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| 型号： | MAX1967EUB+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/15页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 10-UMAX |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 127kHz |
| 占空比： | 95% |
| 电源电压： | 2.7 V ~ 28 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
Low-Cost Voltage-Mode PWM
Step-Down Controllers
and keep a 0.1μF capacitor between VL and GND
close to the chip. The V IN -to-V L dropout voltage is typi-
cally 70mV at 25mA current, so when V VIN is less than
5V, V VL is typically V VIN - 70mV.
The internal linear regulator can source a minimum of
25mA to supply the IC and power the low-side and
high-side FET drivers.
Duty-Factor Limitations for Low
V OUT /V VIN Ratios
The MAX1966/MAX1967s ’ output voltage is adjustable
down to 0.8V. However, the minimum duty factor may
limit the ability to supply low-voltage outputs from high-
voltage inputs. With high-input voltages, the required
duty factor is approximately:
determines the required inductor saturation rating
and the design of the current-limit circuit. Con-
tinuous load current (I LOAD ) determines the thermal
stresses, input capacitor, and MOSFETs, as well as
the RMS ratings of other heat-contributing compo-
nents such as the inductor.
3) Inductor Value : This choice provides tradeoffs
between size, transient response, and efficiency.
Higher inductance value results in lower inductor
ripple current, lower peak current, lower switching
losses, and, therefore, higher efficiency at the cost
of slower transient response and larger size. Lower
inductance values result in large ripple currents,
smaller size, and poorer efficiency, while also pro-
viding faster transient response. Except for low-cur-
( V OUT DS ( ON )
× I LOAD ) VIN
+ R
/ V
rent applications, most circuits exhibit a good
balance between efficiency and economics with a
minimum inductor value that causes the circuit to
where R DS(ON) x I LOAD is the voltage drop across the
synchronous rectifier. The MAX1966/MAX1967s ’ mini-
mum duty factor is 10%, so the maximum input voltage
(V VIN(DFMAX) ) that can supply a given output voltage is:
operate at the edge of continuous conduction
(where the inductor current just touches zero with
every cycle at maximum load). Inductor values lower
than this grant no further size-reduction benefit.
V VIN ( DFMAX ) ≤ 10 ( V OUT + R DS ( ON ) × I LOAD
)
Table 1 shows representative values for some typical
applications up to 5A. With proper component selec-
tion, outputs of 20A or more are practical with the
R 1 = R 2 ? OUT ? 1 ?
If the circuit cannot attain the required duty factor dic-
tated by the input and output voltages, the output volt-
age still remains in regulation. However, there may be
intermittent or continuous half-frequency operation as
the controller attempts to lower the average duty factor
by deleting pulses. This can increase output voltage
ripple and inductor current ripple, which increases
noise and reduces efficiency. Furthermore, circuit sta-
bility is not guaranteed.
Applications Information
Design Procedure
Component selection is primarily dictated by the follow-
ing criteria:
MAX1966/MAX1967. The components listed in Table 1
were selected assuming a minimum cost design goal.
The MAX1966/MAX1967 can effectively operate with a
wide range of components.
Setting the Output Voltage
An output voltage between 0.8V and (0.9V x V VIN ) can
be configured by connecting F B pin to a resistive
divider between the output and GND (Figures 3 and 4).
Select resistor R2 in the 1k ? to 10k ? range. R1 is then
given by:
? V ?
? V FB ?
1) Input Voltage Range : The maximum value
(V VIN(MAX) ) must accommodate the worst-case
high-input voltage. The minimum value (V VIN(MIN) )
where V FB = 0.8V.
Inductor Selection
must account for the lowest input voltage after
drops due to connectors, fuses, and switches are
Determine an appropriate inductor value with the fol-
lowing equation:
considered. In general, lower input voltages pro-
vide the best efficiency.
2) Maximum Load Current : There are two current val-
ues to consider. Peak load current (I LOAD(MAX) )
L = V OUT ×
V VIN × f OSC × LIR × I LOAD ( MAX )
( V IN ? V OUT )
determines the instantaneous component stresses
and filtering requirements and is key in determining
output capacitor requirements. I LOAD(MAX) also
where LIR is the ratio of inductor ripple current to aver-
age continuous current at a minimum duty cycle.
Choosing LIR between 20% to 50% results in a good
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