Rainbow Electronics ATmega8HVD - Manual (Page 100)

100
8052B–AVR–09/08
ATmega4HVD/8HVD
19. Voltage Regulator
19.1 Features
• Linear regulation giving a fixed output voltage (VREG) of 2.2V for VFET > V
FORCE
• Output voltage forced as close as possible to VFET for VFET
≤
V
FORCE
to facilitate low voltage
operation.
• Regulator Short-circuit Detection (RSCD), disconnecting VFET from VREG if VFET drops below
the Regulator Short-Circuit Detection voltage (V
RSCD
)
• RSCD enabling/disabling in software
19.2 Overview
The Voltage Regulator is a linear regulator that nominally provides a fixed output voltage
(VREG). However, to facilitate efficient low-voltage operation with minimum voltage drop
caused by the regulator, voltage regulation is automatically switched off when VFET is below
V
FORCE
(see ”Electrical Characteristics” on page 142 ). VREG as a function VFET and regulator
is illustrated in Figure 19-1 . A discontinuity in VREG can be observed as the point where the
regulator switches from linear mode to FORCE mode, as VREG is being forced as close as
possible to VFET. The voltage drop from VFET to VREG in this mode depends on the load
current on VREG.
Figure 19-1. VREG/VCC as function of VFET
The Voltage regulator mode depending on operating conditions and SW settings, are summa-
rized in
Table 19-1 .
Table 19-1.
VFET Voltage Regular Short-circuit Detection Regular mode
VFET > V
FORCE
Enabled/Disabled Normal Linear Regulation
VFET< V
FORCE
Enabled Battery Pack Short mode
VFET < V
FORCE
Disabled Force mode
2.2V
V
BLOT, NORMAL
V
VREG
LINEAR Regulator Mode FORCE OFF
t
VFET
V
FORCE
ENABLED Short-circuit Detection DISABLED