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| 型号： | MIC2124YMM |
| 厂商： | Micrel Inc |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 10-MSOP |
| 产品培训模块： | MIC2124 Synchronous Current Mode DC-DC Buck Controller |
| 标准包装： | 100 |
| 系列： | Hyper Speed Control™ |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 360kHz |
| 占空比： | 93% |
| 电源电压： | 3 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： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 管件 |
| 其它名称： | 576-3639-5 MIC2124YMM-ND |
Micrel, Inc.
MIC2124
where:
D = duty cycle
R2 =
V REF ? R1
V OUT ? V REF
(26)
C OUT = output capacitance value
f SW = switching frequency
The voltage rating of the capacitor should be twice the
output voltage for a tantalum and 20% greater for
aluminum electrolytic or OS-CON. The output capacitor
RMS current is calculated below:
I C OUT (RMS) =
Δ I L(PP)
12
(20)
The power dissipated in the output capacitor is:
P DISS(C OUT ) = I C OUT (RMS) ? ESR C OUT
2
(21)
Figure 5. Voltage-Divider Configuration
External Schottky Diode (Optional)
Input Capacitor Selection
The input capacitor for the power stage input V HSD
should be selected for ripple current rating and voltage
rating. Tantalum input capacitors may fail when
subjected to high inrush currents, caused by turning the
input supply on. A tantalum input capacitor’s voltage
rating should be at least two times the maximum input
voltage to maximize reliability. Aluminum electrolytic,
An external freewheeling diode, which is not necessary,
is used to keep the inductor current flow continuous
while both MOSFETs are turned off. This dead-time
prevents current from flowing unimpeded through both
MOSFETs and is typically 30ns. The diode conducts
twice during each switching cycle. Although the average
current through this diode is small, the diode must be
able to handle the peak current.
OS-CON, and multilayer polymer film capacitors can
handle the higher inrush currents without voltage de-
rating. The input voltage ripple will primarily depend on
I D(avg) = I OUT ? 2 ? 30ns ? f SW
The reverse voltage requirement of the diode is:
(27)
Δ V IN = I L(pk) ? ESR C IN
the input capacitor’s ESR. The peak input current is
equal to the peak inductor current, so:
(22)
The input capacitor must be rated for the input current
ripple. The RMS value of input capacitor current is
determined at the maximum output current. Assuming
the peak-to-peak inductor current ripple is low:
V DIODE(rrm) = V HSD
The power dissipated by the Schottky diode is:
P DIODE = I D(avg) × V F (28)
where V F = forward voltage at the peak diode current.
The external Schottky diode is not necessary for the
circuit operation since the low-side MOSFET contains a
P DISS(C IN ) = I C IN (RMS) ? ESR C IN
I C IN (RMS) ≈ I OUT(MAX) ? D ? (1 ? D)
The power dissipated in the input capacitor is:
2
Voltage Setting Components
(23)
(24)
parasitic body diode. The external diode will improve
efficiency and decrease the high frequency noise. If the
MOSFET body diode is used, it must be rated to handle
the peak and average current. The body diode has a
relatively slow reverse recovery time and a relatively
high forward voltage drop. The power lost in the diode is
proportional to the forward voltage drop of the diode. As
V OUT = V REF ? (1 +
)
(25)
The MIC2124 requires two resistors to set the output
voltage as shown in Figure 5.
The output voltage is determined by the equation:
R1
R2
where V REF = 0.8V. A typical value of R1 can be between
3k ? and 10k ? . If R1 is too large, it may allow noise to be
introduced into the voltage feedback loop. If R1 is too
small in value, it will decrease the efficiency of the power
supply, especially at light loads. Once R1 is selected, R2
can be calculated using:
the high-side MOSFET starts to turn on, the body diode
becomes a short circuit for the reverse recovery period,
dissipating additional power. The diode recovery and the
circuit inductance will cause ringing during the high-side
MOSFET turn-on.
An external Schottky diode conducts at a lower forward
voltage preventing the body diode in the MOSFET from
turning on. The lower forward voltage drop dissipates
less power than the body diode. The lack of a reverse
recovery mechanism in a Schottky diode causes less
ringing and less power loss. Depending on the circuit
components and operating conditions, an external
Schottky diode will give a 0.5% to 1% improvement in
efficiency.
June 2010
14
M9999-060810-D
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