Datasheet

MAX6952
4-Wire Interfaced, 2.7V to 5.5V,
4-Digit 5
✕
7 Matrix LED Display Driver
14 ______________________________________________________________________________________
• If OSC is driven with an accurate frequency, blink
can be used as a seconds counter or similar.
Scan-Limit Register
The scan-limit register sets how many monocolor digits
are displayed, either two or four. A bicolor digit is con-
nected as two monocolor digits.
The multiplexing scheme drives digits 0 and 1 at the
same time, then digits 2 and 3 at the same time. To
increase the effective brightness of the displays, drive
only two digits instead of four. By doing this, the aver-
age segment current doubles, but also doubles the
number of MAX6952s required to drive a given number
of digits.
Because digit 1 is driven at the same time as digit 0
(and digit 3 is driven at the same time as digit 2), only 1
bit is used to set the scan limit. The bit is clear if one or
two digits are to be driven, and set if three or four digits
are to be driven (Table 20). Change the scan-limit
register only when the MAX6952 is in shutdown mode.
Intensity Registers
Display brightness is controlled digitally by four pulse-
width modulators, one for each display digit. Each digit is
controlled by a nibble of one of the two intensity registers,
Intensity10 and Intensity32. The modulator scales the
average segment current in 16 steps from a maximum of
15/16 down to 1/16 of the peak current. The minimum
interdigit blanking time is, therefore, 1/16 of a cycle. The
maximum duty cycle is 15/16. (Tables 21 and 22).
No-Op Register
A write to the no-op register is ignored.
Selecting External Components R
SET
and
C
SET
to Set Oscillator Frequency and
Segment Current
The RC oscillator uses an external resistor RSET and an
external capacitor C
SET
to set the oscillator frequency,
f
OSC
. The allowed range of f
OSC
is 1MHz to 8MHz.
R
SET
also sets the peak segment current. The recom-
mended values of R
SET
and C
SET
set the oscillator to
4MHz, which makes the blink frequencies 0.5Hz and
1Hz. The recommended value of R
SET
also sets the
peak current to 40mA, which makes the segment cur-
rent adjustable from 2.5mA to 37.5mA in 2.5mA steps:
I
SEG
= K
I
/ R
SET
mA
f
OSC
= K
F
/ (R
SET
✕ C
SET
+ C
STRAY
) MHz
Where:
K
I
= 2144
K
F
= 6000
R
SET
= external resistor in kΩ
C
SET
= external capacitor in pF
C
STRAY
= stray capacitance from OSC pin to GND in
pF, typically 2pF
The recommended value of R
SET
is 53.6kΩ and the
recommended value of C
SET
is 26pF.
ADDRESS CODE
(HEX)
REGISTER
DATA
SPI READ
OR WRITE
FUNCTION
0x85 0x00–0x7F Read
Read 7-bit user-definable font data entry from current font
address. MSB of the register data is clear. Font address
pointer is incremented after the read.
0x05 0x00–0x7F Write
Write 7-bit user-definable font data entry to current font
address. Font address pointer is incremented after the
write.
0x05 0x80–0xFF Write Write font address pointer with the register data.
Table 15. Memory Mapping of User-Defined Font Register 0x05
FONT POINTER ADDRESS ACTION
0x80 to 0xF6
Valid range to set the font address pointer. Pointer autoincrements after a font data read or
write, while pointer address remains in this range.
0xF7 Font address resets to 0x80 after a font data read or write to this pointer address.
0xF8 to 0xFF Invalid range to set the font address pointer. Pointer is set to 0x80 if address.
Table 16. Font Pointer Address Behavior