LM2753SDX/NOPB National Semiconductor, LM2753SDX/NOPB Datasheet - Page 7

• Manufacturer Part Number: LM2753SDX/NOPB
• Description: IC LED DRIVER PHOTO FLASH 10-LLP
• Manufacturer: National Semiconductor
• Type: Photo Flash LEDr

Specifications of LM2753SDX/NOPB

• Topology: PWM, Switched Capacitor (Charge Pump)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 725kHz
• Voltage - Supply: 3 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 10-LLP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 250mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Efficiency: -
• Other names: LM2753SDX

Application Information
CIRCUIT DESCRIPTION
The LM2753 is a Switched Capacitor Doubler with a regulated
5V output. It is capable of continuously supplying up to 200mA
at 5V to a load connected to V
Frequency Modulation and a Multi-Level Switch Array to reg-
ulate and maintain the output voltage. For higher load cur-
rents, such as during Flash operation, the output voltage is
allowed to droop to supply the necessary current. Although
there is no current limit on this device, the device will auto-
matically default to a gain of 1 when the output is brought
below the input voltage. This configuration limits the input
current to about 300mA (typ.). The operating range for the
LM2753 is over the extended Li-Ion battery range from 2.7V
to 5.5V.
Aside from powering Flash LEDs, the LM2753 is suitable for
driving other devices with power requirements up to 200mA.
White LEDs can also be connected to this device to backlight
a cellular phone keypad and display. The LED brightness can
be controlled by applying a PWM (Pulse Width Modulation)
signal to the Enable pin (EN) during "Torch" mode, or to the
Flash pin during "Flash" mode. (see PWM BRIGHTNESS
CONTROL PROCEDURES section).
SOFT START
Soft Start is engaged when the device is taken out of Shut-
down mode (EN = logic HIGH) or when voltage is supplied
simultaneously to the VIN and EN pins. During Soft Start, the
voltage on V
reference voltage is being ramped up. The output voltage is
programmed to rise from 0V to 5V in 640µs (typ.).
ENABLE MODE
The Enable logic pin (EN) disables the part and reduces the
quiescent current to 0.1µA (typ.). The LM2753 has an active-
high enable pin (LOW = shut down, HIGH = operating). The
LM2753 EN pin can be driven with a low-voltage CMOS logic
signal (1.5V logic, 1.8V logic, etc). There is an internal
300kΩ pull-down resistor between the EN and GND pins of
the LM2753.
FLASH MODE
The Flash logic pin (Flash) controls the internal FET connect-
ed between the V
LM2753 has an active-HIGH Flash pin (LOW = shut down,
HIGH = operating). A logic HIGH signal must be present on
the EN pin before a logic HIGH signal is place on the Flash
input pin. The EN and Flash input pins can be connected to-
gether and controlled with the same logic signal. The turn-on
time for I
time of the device. The turn-on time for the internal FET is
typically 10ns when the device is already on (EN signal HIGH,
V
voltage CMOS logic signal (1.5V logic, 1.8V logic, etc). There
is an internal 300kΩ pull-down resistor between the Flash and
GND pins of the LM2753.
CAPACITOR SELECTION
The LM2753 requires 3 external capacitors for proper opera-
tion. Surface-mount multi-layer ceramic capacitors are rec-
ommended. These capacitors are small, inexpensive and
have very low equivalent series resistance (ESR,
typ.). Tantalum capacitors, OS-CON capacitors, and alu-
minum electrolytic capacitors are generally not recommended
for use with the LM2753 due to their high ESR, as compared
to ceramic capacitors.
OUT
at 5V). The LM2753 Flash pin can be driven with a low-
OUT
OUT
in this configuration will be limited by the turn-on
will ramp up in proportion to the rate that the
OUT
and I
OUT
OUT
pins on the LM2753. The
. This device uses Pulse
≤
15mΩ
7
For most applications, ceramic capacitors with X7R or X5R
temperature characteristic are preferred for use with the
LM2753. These capacitors have tight capacitance tolerance
(as good as ±10%), hold their value over temperature (X7R:
±15% over −55°C to 125°C; X5R: ±15% over −55°C to 85°C),
and typically have little voltage coefficient when compared to
other types of capacitors. However selecting a capacitor with
a voltage rating much higher than the voltage it will be sub-
jected to, will ensure that the capacitance will stay closer to
the capacitor's nominal value. Capacitors with Y5V or Z5U
temperature characteristic are generally not recommended
for use with the LM2753. Capacitors with these temperature
characteristics typically have wide capacitance tolerance
(+80%, −20%), vary significantly over temperature (Y5V:
+22%, −82% over −30°C to +85°C range; Z5U: +22%, −56%
over +10°C to +85°C range), and have poor voltage coeffi-
cients. Under some conditions, a nominal 1µF Y5V or Z5U
capacitor could have a capacitance of only 0.1µF. Such detri-
mental deviation is likely to cause Y5V and Z5U capacitors to
fail to meet the minimum capacitance requirements of the
LM2753. Table 1 lists suggested capacitor suppliers for the
typical application circuit.
FLASH LED SELECTION
The LM2753 provides a 5V (typ.) fixed voltage to drive a Flash
LED with a continuous current up to 200mA (typ.). At LED
currents above 200mA (typ.), the output of the LM2753 is al-
lowed to droop to deliver the desired current to the Flash LED.
This droop limits the maximum forward voltage and in turn the
maximum current that can be supplied to a given LED. LEDs
should be chosen such that the LED forward voltage at the
desired maximum LED current does not exceed the output
voltage of the LM2753 when loaded down with that same cur-
rent. It is suggested that the selected LEDs be binned due to
the relatively high forward voltage tolerance of Flash LEDs.
The typical and maximum diode forward voltage depends
highly on the manufacturer and their technology. Table 2 lists
several suggested manufacturers.
PFM REGULATION
The LM2753 achieves its tightly regulated output voltage with
pulse-frequency modulated (PFM) regulation. PFM simply
means the part only pumps when charge needs to be deliv-
Semiconductor
Manufacturer
Manufacturer
Taiyo Yuden
Panasonic
Lumiled
Agilent
Citizen
TABLE 1. Ceramic Capacitor Manufacturers
Osram
Nichia
Murata
Seoul
AOT
TDK
TABLE 2. Flash LED Selection
www.agilent.com/semiconductors
www.panasonic.co.jp/semicon/
www.component.tdk.com
en.seoulsemicon.co.kr
www.osram-os.com
www.lumileds.com
www.t-yuden.com
www.c-e.co.jp/e/
www.murata.com
www.aot.com.tw
www.nichia.com
Contact
Contact
www.national.com