ltc3853euj Linear Technology Corporation, ltc3853euj Datasheet - Page 19

• Manufacturer Part Number: ltc3853euj
• Description: Triple Output, Multiphase Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
is used to match the shifted common mode voltage. The
top two current sources are of the same amplitude. In the
coincident mode, the TK/SS voltage is substantially higher
than 0.8V at steady state and effectively turns off D1. D2
and D3 will therefore conduct the same current and offer
tight matching between V
0.8V reference. In the ratiometric mode, however, TK/SS
equals 0.8V at steady state. D1 will divert part of the bias
current to make V
Figure 7. Equivalent Input Circuit of Error Amplifi er
TK/SS2
V
0.8V
FB2
D1
TK/SS2
V
FB2
OUT1
PIN
TO
(5a) Coincident Tracking
slightly lower than 0.8V.
I
D2
(6a) Coincident Tracking Setup
TIME
FB2
R3
R4
I
D3
and the internal precision
+
–
R1
R2
EA2
Figure 5. Two Different Modes of Output Voltage Tracking
Figure 6. Setup for Coincident and Ratiometric Tracking
TO
V
PIN
FB1
3853 F05a
V
PIN
V
V
FB2
TO
OUT1
OUT2
3853 F07
R3
R4
V
OUT2
Although this error is minimized by the exponential I-V
characteristic of the diode, it does impose a fi nite amount
of output voltage deviation. Furthermore, when the master
channel’s output experiences dynamic excursion (under
load transient, for example), the slave channel output will
be affected as well. For better output regulation, use the
coincident tracking mode instead of ratiometric.
INTV
The LTC3853 features an NPN linear regulator that supplies
power to INTV
gate drivers and much of the LTC3853’s internal circuitry.
The linear regualtor regulates the voltage at the INTV
to 5V when V
INTV
needed power when its voltage is higher than 4.7V. Each
of these can supply a peak current of 150mA and must
be bypassed to ground with a minimum of 1μF ceramic
capacitor or low ESR electrolytic capacitor. No matter
what type of bulk capacitor is used, an additional 0.1μF
V
TK/SS2
OUT1
CC
CC
PIN
TO
through a P-channel MOSFET and can supply the
Regulators and EXTV
(6b) Ratiometric Tracking Setup
IN
R1
R2
CC
is greater than 6.5V. EXTV
TO
V
PIN
from the V
FB1
(5b) Ratiometric Tracking
V
PIN
FB2
TO
TIME
IN
CC
supply. INTV
R3
R4
3853 F06
V
OUT2
LTC3853
3853 F05b
V
V
CC
CC
OUT1
OUT2
connects to
powers the
19
CC
3853f
pin