CAT4104
http://onsemi.com
3
Table 4. RECOMMENDED EN/PWM TIMING (Min and Max values are over the recommended operating conditions unless
specified otherwise. Typical values are at VIN = 5.0 V, T
AMB
= 25°C.)
Symbol
Name Conditions Min Typ Max Units
T
PS
Turn−On time, EN/PWM rising to I
LED
from
shutdown
I
LED
= 175 mA
I
LED
= 80 mA
1.5
1.3
ms
T
P1
Turn−On time, EN/PWM rising to I
LED
I
LED
= 175 mA 600 ns
T
P2
Turn−Off time, EN/PWM falling to I
LED
I
LED
= 175 mA
I
LED
= 80 mA
400
300
ns
T
R
LED rise time I
LED
= 175 mA
I
LED
= 80 mA
700
440
ns
T
F
LED fall time I
LED
= 175 mA
I
LED
= 80 mA
360
320
ns
T
LO
EN/PWM low time 1
ms
T
HI
EN/PWM high time 5
ms
T
PWRDWN
EN/PWM low time to shutdown delay 4 8 ms
Figure 2. CAT4104 EN/PWM Timing
EN/PWM
SHUTDOWN POWERDOWN SHUTDOWN 0 mA
SHUTDOWN 0 mA
0 mA
SHUTDOWN 0 mA SHUTDOWN 0 mA
LED CURRENT
QUIESCENT CURRENT
50%
50%
90%
10%
T
PS
T
P2
T
HI
T
LO
T
P1
T
R
T
F
T
PWRDWN
I
LED
+
1.2 V
R
SET
100
EN/PWM Operation
The EN/PWM pin has two primary functions. One
function enables and disables the device. The other function
turns the LED channels on and off for PWM dimming
control. The device has a very fast turn−on time (from
EN/PWM rising to LED on) and allows “instant on” when
dimming LED using a PWM signal.
Accurate linear dimming is compatible with PWM
frequencies from 100 Hz to 5 kHz for PWM duty cycle
down to 1%. PWM frequencies up to 50 kHz can be
supported for duty cycles greater than 10%.
When performing a combination of low frequencies and
small duty cycles, the device may enter shutdown mode.
This has no effect on the dimming accuracy, because the
turn−on time T
PS
is very short, in the range of 1 ms.
To ensure that PWM pulses are recognized, pulse width
low time T
LO
should be longer than 1 ms. The CAT4104
enters a “zero current” shutdown mode after a 4 ms delay
(typical) when EN/PWM is held low.
