Analog Devices Linear ADI Power LT1964 Demo Manual page 3

DEMO MANUAL LT1964 LOW NOISE, NEGATIVE
CONFIGURATION SETTINGS
Demonstration circuit SCP-LT1964-EVALZ is a –20V,
200mA Low Dropout (LDO) regulator designed to allow
low noise operation in noise sensitive circuits. It is easily
configured for a wide output range and can provide ex-
tremely quiet operation with its high PSRR.
The output of the SCP-LT1964-EVALZ is resistor-program-
mable from –1.22V to –19.5V.
OUTPUT VOLTAGE PROGRAMMING
R6
⎛ ⎞
−V = 1 .2 2 V 1 +
⎝ ⎜ ⎠ ⎟
OUT
R4
Table 2. Resistor Selection Guide for Common Output Voltages
|V | (V)
OUT
1.22
1.25
1.5
1.8
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10
11
12
13
14
15
16
17
18
19
19.5
R6 (Ω) R4 (Ω)
0 Open
1.02k 41.2k
11.5k 49.9k
26.1k 54.9k
13.7k 21.5k
57.6k 54.9k
20.0k 13.7k
49.9k 26.7k
23.2k 10.2k
30.9k 11.5k
31.6k 10.2k
25.7k 10.2k
90.9k 23.2k
174k 40.2k
64.9k 13.7k
137k 26.7k
59.0k 10.7k
63.4k 10.7k
137k 21.5k
169k 24.9k
76.8k 10.7k
150k 18.7k
205k 23.2k
133k 13.7k
110k 10.5k
340k 30.1k
464k 38.3k
102k 7.87k
158k 11.5k
200k 13.7k
102k 6.81k
MICROPOWER LDO REGULATOR
SHDN PIN CONFIGURATION
The SHDN pin is tied to the optional SCP Run/Sequence
header P1. To create a harness for this function, use Molex
part 0510650300 with crimp pin 50212-8000.
To use an active run signal, use a 100k resistor for either
pull-up or pull-down resistors R2 and R7, short R1 with
0W, and use the drive signal from connector P1.
The SHDN pin has fixed 1.6V and –1.9V guaranteed
threshold levels with built-in hysteresis to prevent oscilla-
tions. Holding the said pin to within ±0.8V of ground dis-
ables operation. Choose resistors that can source or sink
at least –3µA or 6µA when active.
BYPASS PIN CONFIGURATION
The addition of a bypass capacitor lowers output noise
considerably, while also increasing startup time. It also al-
lows a lower capacitance to stabilize the loop response for
a given output capacitor ESR. The default 0.01µF capacitor
is recommended for most applications.
Rev. 0
3