SP6648UEB Exar Corporation, SP6648UEB Datasheet - Page 11

• Manufacturer Part Number: SP6648UEB
• Description: Power Management Modules & Development Tools Ultra Low Quies Cur Hi-Eff Boost Reg
• Manufacturer: Exar Corporation
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of SP6648UEB

• Product: Power Management Modules

V
The SP6648 can be programmed as either a
voltage source or a current source. To program
the SP6648 as a voltage source, the SP6648
requires 2 feedback resistors R1 & R2, as shown
in the SP6648EB evaluation board schematic, to
control the output voltage. To set V
voltage mode, use the equation:
R1 = [(V
Using the R
The peak inductor current, I
externally by the R
tween the R
current is defined by:
I
The saturation current specified for the inductor
needs to be greater than the peak current to avoid
saturating the inductor, which would result in a
loss in efficiency and could damage the induc-
tor. The SP6648 evaluation board uses a R
value of 1.87K for an I
the circuit to deliver up to 180mA for 1.3V input
and 400mA for 2.6V input. Other values could
be selected using the above relationships.
Using the LBON - Low Battery Output
Function
The SP6648 will regulate the output until the
input battery is completely discharged or until
the under voltage lock-out (UVLO) occurs at
V
ing, the Low Battery Output function of the
SP6648 can be used. LBON is programmed
externally by the R
connected between V
and GND. The LBON is an open drain output,
which is active low and is pulled up by a 1MΩ
Date: 6/7/06 Rev B
PEAK
OUT
BATT
Programming
= 1600/R
= 0.61V. To provide a low battery warn-
OUT
LIM
LIM
/1.25)-1] * R2
pin and GND. The peak inductor
Function
LIM
LIM
3
BATT
and R
PEAK
resistor connected be-
PEAK
, the LBI input pin
= 850mA to allow
4
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator
, is programmed
resistor divider
OUT
in the
LIM
11
APPLICATIONS INFORMATION : Continued
resistor R
falling threshold of 0.61V is reached, the LBON
output goes low as determined by the relation-
ship:
V
The SP6648 evaluation board R
have been set to trip for a falling battery thresh-
old of about 2.0V. Using this relationship, other
low battery threshold values can be set by the
user.
UVLO the Under Voltage Lock-Out Function
Once started up, the SP6648 will regulate the
output until the input battery is completely dis-
charged or until the under voltage lock-out
(UVLO) occurs at V
function will completely open all switches until
the battery again rises above the 0.61V thresh-
old.
Maximum Startup Current
It should be noted that for low input voltages the
SP6648 startup circuit cannot support large load
currents at startup. In startup the SP6648 needs
to boost the output from zero volts using the
input voltage. Once the output is greater than
1.9V, the operating circuit takes over and the
SP6648 can supply much more current. Curves
of maximum load current in startup for the
SP6648 are shown in the typical performance
characteristics and can be compared with the
page one curve for maximum load current in
operation.
For 1-cell battery applications, it is recommended
to apply any large load current after the SP6648
has started up, typically in a few milliseconds.
This is typically not a problem in many applica-
tions where the load is a processor whose load
current is low until the processor voltage comes
up.
LOWBATT
5
to V
= 0.61 * [(R
OUT
. When the LBI comparator
BATT
3
+ R
= 0.61V. The UVLO
4
)/R
© 2006 Sipex Corporation
3
4
& R
]
4
resistors