U6084B Datasheet, PDF (4/8 Pages) ATMEL Corporation – PWM Power Control with Automatic Duty-cycle Reduction

U6084B
2. Current Limitation
The lamp current is limited by a control amplifier that
protects the external power transistor. The voltage drop
across an external shunt resistor acts as the measured vari-
able. Current limitation takes place for a voltage drop of
 V_T1 100 mV. Owing to the difference
 V_T1–V_T2 10 mV, current limitation occurs only when
the short-circuit detection circuit has responded.
After a power-on reset, the output is inactive for half an
oscillator cycle. During this time , the supply voltage ca-
pacitor can be charged so that current limitation is
guaranteed in the event of a short circuit when the IC is
switched on for the first time.
Pins 13 and 14, Charge Pump and Output
Output, Pin 14, is suitable for controlling a power MOS-
FET. During the active integration phase, the supply
current of the operational amplifier is mainly supplied by
the capacitor C₃ (bootstrapping). Additionally, a trickle
 ^{charge is generated by an integrated oscillator}
(f₁₃ 400 kHz) and a voltage doubler circuit. This per-
mits a gate voltage supply at a duty cycle of 100%.
Pin 16, Supply Voltage, V_s or V_Batt
Undervoltage Detection:
In the event of voltages of approx. V_Batt < 5.0 V, the ex-
ternal FET is switched off and the latch for short-circuit
detection is reset.
 ^{A hysteresis ensures that the FET is switched on again at}
approximately V_Batt 5.4 V.
Overvoltage Detection
Stage 1
If overvoltages V_Batt > 20 V (typ.) occur, the external
transistor is switched off and switched on again at
V_Batt < 18.5 V (hysteresis).
Stage 2
If V_Batt > 28.5 V (typ.), the voltage limitation of the IC
is reduced from 26 V to 20 V. The gate of the external
transistor remains at the potential of the IC ground, thus
producing voltage sharing between FET and lamps in the
event of overvoltage pulses occuring (e.g., load-dump).
The short-circuit protection is not in operation. At
V_Batt < 23 V, the overvoltage detection stage 2 is
switched off.
Absolute Maximum Ratings
Parameters
Junction temperature
Ambient temperature range
Storage temperature range
Symbol
Value
Unit
T_j
150
°C
T_amb
–40 to +110
°C
T_stg
–55 to +125
°C
Thermal Resistance
Junction ambient
Parameters
Symbol
R_thJA
Value
120
Unit
K/W
Electrical Characteristics
T_amb = –40 to +110°C, V_Batt = 9 to 16.5 V, (basic function is guaranteed between 6.0 V to 9.0 V) reference point ground,
unless otherwise specified (see figure 1). All other values refer to Pin GND (Pin 1).
Parameters
Current consumption
Supply voltage
Stabilized voltage
Battery undervoltage
detection
Test Conditions / Pins Symbol Min.
Typ.
Max.
Unit
Pin 16
Overvoltage detection,
stage 1
I_S
V_Batt
6.8
mA
25
V
I_S = 10 mA
– on
– off
Pin 16
V_S
24.5
27.0
V
V_Batt
4.4
5.0
5.6
V
4.8
5.4
6.0
4 (8)
TELEFUNKEN Semiconductors
Rev. A1, 14-Feb-97