
2002 May 14
7
Philips Semiconductors
Product specification
0.95 V starting DC-to-DC converter
with low battery indicator
TEA1200TS
handbook, full pagewidth
MGU269
maximum positive spread of VO
Vwdw(high)
maximum negative spread of VO
typical situation
lower specification limit
upper specification limit
+
2%
2%
2%
VO (typ)
Vwdw(high)
Vwdw(low)
2%
Vwdw(low)
Vwdw(high)
Vwdw(low)
2%
Fig.4 Output voltage window spread.
Synchronous rectification
For optimum efficiency over the whole load range,
synchronous rectifiers within the TEA1200TS ensure that
during the whole second switching phase, all inductor
current will flow through the low-ohmic power MOSFETs.
Special circuitry is included which detects when the
inductorcurrentreacheszero.Followingthisdetection,the
digital controller switches off the power MOSFET and
proceeds with regulation.
Start-up
Start-up from low input voltage in the boost mode is
realized by an independent start-up oscillator, which starts
switching the N-type power MOSFET as soon as the
low-battery detector detects a sufficiently high voltage.
The inductor current is limited internally to ensure
soft-starting. The switch actions of the start-up oscillator
will increase the output voltage. As soon as the output
voltage is high enough for normal regulation, the digital
control system will take control over the power MOSFETs.
Undervoltage lockout
As a result of too high a load or disconnection of the input
power source, the output voltage can drop so low that
normal regulation cannot be guaranteed. In this event, the
device switches back to start-up mode. If the output
voltage drops even further, switching is stopped
completely.
Shut-down
When the shut-down input is set HIGH, the DC-to-DC
converter disables both switches and power consumption
is reduced to a few microamperes.
Power switches
The power switches in the IC are one N-type and one
P-type power MOSFET, both having a typical
drain-to-source resistance of 100 m
. The maximum
continuous current in the power switches is 1.0 A at
T
amb
= 80
°
C.