MAX8678 Maxim Integrated Products, MAX8678 Datasheet - Page 9

• Manufacturer Part Number: MAX8678
• Description: White LED Charge Pump
• Manufacturer: Maxim Integrated Products

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The short-circuit protection detects when an LED is
shorted and disables the corresponding current regula-
tor to avoid wasting battery power. If any LED fails as an
open circuit, the charge pump is forced on and the cor-
responding LED_ pin is internally connected to NEG.
Table 2. LED Current Levels
Figure 3. Serial-Pulse Gain Adjustment
RISING
EDGES
ENLED
10
11
12
13
14
15
16
INTERNAL
1
2
3
4
5
6
7
8
9
SETTING
ENAMP
GAIN
GAIN
Open-Circuit and Short-Circuit Protection
LED CURRENT
OFF
OFF
(mA)
24.0
22.4
20.8
19.2
17.6
16.0
14.4
12.8
11.2
1
9.6
8.0
6.4
5.6
4.8
4.0
3.2
_______________________________________________________________________________________
_______________________________________________________________________________________
-9dB
t
HI
2
-6dB
t
LO
EDGES
ENLED
RISING
3
-3dB
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
—
4
0dB
3.2ms
t
HOLD
LED CURRENT
10ms typ
(mA)
t
2.8
2.4
2.0
1.6
1.4
1.2
1.0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
UP
White LED Charge Pump with
—
0dB
1
-9dB
2
-6dB
The MAX8678 contains a 1.1W RMS DirectDrive mono
speaker amplifier. It features a low-power shutdown
mode and click-and-pop suppression.
An internally generated common-mode BIAS voltage of
V
BIAS capacitor (C4 in Figure 1) improves PSRR and
THD+N by reducing power supply and other noise
sources at the common-mode bias node, and also
generates the clickless/popless startup DC bias wave-
form for the speaker amplifier. A 0.1µF BIAS capacitor
is recommended for most applications. Increasing C4
to 1µF slows turn-on and turn-off times by a factor of 10
and improves PSRR by 20dB (at 1kHz). Do not connect
external loads to BIAS.
The MAX8678 audio amplifier features a low-power shut-
down mode for reduced current consumption. Hold
ENAMP low for 3.2ms to shut down the audio amplifier.
Entering shutdown disables the amplifier’s bias circuitry,
causes the audio outputs to go high impedance, and
drives BIAS to GND.
The MAX8678 features Maxim’s industry-leading click-
and-pop suppression circuitry. During startup, the amplifi-
er common-mode bias voltage ramps to the DC bias
point. When entering shutdown, the amplifier outputs are
high impedance to 100kΩ between the outputs. This
scheme minimizes the energy present in the audio band.
IN
3
/ 2 sets the DC bias level for the audio outputs. The
-3dB
1.1W Audio Amplifier
7
+9dB
8
+12dB
3.2ms
t
HOLD
10ms (typ)
Click-and-Pop Suppression
t
UP
+12dB
t
t
HI
LO
3.2ms
t
SHDN
Audio Amplifier
= 500ns TO 500μs
= 500ns TO 500μs
Shutdown Mode
OFF
t
1μs (typ)
PD
OFF
Bias
9
9