NCP5010 Просмотр технического описания (PDF) - ON Semiconductor

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NCP5010

500 mW Boost Converter for White LEDs

ON Semiconductor 

NCP5010

Finally an acceptable DCR must be selected regarding

losses in the coil and must be lower than 1.4 W to limit

excessive voltage drop. In addition, as DCR is reduced,

overall efficiency will improve. Some recommended

inductors include but are not limited to:

TDK VLF4012AT−220MR51

TDK VLP4612T−220MR34

TDK VLP5610T−220MR45

Coilcraft LPO6610−223M

Coilcraft DO1605T−223MX

Coilcraft DT1608C−223

Capacitor Selection

To minimize the output ripple, a low ESR multi−layer

ceramic capacitor type X5R or equivalent should be

selected. For LED driver applications a 1 mF (min) 25 V is

adequate. The NCP5010 can be operated in a voltage mode

configuration (see Figure 34) for applications such as

OLED power. Under these conditions, COUT can be

increased to 2.2 mF, 25 V or more to reduce the output

ripple.

The input needs to be bypassed by a X5R or an equivalent

low ESR ceramic capacitor near the VIN pin. A 1 mF, 6.3 V

is enough for most applications. However, if the connection

between VIN and the battery is too long then a 4.7 mF or

higher ceramic capacitor may be needed. Some

recommended capacitors include but are not limited to:

TDK C1608X5R1E105MT

TDK C2012X5R1E105MT

TDK C1608X5R0J105MT

TDK C2012X5R1E225MT

Murata GRM185R61A105KE36D

Murata GRM188R60J475KE19D

Murata GRM216R61E105KA12D

Short−Circuit Protection

If VOUT is falls below 50% of VIN then a short−circuit

condition is detected. When this event is detected, the

PWM circuitry is disabled and the NMOS power switch is

not turned on. Power will be supplied to the load through

the inductor, rectifier and high side switch. Once VOUT

reaches 66% of VIN, then the PWM circuitry is enabled. In

normal conditions when the device is enabled by an active

high signal on CTRL, the short circuit condition continues

until the output capacitor is charged by the limited current

up to 66% of VIN.

VOUT

2/3 VIN

1/2 VIN

Normal

Running

T

SC Short−Circuit Condition End of Short−Circuit

Occurs Current limited at 20mA Detected Converter

Converter in Standby Starts Again

Figure 27. Example of the VOUT Voltage Behavior

When Short−Circuit Arises

Overvoltage Protection (OVP)

If there is an open load condition such as a loose

connection to the White LED string, the converter will

provide current to the Cout capacitor and the voltage at the

output will rise rapidly. This could cause damage to the part

if there was not some external clamping Zener clamping

circuit. To eliminate the need for these external

components, the NCP5010 incorporates an OVP circuit

which monitors the output voltage with a resistive divider

network and a comparator and voltage reference. If the

output reaches 22 V (nominal), the OVP circuit will detect

a fault and inhibit PWM operation. This comparator has

1 V of hysteresis so when the load is reconnected and the

voltage drops below 21 V, the PWM operation will resume

automatically. The 22 V OVP threshold allows the use of

25 V ceramic capacitors for the output filter capacitor.

Undervoltage Lock Out (UVLO)

To ensure proper operation under all conditions, the

device has a built−in undervoltage lock out (UVLO)

circuit. During power−up, the device will remain disabled

until the input voltage exceeds 2.4 V nominal. This circuit

has 200 mV of hysteresis to provide noise immunity to

transient conditions.

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