LTM4600 LINER [Linear Technology], LTM4600 Datasheet - Page 10

• Manufacturer Part Number: LTM4600
• Description: 10A High Effi ciency DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTM4600
the module input pins in the PCB layout to minimize the
trace inductance and high frequency AC noise.
Output Capacitors
The LTM4600 is designed for low output voltage ripple.
The bulk output capacitors C
effective series resistance (ESR) to meet the output voltage
ripple and transient requirements. C
tantalum capacitor, low ESR polymer capacitor or ceramic
capacitor (X5R or X7R). The typical capacitance is 200µF
if all ceramic output capacitors are used. The internally
optimized loop compensation provides suffi cient stability
margin for all ceramic capacitors applications. Additional
output fi ltering may be required by the system designer,
if further reduction of output ripple or dynamic transient
spike is required. Refer to Table 2 for an output capaci-
tance matrix for each output voltage Droop, peak to peak
deviation and recovery time during a 5A/µs transient with
a specifi c output capacitance.
Fault Conditions: Current Limit and Over current
Foldback
The LTM4600 has a current mode controller, which inher-
ently limits the cycle-by-cycle inductor current not only in
steady state operation, but also in transient.
To further limit current in the event of an over load condi-
tion, the LTM4600 provides foldback current limiting. If the
output voltage falls by more than 50%, then the maximum
output current is progressively lowered to about one sixth
of its full current limit value.
10
U
U
OUT
is chosen with low enough
W
OUT
can be low ESR
U
Soft-Start and Latchoff with the RUN/SS pin
The RUN/SS pin provides a means to shut down the
LTM4600 as well as a timer for soft-start and over-cur-
rent latchoff. Pulling the RUN/SS pin below 0.8V puts
the LTM4600 into a low quiescent current shutdown (I
≤ 75µA). Releasing the pin allows an internal 1.2µA cur-
rent source to charge up the timing capacitor CSS. Inside
LTM4600, there is an internal 1000pF capacitor from
RUN/SS pin to ground. If RUN/SS pin has an external
capacitor CSS_EXT to ground, the delay before starting
is about:
When the voltage on RUN/SS pin reaches 1.5V, the
LTM4600 internal switches are operating with a clamping
of the maximum output inductor current limited by the
RUN/SS pin total soft-start capacitance. As the RUN/SS pin
voltage rises to 3V, the soft-start clamping of the inductor
current is released.
V
There are restrictions in the maximum V
down ratio that can be achieved for a given input voltage.
These contraints are shown in the Typical Performance
Characteristics curves labeled “V
Ratio”. Note that additional thermal de-rating may apply.
See the Thermal Considerations and Output Current De-
Rating sections of this data sheet.
IN
t
DELAY
to V
OUT
=
Stepdown Ratios
1 2
1 5
.
.
µ
V
A
•(
C
SS EXT
_
+
1000
IN
to V
pF
)
IN
OUT
to V
Stepdown
OUT
step
4600fa
Q