SP6642EU 查看數據表（PDF） - Signal Processing Technologies

零件编号

产品描述 (功能)

比赛名单

SP6642EU

Single Alkaline Cell, High Efficiency Step-Up DC-DC Converter

Signal Processing Technologies 

VBATT

FB

PFI

VREF

VREF

VREF

0.5VREF

1.0V

TIMING

T-ON

T-OFF

EN LOGIC DRV-P

P

DRV-N

START

UP

OSC

N

N

1.0V

0.5VREF

SP6643

VOUT

LX

BATTLO

PFO

VTH

R3

SP6642

PFI

R4

GND

Figure 22. Internal block diagram of the SP6643

Figure 24. Power-Fail Detection Circuitry

0.85V to

1.65V Input

22µF

0.1µF

100µH

350mA

VBATT

LX

OUT

SP6643

PFO

PFI

BATTLO

0.1µF

+3.3VOUT

22µF

GND

FB

Figure 23. SP6643 +3.3V Typical Application Circuit

Power-Fail Detection Circuitry

The SP6642/6643 devices have an internal

comparator for power-fail detection. This

comparator can detect a loss of power at the

input or output. If the voltage at PFI falls below

614mV, the PFO output sinks current to ground.

Hysteresis at the power-fail input is 1%. The

power-fail monitor's threshold voltage is

determined by two resistors, R3 and R4. Refer

to Figure 24. The power-fail monitor threshold

voltage can be set using the following equation:

R3 = R4 x

VTH

VPFI

-1

where R3 and R4 are the resistors in Figure 24,

VTH is the desired threshold voltage of the power-

fail detector, and V is the 614mV reference of

PFI

the power-fail comparator. Since PFI leakage is

10nA max, select feedback resistor R4 in the

100kΩ to 1MΩ.

BATTLO for the SP6643

The SP6643 device has an internal comparator

for low-battery detection. If VBATT drops below

1V, BATTLO will sink current. BATTLO is an

open-drain output. BATTLO used in conjunction

with the power-fail detection circuitry (PFI/

PFO) will monitor both the input and output

voltages.

Shutdown for the SP6642

A logic LOW at SHDN will drive the SP6642

into a shutdown mode where PFO goes into a

high-impedance state, the internal switching

MOSFET turns off, and the synchronous rectifier

turns off to prevent reverse current from flowing

from the output back to the input. Designers

should note that in shutdown, the output can

drift to one diode drop below VBATT because

there is still a forward current path through the

Rev. 10-6-00

SP6642/6643 High Efficiency Step-Up DC-DC Converter

12

© Copyright 2000 Sipex Corporation

Share Link: