LTM4641
APPLICATIONS INFORMATION—POWER SUPPLY FEATURES
8.0
It is best to avoid operation in dropout scenarios, because
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
the control loop will rail COMP high to command M
TOP
at highest possible duty cycle. If input voltage “snaps
upwards” at a sufficiently high slew rate when COMP has
railed, the control loop may be unable provide satisfactory
line rejection.
SeeFigure11tosettheUVLOfallingresponseofLTM4641
above the computed V
voltage; this will inhibit
. Input voltage
IN(DROPOUT)
IN(DROPOUT)
switching action for V < V
IN
ripple, and any line sag between the input source supply
and the V pins—and voltage drop across the power
3
3.5
OUTPUT VOLTAGE SETTING (V)
10A OUTPUT, DRV BIASED FROM INTV (5.3V
4
4.5
5
5.5
6
4641 F04
INH
interrupt MOSFET, MSP, if used—must be taken into ac-
count by the system designer.
)
CC
CC
NOM
10A OUTPUT, DRV BIASED TO 5.3V BY EXTERNAL SUPPLY
NO LOAD, DRV ≥ 4.2V(UVLO RISING) AND 3.5V
CC
(UVLO FALLING)
CC
Setting the Output Voltage; the Differential Reꢃote
Sense Aꢃplifier
Figure 4. Line Dropout Voltage vs Output Voltage at No
Load and Full Load. Figure 45, Figure 46 and Figure 47
Circuit Applications. RfSET = Open and RSET1A, RSET1B
,
Abuilt-indifferentialremote-senseamplifierenablespreci-
sion regulation at the point-of-load (POL), compensating
for any voltage drops in the system’s output distribution
path: the total variation of LTM4641’s output DC voltage
over line, load, and temperature is better than 1.5%.
RSET2 Values Setting VOUT for Regulation at or Above 3V
GiventhatthePFMcontrolschemeincreasesswitching
frequency (to as high as f ) to maintain regulation
MAX
during a transient load step-up, the design guidance
is: set the steady-state operating frequency f to be
SW
The basic feedback connection between the POL and the
module’s feedback sense pins is shown in Figure 5.
less than f
. Furthermore, when the LTM4641 is
in dropout operation, the switching frequency of the
MAX
converter is f
.
MAX
C
, C : FEEDFORWARD CAPACITORS YEILD IMPROVED TRANSIENT
FFA FFB
RESPONSE WHEN FILTERING V
WITH ONLY MLCC OUTPUT CAPACITORS
OUT
(C
)
OUT(MLCC)
V
OUT
+
V
OUT
+
LTM4641
C
FFA
C
C
OUT(MLCC)
OUT(BULK)
ICT
TEST
POINT
V
ORB
R
8.2k
8.2k V
SET1A
V
+
FB
OSNS
TO ERROR
+
AMPLIFIER
R
LOAD
SET2
8.2k
R
SET1B
–
–
–
V
OSNS
8.2k
4641 F05
C
ICT
TEST
POINT
FFB
V
ORB
TRUE DIFFERENTIAL REMOTE
SENSE AMPLIFIER
SGND
GND
ROUTE FEEDBACK SIGNAL AS
A DIFFERENTIAL PAIR (OR
TWISTED PAIR IF USING WIRES).
SANDWICH BETWEEN GROUND
PLACE ALL
FEEDBACK
COMPONENTS
LOCAL TO THE
LTM4641
PLANES TO FORM A PROTECTIVE SHIELD
GUARDING AGAINST STRAY NOISE
SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP
MODULE SGND ROUTES/PLANES SEPARATE FROM GND
ON MOTHERBOARD
Figure 5. Basic Feedback Reꢃote Sense Connections and Techniques; Setting the Output Voltage
4641f
21
Linear [ Linear ]
