Datasheet

LT1512
11
1512fb
For more information www.linear.com/LT1512
applicaTions inForMaTion
input to R5 is equal to the processor V
CC
level multiplied
by the inverse PWM ratio. This assumes that the PWM
signal is a CMOS output that swings rail-to-rail with a
source resistance less than a few hundred ohms. The
negative voltage is converted to a current by R5 and R6
and filtered by C7. This current multiplied by R4 generates
a voltage that subtracts from the 100mV sense voltage
of the LT1512. This is not a high precision technique
because of the errors in V
CC
and the diode voltage, but
it can typically be used to adjust charging current over a
20% to 100% range with good repeatability (full charg
-
ing current accuracy is not affected). To reduce the load
on the logic signal, R4 has been increased from 24 to
200. This causes a known increase in full-scale charging
package DescripTion
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510 Rev I)
Dimensions in inches (millimeters) unless otherwise noted.
N8 REV I 0711
.065
(1.651)
TYP
.045 – .065
(1.143 – 1.651)
.130 ±.005
(3.302 ±0.127)
.020
(0.508)
MIN
.018 ±.003
(0.457 ±0.076)
.120
(3.048)
MIN
.008 – .015
(0.203 – 0.381)
.300 – .325
(7.620 – 8.255)
.325
+.035
–.015
+0.889
–0.381
8.255
( )
1 2
3
4
8 7 6
5
.255 ±.015*
(6.477 ±0.381)
.400*
(10.160)
MAX
NOTE:
1. DIMENSIONS ARE
INCHES
MILLIMETERS
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
.100
(2.54)
BSC
N Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510 Rev I)
current (PWM = 0) of 3% due to the 5k input resistance of
the I
FB
pin. Note that 100% duty cycle gives full charging
current and that very low duty cycles (especially zero!)
will not operate correctly. Very low duty cycle (<10%)
is a problem because the peak detector requires a finite
up-time to reset C6.
More Help
Linear Technology Field Application Engineers have a CAD
spreadsheet program for detailed calculations of circuit
operating conditions, and our Applications Department is
always ready to lend a helping hand. For additional informa
-
tion refer to the LT1372 data sheet. This part is identical to
the LT1512 except for the current amplifier cir
cuitry.