LTM4641 Datasheet, PDF (21/64 Pages) Linear Technology – 38V, 10A DC/DC Module Regulator with Advanced Input and Load Protection

LTM4641
APPLICATIONS INFORMATION—POWER SUPPLY FEATURES
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
3
3.5 4 4.5 5 5.5 6
OUTPUT VOLTAGE SETTING (V) 4641 F04
10A OUTPUT, DRV_CC BIASED FROM INTV_CC (5.3V_NOM)
10A OUTPUT, DRV_CC BIASED TO 5.3V BY EXTERNAL SUPPLY
NO LOAD, DRV_CC ≥ 4.2V(UVLO RISING) AND 3.5V
(UVLO FALLING)
Figure 4. Line Dropout Voltage vs Output Voltage at No
Load and Full Load. Figure 45, Figure 46 and Figure 47
Circuit Applications. R_fSET = Open and R_SET1A, R_SET1B,
R_SET2 Values Setting V_OUT for Regulation at or Above 3V
Given that the PFM control scheme increases switching
frequency (to as high as f_MAX) to maintain regulation
during a transient load step-up, the design guidance
is: set the steady-state operating frequency f_SW to be
less than f_MAX. Furthermore, when the LTM4641 is
in dropout operation, the switching frequency of the
converter is f_MAX.
It is best to avoid operation in dropout scenarios, because
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.
See Figure 11 to set the UVLO falling response of LTM4641
above the computed V_IN(DROPOUT) voltage; this will inhibit
switching action for V_IN < V_IN(DROPOUT). Input voltage
ripple, and any line sag between the input source supply
and the V_INH pins—and voltage drop across the power
interrupt MOSFET, MSP, if used—must be taken into ac-
count by the system designer.
Setting the Output Voltage; the Differential Remote
Sense Amplifier
A built-in differential remote-sense amplifier enables preci-
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%.
The basic feedback connection between the POL and the
module’s feedback sense pins is shown in Figure 5.
LTM4641
V_OUT
V_FB
TO ERROR
AMPLIFIER
V_ORB+
8.2k
8.2k V_OSNS+
8.2k
8.2k
TRUE DIFFERENTIAL REMOTE
SENSE AMPLIFIER
V_OSNS–
V_ORB–
SGND
GND
SGND CONNECTS TO GND INTERNAL TO MODULE. KEEP
MODULE SGND ROUTES/PLANES SEPARATE FROM GND
ON MOTHERBOARD
C_FFA, C_FFB: FEEDFORWARD CAPACITORS YEILD IMPROVED TRANSIENT
RESPONSE WHEN FILTERING V_OUT WITH ONLY MLCC OUTPUT CAPACITORS
(C_OUT(MLCC))
ICT
TEST
POINT
C_FFA
R_SET1A
+
C_OUT(BULK)
C_OUT(MLCC)
V_OUT
R_SET2
R_SET1B
LOAD
ICT
C_FFB
TEST
POINT
PLACE ALL
FEEDBACK
COMPONENTS
LOCAL TO THE
LTM4641
4641 F05
ROUTE FEEDBACK SIGNAL AS
A DIFFERENTIAL PAIR (OR
TWISTED PAIR IF USING WIRES).
SANDWICH BETWEEN GROUND
PLANES TO FORM A PROTECTIVE SHIELD
GUARDING AGAINST STRAY NOISE
Figure 5. Basic Feedback Remote Sense Connections and Techniques; Setting the Output Voltage
4641f
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