Datasheet
LTC6990
11
6990fc
For more information www.linear.com/LTC6990
Table 1. DIVCODE Programming
DIVCODE Hi-Z N
DIV
Recommended f
OUT
R1 (k) R2 (k) V
DIV
/V
+
0 0 1 62.5kHz to 1MHz Open Short ≤ 0.03125 ±0.015
1 0 2 31.25kHz to 500kHz 976 102 0.09375 ±0.015
2 0 4 15.63kHz to 250kHz 976 182 0.15625 ±0.015
3 0 8 7.813kHz to 125kHz 1000 280 0.21875 ±0.015
4 0 16 3.906kHz to 62.5kHz 1000 392 0.28125 ±0.015
5 0 32 1.953kHz to 31.25kHz 1000 523 0.34375 ±0.015
6 0 64 976.6Hz to 15.63kHz 1000 681 0.40625 ±0.015
7 0 128 488.3Hz to 7.813kHz 1000 887 0.46875 ±0.015
8 1 128 488.3Hz to 7.813kHz 887 1000 0.53125 ±0.015
9 1 64 976.6Hz to 15.63kHz 681 1000 0.59375 ±0.015
10 1 32 1.953kHz to 31.25kHz 523 1000 0.65625 ±0.015
11 1 16 3.906kHz to 62.5kHz 392 1000 0.71875 ±0.015
12 1 8 7.813kHz to 125kHz 280 1000 0.78125 ±0.015
13 1 4 15.63kHz to 250kHz 182 976 0.84375 ±0.015
14 1 2 31.25kHz to 500kHz 102 976 0.90625 ±0.015
15 1 1 62.5kHz to 1MHz Short Open ≥ 0.96875 ±0.015
OPERATION
Table 1 offers recommended 1% resistor values that ac-
curately produce
the correct voltage division as well as the
corresponding N
DIV
and Hi-Z values for the recommended
resistor pairs. Other values may be used as long as:
1. The V
DIV
/V
+
ratio is accurate to ±1.5% (including resis-
tor tolerances and temperature effects)
2.
The driving impedance (R1||R2) does not exceed 500kΩ.
If the voltage is generated by other means (i.e. the output
of a DAC) it must track the V
+
supply voltage. The last
column in Table 1 shows the ideal ratio of V
DIV
to the
supply voltage, which can also be calculated as:
V
DIV
V
+
=
DIVCODE
+
0.5
16
±1.5%
For example, if the supply is 3.3V and the desired DIVCODE
is 4, V
DIV
= 0.281 • 3.3V = 928mV ± 50mV.
Figure 2 illustrates the information in Table 1, showing
that N
DIV
is symmetric around the DIVCODE midpoint.
On start-up, the DIV pin A/D converter must determine
the correct DIVCODE before the output is enabled. If V
DIV
0.5•V
+
f
OUT
(kHz)
6990 F02
1000
100
10
1
0.1
INCREASING V
DIV
V
+
0V
RECOMMENDED RANGE
EXTENDED RANGE
Hi-Z BIT = 0 Hi-Z BIT = 1
0 15
1
3
2
5
4
7
6
9
8
11
10
13
12
14
Figure 2. Frequency Range and Hi-Z Bit vs DIVCODE