MAX16810 Maxim Integrated Products, MAX16810 Datasheet - Page 14

• Manufacturer Part Number: MAX16810
• Description: (MAX16809 / MAX16810) Integrated 16-Channel LED Drivers
• Manufacturer: Maxim Integrated Products

Integrated 16-Channel LED Drivers with
Switch-Mode Boost and SEPIC Controller
Figure 1c. OUT_ _ Driver Internal Diagram
The advantages of current-mode control over voltage-
mode control are twofold. First, there is the feed-for-
ward characteristic brought on by the controller’s ability
to adjust for variations in the input voltage on a cycle-
by-cycle basis. Second, the stability requirements of
the current-mode controller are reduced to that of a sin-
gle-pole system unlike the double pole in the voltage-
mode control scheme. The MAX16809/MAX16810 use
a current-mode control loop where the output of the
error amplifier is compared to the current-sense voltage
(V
inverting input of the CPWM comparator, the output of
the comparator is low and the switch is turned on at
each clock pulse. When the current-sense signal is
higher than the inverting input of the CPWM compara-
tor, the output is high and the switch is turned off.
The turn-on supply voltage for the MAX16809/
MAX16810 is 8.4V (typ). Once V
reference powers up. There is a 0.8V of hysteresis from
the turn-on voltage to the UVLO threshold. Once V
reaches 8.4V, the MAX16809/MAX16810 operate with
V
the device is in UVLO. When in UVLO, the quiescent
supply current into V
OUT and REF are pulled low.
OUT drives an external n-channel MOSFET and swings
from AGND to V
absolute maximum V
14
CC
CS
1.23V
______________________________________________________________________________________
). When the current-sense signal is lower than the
down to 7.6V. Once V
R
1.23
EST
SET
68W/L
CC
Undervoltage Lockout (UVLO)
Switch-Mode Controller
. Ensure that V
Current-Mode Control Loop
GS
CC
V+
rating of the external MOSFET.
falls back to 32µA (typ), and
945R
CC
W/L
goes below 7.6V (typ),
CC
CC
MOSFET Driver
reaches 8.4V, the
remains below the
PGND
R
OUT_ _
CC
OUT is a push-pull output with the on-resistance of the
pMOS typically 3.5Ω and the on-resistance of the nMOS
typically 4.5Ω. The driver can source 2A and sink 1A typi-
cally. This allows for the MAX16809/MAX16810 to quickly
turn on and off high gate-charge MOSFETs. Bypass V
with one or more 0.1µF ceramic capacitors to AGND,
placed close to V
drive the external MOSFET depends on the total gate
charge (Q
The power dissipation in the MAX16809/MAX16810 is a
function of the average output drive current (I
the following equation to calculate the power dissipation
in the device due to I
where I
Typical Operating Characteristics for the operating
supply current at a given frequency.
The MAX16809/MAX16810 include an internal error
amplifier. The inverting input is at FB and the noninvert-
ing input is internally connected to a 2.5V reference.
Set the output voltage using a resistive divider between
output of the converter V
following formula to set the output voltage:
where V
The oscillator frequency is programmable using an
external capacitor and a resistor at RTCT (see RTCT in
the Typical Operating Circuits ). R
RTCT to the 5V reference (REF), and C
from RTCT to AGND. REF charges C
its voltage reaches 2.8V. C
an 8.3mA internal current sink until C
es 1.1V, at which time C
R
charge and discharge times of C
charge time as follows:
where t
Farads (F).
The discharge time is then:
where t
Farads (F).
T
t
again. The oscillator’s period is the sum of the
D
= (R
CC
FB
C
D
T
G
is in seconds, R
is in seconds, R
= 2.5V.
) and operating frequency of the converter.
is the operating supply current. See the
x C
PD = (I
V
T
OUT
x 1000) / [(4.88 x R
I
CC
t
DRIVE
C
DRIVE
= 0.57 x R
. The average current sourced to
=
DRIVE
⎛
⎜
⎝
T
= (Q
1
OUT
:
is allowed to charge through
+
+ I
T
T
T
G
, FB, and AGND. Use the
R
R
then discharges through
in ohms (Ω), and C
in ohms (Ω), and C
CC
2
1
T
x f
⎞
⎟
⎠
x C
) x V
SW
x V
T
T
T
Error Amplifier
)
is connected from
) - (1.8 x 1000)]
T
T
T
CC
FB
’s voltage reach-
. Calculate the
through R
T
is connected
Oscillator
DRIVE
T
). Use
until
T
T
CC
in
in