SP7651ER-L Exar Corporation, SP7651ER-L Datasheet - Page 5

• Manufacturer Part Number: SP7651ER-L
• Description: IC BUCK REG 900KHZ 26DFN
• Manufacturer: Exar Corporation
• Series: Power Blox™r
• Type: Step-Down (Buck)r

Specifications of SP7651ER-L

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 V ~ 19 V
• Current - Output: 3A
• Frequency - Switching: 900kHz
• Voltage - Input: 2.5 V ~ 20 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: 26-VFDFN Exposed Pad
• Primary Input Voltage: 20V
• No. Of Outputs: 1
• Output Voltage: 19V
• Output Current: 3A
• No. Of Pins: 26
• Operating Temperature Range: -40°C To +85°C
• Supply Voltage Range: 2.5V To 20V
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

safely begin down conversion, and an inter-
nal V
itself has enough voltage to properly operate.
Other protection features include thermal
shutdown and short-circuit detection. In the
event that either a thermal, short-circuit, or
UVLO fault is detected, the SP765 is forced
into an idle state where the output drivers are
held off for a finite period before a re-start
is attempted.
Soft Start
“Soft Start” is achieved when a power con-
verter ramps up the output voltage while
controlling the magnitude of the input sup-
ply source current. In a modern step down
converter, ramping up the positive terminal
of the error amplifier controls soft start. As a
result, excess source current can be defined
as the current required to charge the output
capacitor.
The SP765 provides the user with the op-
tion to program the soft start rate by tying
a capacitor from the SS pin to GND. The
selection of this capacitor is based on the
0µA pullup current present at the SS pin
and the 0.8V reference voltage. Therefore,
the excess source can be redefined as:
Under Voltage Lock Out (UVLO)
The SP765 contains two separate UVLO
comparators to monitor the internal bias (V
and conversion (V
The V
to 4.25V, whereas the V
is programmable through the UVIN pin.
When the UVIN pin is greater than 2.5V,
the SP765 is permitted to start up pend-
ing the removal of all other faults. Both the
V
designed with hysteresis to prevent noise
from resetting a fault.
Rev J: 3/4/07
I
CC
VIN
I
VIN
and V
= C
CC
CC
= C
OUT
UVLO ensures that the controller
UVLO threshold is internally set
IN
OUT
UVLO comparators have been
* (∆V
* (∆V
IN
OUT
) voltages independently.
OUT
*0µA / (C
IN
/ ∆T
SP765 Wide Input Voltage Range 3A, 900kHz, Buck Regulator
UVLO threshold
SOFT-START
SS
* 0.8V)
)
CC
)
5
Thermal and Short-Circuit
Protection
Because the SP765 is designed to drive
large output current, there is a chance that the
power converter will become too hot. There-
fore, an internal thermal shutdown (145°C)
has been included to prevent the IC from
malfunctioning at extreme temperatures.
A short-circuit detection comparator has
also been included in the SP765 to protect
against an accidental short at the output
of the power converter. This comparator
constantly monitors the positive and nega-
tive terminals of the error amplifier, and if
the V
below the positive reference, a short-circuit
fault is set. Because the SS pin overrides the
internal 0.8V reference during soft start, the
SP765 is capable of detecting short-circuit
faults throughout the duration of soft start as
well as in regular operation.
Handling of Faults:
Upon the detection of power (UVLO), ther-
mal, or short-circuit faults, the SP765 is
forced into an idle state where the SS and
COMP pins are pulled low and the NFETS
are held off. In the event of UVLO fault, the
SP765 remains in this idle state until the
UVLO fault is removed. Upon the detection
of a thermal or short-circuit fault, an internal
200ms timer is activated. In the event of a
short-circuit fault, a re-start is attempted im-
mediately after the 200ms timeout expires.
Whereas, when a thermal fault is detected
the 200ms delay continuously recycles and a
re-start cannot be attempted until the thermal
fault is removed and the timer expires.
Error Amplifier and Voltage Loop
Since the heart of the SP765 voltage error
loop is a high performance, wide bandwidth
transconductance amplifier, great care
should be taken to select the optimal compen-
sation network. Because of the amplifier’s
FB
pin falls more than 250mV (typical)
THEORY OF OPERATION
© Copyright 2007 Sipex Corporation