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L296-L296HT-L296P-L296PHT
HIGH CURRENT SWITCHING REGULATORS
96L296PJune 2000
HIGH CURRENT SWITCHING REGULATORS 4 A OUTPUT CURRENT. 5.1 V TO 40 V OUTPUT VOLTAGE RANGE. 0 TO 100 % DUTY CYCLE RANGE. PRECISE (±2 %) ON-CHIP REFERENCE. SWITCHING FREQUENCY UP TO 200 KHz. VERY HIGH EFFICIENCY (UP TO 90 %). VERY FEW EXTERNAL COMPONENTS. SOFT START. RESET OUTPUT. EXTERNAL PROGRAMMABLE LIMITING
CURRENT (L296P). CONTROL CIRCUIT FOR CROWBAR SCR. INPUT FOR REMOTE INHIBIT AND
SYNCHRONUS PWM. THERMAL SHUTDOWN
DESCRIPTIONThe L296 and L296P are stepdown power switching
regulators delivering 4 A at a voltage variable from
5.1 V to 40 V.
Features of the devices include soft start, remote in-
hibit, thermal protection, a reset output for micro-
processors and a PWM comparator input for syn-
chronization in multichip configurations.
The L296P incudes external programmable limiting
current.
The L296 and L296P are mounted in a 15-lead Mul-
tiwatt plastic power package and requires very few
external components.
Efficient operation at switching frequencies up to
200 KHz allows a reduction in the size and cost of
external filter components. A voltage sense input
and SCR drive output are provided for optional
crowbar overvoltage protection with an external
SCR.
PIN CONNECTION (top view)1/22
PIN FUNCTIONS
BLOCK DIAGRAM
L296 - L296P2/22
CIRCUIT OPERATION(refer to the block diagram)
The L296 and L296P are monolithic stepdown
switching regulators providing output voltages from
5.1V to 40V and delivering 4A.
The regulation loop consists of a sawtooth oscillator,
error amplifier, comparator and the output stage. An
error signal is produced by comparing the output
voltage with a precise 5.1V on-chip reference (zener
zap trimmed to ± 2 %). This error signal is then com-
pared with the sawtooth signal to generate the fixed
frequency pulse width modulated pulses which drive
the output stage. The gain and frequency stability of
the loop can be adjusted by an external RC network
connected to pin 9. Closing the loop directly gives an
output voltage of 5.1V. Higher voltages are obtained
by inserting a voltage divider.
Output overcurrents at switch on are prevented by
the soft start function. The error amplifier output is
initially clamped by the external capacitor Css and
allowed to rise, linearly, as this capacitor is charged
by a constant current source.
Output overload protection is provided in the form of
a current limiter. The load current is sensed by an
internal metal resistor connected to a comparator.
When the load current exceeds a preset threshold
this comparator sets a flip flop which disables the
output stage and discharges the soft start capacitor.
A second comparator resets the flip flop when the
voltage across the soft start capacitor has fallen to
0.4V. The output stage is thus re-enabled and the
output voltage rises under control of the soft start
network. If the overload condition is still present the
limiter will trigger again when the threshold current
is reached. The average short circuit current is lim-
ited to a safe value by the dead time introduced by
the soft start network.
The reset circuit generates an output signal when
the supply voltage exceeds a threshold pro-
grammed by an external divider. The reset signal is
generated with a delay time programmed by an ex-
ternal capacitor. When the supply falls below the
threshold the reset output goes low immediately.
The reset output is an open collector.
The scrowbar circuit senses the output voltage and
the crowbar output can provide a current of 100mA
to switch on an external SCR. This SCR is triggered
when the output voltage exceeds the nominal by
20%. There is no internal connection between the
output and crowbar sense input therefore the crow-
bar can monitor either the input or the output.
A TTL - level inhibit input is provided for applications
such as remote on/off control. This input is activated
by high logic level and disables circuit operation. Af-
ter an inhibit the L296 restarts under control of the
soft start network.
The thermal overload circuit disables circuit opera-
tion when the junction temperature reaches about
150 °C and has hysteresis to prevent unstable con-
ditions.
Figure 1 : Reset Output Waveforms
L296 - L296P3/22
Figure 2 : Soft Start Waveforms
Figure 3 : Current Limiter Waveforms
ABSOLUTE MAXIMUM RATINGS
L296 - L296P4/22
THERMAL DATA
ELECTRICAL CHARACTERISTICS(refer to the test circuits Tj = 25o C, Vi = 35V, unless otherwise specified)
DYNAMIC CHARACTERISTICS (pin 6 to GND unless otherwise specified)
DC CHARACTERISTICS
Note (1) : Using min. 7 A schottky diode.
(2) : Guaranteed by design, not 100 % tested in production.
L296 - L296P5/22
