LT1508
DESCRIPTION
By using fixed high frequency PWM current averaging
without the need for slope compensation, the LT1508
achieves far lower line current distortion with a smaller
magnetic element than systems that use either peak
current detection, or zero current switching approach, in
both continuous and discontinuous modes of operation.
The LT1508 also provides filtering capability to reject line
switching noise which can cause instability when fed into
the multiplier. Line current dead zone is minimized with
low bias voltage at the current input to the multiplier. The
LT1508 provides many protection features including peak
current limiting and overvoltage protection. Implemented
with a very high speed process, the LT1508 can be
operated at frequencies as high as 300kHz.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage ........................................................ 27V
GTDR Current Continuous ...................................... 0.5A
GTDR Output Energy ................................................ 5µJ
IAC, RSET, PKLIM Input Current .............................. 20mA
VSENSE, OVP Input Voltage .................................... VMAX
ILIM, VC Input Voltage ................................................ 8V
ISENSE, MOUT Input Current ................................... ±5mA
Operating Junction Temperature Range
LT1508C ................................................ 0°C to 100°C
LT1508I ............................................ – 40°C to 125°C
Thermal Resistance (Junction-to-Ambient)
N Package ................................................... 100°C/W
SW Package ................................................ 120°C/W
PACKAGE/ORDER INFORMATION
TOP VIEW
GTDR1 1
GND2 2
GND1 3
CSET 4
PKLIM 5
CAOUT 6
ISENSE 7
MOUT 8
IAC 9
VAOUT 10
20 GTDR2
19 ILIM
18 VC
17 VCC
16 SS1
15 RSET
14 VSENSE
13 SS2
12 VREF
11 OVP
N PACKAGE
20-LEAD PDIP
SW PACKAGE
20-LEAD PLASTIC SO WIDE
TJMAX = 125°C, θJA = 100°C/ W (N)
TJMAX = 125°C, θJA = 120°C/ W (SW)
Consult factory for Military grade parts.
ORDER PART
NUMBER
LT1508CN
LT1508CSW
LT1508IN
LT1508ISW
ELECTRICAL CHARACTERISTICS
Maximum operating voltage (VMAX) = 25V, VCC = 18V, RSET = 15k to GND, CSET = 1nF to GND, IAC = 100µA, ISENSE = 0V, CAOUT = 3.5V,
VAOUT = 5V, OVP = VREF. No load on any outputs unless otherwise noted.
PARAMETER
Overall
Supply Current (VCC in Undervoltage Lockout)
Supply Current On
VCC Turn-On Threshold (Undervoltage Lockout)
VCC Turn-Off Threshold
Voltage Amplifier (PFC Section)
Voltage Amp Offset
Input Bias Current
Voltage Gain
Voltage Amp Unity-Gain Bandwidth
Voltage Amp Output High (Internally Clamped)
Voltage Amp Output Low
Voltage Amp Short-Circuit Current
CONDITIONS
VCC = Lockout Voltage – 0.2V
11.5V ≤ VCC ≤ VMAX
VAOUT = 3.5V
VSENSE = 0V to 7V
VAOUT = 0V
MIN TYP MAX
UNITS
q 0.25 0.45
q 13 19
q 15.5 16.5 17.5
q 9.5 10.5 11.5
mA
mA
V
V
q – 10
10
q – 25 – 250
70 100
3
q 11.3 13.3
q 1.1 2
q3
8 17
mV
nA
dB
MHz
V
V
mA
2
