MIC2176-2YMM Micrel Inc, MIC2176-2YMM Datasheet - Page 20

• Manufacturer Part Number: MIC2176-2YMM
• Description: IC CTLR BUCK ADJ 10-MSOP
• Manufacturer: Micrel Inc
• Series: Hyper Speed Control™r
• Type: Step-Down (Buck)r

Specifications of MIC2176-2YMM

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: Adj to 0.8V
• Frequency - Switching: 200kHz
• Voltage - Input: 4.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Power - Output: 421mW
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Other names: 576-3757-5

Micrel, Inc.
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:
The power dissipated in the input capacitor is:
Voltage Setting Components
The MIC2176 requires two resistors to set the output
voltage as shown in Figure 5:
The output voltage is determined by the equation:
where, V
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 in value, it will decrease the efficiency of the power
supply, especially at light loads. Once R1 is selected, R2
can be calculated using:
Ripple Injection
The V
MIC2176 g
100mV. However, the output voltage ripple is generally
designed as 1% to 2% of the output voltage. For a low
output voltage, such as a 1V, the output voltage ripple is
only 10mV to 20mV, and the feedback voltage ripple is
November 2010
FB
FB
Figure 5. Voltage-Divider Configuration
ripple required for proper operation of the
m
= 0.8V. A typical value of R1 can be between
P
I
R2
V
CIN(RMS)
amplifier and error comparator is 20mV to
DISS(CIN)
OUT
=
V
=
OUT
V
V
FB
≈
= I
FB
I
×
−
OUT(max)
CIN(RMS)
×
R1
V
(1
FB
+
R2
R1
2
×
)
× ESR
D
×
(1
CIN
−
D)
(25)
(26)
(27)
(28)
20
less than 20mV. If the feedback voltage ripple is so small
that the g
then the MIC2176 will lose control and the output voltage
is not regulated. In order to have some amount of V
ripple, a ripple injection method is applied for low output
voltage ripple applications.
The applications are divided into three situations
according to the amount of the feedback voltage ripple:
1. Enough ripple at the feedback voltage due to the
2. Inadequate ripple at the feedback voltage due to the
3. Virtually no ripple at the FB pin voltage due to the
large ESR of the output capacitors.
As shown in Figure 6a, the converter is stable
without any ripple injection. The feedback voltage
ripple is:
where ΔI
inductor current ripple.
small ESR of the output capacitors.
The output voltage ripple is fed into the FB pin
through a feedforward capacitor C
as shown in Figure 6b. The typical C
between 1nF and 100nF. With the feedforward
capacitor, the feedback voltage ripple is very close
to the output voltage ripple:
very-low ESR of the output capacitors:
ΔV
m
amplifier and error comparator can’t sense it,
FB(pp)
ΔV
Figure 6a. Enough Ripple at FB
L(pp)
FB(pp)
=
is the peak-to-peak value of the
R1
≈
R2
+
ESR
R2
×
×
ESR
ΔI
L
(pp)
C
OUT
×
ff
M9999-111710-A
ΔI
in this situation,
L
(pp)
ff
MIC2176
value is
(29)
(30)
FB