MIC4742YTSE Micrel Inc, MIC4742YTSE Datasheet - Page 11

• Manufacturer Part Number: MIC4742YTSE
• Description: 2 MHz Dual 2A Integrated Switch Buck Regulator
• Manufacturer: Micrel Inc
• Type: Step-Down (Buck)r

Specifications of MIC4742YTSE

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: Adj to 0.6V
• Current - Output: 2A
• Frequency - Switching: 2MHz
• Voltage - Input: 2.9 ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-3355-5

Micrel, Inc.
Figure 4 demonstrates the off-time. During the off-time,
the high-side internal P-channel MOSFET turns off.
Since the current in the inductor has to discharge, the
current flows through the free-wheeling Schottky diode
to the output. In this case, the inductor discharge rate is
(where V
The total off time can be calculated as;
Discontinuous Operation
Discontinuous operation is when the inductor current
discharges to zero during the off cycle. Figure 5
demonstrates the switch voltage and inductor currents
during discontinuous operation.
March 2009
I
−
T
D
pk
OFF
(
is the diode forward voltage);
V
=
OUT
I
=
OUT
L
1
fsw
+
−
V
D
Figure 4. Off-Time
+
D
(
)
V
IN
−
2
V
×
OUT
fsw
)
×
×
L
V
V
OUT
IN
11
When
discharged, the voltage on the switch node rings at the
frequency determined by the parasitic capacitance and
the inductor value. In Figure 5, it is drawn as a DC
voltage, but to see actual operation (with ringing) refer to
the functional characteristics.
Discontinuous mode of operation has the advantage
over full PWM in that at light loads, the MIC4742 will skip
pulses as necessary, reducing gate drive losses,
drastically improving light load efficiency.
Efficiency Considerations
Calculating the efficiency is as simple as measuring
power out and dividing it by the power in;
Where input power (P
and output power (P
The Efficiency of the MIC4742 is determined by several
factors.
Rdson losses are caused by the current flowing through
the high side P-channel MOSFET. The amount of power
loss can be approximated by;
•
•
•
•
Rdson (Internal P-channel Resistance)
Diode conduction losses
Inductor Conduction losses
Switching losses
the
Efficiency
P
P
P
IN
OUT
SW
Figure 5. Discontinuous Operation
=
inductor
=
V
=
R
IN
V
DSON
OUT
×
=
I
OUT
IN
P
IN
P
OUT
×
) is;
IN
) is calculated as;
×
I
current
I
OUT
OUT
×
100
2
×
D
(IL)
has
M9999-030209-D
completely
MIC4742