LTC1649CS#PBF Linear Technology, LTC1649CS#PBF Datasheet - Page 4

• Manufacturer Part Number: LTC1649CS#PBF
• Description: IC BUCK/SW CAP SYNC ADJ 16SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck), Switched Capacitor (Charge Pump)r

Specifications of LTC1649CS#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.26 ~ 2.5 V
• Current - Output: 20A
• Frequency - Switching: 200kHz
• Voltage - Input: 2.7 ~ 5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC1649
PIN
G1 (Pin 1): Driver Output 1. Connect this pin to the gate of
the upper N-channel MOSFET, Q1. This output will swing
from P
In shutdown, G1 and G2 go low.
P
supply input for G1. G1 will swing from P
P
V
simple charge pump connected to the switching node
between the two external MOSFETs as shown in Figure 1.
GND (Pin 3): System Ground. Connect to a low impedance
ground in close proximity to the source of Q2. The system
signal and power grounds should meet at only one point,
at the GND pin of the LTC1649.
FB (Pin 4): Feedback. The FB pin is connected to the output
through a resistor divider to set the output voltage.
V
SHDN (Pin 5): Shutdown, Active Low. A TTL compatible
LOW level at SHDN for more than 50 s puts the LTC1649
into shutdown mode. In shutdown, G1, G2, COMP and SS
go low, and the quiescent current drops to 25 A max.
CP
HIGH level at SHDN allows the LTC1649 to operate nor-
mally.
SS (Pin 6): Soft Start. An external capacitor from SS to
GND controls the startup time and also compensates the
current limit loop, allowing the LTC1649 to enter and exit
current limit cleanly.
V
voltage power supply input. V
between 3V and 5V. Bypass V
ceramic capacitor located close to the LTC1649.
C
a 1 F ceramic capacitor from C
4
VCC1
VCC1
GS(ON)
OUT
IN
–
OUT
U
(Pin 8): Flying Capacitor, Negative Terminal. Connect
(Pin 7): Charge Pump Input. This is the main low
= V
(Pin 2): Power V
VCC1
must be connected to a potential of at least V
FUNCTIONS
remains at 5V in shutdown mode. A TTL compatible
(Q1). This potential can be generated using a
REF
U
to GND. G1 will always be low when G2 is high.
[1 + (R1/R2)].
U
CC
for Driver 1. This is the power
IN
IN
–
requires an input voltage
to C
to ground with a 1 F
+
.
VCC1
to GND.
IN
+
C
CP
regulated 5V output to provide power for the internal
switching circuitry and gate drive for the external MOSFETs.
CP
applications. At least 10 F of reservoir capacitance to
ground is required at CP
be met by the bypass capacitor at P
COMP (Pin 11): External Compensation. The COMP pin is
connected directly to the output of the internal error
amplifier and the input of the PWM generator. An RC
network is used at this node to compensate the feedback
loop to provide optimum transient response.
I
for the internal current limit comparator. If I
I
I
at I
Q1 or with an external voltage source.
I
node at the source of Q1 and the drain of Q2 through a 1k
resistor. The resistor is required to prevent voltage tran-
sients at the switched node from damaging the I
can be taken up to 18V above GND without damage.
V
to the feedback amplifier and switching control circuits.
V
CP
P
supply input for G2. G2 will swing from P
P
V
pin. P
capacitor also provides the reservoir capacitance required
by the CP
G2 (Pin 16): Driver Output 2. Connect this pin to the gate
of the lower N-channel MOSFET, Q2. This output will
swing from P
is high. In shutdown, G1 and G2 go low.
MAX
MAX
MAX
FB
+
CC
CC
VCC2
VCC2
GS(ON)
OUT
OUT
OUT
(Pin 9): Flying Capacitor, Positive Terminal.
MAX
(Pin 13): Current Limit Sense. Connect to the switched
(Pin 14): Internal Power Supply. V
is designed to run from the 5V supply provided by
(Pin 12): Current Limit Set. I
has an internal 12 A pull-down to GND. The voltage
with G1 on, the LTC1649 will go into current limit.
. V
(Pin 15): Power V
VCC2
(Pin 10): Charge Pump Output. CP
must be connected to a potential of at least
should be connected directly to P
can be set with an external resistor to the drain of
(Q2). This voltage is usually supplied by the CP
CC
OUT
requires a 10 F bypass capacitor to GND.
requires a bypass capacitor to GND; this
VCC2
pin.
to GND. G2 will always be low when G1
OUT
CC
for Driver 2. This is the power
. This requirement can usually
MAX
VCC2
CC
sets the threshold
.
provides power
OUT
FB
VCC2
VCC2
drops below
provides a
FB
to GND.
in most
pin. I
OUT
FB