SP6650 Datasheet, PDF (7/17 Pages) Sipex Corporation – High Efficiency 600mA Synchronous Buck Regulator Ideal for portable designs powered with Li Ion battery

Under-Current Detection
The synchronous rectifier is comprised of the
inductor discharge switch, a voltage compara-
tor, and a latch. During the off-time, positive
inductor current flows into the PGND pin 9
through the low side NMOS switch to LX pin
10, through the inductor and the output capaci-
tor, and back to pin 9. The comparator monitors
the voltage drop across the discharge NMOS.
As the inductor current approaches zero, the
channel voltage sign goes from negative to
positive, causing the comparator to trigger the
latch and open the switch to prevent inductor
current reversal. This circuit along with the on-
time one shot puts the converter into PFM mode
and improves light load efficiency when the
load current is less than half the inductor ripple
current defined by K_ON/L.
Thermal Shutdown
The converter will open both power switches if
the die junction temperature rises above 140°C.
The die must cool down below 126°C before the
regulator is re-enabled. This feature protects the
SP6650 and surrounding circuitry from exces-
sive power dissipation due to fault conditions.
Shutdown/Enable Control
Pin 5 of the device is a logic level control pin that
shuts down the converter with a logic low, or
enables the converter with a logic high. When
the converter is shut down, the power switches
are opened and all circuit biasing is extinguished
leaving only junction leakage currents on sup-
ply pins 1 and 2. After pin 5 is brought high to
enable the converter, there is a turn on delay to
allow the regulator circuitry to re-establish it-
self. Power conversion begins with the assertion
of the internal reference ready signal which
occurs approximately 150µs after the enable
signal is received.
Battery Low Indicator
The regulator bias voltage on pin 2 (V_IN) is
divided down and compared to the internal
+1.25V reference voltage. When pin 2 voltage
drops below +3.00V, an open drain NMOS on
pin 3 (BLON) sinks current to ground. Tying a
resistor from pin 3 to V_IN or V_OUT creates a logic
level battery low indicator. A low bandwidth
comparator and 2.9% hysteresis filter the input
voltage ripple to prevent noisy transitions at the
threshold.
External Feedback Pin
The SP6650 comes with a factory preset output
voltage of +3.3V when pin 6 (FB) is grounded.
Otherwise, the output voltage can be externally
programmed within the range +1.25V to +5.0V
by tying a resistor from FB to ground and FB to
V_OUT (pin7). See the applications section for
resistor selection information.
Date: 5/25/04
SP6650 High Efficiency 600mA Synchronous Buck Regulator
7
© Copyright 2004 Sipex Corporation