RT9832 datasheet(10/12 Pages) RICHTEK

10 / 12 page

RT9832

DS9832-00

January 2013

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Application Information

The RT9832 is a PWM duty generator with adjustable

duty setting. The PWM frequency is fixed 0.5Hz typically.

The device operates over a wide input voltage range from

2.8V to 20V.

Capacitor Selection

Input ceramic capacitor of 0.47

μF is recommended for the

RT9832. For better voltage filtering, ceramic capacitors

with low ESR are recommended. X5R and X7R types are

suitable because of their wider voltage and temperature

ranges.

UVLO/OTP

As the input voltage is lower than a specified value, the

chip will enter protection mode to prevent abnormal

function. As the die temperature is higher then 160

°C, the

chip will also enter protection mode. The output will be

turned off during protection mode to prevent abnormal

operation.

Duty Cycle Setting

The duty cycle is set by an external resistor on RSET

pin, and the PWM duty is adjustable from 1% to 100%,

according to following equation :

Figure 2. Derating Curve of Maximum Power Dissipation

0.0

0.2

0.4

0.6

0.8

1.0

025

100

125

Ambient Temperature (°C)

Four-Layer PCB

SET

Duty Cycle =

10k

When the RSET is floating, the duty cycle is set at 50%

typically.

Enable

The RT9832 enable is an active low logic signal control for

output. The enable pin is pulled to low with internal

resistors. When enable logic is low, a PWM duty will be

on; when enable logic is high, a PWM duty will be off.

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature. The

maximum power dissipation can be calculated by the

following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA

where TJ(MAX) is the maximum junction temperature, TA is

the ambient temperature, and

θJAis the junction to ambient

thermal resistance.

For recommended operating condition specifications, the

maximum junction temperature is 125

°C. The junction to

ambient thermal resistance,

θJA, is layout dependent. For

WL-CSP-6B 0.8x1.2 (BSC) package, the thermal

resistance,

θJA, is 148°C/W on a standard JEDEC 51-7

four-layer thermal test board. The maximum power

dissipation at TA = 25

°C can be calculated by the following

formula :

PD(MAX) = (125

°C − 25°C) / (148°C/W) = 0.68W for

WL-CSP-6B 0.8x1.2 (BSC) package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance,

θJA. The derating curve in Figure 2 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

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