LTC3736EGN-2#PBF Linear Technology, LTC3736EGN-2#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC3736EGN-2#PBF
• Description: IC CTRLR SW SYNC DUAL 2PH 24SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3736EGN-2#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 550kHz ~ 750kHz
• Voltage - Input: 2.75 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATION
higher than forced continuous mode. During start-up or
a short-circuit condition (V
LTC3736-2 operates in pulse-skipping mode (no current
reversal allowed), regardless of the state of the SYNC/
FCB pin.
Short-Circuit Protection
When an output is shorted to ground (V
switching frequency of that controller is reduced to one
fi fth of the normal operating frequency. The other controller
is unaffected and maintains normal operation.
The short-circuit threshold on V
of 0.12V and a fraction of the voltage on the TRACK pin.
This also allows V
easily. Note that if V
V
to 0V if a resistor divider on V
TRACK pin.
Output Overvoltage Protection
As a further protection, the overvoltage comparator (OV)
guards against transient overshoots, as well as other more
serious conditions that may overvoltage the output. When
the feedback voltage on the V
above the reference voltage of 0.6V, the external P-chan-
nel MOSFET is turned off and the N-channel MOSFET is
turned on until the overvoltage is cleared.
Frequency Selection and Phase-Locked Loop (PLLLPF
and SYNC/FCB Pins)
The selection of switching frequency is a tradeoff between
effi ciency and component size. Low frequency opera-
tion increases effi ciency by reducing MOSFET switching
losses, but requires larger inductance and/or capacitance
to maintain low output ripple voltage.
The switching frequency of the LTC3736-2’s controllers
can be selected using the PLLLPF pin.
If the SYNC/FCB is not being driven by an external
clock source, the PLLLPF can be fl oated, tied to V
or tied to SGND to select 550kHz, 750kHz or 300kHz,
respectively.
FB1
= 0V), then the LTC3736-2 will try to regulate V
OUT2
OUT1
(Refer to Functional Diagram)
to start up and track V
is truly short-circuited (V
FB1
FB2
FB
OUT1
or V
pin has risen 13.33%
is based on the smaller
is connected to the
FB2
FB
≤ 0.54V), the
< 0.12V), the
OUT1
OUT1
more
OUT2
IN
=
A phase-locked loop (PLL) is available on the LTC3736-2
to synchronize the internal oscillator to an external clock
source that is connected to the SYNC/FCB pin. In this
case, a series RC should be connected between the
PLLLPF pin and SGND to serve as the PLL’s loop fi lter.
The LTC3736-2 phase detector adjusts the voltage on the
PLLLPF pin to align the turn-on of controller 1’s external
P-channel MOSFET to the rising edge of the synchronizing
signal. Thus, the turn-on of controller 2’s external P-chan-
nel MOSFET is 180 degrees out-of-phase with the rising
edge of the external clock source.
The typical capture range of the LTC3736-2’s phase-locked
loop is from approximately 200kHz to 1MHz, and is guaran-
teed over temperature to be between 250kHz and 850kHz.
In other words, the LTC3736-2’s PLL is guaranteed to lock
to an external clock source whose frequency is between
250kHz and 850kHz.
Dropout Operation
When the input supply voltage (V
the output voltage, the rate of change of the inductor
current while the external P-channel MOSFET is on (ON
cycle) decreases. This reduction means that the P-channel
MOSFET will remain on for more than one oscillator cycle
if the inductor current has not ramped up to the threshold
set by the EAMP on the I
input supply voltage will eventually cause the P-channel
MOSFET to be turned on 100%, i.e., DC. The output volt-
age will then be determined by the input voltage minus
the voltage drop across the P-channel MOSFET and the
inductor.
Undervoltage Lockout
To prevent operation of the external MOSFETs below safe
input voltage levels, an undervoltage lockout is incorpo-
rated in the LTC3736-2. When the input supply voltage
(V
MOSFETs and all internal circuitry are turned off except
for the undervoltage block, which draws only a few
microamperes.
IN
) drops below 2.3V, the external P- and N-channel
TH
pin. Further reduction in the
IN
LTC3736-2
) decreases towards
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