MIC4742YTSE Micrel Inc, MIC4742YTSE Datasheet - Page 10

• 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.
Application Information
The MIC4742 is a dual 2A PWM non-synchronous buck
regulator. By switching an input voltage supply, and
filtering the switched voltage through an inductor and
capacitor, a regulated DC voltage is obtained. Figure 1
shows a simplified example of a non-synchronous buck
converter.
For a non-synchronous buck converter, there are two
modes of operation; continuous and discontinuous.
Continuous or discontinuous refer to the inductor
current. If current is continuously flowing through the
inductor throughout the switching cycle, it is in
continuous operation. If the inductor current drops to
zero during the off time, it is in discontinuous operation.
Critically continuous is the point where any decrease in
output current will cause it to enter discontinuous
operation. The critically continuous load current can be
calculated as follows;
Continuous or discontinuous operation determines how
we calculate peak inductor current.
Continuous Operation
Figure 2 illustrates the switch voltage and inductor
current during continuous operation.
March 2009
Figure 1. Example of Non-synchronous Buck Converter
I
OUT
Figure 2. Continuous Operation
=
⎡
⎢
⎢
⎣
V
OUT
fsw
−
×
2
V
×
OUT
V
IN
L
2
⎤
⎥
⎥
⎦
10
The output voltage is regulated by pulse width
modulating (PWM) the switch voltage to the average
required output voltage. The switching can be broken up
into two cycles; On and Off.
During the On-Time, Figure 3 illustrates the high side
switch is turned on, current flows from the input supply
through the inductor and to the output. The inductor
current is charged at the rate;
To determine the total on-time, or time at which the
inductor charges, the duty cycle needs to be calculated.
The duty cycle can be calculated as;
and the On time is;
Therefore, peak to peak ripple current is;
Since the average peak to peak current is equal to the
load current. The actual peak (or highest current the
inductor will see in a steady-state condition) is equal to
the output current plus ½ the peak-to-peak current.
D =
T
I
(
V
pk
ON
IN
−
V
pk
−
=
V
L
OUT
V
IN
fsw
=
D
OUT
(
V
Figure 3. On-Time
IN
)
−
V
fsw
OUT
×
)
L
×
V
V
OUT
IN
M9999-030209-D
MIC4742