ltc3827ig-1 Linear Technology Corporation, ltc3827ig-1 Datasheet - Page 17

• Manufacturer Part Number: ltc3827ig-1
• Description: Low Iq, Dual, 2-phase Synchronous Step-down Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Alternatively, the TRACK/SS pin can be used to track two
(or more) supplies during start-up, as shown qualitatively
in Figures 6a and 6b. To do this, a resistor divider should
be connected from the master supply (V
SS pin of the slave supply (V
During start-up V
by the resistor divider:
For coincident tracking (V
R
R
V
A
B
V
OUT
X
= R
= R
=
TRACKA
TRACKB
Figure 6. Two Different Modes of Output
Voltage Tracking
R
TRACKA
R
(6b) Ratiometric Tracking
OUT
A
(6a) Coincident Tracking
U
will track V
•
TIME
TIME
R
U
TRACKA
OUT
OUT
= V
R
X
A
according to the ratio set
), as shown in Figure 7.
X
+
+
W
during start-up),
R
R
38271 F06A
38271 F06B
B
TRACKB
V
V
V
V
X
X
OUT
X
OUT
(MASTER)
) to the TRACK/
(MASTER)
(SLAVE)
(SLAVE)
U
INTV
The LTC3827-1 features two separate internal P-channel
low dropout linear regulators (LDO) that supply power at
the INTV
EXTV
the EXTV
of the LTC3827-1’s internal circuitry. The V
lates the voltage at the INTV
LDO regulates it to 7.5V. Each of these can supply a peak
current of 50mA and must be bypassed to ground with a
minimum of 4.7μF tantalum, 10μF special polymer, or low
ESR electrolytic capacitor. A ceramic capacitor with a
minimum value of 4.7μF can also be used if a 1Ω resistor
is added in series with the capacitor. No matter what type
of bulk capacitor is used, an additional 1μF ceramic
capacitor placed directly adjacent to the INTV
IC pins is highly recommended. Good bypassing is needed
to supply the high transient currents required by the
MOSFET gate drivers and to prevent interaction between
the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3827-1 to be
exceeded. The INTV
gate charge current, may be supplied by either the 5.25V
V
EXTV
Power dissipation for the IC in this case is highest and is
equal to V
on operating frequency as discussed in the Efficiency
Considerations section. The junction temperature can be
estimated by using the equation given in Note 2 of the
Electrical Characteristics. For example, the LTC3827-1
IN
LDO or the 7.5V EXTV
CC
CC
CC
Regulators
pin, respectively, depending on the connection of
Figure 7. Using the TRACK/SS Pin for Tracking
pin is less than 4.7V, the V
CC
CC
IN
pin. INTV
• I
pin from either the V
NTVCC
R
R
TRACKB
TRACKA
. The gate charge current is dependent
CC
CC
V
x
current, which is dominated by the
powers the gate drivers and much
V
OUT
CC
RB
RA
CC
LDO. When the voltage on the
pin to 5.25V and the EXTV
1/2 LTC3827-1
TRACK/SS
V
FB
IN
LTC3827-1
38271 F07
IN
supply pin or the
LDO is enabled.
IN
CC
LDO regu-
and PGND
17
38271fd
CC