Rainbow Electronics MAX8596Z - Manual (Page 5)

MAX8595Z/MAX8596Z
High-Efficiency, 32V Step-Up Converters
with T A Derating Option for 2 to 8 White LEDs
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 3.6V, I
LED
= 25mA, L = 22µH, C
IN
= 2.2µF, C
OUT
= 0.1µF, C
COMP
= 0.1µF, R
SENSE
= 13 Ω, 4 LEDs,
T A = +25°C, unless otherwise noted.)
Pin Description
PIN NAME FUNCTION
1 OUT
Overvoltage Sense. When V
OUT
is greater than 34V (typ), the internal n-channel MOSFET turns off
until V
OUT
drops below 32V (typ), then the IC re-enters soft-start. Connect a 0.1µF ceramic capacitor
from OUT to ground. In shutdown, V OUT is one diode drop below V IN .
2 IN
Input Voltage Supply. The input voltage range is 2.6V to 5.5V. Connect a 2.2µF ceramic capacitor
from IN to GND.
3 CTRL
Brightness Control Input. The voltage applied to CTRL controls LED brightness. Varying the voltage
from 0.24V to 1.65V (1.72V for the MAX8596Z) adjusts the brightness from dim to 100% brightness,
respectively. Any voltage above 1.65V (1.72V) does not increase brightness. Hold CTRL below
100mV to shut down the IC after an 8.2ms delay.
4 CS
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The
voltage at CS regulates to V
CTRL / 5 or 0.330V (0.343V for the MAX8596Z), whichever is lower.
5 COMP
Compensation Input. Connect a 0.1µF ceramic capacitor (C COMP ) from COMP to GND. C COMP
stabilizes the converter, controls soft-start, and lowpass filters direct PWM dimming at CTRL. C COMP
discharges to 0V through an internal 20k Ω resistor in shutdown.
6 GND Ground. Connect to PGND and the exposed pad directly under the IC.
7 PGND Power Ground. Connect to GND and the exposed pad directly under the IC.
8 LX
Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is
high impedance in shutdown.
— EP
Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect
directly to GND and PGND under the IC.
DIRECT-PWM DIMMING RESPONSE
MAX8595Z toc08
10 µs/div
V
CTRL
2V/div
32kHz 50%
DUTY CYCLE
0
0
0
0
500mV/div
AC-COUPLED
10mA/div
20mV/div
AC-COUPLED
V IN
V
OUT
I LED
CTRL STEP RESPONSE
MAX8595Z toc07
20ms/div
V CTRL 1V/div
0
0
0
0
40mA/div
10V/div
100mA/div I
IN
I LED
V OUT