IRPP3624-12A International Rectifier, IRPP3624-12A Datasheet - Page 9

• Manufacturer Part Number: IRPP3624-12A
• Description: KIT REF DES 12A 1PH SYNC BUCK
• Manufacturer: International Rectifier
• Series: POWIR+™r

Specifications of IRPP3624-12A

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.8V
• Current - Output: 12A
• Voltage - Input: 10.8 ~ 13.2V
• Regulator Topology: Buck
• Frequency - Switching: 600kHz
• Board Type: Fully Populated
• Utilized Ic / Part: IR3624, IRF7823, IRF7832Z
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

For a given start-up time, the soft-start capacitor
(nF) can be estimated as:
Soft-Start
The IR3624 has programmable soft-start to
control the output voltage rise and limit the inrush
current during start-up.
To
sequence initiates when Vcc and Vc rise above
their threshold and generate the Power On
Ready (POR) signal. The soft-start function
operates by sourcing current to charge an
external capacitor to about 3V.
Initially, the soft-start function clamps the output
of error amplifier by injecting a current (40uA)
into the Fb pin and generates a voltage about
0.96V (40ux24K) across the negative input of
error amplifier (see figure 5).
The magnitude of the injected current is inversely
proportional to the voltage at the soft-start pin. As
the soft-start voltage ramps up, the injected
current decreases linearly and so does the
voltage at negative input of error amplifier.
When the soft-start capacitor is around 1V, the
voltage at the positive input of the error amplifier
is approximately 0.6V.
The output of error amplifier will start increasing
and generating the first PWM signal. As the soft-
start capacitor voltage continues to go up, the
current flowing into the Fb pin will keep
decreasing.
The feedback voltage increases linearly as the
soft start voltage ramps up. When soft-start
voltage is around 2V the output voltage is
reached the steady state and the injected current
is zero.
Figure 6 shows the theoretical operational
waveforms during soft-start.
The output voltage start-up time is the time
period
increases from 1V to 2V.
The start-up time will be dependent on the size of
the external soft-start capacitor and can be
estimate by:
ensure
C
when
SS
20
≅
20
µA
correct
µ
∗
A
soft-start
T
C
*
start
ss
T
start
=
2
(
start-up,
ms
V
−
)
1
V
capacitor
--(
) 1
the
soft-start
voltage
Voltage at negative input
SS/SD
Comp
Voltage at Fb pin
Output of UVLO
Current flowing
0.6V
Fig. 6: Theoretical operation waveforms
Fig. 5: Soft-Start circuit for IR3624
Fb
of Error Amp
POR
into Fb pin
Soft-Start
20uA
Voltage
POR
≅ 0.96V
during soft-start
24K
24K
40uA
0V
0V
IR3624MPBF
3V
40uA
Error Amp
0uA
0.6V
0.6V
≅ 1V
≅ 2V
3V
9