ZL2105ALNF Intersil, ZL2105ALNF Datasheet - Page 21

• Manufacturer Part Number: ZL2105ALNF
• Description: IC DGTL DC-DC CTRLR 3A 36QFN
• Manufacturer: Intersil
• Type: Step-Down (Buck), PWM - Voltage Moder

Specifications of ZL2105ALNF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 V ~ 5.5 V
• Current - Output: 3A
• Frequency - Switching: 200kHz ~ 2MHz
• Voltage - Input: 4.5 V ~ 14 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

After a capacitor has been selected, the resulting output
voltage ripple can be calculated using the following
equation:
Because each part of this equation was made to be less
than or equal to half of the allowed output ripple
voltage, the V
maximum output ripple.
For more information on the performance of the power
supply in response to a transient load, refer to
Application Note AN2011.
5.9.4 Input Capacitor
It is highly recommended that dedicated input
capacitors be used in any point-of-load design, even
when the supply is powered from a heavily filtered 5 or
12 V “bulk” supply from an off-line power supply.
This is because of the high RMS ripple current that is
drawn by the buck converter topology. This ripple
(I
equation:
Without capacitive filtering near the power supply
circuit, this current would flow through the supply bus
and return planes, coupling noise into other system
circuitry. The input capacitors should be rated at 1.4X
the
overheating of the capacitors due to the high ripple
current, which can cause premature failure. Ceramic
capacitors with X7R or X5R dielectric with low ESR
and 1.1X the maximum expected input voltage are
recommended.
5.9.5 Bootstrap Capacitor Selection
The high-side driver boost circuit utilizes an internal
Schottky diode (D
capacitor (C
high-side MOSFET driver. C
ceramic type rated for at least 6.3V.
5.9.6 C
This capacitor is used to both stabilize and provide
noise filtering for the 2.5 V internal power supply. It
should be between 4.7 and 10 µF, and should use a
semi-stable X5R or X7R dielectric ceramic with a low
(less than 10 m ) ESR, and should have a rating of 4
V or more.
CINrms
ripple
) can be determined from the following
V25
V
orip
Selection
I
B
CINrms
) to supply sufficient gate drive for the
current
orip
I
opp
should be less than the desired
21
B
I
) and an external bootstrap
OUT
ESR
calculated
8
D
B
should be a 47 nF
f
1 ( D
sw
I
above
opp
C
)
OUT
to
avoid
ZL2105
5.9.7 C
This capacitor is used to both stabilize and provide
noise filtering for the 5 V reference supply (V
should be between 4.7 and 10 µF, and be a semi-stable
X5R or X7R dielectric ceramic capacitor with a low
ESR less than 10 m , and be rated 6.3 V or more.
Because the current for the bootstrap supply is drawn
from this capacitor, C
the value of C
the voltage on it to droop excessively during a C
recharge pulse.
5.9.8 C
This capacitor is used to both stabilize and provide
noise filtering for the analog 5 V reference supply
(V
stable X5R or X7R dielectric ceramic capacitor with a
low ESR less than 10 m , and be rated 6.3 V or more.
5.9.9 R
A 91Ω resistor should be placed between VR and VRA
to reduce noise and help the stability of the VR and
VRA regulators over all operating conditions.
5.9.10 Thermal Considerations
In typical applications, the ZL2105’s high efficiency
will limit the internal power dissipation inside the
package. However, in applications that require a high
ambient operating temperature the user must perform
some thermal analysis to ensure that the ZL2105’s
maximum junction temperature is not violated.
The ZL2105 has a maximum junction temperature
limit of 125°C, and the internal over temperature
limiting circuitry will force the device to shut down if
its junction temperature exceeds this threshold. In
order to calculate the maximum junction temperature,
the user must first calculate the power dissipated inside
the IC (P
The maximum operating junction temperature can then
be calculated using the following equation:
Where T
board temperature, and
thermal resistance for the ZL2105 package.
RA
P
Q
). It should be between 2.2 and 10 µF, be a semi-
= (I
VR
VRA
VR
Q
PCB
) as follows:
LOAD
Selection
Selection
Selection
is the expected maximum printed circuit
B
2
)[R
T
so that a discharged C
j
max
DS(ON)QH
VR
T
PCB
should be sized at least 10X
)(DC)+(R
JC
P
is the junction-to-case
Q
DS(ON)QL
θ
JC
B
March 30, 2011
does not cause
)(1-DC)]
FN6851.2
R
). It
B