RT8901 datasheet(8/10 Pages) RICHTEK

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RT8901

DS8901-03 October 2013

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Applications Information

The GPM consists of two high-voltage MOSFETs which

include P1 between VGH and VGHM and P2 between

VGHM and RE. The switch-control block is enabled when

VDPM exceeds VREF and then P1 and P2 are controlled

by VFLK and CD. There are three different modes of

operation (see the Typical Application Circuit and Timing

Diagram).

Activate the Mode A by connecting CD to 5V. When VFLK

is logic high, P1 turns on and P2 turns off, VGHM is

connected to VGH. When VFLK is logic low, P1 turns off

and P2 turns on, VGHM is connected to RE, and VGHM

is discharged through the resistor between RE and GND.

P2 turns off and stops discharging VGHM when VGHM

reaches 10 times the voltage of the VD pin.

When CD is connected with a capacitor, the switch control

block works in the Mode B. The rising edge of the VFLK

will turns on P1 and turns off P2, connecting VGHM to

VGH. An internal N-MOSFET Q3 between CDO and GND

is also turned on to discharge the external capacitor

between CD and GND. The falling edge of VFLK turns off

Q3, and an internal 50

μA current source starts charging

the CD capacitor. Once VCD exceeds VREF, the switch

control circuit turns off P1 and turns on P2, connecting

VGHM to RE. VGHM is discharged through the resistor

connected between RE and GND. P2 turns off and stops

discharging VGHM when VGHM reaches 10 times the

voltage of the VD pin.

Activate the Mode C by connecting CD to 3.3V. P1 will be

turned on, P2 will be turned off and Q3 will be turned on

respectively when VFLK is high. When VFLK is low, Q3

will be turned off and CDO will be pull to the same voltage

level as CD through a 1k

Ω resistor. P1 and P2 will be turn

off and on respectively when comparator detects CDO

voltage is greater than 2.5V. VGHM is discharged through

the resistor connected between RE and GND. P2 turns

off and stops discharging VGHM when VGHM reaches 10

times the voltage of VD pin.

The timing of enabling the switch control block can be

adjusted with an external capacitor connected between

VDPM and GND. An internal 5

μA current source starts

charging the VDPM capacitor if all internal power is ready.

The voltage on the VDPM linearly rises because of the

constant-charging current. When VDPM goes above VREF,

the switch control block is enabled.

Output Current Maximum Rating (rms value)

TheGPM output current is RMS value and the RMS current

boundary depends on ambient temperature with fixed P1

and P2 on-resistance. In figure 6, the test condition is

VGH = 30V with R1 = 0

Ω and R1 = 43Ω. The boundary is

located at 125

°C junction temperature for safe operation

in SOP-8 package.

Figure 6. Output Current Maximum Rating vs. Ambient

Temperature with R1 = 0

Ω and R1 = 43Ω

Thermal Considerations

For continuous operation, do not exceed absolute

maximum operation junction temperature. The maximum

power dissipation depends on the thermal resistance of

IC package, PCB layout, the rate of surroundings airflow

and temperature difference between junction to ambient.

The maximum power dissipation can be calculated by

following formula :

PD(MAX) = ( TJ(MAX) - TA ) /

θJA

Where TJ(MAX) is the maximum operation junction

temperature, TA is the ambient temperature and the

θJAis

the junction to ambient thermal resistance.

RMS Current vs. Ambient Temperature

100

120

140

160

180

20406080

100

120

140

Ambient Temperature (°C)

R1 = 0

R1 = 43

RMS Curent vs. Ambient Temperature

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