to the
FB pin, and minimize the PC trace length at the FB
circuit node.
V RIPPLE =
I OUT
2 x f OSC C OUT
2 x I OUT ESR COUT
+
3) Keep traces short to minimize parasitic inductance
and capacitance.
4) Use a ground plane with C IN and C OUT placed in a
star ground configuration (see the MAX889SEVKIT
where C OUT is the output capacitor value, ESR COUT is
the output capacitor ’ s ESR, and f OSC is the MAX889
switching frequency. Ceramic capacitors have the lowest
ESR and are recommended for C OUT . Where larger
capacitance at low cost is desired, a low-ESR tantalum
capacitor may be used for C OUT . See Table 2 for a list of
suggested capacitor suppliers.
To ensure stability over the entire operating temperature
range, choose a low-ESR output capacitor using the fol-
lowing equation:
layout).
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