A5974ADTR STMicroelectronics, A5974ADTR Datasheet - Page 36

• Manufacturer Part Number: A5974ADTR
• Description: IC REG SW STEP-DOWN 2A 8SOIC
• Manufacturer: STMicroelectronics
• Series: -r
• Type: Step-Down (Buck), PWMr

Specifications of A5974ADTR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.235 V ~ 35 V
• Current - Output: 2A
• Frequency - Switching: 500kHz
• Voltage - Input: 4 V ~ 36 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-11423-2

Application information
8.6
36/49
Positive buck-boost regulator
The device can be used to implement a step-up/down converter with a positive output
voltage.
The output voltage is given by:
Equation 33
where the ideal duty cycle D for the buck-boost converter is:
Equation 34
However, due to power losses in the passive elements, the real duty cycle is always higher
than this. The real value (that can be measured in the application) should be used in the
following formulas.
The peak current flowing in the embedded switch is:
Equation 35
while its average current is equal to:
Equation 36
This is due to the fact that the current flowing through the internal power switch is delivered
to the output only during the OFF phase.
The switch peak current must be lower than the minimum current limit of the overcurrent
protection (see
DC current of the device.
As a consequence, the maximum output current is:
Equation 37
where I
The current capability is reduced by the term (1-D) and so, for example, with a duty cycle of
0.5, and considering an average current through the switch of 2 A, the maximum output
current deliverable to the load is 1 A.
Figure 25
5 V input.
SW MAX
below shows the circuit schematic of this topology for a 12 V output voltage and
represents the rated current of the device.
Table 4
for details) while the average current must be lower than the rated
I
SW
=
Doc ID 018762 Rev 1
I
-------------- -
1 D
LOAD
I
–
OUT MAX
V
+
D
OUT
I
------------------- -
I
RIPPLE
SW
=
≅
2
----------------------------- -
V
=
I
SW MAX
=
IN
V
V
I
-------------- -
IN
+
1 D
LOAD
OUT
=
V
–
⋅
OUT
I
-------------- -
------------ -
1 D
1 D
LOAD
⋅
D
–
–
(
1 D
–
+
---------- -
2 L
)
V
⋅
IN
⋅
---------
f
SW
D
A5974AD