TPS51116MPWPREP datasheet(11/38 Pages) TI1

11 / 38 page

OUT(LL) +

IN * VOUT)

OUT

TPS51116-EP

www.ti.com

SLUSB52A – OCTOBER 2012 – REVISED NOVEMBER 2012

VDDQ SMPS, Light Load Condition

TPS51116 automatically reduces switching frequency at light load condition to maintain high efficiency. This

reduction of frequency is achieved smoothly and without increase of VOUTripple or load regulation. Detail

operation is described as follows. As the output current decreases from heavy load condition, the inductor current

is also reduced and eventually comes to the point that its valley touches zero current, which is the boundary

between continuous conduction and discontinuous conduction modes. The rectifying MOSFET is turned off when

this zero inductor current is detected. As the load current further decreased, the converter runs in discontinuous

conduction mode and it takes longer and longer to discharge the output capacitor to the level that requires next

ON cycle. The ON-time is kept the same as that in the heavy load condition. In reverse, when the output current

increase from light load to heavy load, switching frequency increases to the constant 400 kHz as the inductor

current reaches to the continuous conduction. The transition load point to the light load operation IOUT(LL) (i.e. the

threshold between continuous and discontinuous conduction mode) can be calculated in Equation 1:

where

•

f is the PWM switching frequency (400 kHz)

(1)

Switching frequency versus output current in the light load condition is a function of L, f, VIN and VOUT, but it

decreases almost proportional to the output current from the IOUT(LL) given above. For example, it is 40 kHz at

IOUT(LL)/10 and 4 kHz at IOUT(LL)/100.

Low-Side Driver

The low-side driver is designed to drive high-current, low-RDS(on), N-channel MOSFET(s). The drive capability is

represented by the internal resistance, which is 3

Ω for V5IN to DRVL and 0.9 Ω for DRVL to PGND. A dead-

time to prevent shoot through is internally generated between high-side MOSFET off to low-side MOSFET on,

and low-side MOSFET off to high-side MOSFET on. 5-V bias voltage is delivered from V5IN supply. The

instantaneous drive current is supplied by an input capacitor connected between V5IN and GND. The average

drive current is equal to the gate charge at VGS = 5 V times switching frequency. This gate drive current as well

as the high-side gate drive current times 5 V makes the driving power which needs to be dissipated from

TPS51116 package.

High-Side Driver

The high-side driver is designed to drive high-current, low on-resistance, N-channel MOSFET(s). When

configured as a floating driver, 5-V bias voltage is delivered from V5IN supply. The average drive current is also

calculated by the gate charge at VGS = 5V times switching frequency. The instantaneous drive current is supplied

by the flying capacitor between VBST and LL pins. The drive capability is represented by the internal resistance,

which is 3

Ω for VBST to DRVH and 0.9 Ω for DRVH to LL.

Current Sensing Scheme

In order to provide both good accuracy and cost effective solution, TPS51116 supports both of external resistor

sensing and MOSFET RDS(on) sensing. For resistor sensing scheme, an appropriate current sensing resistor

should be connected between the source terminal of the low-side MOSFET and PGND. CS pin is connected to

the MOSFET source terminal node. The inductor current is monitored by the voltage between PGND pin and CS

pin. For RDS(on) sensing scheme, CS pin should be connected to V5IN through the trip voltage setting resistor,

RTRIP. In this scheme, CS terminal sinks 10-μA ITRIP current and the trip level is set to the voltage across the

RTRIP. The inductor current is monitored by the voltage between PGND pin and LL pin so that LL pin should be

connected to the drain terminal of the low-side MOSFET. ITRIP has 4500ppm/°C temperature slope to

compensate the temperature dependency of the RDS(on). In either scheme, PGND is used as the positive current

sensing node so that PGND should be connected to the proper current sensing device, i.e. the sense resistor or

the source terminal of the low-side MOSFET.

Submit Documentation Feedback

Product Folder Links: TPS51116-EP

TPS51116MPWPREP 数据表(PDF) 11 Page - Texas Instruments

TPS51116MPWPREP 数据表(HTML) 11 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38

数据表下载