Datasheet

LTM8052/LTM8052A
16
8052fc
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Maximum Output Current Adjust
To adjust the regulated load current, an analog voltage
is applied to the CTL_I pin or CTL_T pins. Varying the
voltage between 0V and 1.5V adjusts the maximum
current between the minimum and the maximum current,
typically 5.6A positive and 7.7A negative. Graphs of the
output current vs CTL_I and CTL_T voltages are given
in the Typical Performance Characteristics section. The
LTM8052/LTM8052A provides a 2V reference voltage for
conveniently applying resistive dividers to set the current
limit. The current limit can be set as shown in Figure 1
with the following equation:
I
MAX
=
7.467 • R2
R1+R2
Amps Positive Current
( )
I
MAX
= −
7.467 • R2
R1+R2
+ 2.1Amps Negative Current
( )
applicaTions inForMaTion
Figure 1. Setting the Output Current Limit
resistor network with a temperature dependant resistance
(Figure2). When the board/load temperature rises, the
CTL_T voltage will decrease. To reduce the regulated
current, the CTL_T voltage must be lower than the voltage
at the CTL_I pin. V
CTL_T
may be higher than V
CTL_I
, but
then it will have no effect.
Figure 2. Load Current Derating vs
Temperature Using NTC Resistor
LTM8052
V
REF
R1
2V
R2
8052 F01
CTL_I OR CTL_T
LTM8052
V
REF
R
NTC
R
X
R
V
R
V
R1
R2
(OPTION A TO D)
8052 F02
CTL_T
B
R
NTC
A
R
NTC
R
X
D
R
NTC
C
Figure 3. Voltage Regulation and Overvoltage Protection
Feedback Connections
LTM8052
V
OUT
V
OUT
R
ADJ
8052 F03
ADJ
Load Current Derating Using the CTL_T Pin
In high current applications, derating the maximum current
based on operating temperature may prevent damage
to the load. In addition, many applications have thermal
limitations that will require the regulated current to be
reduced based on the load and/or board temperature. To
achieve this, the LTM8052/LTM8052A uses the CTL_T
pin to reduce the effective regulated current in the load.
While CTL_I programs the regulated current in the load,
CTL_T can be configured to reduce this regulated current
based on the analog voltage at the CTL_T pin. The load/
board temperature derating is programmed using a
Voltage Regulation and Output Overvoltage Protection
The LTM8052/LTM8052A uses the ADJ pin to regulate the
output voltage and to provide a high speed overvoltage
lockout to avoid high voltage conditions. If the output
voltage exceeds 125% of the regulated voltage level (1.5V
at the ADJ pin), the LTM8052/LTM8052A terminates
switching and shuts down switching for a brief time before
restarting. The regulated output voltage must be greater
than 1.19V and is set by the equation:
V
OUT
= 1.19V 1+
10k
R
ADJ
⎛
⎝
⎜
⎞
⎠
⎟
where R
ADJ
is shown in Figure 3.