LMZ23605TZ National Semiconductor, LMZ23605TZ Datasheet - Page 14

• Manufacturer Part Number: LMZ23605TZ
• Description: POWER MODULE, 36V, 5A, 7TO-PMOD
• Manufacturer: National Semiconductor

Specifications of LMZ23605TZ

• Primary Input Voltage: 36V
• No. Of Outputs: 1
• Output Voltage: 6V
• Output Current: 5A
• Voltage Regulator Case Style: TO-PMOD
• No. Of Pins: 7
• Operating Temperature Range: -40°C To +125°C
• Rohs Compliant: Yes

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Block Diagram
General Description
The LMZ23605 SIMPLE SWITCHER© power module is an
easy-to-use step-down DC-DC solution capable of driving up
to 5A load. The LMZ23605 is available in an innovative pack-
age that enhances thermal performance and allows for hand
or machine soldering.
The LMZ23605 can accept an input voltage rail between 6V
and 36V and deliver an adjustable and highly accurate output
voltage as low as 0.8V. The LMZ23605 only requires two ex-
ternal resistors and three external capacitors to complete the
power solution. The LMZ23605 is a reliable and robust design
with the following protection features: thermal shutdown, pro-
grammable input under-voltage lockout, output over-voltage
protection, short-circuit protection, output current limit, and
allows startup into a pre-biased output. The sync input allows
synchronization over the 650 to 950 kHz switching frequency
range.
Design Steps for the LMZ23605
Application
The LMZ23605 is fully supported by Webench® which offers:
component selection, electrical and thermal simulations. Ad-
ditionally there are both evaluation and demonstration boards
that may be used as a starting point for design. The following
list of steps can be used to manually design the LMZ23605
application.
All references to values refer to the typical applications
schematic figure 4.
• Select minimum operating V
• Program V
• Select C
• Select C
• Determine module power dissipation
• Layout PCB for required thermal performance
O
IN
O
with resistor divider selection
IN
with enable divider resistors
14
ENABLE DIVIDER, R
Internal to the module is a 2 mega ohm pull-up resistor con-
nected from V
precision under voltage lock out (UVLO), the Enable input
may be left open circuit and the internal resistor will always
enable the module. In such case, the internal UVLO occurs
typically at 4.3V (V
In applications with separate supervisory circuits Enable can
be directly interfaced to a logic source. In the case of se-
quencing supplies, the divider is connected to a rail that
becomes active earlier in the power-up cycle than the
LMZ23605 output rail.
Enable provides a precise 1.279V threshold to allow direct
logic drive or connection to a voltage divider from a higher
enable voltage such as V
switched offset current allowing programmable hysteresis.
See Figure 1.
The function of the enable divider is to allow the designer to
choose an input voltage below which the circuit will be dis-
abled. This implements the feature of programmable UVLO.
The two resistors should be chosen based on the following
ratio:
R
The LMZ23605 typical application shows 12.7kΩ for R
42.2kΩ for R
this divider presents 8.33V to the input when the divider is
raised to 36V which would exceed the recommended 5.5V
limit for Enable. A midpoint 5.1V Zener clamp is applied to
allow the application to cover the full 6V to 36V range of op-
eration. The zener clamp is not required if the target applica-
tion prohibits the maximum Enable input voltage from being
exceeded.
Additional enable voltage hysteresis can be added with the
inclusion of R
R
from the design.
Rising threshold can be calculated as follows:
V
EN
ENT
ENB
(rising) = 1.279 ( 1 + (R
/ R
such that R
ENB
= (V
ENT
ENH
IN
resulting in a rising UVLO of 5.46V. Note that
IN UVLO
ENH
. It is possible to select values for R
to Enable. For applications not requiring
IN
rising).
is a value of zero allowing it to be omitted
ENT
/ 1.279V) – 1 (1)
IN
, R
. Additionally there is 21 μA(typ) of
ENT
ENB
|| 2 meg)/ R
AND R
ENH
ENB
SELECTION
)
ENT
ENB
30116910
and
and