SP6650 datasheet(7/17 Pages) SIPEX

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Date: 5/25/04

SP6650 High Efficiency 600mA Synchronous Buck Regulator

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 KON/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 150

µs after the enable

signal is received.

Battery Low Indicator

The regulator bias voltage on pin 2 (VIN) 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 VIN or VOUT 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

VOUT (pin7). See the applications section for

resistor selection information.

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