LTC3701EGN Linear Technology, LTC3701EGN Datasheet - Page 8

• Manufacturer Part Number: LTC3701EGN
• Description: IC DC/DC CNTRLR STPDN DUAL16SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3701EGN

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 10 V
• Current - Output: 1A
• Frequency - Switching: 550kHz
• Voltage - Input: 2.5 ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

OPERATIO
LTC3701
Dropout Operation
When the input supply voltage decreases towards the
output voltage, the rate of change of the inductor current
during the ON cycle decreases. This reduction means that
the external 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 EAMP on the I
pin. Further reduction in input supply voltage will eventu-
ally cause the P-channel MOSFET to be turned on 100%,
i.e., DC. The output voltage will then be determined by the
input voltage minus the voltage drop across the MOSFET,
the sense resistor and the inductor.
Undervoltage Lockout
To prevent operation of the P-channel MOSFET below safe
input voltage levels, an undervoltage lockout is incorpo-
rated into the LTC3701. When the input supply voltage
drops below 2V, the P-channel MOSFET and all circuitry
are turned off except the undervoltage block, which draws
only several microamperes.
Short-Circuit Protection
When an output is shorted to ground (V
switching frequency of that channel is reduced to 1/5 of
the normal operating frequency. The other controller
channel is unaffected and maintains normal operation.
This lower frequency allows the inductor current to safely
discharge, thereby preventing current runaway. The switch-
ing frequency will return to its normal value when the
feedback voltage rises above 0.3V. During the first 64
cycles (nonzero-current cycles) of soft-start, however, the
controller operates at its full frequency.
Output Overvoltage Protection
As a further protection, the overvoltage comparator in the
LTC3701 will turn the external MOSFET off when the
feedback voltage has risen 10% above the reference
voltage of 0.8V. This comparator has a typical hysteresis
of 20mV.
8
U
(Refer to Functional Diagram)
FB
< 0.3V), the
TH
/RUN
Slope Compensation and Peak Inductor Current
The inductor’s peak current is determined by:
when the LTC3701 is operating below 20% duty cycle.
However, once the duty cycle exceeds 20%, slope
compensation begins and effectively reduces the peak
inductor current. The amount of reduction is given by the
curve in Figure 2.
Power Good (PGOOD) Pin
A window comparator monitors both output voltages and
the open-drain PGOOD output is pulled low when the
divided down output voltages are not within 8% of the
reference voltage of 0.8V. PGOOD is pulled low when
channel 1 or both channels are shut down. When chan-
nel 2 is shut down and channel 1 enabled, the PGOOD
output indicates the state of channel 1 only.
2-Phase Operation
The LTC3701 dual switching controller offers the consid-
erable benefits of using 2-phase operation. Circuit ben-
efits include lower input filtering requirements, reduced
electromagnetic interference (EMI) and increased effi-
ciency associated with 2-phase operation.
I
PK
Figure 2. Maximum Peak Current vs Duty Cycle
V
ITH RUN
110
100
10
90
80
70
60
50
40
30
20
10
0
/
0
•
R
10
SENSE
– .
20
0 7
30
DUTY CYCLE (%)
V
40
50
60
70
80
90
3701 F02
100
3701fa