MIC2164 datasheet(21/39 Pages) MICREL

21 / 39 page

Micrel, Inc.

MIC2164/-2/-3/C

September 2010

M9999-091310-D

Setting Output Voltage

In addition to the external ripple injection added at the

FB pin, internal ripple injection is added at the inverting

input of the comparator inside the MIC2164/-2/-3, as

shown in Figure 7. The inverting input voltage VINJ is

clamped to 1.2V. As VOUT is increased, the swing of VINJ

will be clamped. The clamped VINJ reduces the line

regulation because it is reflected back as a DC error on

the FB terminal. Therefore, the maximum output voltage

of the MIC2164/-2/-3 should be limited to 5.5V to avoid

this problem. If a higher output voltage is required, use

the MIC2176 instead.

The MIC2164/-2/-3 requires two resistors to set the

output voltage, as shown in Figure 6:

Figure 6. Voltage-Divider Configuration

The output voltage is determined by the equation:

)

REF

OUT

(33)

Figure 7. Internal Ripple Injection

where VREF = 0.8V. A typical value of R1 can be between

3kΩ and 10kΩ. If R1 is too large, it may allow noise to be

introduced into the voltage feedback loop. If R1 is too

small, it will decrease the efficiency of the power supply,

especially at light loads. Once R1 is selected, R2 can be

calculated using:

REF

OUT

REF

−

(34)

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