RT2702 datasheet(16/20 Pages) RICHTEK

16 / 20 page

RT2702

www.richtek.com

DS2702-00 October 2016

is a registered trademark of Richtek Technology Corporation.

Let

EQU

NTC

= R

(R / /R

)



EQU

SEN

= CSEN

L,DCR

EQU

SEN





According to current sense network and temperate, the

corresponding equation is represented as follows :

Next, let

m =

L,DCR

SEN



Then

NTC

= R

SEN

NTCP































Step 1 : Given the two system temperature TL and TH at

which are compensated.

Step 2 : Two equations can be listed as

R(T ) R

NTC L

m(T )

LSEN

S R(T ) R

NTC L

R(T ) R

NTC L

= R

SEN

S R(T ) R

NTC L



























R(T ) R

NTC H

m(T )

SEN

S R(T ) R

NTC H

R(T ) R

NTC H

= R

SEN

S R(T ) R

NTC H



























Step 3 : Since R

P is usually set equal to RNTC(25°C), two

unknowns, RSEN and RS, can be calculated using two

equations.

Output Over-Voltage Protection (OVP)

The voltage on the FB pin is monitored for over-voltage

protection. When the FB voltage exceeds 12.5% of its

set voltage threshold, over-voltage protection is triggered,

then the signal of POK and PWM go low. This behavior

should command DrMOS to discharge the output capacitor.

A 10

μs delay is applied to OVP detection circuit to prevent

false trigger.

Besides, anti-overshoot(AOS) would be triggered when

VFB is above 642mV (VREF + 42mV) and then PWM

becomes tri-state. Thus more power, which is stored in

inductor, would be eliminated by the body diode of LSMOS

in DrMOS, and prevents VOUT from having too much

overshoot. If inductor has too much power stored in itself,

FB1

OUT

REF

FB2

VV1



 





where the VREF is 0.6V (typical), and the recommended

output voltage range is between 0.6V and 3V.

then AOS won't be able to prevent system from triggering

OVP. In this case, OVP would over-write AOS behavior,

makes PWM go low and intends to discharge VOUT with

negative current on inductor.

Output Under-Voltage Protection (UVP)

The FB voltage is monitored for under voltage protection.

When the FB voltage is less than 12.5% of its set voltage

threshold during normal operation, under-voltage protection

is triggered, then the signal of POK and DISB to be low.

This behavior should turn off DrMOS. When UVP is

triggered, the controller begins hiccup procedure and re-

boost after 20ms. A 10

μs delay is applied to UVP detection

circuit to prevent false trigger.

Over-Thermal Protection (OTP)

The RT2702 features an over-thermal protection circuitry

to prevent damage from excessive heat dissipation. The

OTP function occurs when the die temperature exceeds

150

°C, then DISB goes low and turns off internal linear

regulator. Once the junction temperature is cooled down

by approximately 25

°C, the RT2702 will reboost from the

beginning.

Thermal Shutdown Detection (THWN)

The RT2702 has a thermal shutdown detection input THWN

pin for external driver DrMOS. The RT2702 will pull low

DISB if the voltage of thermal warning flag is lower than

0.4V.

Output Voltage Setting

The output voltage waveform is shown as Figure 7, which

can be adjusted from 0.6V to 3.3V by setting the feedback

resistors, RFB1 and RFB2 (see Figure 8). Choose RFB2 to

be approximately 30k and solve for RFB1 using the equation

below :

RT2702 Datasheet(PDF) 16 Page - Richtek Technology Corporation

RT2702 Datasheet(HTML) 16 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL