LTM4641
APPLICATIONS INFORMATION—EMI PERFORMANCE
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
–10
–10
30
814.8
1010
30
814.8
1010
226.2
422.4
618.6
FREQUENCY (MHz)
226.2
422.4
618.6
FREQUENCY (MHz)
4641 F15
4641 F16
Figure 15. Radiated Eꢃissions Scan of LTꢁ4641 Producing
2.5VOUT at 10A, froꢃ 24VIN. DC1543 Hardware with No Snubber
Network Installed. fSW = 335kHz. CIN(BULK) = 2 × 100μF,
CIN(ꢁLCC) = 4 × 10μF X7R + 2 × 4.7μF X7R. ꢁeasured in a 10
ꢁeter Chaꢃber. Quasi-Peak Detect ꢁethod
Figure 16. Radiated Eꢃissions Scan of LTꢁ4641 Producing
2.5VOUT at 10A, froꢃ 24VIN. DC1543 Hardware with Ad Hoc
Snubber Network Installed Directly Between SW Probe Point
and GND, CSW = 2.2nF, RSW = 2.2Ω (1W Rated). fSW = 335kHz.
CIN(BULK) = 2 × 100μF, CIN(ꢁLCC) = 4 × 10μF X7R + 2 × 4.7μF
X7R. ꢁeasured in a 10 ꢁeter Chaꢃber. Quasi-Peak Detect
ꢁethod
APPLICATIONS INFORMATION—MULTIMODULE PARALLEL OPERATION
The LTM4641 device is a current mode controlled device,
so paralleled modules demonstrate good current sharing.
This helps equilibrate power losses and reduce thermal
differences between paralleled modules.
For loads that demand more than 10A of load current,
multiple LTM4641 devices can be paralleled to provide
more output current. See Figures 56 and 66 for examples
of four or two LTM4641 operating in parallel to deliver 40A
or 20A load current, respectively, while providing robust
output overvoltage protection.
The following pins should be connected to all correspond-
ing LTM4641s’ pin(s) when paralleling LTM4641 outputs:
The LTM4641 does not support phase interleaving or
clock synchronization, and therefore no ripple-current
cancelationeffectandnomultiplicationeffectontheoutput
voltage ripple frequency occurs when modules are paral-
leled. Therefore, it should be anticipated that paralleled
applicationscontainbeatfrequenciesintheoutputvoltage
waveform and are contained in the reflected input current.
For example, if one module operates freely at 400kHz
while its paralleled sibling operates freely at 410kHz, the
conducted EMI content will include not only the switching
fundamentalfrequencies—400kHzand410kHz—butalso
a beat frequency at the difference of those frequencies,
10kHz. The system designer may be motivated to apply an
external LC (or “pi”) filter on the input to each LTM4641
if attenuation of the reflected input currents is desired.
•ꢀ V
OUT
•ꢀ GND
•ꢀ V
•ꢀ V
INH
INL
•ꢀ HYSTꢀ(toꢀsynchronizeꢀstart-upꢀandꢀshutdown)
•ꢀ TRACK/SS
•ꢀ COMPꢀ(toꢀaccomplishꢀcurrentꢀsharing)
•ꢀ CROWBARꢀ (toꢀ synchronizeꢀ outputꢀ overvoltageꢀ
response)
•ꢀ LATCH (to reset all modules after a latchoff event)
•ꢀ V , if MSP is used
ING
4641f
36
Linear [ Linear ]
