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LTC3610_15 Datasheet, PDF (14/24 Pages) Linear Technology – 24V, 12A Monolithic Synchronous Step-Down DC/DC Converter
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LTC3610
Applications Information
VOUT2
CSEC +
1µF
VOUT1
+
COUT
SW
GND
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
IN4148
T1
1:N
VIN
+
CIN
1 PGND
2 PGND
3 PGND
4 SW
5 SW
6 SW
7 SW
8 SW
9 SW
10 SW
11 SW
12 PVIN
13 PVIN
14 PVIN
15 PVIN
16 PVIN
LTC3610
SGND 48
SGND 47
SGND 46
SGND 45
EXTVCC 44
VFB 43
SGND 42
ION 41
SGND 40
FCB 39
ITH 38
VRNG 37
PGOOD 36
VON 35
SGND 34
SGND 33
R4
OPTIONAL EXTVCC
CONNECTION
5V < VOUT2 < 7V
R3
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
SGND
SW
3610 F04
Figure 4. Secondary Output Loop and EXTVCC Connection
INTVCC Regulator and EXTVCC Connection
An internal P-channel low dropout regulator produces the
5V supply that powers the drivers and internal circuitry
within the LTC3610. The INTVCC pin can supply up to 50mA
RMS and must be bypassed to ground with a minimum of
4.7µF tantalum or ceramic capacitor. Good bypassing is
necessary to supply the high transient currents required
by the MOSFET gate drivers.
The EXTVCC pin can be used to provide MOSFET gate drive
and control power from the output or another external
source during normal operation. Whenever the EXTVCC
pin is above 4.7V the internal 5V regulator is shut off and
an internal 50mA P-channel switch connects the EXTVCC
pin to INTVCC. INTVCC power is supplied from EXTVCC
until this pin drops below 4.5V. Do not apply more than
7V to the EXTVCC pin and ensure that EXTVCC ≤ VIN. The
following list summarizes the possible connections for
EXTVCC:
1. EXTVCC grounded. INTVCC is always powered from the
internal 5V regulator.
2. EXTVCC connected to an external supply. A high efficiency
supply compatible with the MOSFET gate drive require-
ments (typically 5V) can improve overall efficiency.
3. EXTVCC connected to an output derived boost network.
The low voltage output can be boosted using a charge
pump or flyback winding to greater than 4.7V. The
system will start-up using the internal linear regulator
until the boosted output supply is available.
Soft-Start and Latchoff with the RUN/SS Pin
The RUN/SS pin provides a means to shut down the LTC3610
as well as a timer for soft-start and overcurrent latchoff.
Pulling the RUN/SS pin below 0.8V puts the LTC3610 into
a low quiescent current shutdown (IQ < 30µA). Releasing
the pin allows an internal 1.2µA current source to charge
up the external timing capacitor CSS. If RUN/SS has been
pulled all the way to ground, there is a delay before start-
ing of about:
( ) tDELAY
=
1.5V
1.2µA
CSS
=
1.3s/µF
CSS
3610ff
14
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