MAX8607 データシートの表示（PDF） - Maxim Integrated

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MAX8607

1MHz PWM Boost Converter for 1.5A White LED Camera Flash

Maxim Integrated 

1MHz PWM Boost Converter for 1.5A

White LED Camera Flash

Mode-Select Inputs (EN1, EN2)

Drive EN1 high and EN2 low to enable movie mode. In

this mode, the current regulator regulates the current

through the LED to 1200 times the current set by the

MOV resistor. See the Setting the Movie-Mode Current

section for details on setting the movie-mode current.

Drive EN1 and EN2 high to enable flash mode. In this

mode, the current through the LED is regulated to 5000

times the current set by the FLSH resistor. See the

Setting the Flash-Mode Current section for details on set-

ting the flash-mode current. The time duration of the flash

mode must be set using external circuitry or software.

Drive EN1 low and EN2 high to enable disco mode. In

this mode, the output of the boost converter provides a

regulated +5V at up to 1A for external circuitry, while

the LED current is regulated to 80mA. The LED current

is not adjustable in this mode.

Drive EN1 and EN2 low to place the IC into a low-

power shutdown mode. See the Shutdown section for

more details.

Overvoltage Protection

The output voltage of the MAX8607 is limited by internal

overvoltage-protection (OVP) circuitry, which prevents

the output from exceeding 5.7V under any conditions.

In flash and movie modes, if the output voltage nears

5.5V, the LED current is smoothly reduced through pro-

prietary means to prevent overvoltage without sudden

termination of the output current. In case of an LED with

very high forward voltage (VF), this circuit provides

more reliable and repeatable flash than would a simple

on/off comparator. In disco mode, the output is limited

by the internal 5.0V regulation.

Undervoltage Lockout

The MAX8607 contains undervoltage-lockout (UVLO)

circuitry that disables the IC until VOUTS is greater than

2.38V. Prior to startup, VOUTS is one diode drop below

the input voltage. This ensures a great enough input

voltage for startup.

Soft-Start

The MAX8607 attains soft-start by charging CCOMP

with a 100µA current source. During this time, the inter-

nal MOSFET is switching at the minimum duty cycle.

Once VCOMP rises above 1V, the duty cycle increases

until output reaches the desired regulation level. COMP

is pulled to GND with a 140Ω internal resistor during

UVLO, OVP, or shutdown. See the Typical Operating

Characteristics for an example of soft-start operation.

Table 1. EN1 and EN2 Mode Selection

EN1

EN2

MODE

0

0

Shutdown

0

1

Disco Mode

1

0

Movie Mode

1

1

Flash Mode

Shutdown

Drive EN1 and EN2 low to place the MAX8607 into a

low-power shutdown mode. In shutdown, supply cur-

rent is reduced to 0.1µA (typ). CCOMP is discharged

during shutdown, allowing the device to reinitiate soft-

start when it is enabled. The internal MOSFET and syn-

chronous rectifier are turned off during shutdown;

however, OUT is one body-diode drop below the input.

LED is high impedance so the external LED is off, but

any external circuitry on OUT is not disconnected and,

therefore, should include its own shutdown capability.

Typical shutdown timing characteristics are shown in

the Typical Operating Characteristics.

Ambient Temperature Derating Function

The MAX8607 limits the maximum LED current depend-

ing on its die temperature. Once the die temperature

reaches +40°C, the LED current decreases by 1.67%

per °C. This corresponds to approximately 0mA of LED

current at +100°C. Due to the package’s exposed pad-

dle, the die temperature is very close to the PC board

temperature. The temperature derating function allows

the LED current to be safely set higher at normal oper-

ating temperatures, thereby allowing either a brighter

flash or movie light to be used for normal ambient tem-

peratures. See the Typical Operating Characteristics

for a graph of LED Current vs. Ambient Temperature.

Applications Information

Setting the Movie-Mode Current

To set the LED current during movie mode, connect a

resistor from MOV to GND (RMOV). VMOV is regulated

to 0.6V and the current through RMOV is mirrored to

LED with a gain of 1200. RMOV is calculated as:

RMOV = (0.6V x 1200) / ILED(MOV)

Setting the Flash-Mode Current

To set the LED current during flash mode, connect a

resistor from FLSH to GND (RFLSH). VFLSH is regulated

to 0.6V and the current through RFLSH is mirrored to

LED with a gain of 5000. RFLSH is calculated as:

RFLSH = (0.6V x 5000) / ILED(FLSH)

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