SP6644EU SIPEX [Sipex Corporation], SP6644EU Datasheet - Page 8

• Manufacturer Part Number: SP6644EU
• Description: Single/Dual Alkaline Cell, High Efficiency Step-Up DC-DC Converter
• Manufacturer: SIPEX [Sipex Corporation]

DESCRIPTION
The SP6644/6645 devices are high-efficiency,
low-power step-up DC-DC converters ideal for
single or dual alkaline cell applications such as
pagers, remote controls, and other low-power
portable end products.
The SP6644/6645 devices feature a 5nA logic-
controlled shutdown mode and a dedicated
low-battery detector circuitry. Both devices
contain a 0.8Ω synchronous rectifier, a 0.5Ω
N-channel MOSFET power switch, an internal
voltage reference, circuitry for pulse-frequency-
modulation, and an under voltage comparator.
The output voltage for the SP6644/6645 devices
can be adjusted from +2V to +5.5V by
manipulating two external resistors. The output
voltage is preset to +3.3V.
THEORY OF OPERATION
The SP6644/6645 devices are ideal for end
products that function with a single or dual alkaline
cell, such as remote controls, pagers, and other
portable consumer products. Designers can
implement the SP6644/6645 devices into
applications with the following power
management operating states: 1. where the
primary battery is good and the load is active, and
2. where the primary battery is good and
the load is sleeping.
In the first operating state where the primary
supply is good and the load is active, the
SP6644/6645 devices typically offer 88%
efficiency, drawing tens of milliamps.
Applications will predominantly operate in the
second state where the primary supply is good
and the load is sleeping. The SP6644/6645 devices
draw a very low quiescent current while the load
in its disabled state will draw typically hundreds
of microamps.
The pulse-frequency-modulation (PFM) circuitry
provides higher efficiencies at low to moderate
output loads than traditional PWM converters are
capable of delivering.
In a state where the error comparator detects that
the output voltage at V
N-channel MOSFET switch is turned on until the
Rev:B Date 4/13/04
OUT
is too low, the internal
SP6644/6645 High Efficiency Boost Regulator
8
peak inductor current is satisfied. This is indicated
by the falling edge of the I-Charge comparator
output. The approximate inductor charging time
is defined by:
where t
charging time, L [H] is the inductance, I
is the peak inductor current, and V
input voltage to the device.
The peak inductor current, I
externally by putting a resistor between the R
pin and ground. This is defined by:
where I
R
from pin R
When the charging N MOSFET turns off, the
discharging P MOSFET turns on and the inductor
current flows into the output capacitor and the
load recharging the output. When the current
through the discharging P MOSFET approaches
zero, the I-Discharge comparator indicates to the
logic to turn off the P MOSFET. The approximate
time for discharging the inductor current can be
determined by:
where t
inductor, L [H] is the inductance, I
peak inductor current, V
voltage, and V
device.
The output filter capacitor stores charge while
current from the inductor is high and holds the
output voltage high until the discharge phase of
the next switching cycle, smoothing power flow
to the load. Between switching cycles, the
inductor damping switch is closed suppressing
the ringing caused by the inductor and the parasitic
capacitance on the LX node.
LIM
[Ω] is the value of the resistor connected
PEAK
CHARGE
DCHG
t
CHARGE
LIM
[A] is the peak inductor current and
t
DCHG
[s] is the time to discharge the
to ground.
BATT
[s] is the approximate inductor
I
PEAK
≅ ≅ ≅ ≅ ≅
≅ ≅ ≅ ≅ ≅ L x I
[V] is the input voltage to the
= 1400
V
L x I
© Copyright 2004 Sipex Corporation
OUT
R
PEAK
OUT
LIM
- V
PEAK
PEAK
[V] is the output
/ V
BATT
, is programmed
BATT
BATT
PEAK
[V] is the
[A] is the
PEAK
[A]
LIM