zl2106 Intersil Corporation, zl2106 Datasheet - Page 22

• Manufacturer Part Number: zl2106
• Description: 6a Digital-dc Synchronous Step-down Dc-dc Converter
• Manufacturer: Intersil Corporation

6.8.7 C
This capacitor is used to both stabilize and provide
noise filtering for the 7 V reference supply. It should
be between 4.7 and 10 µF, should use a semi-stable
X5R or X7R dielectric ceramic capacitor with a low
ESR (less than 10 mΩ) and should have a rating of 10
V or more. Because the current for the bootstrap
supply is drawn from this capacitor, C
sized at least 10X the value of C
C
excessively during a C
6.8.8 C
This capacitor is used to both stabilize and provide
noise filtering for the analog 5 V reference supply. It
should be between 2.2 and 10 µF, should use a semi-
stable X5R or X7R dielectric ceramic capacitor with a
low ESR (less than 10 mΩ) and should have a rating of
6.3 V or more.
6.8.9 Thermal Considerations
In typical applications, the ZL2106’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 ZL2106’s
maximum junction temperature is not exceeded.
The ZL2106 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 θ
thermal resistance for the ZL2106 package.
P
Q
B
=
does not cause the voltage on it to droop
(
I
LOAD
VR
VRA
Q
PCB
) as follows:
Selection
2
Selection
)
[
is the expected maximum printed circuit
(
R
T
DS
j
max
(
ON
)
22
QH
=
B
T
)
( )
recharge pulse.
PCB
D
+
JC
+
(
R
(
P
is the junction-to-case
DS
Q
B
(
ON
×
so that a discharged
θ
)
QL
JC
)
(
)
1
−
VR
D
should be
)
]
ZL2106
6.9 Current Sensing and Current Limit Threshold
The ZL2106 incorporates a patented “lossless” current
sensing method across the internal low-side MOSFET
that is independent of
temperature. The default value for the gain, which does
not represent a
internal current sensing circuit can be modified by the
IOUT_CAL_GAIN
commands.
The design should include a current limiting
mechanism to protect the power supply from damage
and prevent excessive current from being drawn from
the input supply in the event that the output is shorted
to ground or an overload condition is imposed on the
output. Current limiting is accomplished by sensing the
current through the circuit during a portion of the duty
cycle. The current limit threshold is set to 9 A by
default. The current limit threshold can set to a custom
value via the I
Application Note AN33 for further details.
Additionally, the ZL2106 gives the power supply
designer several choices for the fault response during
over or under current conditions. The user can select
the number of violations allowed before declaring a
fault, a blanking time and the action taken when a fault
is detected. The blanking time represents the time
when no current measurement is taken. This is to avoid
taking a reading just after a current load step (less
accurate due to potential ringing). Please refer to
Application note AN33 for further details.
Selection
2
R
C/SMBus interface. Please refer to
DS(ON)
and
value, and the offset of the
Data Sheet Revision 2/19/2009
R
DS(ON)
IOUT_CAL_OFFSET
variations, including
www.intersil.com