HM4033 Ver la hoja de datos (PDF) - Unspecified

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componentes Descripción

Fabricante

HM4033

PFM Step-up Battery Charger Controller IC

Unspecified 

HM4033

VIN is input voltage in Volt(V)

VBAT is battery voltage in Volt(V)

VD is the forward voltage of diode D1 in Volt(V)

RCS is inductor current sense resistor in ohm(Ω)

Estimate Charge Current

HM4033 controls the charge current by controling inductor current(Input current), so the charge current will vary

with the input voltage and battery voltage.

Generally, the charge current can be estimated by the following equation:

Where,

ICH is the charge current in Ampere (A)

VIN is input supply in Volt(V)

IL is average inductor current, which is determined by 0.135／RCS in Ampere(A)

ηis converter’s efficiency, which is around 85%

VBAT is battery voltage in Volt(V)

Charge Termination Voltage at Battery Terminal

In the application circuit shown in Figure 1, battery voltage is feedback to FB pin via the resistor divider formed

by R1 and R2, HM4033 decides the charge status based on FB’s voltage. When FB voltage rises to 1.205V

(Typical), HM4033 enters termination mode.

The voltage at battery terminal when the charging is terminated:

VBAT＝1.205×(1＋R1／R2)

Since R1 and R2 will draw some current from the battery, R1+R2 should be chosen first according to the current

consumption affordable, then calculate R1 and R2 based on the above equation.

When designing the charge termination voltage at the battery terminal, the battery’s internal resistance and the

parasitic resistance from the PCB to the battery’s terminals should be taken into consideration. As illustrated in

Figure 3, RB is the battery’s internal resistance, RW is the parasitic resistance including the metal wire’s

resistance, plug contact resistance, etc.

VR

RW

RB

Charge Current

VBAT

Battery

Figure 3 Battery’s Internal Resistance and Parasitic Resistance

In charge mode, charge current flows through the resistor RB and RW, a voltage drop VR is generated. Assume

that the true battery voltage is VBAT, but the detected voltage by HM4033 is VBAT + VR, which does not

accurately reflect the battery voltage. Therefore, when designing the charge termination voltage, the voltage

drop VR should be considered to make sure that the battery is fully charged.

The simple way to compensate VR is to make:

Vfinal＝VBAT＋VR

Where, Vfinal is the designed charge termination voltage at battery terminal

VBAT is battery voltage when fully charged

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