Datasheet
LTC3880/LTC3880-1
59
3880fc
For more information www.linear.com/LTC3880
P
MAIN
=
3.3V
20V
• 17.39
( )
2
• 1+ 0.005
( )
50°C – 25°C
( )
• 0.006Ω+ 20V
( )
2
8.695A
( )
•
1
5– 2.3
+
1
2.3
75pF
( )
500kHz
( )
= 0.386W
The loss in the bottom side MOSFET is:
P
SYNC
=
20V – 3.3V
( )
20V
• 17.39A
( )
2
•
1+ 0.005
( )
50°C – 25°C
( )
•0.001Ω
= 0.312W
Both MOSFETS have I
2
R losses while the P
MAIN
equation
includes an additional term for transition losses, which
are highest at high input voltages.
C
IN
is chosen for an RMS current rating of:
C
IN
Required I
RMS
=
17.39
20
3.3
( )
• 20 – 3.3
( )
1/2
= 6.5A
APPLICATIONS INFORMATION
V
IN
V
IN
V
DD33
V
DD25
SDA
1µF
1µF
VGS MAX ON THE TP0101K IS 8V IF V
IN
> 16V
CHANGE THE RESISTOR DIVIDER ON THE PFET GATE
1µF
1µF
3880 F28
10k
100k
TP0101K
ISOLATED 3.3V
SDA
SCL
TP0101K
100k
LTC
CONTROLLER
HEADER
TO LTC DC1613
USB TO I
2
C/SMBus/PMBus
CONTROLLER
SCL
WP SGND
LTC3880
V
IN
V
DD33
SDA
SCL
WP SGND
LTC3880
10k
V
DD25
Figure 28. LTC Controller Connection
at temperature assuming only channel 0 or 1 is on. C
OUT
is chosen with an ESR of 0.006Ω for low output ripple.
The output ripple in continuous mode will be highest at
the maximum input voltage. The output voltage ripple
due to ESR is
V
ORIPPLE
= R(∆I
L
) = 0.006Ω • 5.5A = 33mV.
CONNECTING THE USB TO THE I
2
C/SMBus/PMBus
CONTROLLER TO THE LTC3880 IN SYSTEM
The LTC USB to I
2
C/SMBus/PMBus controller can be
interfaced to the LTC3880 on the user’s board for program-
ming, telemetry and system debug. The controller, when
used in conjunction with L
TpowerPlay
, provides a powerful
way to debug an entire power system. Faults are quickly
diagnosed using telemetry, fault status registers and the
fault log. The final configuration can be quickly developed
and stored to the LTC3880 EEPROM.
Figure 28 illustrates the application schematic for pow-
ering, programming and communication with one or
more LTC3880s via the L
TC I
2
C/SMBus/PMBus controller
regardless of whether or not system power is present. If